add MIR code (unused thus far)

src/librustc/middle/region.rs

@@ -329,6 +329,9 @@ impl RegionMaps {
     pub fn item_extent(&self, n: ast::NodeId) -> CodeExtent {
         self.lookup_code_extent(CodeExtentData::DestructionScope(n))
     }
+    pub fn opt_destruction_extent(&self, n: ast::NodeId) -> Option<CodeExtent> {
+        self.code_extent_interner.borrow().get(&CodeExtentData::DestructionScope(n)).cloned()
+    }
     pub fn intern_code_extent(&self,
                               e: CodeExtentData,
                               parent: CodeExtent) -> CodeExtent {

src/librustc/middle/ty.rs

@@ -3475,6 +3475,13 @@ impl<'tcx, 'container> AdtDefData<'tcx, 'container> {
             .expect("variant_with_id: unknown variant")
     }
 
+    pub fn variant_index_with_id(&self, vid: DefId) -> usize {
+        self.variants
+            .iter()
+            .position(|v| v.did == vid)
+            .expect("variant_index_with_id: unknown variant")
+    }
+
     pub fn variant_of_def(&self, def: def::Def) -> &VariantDefData<'tcx, 'container> {
         match def {
             def::DefVariant(_, vid, _) => self.variant_with_id(vid),
@@ -5223,14 +5230,11 @@ impl<'tcx> TyS<'tcx> {
     {
         let method_call = MethodCall::autoderef(expr_id, autoderef);
         let mut adjusted_ty = self;
-        match method_type(method_call) {
-            Some(method_ty) => {
-                // Method calls always have all late-bound regions
-                // fully instantiated.
-                let fn_ret = cx.no_late_bound_regions(&method_ty.fn_ret()).unwrap();
-                adjusted_ty = fn_ret.unwrap();
-            }
-            None => {}
+        if let Some(method_ty) = method_type(method_call) {
+            // Method calls always have all late-bound regions
+            // fully instantiated.
+            let fn_ret = cx.no_late_bound_regions(&method_ty.fn_ret()).unwrap();
+            adjusted_ty = fn_ret.unwrap();
         }
         match adjusted_ty.builtin_deref(true, NoPreference) {
             Some(mt) => mt.ty,

src/librustc_mir/build/block.rs

@@ -0,0 +1,28 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use hair::*;
+use repr::*;
+use build::{BlockAnd, Builder};
+
+impl<H:Hair> Builder<H> {
+    pub fn ast_block(&mut self,
+                     destination: &Lvalue<H>,
+                     mut block: BasicBlock,
+                     ast_block: H::Block)
+                     -> BlockAnd<()> {
+        let this = self;
+        let Block { extent, span: _, stmts, expr } = this.hir.mirror(ast_block);
+        this.in_scope(extent, block, |this| {
+            unpack!(block = this.stmts(block, stmts));
+            this.into(destination, block, expr)
+        })
+    }
+}

src/librustc_mir/build/cfg.rs

@@ -0,0 +1,88 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+
+
+
+//! Routines for manipulating the control-flow graph.
+
+use build::CFG;
+use hair::*;
+use repr::*;
+
+impl<H:Hair> CFG<H> {
+    pub fn block_data(&self, blk: BasicBlock) -> &BasicBlockData<H> {
+        &self.basic_blocks[blk.index()]
+    }
+
+    pub fn block_data_mut(&mut self, blk: BasicBlock) -> &mut BasicBlockData<H> {
+        &mut self.basic_blocks[blk.index()]
+    }
+
+    pub fn end_point(&self, block: BasicBlock) -> ExecutionPoint {
+        ExecutionPoint {
+            block: block,
+            statement: self.block_data(block).statements.len() as u32
+        }
+    }
+
+    pub fn start_new_block(&mut self) -> BasicBlock {
+        let node_index = self.basic_blocks.len();
+        self.basic_blocks.push(BasicBlockData::new(Terminator::Diverge));
+        BasicBlock::new(node_index)
+    }
+
+    pub fn push(&mut self, block: BasicBlock, statement: Statement<H>) {
+        debug!("push({:?}, {:?})", block, statement);
+        self.block_data_mut(block).statements.push(statement);
+    }
+
+    pub fn push_assign_constant(&mut self,
+                                block: BasicBlock,
+                                span: H::Span,
+                                temp: &Lvalue<H>,
+                                constant: Constant<H>) {
+        self.push_assign(block, span, temp, Rvalue::Use(Operand::Constant(constant)));
+    }
+
+    pub fn push_drop(&mut self, block: BasicBlock, span: H::Span,
+                     kind: DropKind, lvalue: &Lvalue<H>) {
+        self.push(block, Statement {
+            span: span,
+            kind: StatementKind::Drop(kind, lvalue.clone())
+        });
+    }
+
+    pub fn push_assign(&mut self,
+                       block: BasicBlock,
+                       span: H::Span,
+                       lvalue: &Lvalue<H>,
+                       rvalue: Rvalue<H>) {
+        self.push(block, Statement {
+            span: span,
+            kind: StatementKind::Assign(lvalue.clone(), rvalue)
+        });
+    }
+
+    pub fn terminate(&mut self,
+                     block: BasicBlock,
+                     terminator: Terminator<H>) {
+        // Check whether this block has already been terminated. For
+        // this, we rely on the fact that the initial state is to have
+        // a Diverge terminator and an empty list of targets (which
+        // is not a valid state).
+        debug_assert!(match self.block_data(block).terminator { Terminator::Diverge => true,
+                                                                _ => false },
+                      "terminate: block {:?} already has a terminator set", block);
+
+        self.block_data_mut(block).terminator = terminator;
+    }
+}
+

src/librustc_mir/build/expr/as_constant.rs

@@ -0,0 +1,123 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! See docs in build/expr/mod.rs
+
+use rustc_data_structures::fnv::FnvHashMap;
+
+use build::{Builder};
+use hair::*;
+use repr::*;
+
+impl<H:Hair> Builder<H> {
+    /// Compile `expr`, yielding a compile-time constant. Assumes that
+    /// `expr` is a valid compile-time constant!
+    pub fn as_constant<M>(&mut self, expr: M) -> Constant<H>
+        where M: Mirror<H, Output=Expr<H>>
+    {
+        let expr = self.hir.mirror(expr);
+        self.expr_as_constant(expr)
+    }
+
+    fn expr_as_constant(&mut self, expr: Expr<H>) -> Constant<H> {
+        let this = self;
+        let Expr { ty: _, temp_lifetime: _, span, kind } = expr;
+        let kind = match kind {
+            ExprKind::Scope { extent: _, value } => {
+                return this.as_constant(value);
+            }
+            ExprKind::Paren { arg } => {
+                return this.as_constant(arg);
+            }
+            ExprKind::Literal { literal } => {
+                ConstantKind::Literal(literal)
+            }
+            ExprKind::Vec { fields } => {
+                let fields = this.as_constants(fields);
+                ConstantKind::Aggregate(AggregateKind::Vec, fields)
+            }
+            ExprKind::Tuple { fields } => {
+                let fields = this.as_constants(fields);
+                ConstantKind::Aggregate(AggregateKind::Tuple, fields)
+            }
+            ExprKind::Adt { adt_def, variant_index, substs, fields, base: None } => {
+                let field_names = this.hir.fields(adt_def, variant_index);
+                let fields = this.named_field_constants(field_names, fields);
+                ConstantKind::Aggregate(AggregateKind::Adt(adt_def, variant_index, substs), fields)
+            }
+            ExprKind::Repeat { value, count } => {
+                let value = Box::new(this.as_constant(value));
+                let count = Box::new(this.as_constant(count));
+                ConstantKind::Repeat(value, count)
+            }
+            ExprKind::Binary { op, lhs, rhs } => {
+                let lhs = Box::new(this.as_constant(lhs));
+                let rhs = Box::new(this.as_constant(rhs));
+                ConstantKind::BinaryOp(op, lhs, rhs)
+            }
+            ExprKind::Unary { op, arg } => {
+                let arg = Box::new(this.as_constant(arg));
+                ConstantKind::UnaryOp(op, arg)
+            }
+            ExprKind::Field { lhs, name } => {
+                let lhs = this.as_constant(lhs);
+                ConstantKind::Projection(
+                    Box::new(ConstantProjection {
+                        base: lhs,
+                        elem: ProjectionElem::Field(name),
+                    }))
+            }
+            ExprKind::Deref { arg } => {
+                let arg = this.as_constant(arg);
+                ConstantKind::Projection(
+                    Box::new(ConstantProjection {
+                        base: arg,
+                        elem: ProjectionElem::Deref,
+                    }))
+            }
+            ExprKind::Call { fun, args } => {
+                let fun = this.as_constant(fun);
+                let args = this.as_constants(args);
+                ConstantKind::Call(Box::new(fun), args)
+            }
+            _ => {
+                this.hir.span_bug(
+                    span,
+                    &format!("expression is not a valid constant {:?}", kind));
+            }
+        };
+        Constant { span: span, kind: kind }
+    }
+
+    fn as_constants(&mut self,
+                    exprs: Vec<ExprRef<H>>)
+                    -> Vec<Constant<H>>
+    {
+        exprs.into_iter().map(|expr| self.as_constant(expr)).collect()
+    }
+
+    fn named_field_constants(&mut self,
+                             field_names: Vec<Field<H>>,
+                             field_exprs: Vec<FieldExprRef<H>>)
+                             -> Vec<Constant<H>>
+    {
+        let fields_map: FnvHashMap<_, _> =
+            field_exprs.into_iter()
+                       .map(|f| (f.name, self.as_constant(f.expr)))
+                       .collect();
+
+        let fields: Vec<_> =
+            field_names.into_iter()
+                       .map(|n| fields_map[&n].clone())
+                       .collect();
+
+        fields
+    }
+}

src/librustc_mir/build/expr/as_lvalue.rs

@@ -0,0 +1,131 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! See docs in build/expr/mod.rs
+
+use build::{BlockAnd, Builder};
+use build::expr::category::Category;
+use hair::*;
+use repr::*;
+
+impl<H:Hair> Builder<H> {
+    /// Compile `expr`, yielding an lvalue that we can move from etc.
+    pub fn as_lvalue<M>(&mut self,
+                        block: BasicBlock,
+                        expr: M)
+                        -> BlockAnd<Lvalue<H>>
+        where M: Mirror<H, Output=Expr<H>>
+    {
+        let expr = self.hir.mirror(expr);
+        self.expr_as_lvalue(block, expr)
+    }
+
+    fn expr_as_lvalue(&mut self,
+                      mut block: BasicBlock,
+                      expr: Expr<H>)
+                      -> BlockAnd<Lvalue<H>>
+    {
+        debug!("expr_as_lvalue(block={:?}, expr={:?})",
+               block, expr);
+
+        let this = self;
+        let expr_span = expr.span;
+        match expr.kind {
+            ExprKind::Scope { extent, value } => {
+                this.in_scope(extent, block, |this| {
+                    this.as_lvalue(block, value)
+                })
+            }
+            ExprKind::Paren { arg } => {
+                this.as_lvalue(block, arg)
+            }
+            ExprKind::Field { lhs, name } => {
+                let lvalue = unpack!(block = this.as_lvalue(block, lhs));
+                let lvalue = lvalue.field(name);
+                block.and(lvalue)
+            }
+            ExprKind::Deref { arg } => {
+                let lvalue = unpack!(block = this.as_lvalue(block, arg));
+                let lvalue = lvalue.deref();
+                block.and(lvalue)
+            }
+            ExprKind::Index { lhs, index } => {
+                let (usize_ty, bool_ty) = (this.hir.usize_ty(), this.hir.bool_ty());
+
+                let slice = unpack!(block = this.as_lvalue(block, lhs));
+
+                let idx = unpack!(block = this.as_operand(block, index));
+
+                // bounds check:
+                let (len, lt) = (this.temp(usize_ty.clone()), this.temp(bool_ty));
+                this.cfg.push_assign(block, expr_span, // len = len(slice)
+                                     &len, Rvalue::Len(slice.clone()));
+                this.cfg.push_assign(block, expr_span, // lt = idx < len
+                                     &lt, Rvalue::BinaryOp(BinOp::Lt,
+                                                           idx.clone(),
+                                                           Operand::Consume(len)));
+
+                let (success, failure) = (this.cfg.start_new_block(),
+                                          this.cfg.start_new_block());
+                this.cfg.terminate(block,
+                                   Terminator::If {
+                                       cond: Operand::Consume(lt),
+                                       targets: [success, failure]
+                                   });
+                this.panic(failure);
+                success.and(slice.index(idx))
+            }
+            ExprKind::SelfRef => {
+                block.and(Lvalue::Arg(0))
+            }
+            ExprKind::VarRef { id } => {
+                let index = this.var_indices[&id];
+                block.and(Lvalue::Var(index))
+            }
+            ExprKind::StaticRef { id } => {
+                block.and(Lvalue::Static(id))
+            }
+
+            ExprKind::Vec { .. } |
+            ExprKind::Tuple { .. } |
+            ExprKind::Adt { .. } |
+            ExprKind::Closure { .. } |
+            ExprKind::Unary { .. } |
+            ExprKind::Binary { .. } |
+            ExprKind::LogicalOp { .. } |
+            ExprKind::Box { .. } |
+            ExprKind::Cast { .. } |
+            ExprKind::ReifyFnPointer { .. } |
+            ExprKind::UnsafeFnPointer { .. } |
+            ExprKind::Unsize { .. } |
+            ExprKind::Repeat { .. } |
+            ExprKind::Borrow { .. } |
+            ExprKind::If { .. } |
+            ExprKind::Match { .. } |
+            ExprKind::Loop { .. } |
+            ExprKind::Block { .. } |
+            ExprKind::Assign { .. } |
+            ExprKind::AssignOp { .. } |
+            ExprKind::Break { .. } |
+            ExprKind::Continue { .. } |
+            ExprKind::Return { .. } |
+            ExprKind::Literal { .. } |
+            ExprKind::InlineAsm { .. } |
+            ExprKind::Call { .. } => {
+                // these are not lvalues, so we need to make a temporary.
+                debug_assert!(match Category::of(&expr.kind) {
+                    Some(Category::Lvalue) => false,
+                    _ => true,
+                });
+                this.as_temp(block, expr)
+            }
+        }
+    }
+}

src/librustc_mir/build/expr/as_operand.rs

@@ -0,0 +1,68 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! See docs in build/expr/mod.rs
+
+use build::{BlockAnd, Builder};
+use build::expr::category::Category;
+use hair::*;
+use repr::*;
+
+impl<H:Hair> Builder<H> {
+    /// Compile `expr` into a value that can be used as an operand.
+    /// If `expr` is an lvalue like `x`, this will introduce a
+    /// temporary `tmp = x`, so that we capture the value of `x` at
+    /// this time.
+    pub fn as_operand<M>(&mut self,
+                         block: BasicBlock,
+                         expr: M)
+                         -> BlockAnd<Operand<H>>
+        where M: Mirror<H, Output=Expr<H>>
+    {
+        let expr = self.hir.mirror(expr);
+        self.expr_as_operand(block, expr)
+    }
+
+    fn expr_as_operand(&mut self,
+                       mut block: BasicBlock,
+                       expr: Expr<H>)
+                       -> BlockAnd<Operand<H>>
+    {
+        debug!("expr_as_operand(block={:?}, expr={:?})",
+               block, expr);
+        let this = self;
+
+        match expr.kind {
+            ExprKind::Scope { extent, value } => {
+                return this.in_scope(extent, block, |this| {
+                    this.as_operand(block, value)
+                });
+            }
+            ExprKind::Paren { arg } => {
+                return this.as_operand(block, arg);
+            }
+            _ => { }
+        }
+
+        let category = Category::of(&expr.kind).unwrap();
+        debug!("expr_as_operand: category={:?} for={:?}", category, expr.kind);
+        match category {
+            Category::Constant => {
+                let constant = this.as_constant(expr);
+                block.and(Operand::Constant(constant))
+            }
+            Category::Lvalue |
+            Category::Rvalue(..) => {
+                let operand = unpack!(block = this.as_temp(block, expr));
+                block.and(Operand::Consume(operand))
+            }
+        }
+    }
+}

src/librustc_mir/build/expr/as_rvalue.rs

@@ -0,0 +1,220 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! See docs in build/expr/mod.rs
+
+use rustc_data_structures::fnv::FnvHashMap;
+
+use build::{BlockAnd, Builder};
+use build::expr::category::{Category, RvalueFunc};
+use hair::*;
+use repr::*;
+
+impl<H:Hair> Builder<H> {
+    /// Compile `expr`, yielding an rvalue.
+    pub fn as_rvalue<M>(&mut self,
+                        block: BasicBlock,
+                        expr: M)
+                        -> BlockAnd<Rvalue<H>>
+        where M: Mirror<H, Output=Expr<H>>
+    {
+        let expr = self.hir.mirror(expr);
+        self.expr_as_rvalue(block, expr)
+    }
+
+    fn expr_as_rvalue(&mut self,
+                      mut block: BasicBlock,
+                      expr: Expr<H>)
+                      -> BlockAnd<Rvalue<H>>
+    {
+        debug!("expr_as_rvalue(block={:?}, expr={:?})",
+               block, expr);
+
+        let this = self;
+        let expr_span = expr.span;
+
+        match expr.kind {
+            ExprKind::Scope { extent, value } => {
+                this.in_scope(extent, block, |this| {
+                    this.as_rvalue(block, value)
+                })
+            }
+            ExprKind::Paren { arg } => {
+                this.as_rvalue(block, arg)
+            }
+            ExprKind::InlineAsm { asm } => {
+                block.and(Rvalue::InlineAsm(asm))
+            }
+            ExprKind::Repeat { value, count } => {
+                let value_operand = unpack!(block = this.as_operand(block, value));
+                let count_operand = unpack!(block = this.as_operand(block, count));
+                block.and(Rvalue::Repeat(value_operand, count_operand))
+            }
+            ExprKind::Borrow { region, borrow_kind, arg } => {
+                let arg_lvalue = unpack!(block = this.as_lvalue(block, arg));
+                block.and(Rvalue::Ref(region, borrow_kind, arg_lvalue))
+            }
+            ExprKind::Binary { op, lhs, rhs } => {
+                let lhs = unpack!(block = this.as_operand(block, lhs));
+                let rhs = unpack!(block = this.as_operand(block, rhs));
+                block.and(Rvalue::BinaryOp(op, lhs, rhs))
+            }
+            ExprKind::Unary { op, arg } => {
+                let arg = unpack!(block = this.as_operand(block, arg));
+                block.and(Rvalue::UnaryOp(op, arg))
+            }
+            ExprKind::Box { place: _, value } => {
+                let value = this.hir.mirror(value);
+                let value_ty = value.ty.clone();
+                let result = this.temp(value_ty.clone());
+
+                // to start, malloc some memory of suitable type (thus far, uninitialized):
+                let rvalue = Rvalue::Box(value.ty.clone());
+                this.cfg.push_assign(block, expr_span, &result, rvalue);
+
+                // schedule a shallow free of that memory, lest we unwind:
+                let extent = this.extent_of_innermost_scope().unwrap();
+                this.schedule_drop(expr_span, extent, DropKind::Shallow, &result, value_ty);
+
+                // initialize the box contents:
+                let contents = result.clone().deref();
+                unpack!(block = this.into(&contents, block, value));
+
+                // now that the result is fully initialized, cancel the drop
+                // by "using" the result (which is linear):
+                block.and(Rvalue::Use(Operand::Consume(result)))
+            }
+            ExprKind::Cast { source } => {
+                let source = unpack!(block = this.as_operand(block, source));
+                block.and(Rvalue::Cast(CastKind::Misc, source, expr.ty))
+            }
+            ExprKind::ReifyFnPointer { source } => {
+                let source = unpack!(block = this.as_operand(block, source));
+                block.and(Rvalue::Cast(CastKind::ReifyFnPointer, source, expr.ty))
+            }
+            ExprKind::UnsafeFnPointer { source } => {
+                let source = unpack!(block = this.as_operand(block, source));
+                block.and(Rvalue::Cast(CastKind::UnsafeFnPointer, source, expr.ty))
+            }
+            ExprKind::Unsize { source } => {
+                let source = unpack!(block = this.as_operand(block, source));
+                block.and(Rvalue::Cast(CastKind::Unsize, source, expr.ty))
+            }
+            ExprKind::Vec { fields } => {
+                // (*) We would (maybe) be closer to trans if we
+                // handled this and other aggregate cases via
+                // `into()`, not `as_rvalue` -- in that case, instead
+                // of generating
+                //
+                //     let tmp1 = ...1;
+                //     let tmp2 = ...2;
+                //     dest = Rvalue::Aggregate(Foo, [tmp1, tmp2])
+                //
+                // we could just generate
+                //
+                //     dest.f = ...1;
+                //     dest.g = ...2;
+                //
+                // The problem is that then we would need to:
+                //
+                // (a) have a more complex mechanism for handling
+                //     partial cleanup;
+                // (b) distinguish the case where the type `Foo` has a
+                //     destructor, in which case creating an instance
+                //     as a whole "arms" the destructor, and you can't
+                //     write individual fields; and,
+                // (c) handle the case where the type Foo has no
+                //     fields. We don't want `let x: ();` to compile
+                //     to the same MIR as `let x = ();`.
+
+                // first process the set of fields
+                let fields: Vec<_> =
+                    fields.into_iter()
+                          .map(|f| unpack!(block = this.as_operand(block, f)))
+                          .collect();
+
+                block.and(Rvalue::Aggregate(AggregateKind::Vec, fields))
+            }
+            ExprKind::Tuple { fields } => { // see (*) above
+                // first process the set of fields
+                let fields: Vec<_> =
+                    fields.into_iter()
+                          .map(|f| unpack!(block = this.as_operand(block, f)))
+                          .collect();
+
+                block.and(Rvalue::Aggregate(AggregateKind::Tuple, fields))
+            }
+            ExprKind::Closure { closure_id, substs, upvars } => { // see (*) above
+                let upvars =
+                    upvars.into_iter()
+                          .map(|upvar| unpack!(block = this.as_operand(block, upvar)))
+                          .collect();
+                block.and(Rvalue::Aggregate(AggregateKind::Closure(closure_id, substs), upvars))
+            }
+            ExprKind::Adt { adt_def, variant_index, substs, fields, base } => { // see (*) above
+                // first process the set of fields
+                let fields_map: FnvHashMap<_, _> =
+                    fields.into_iter()
+                          .map(|f| (f.name, unpack!(block = this.as_operand(block, f.expr))))
+                          .collect();
+
+                let field_names =
+                    this.hir.fields(adt_def, variant_index);
+
+                let base =
+                    base.map(|base| unpack!(block = this.as_lvalue(block, base)));
+
+                // for the actual values we use, take either the
+                // expr the user specified or, if they didn't
+                // specify something for this field name, create a
+                // path relative to the base (which must have been
+                // supplied, or the IR is internally
+                // inconsistent).
+                let fields: Vec<_> =
+                    field_names.into_iter()
+                               .map(|n| match fields_map.get(&n) {
+                                   Some(v) => v.clone(),
+                                   None => Operand::Consume(base.clone().unwrap().field(n)),
+                               })
+                               .collect();
+
+                block.and(Rvalue::Aggregate(AggregateKind::Adt(adt_def, variant_index, substs),
+                                            fields))
+            }
+            ExprKind::Literal { .. } |
+            ExprKind::Block { .. } |
+            ExprKind::Match { .. } |
+            ExprKind::If { .. } |
+            ExprKind::Loop { .. } |
+            ExprKind::LogicalOp { .. } |
+            ExprKind::Call { .. } |
+            ExprKind::Field { .. } |
+            ExprKind::Deref { .. } |
+            ExprKind::Index { .. } |
+            ExprKind::VarRef { .. } |
+            ExprKind::SelfRef |
+            ExprKind::Assign { .. } |
+            ExprKind::AssignOp { .. } |
+            ExprKind::Break { .. } |
+            ExprKind::Continue { .. } |
+            ExprKind::Return { .. } |
+            ExprKind::StaticRef { .. } => {
+                // these do not have corresponding `Rvalue` variants,
+                // so make an operand and then return that
+                debug_assert!(match Category::of(&expr.kind) {
+                    Some(Category::Rvalue(RvalueFunc::AsRvalue)) => false,
+                    _ => true,
+                });
+                let operand = unpack!(block = this.as_operand(block, expr));
+                block.and(Rvalue::Use(operand))
+            }
+        }
+    }
+}

src/librustc_mir/build/expr/as_temp.rs

@@ -0,0 +1,85 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! See docs in build/expr/mod.rs
+
+use build::{BlockAnd, Builder};
+use build::expr::category::Category;
+use hair::*;
+use repr::*;
+
+impl<H:Hair> Builder<H> {
+    /// Compile `expr` into a fresh temporary. This is used when building
+    /// up rvalues so as to freeze the value that will be consumed.
+    pub fn as_temp<M>(&mut self,
+                      block: BasicBlock,
+                      expr: M)
+                      -> BlockAnd<Lvalue<H>>
+        where M: Mirror<H, Output=Expr<H>>
+    {
+        let expr = self.hir.mirror(expr);
+        self.expr_as_temp(block, expr)
+    }
+
+    fn expr_as_temp(&mut self,
+                    mut block: BasicBlock,
+                    expr: Expr<H>)
+                    -> BlockAnd<Lvalue<H>>
+    {
+        debug!("expr_as_temp(block={:?}, expr={:?})",
+               block, expr);
+        let this = self;
+
+        match expr.kind {
+            ExprKind::Scope { extent, value } => {
+                return this.in_scope(extent, block, |this| {
+                    this.as_temp(block, value)
+                });
+            }
+            ExprKind::Paren { arg } => {
+                return this.as_temp(block, arg);
+            }
+            _ => { }
+        }
+
+        let expr_ty = expr.ty.clone();
+        let temp = this.temp(expr_ty.clone());
+        let temp_lifetime = match expr.temp_lifetime {
+            Some(t) => t,
+            None => {
+                this.hir.span_bug(
+                    expr.span,
+                    &format!("no temp_lifetime for expr"));
+            }
+        };
+        this.schedule_drop(expr.span, temp_lifetime, DropKind::Deep, &temp, expr_ty);
+
+        // Careful here not to cause an infinite cycle. If we always
+        // called `into`, then for lvalues like `x.f`, it would
+        // eventually fallback to us, and we'd loop. There's a reason
+        // for this: `as_temp` is the point where we bridge the "by
+        // reference" semantics of `as_lvalue` with the "by value"
+        // semantics of `into`, `as_operand`, `as_rvalue`, and (of
+        // course) `as_temp`.
+        match Category::of(&expr.kind).unwrap() {
+            Category::Lvalue => {
+                let expr_span = expr.span;
+                let lvalue = unpack!(block = this.as_lvalue(block, expr));
+                let rvalue = Rvalue::Use(Operand::Consume(lvalue));
+                this.cfg.push_assign(block, expr_span, &temp, rvalue);
+            }
+            _ => {
+                unpack!(block = this.into(&temp, block, expr));
+            }
+        }
+
+        block.and(temp)
+    }
+}

src/librustc_mir/build/expr/category.rs

@@ -0,0 +1,93 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use hair::*;
+
+#[derive(Debug, PartialEq)]
+pub enum Category {
+    // An assignable memory location like `x`, `x.f`, `foo()[3]`, that
+    // sort of thing. Something that could appear on the LHS of an `=`
+    // sign.
+    Lvalue,
+
+    // A literal like `23` or `"foo"`. Does not include constant
+    // expressions like `3 + 5`.
+    Constant,
+
+    // Something that generates a new value at runtime, like `x + y`
+    // or `foo()`.
+    Rvalue(RvalueFunc),
+}
+
+// Rvalues fall into different "styles" that will determine which fn
+// is best suited to generate them.
+#[derive(Debug, PartialEq)]
+pub enum RvalueFunc {
+    // Best generated by `into`. This is generally exprs that
+    // cause branching, like `match`, but also includes calls.
+    Into,
+
+    // Best generated by `as_rvalue`. This is usually the case.
+    AsRvalue,
+}
+
+/// Determines the category for a given expression. Note that scope
+/// and paren expressions have no category.
+impl Category {
+    pub fn of<H:Hair>(ek: &ExprKind<H>) -> Option<Category> {
+        match *ek {
+            ExprKind::Scope { .. } |
+            ExprKind::Paren { .. } =>
+                None,
+
+            ExprKind::Field { .. } |
+            ExprKind::Deref { .. } |
+            ExprKind::Index { .. } |
+            ExprKind::SelfRef |
+            ExprKind::VarRef { .. } |
+            ExprKind::StaticRef { .. } =>
+                Some(Category::Lvalue),
+
+            ExprKind::LogicalOp { .. } |
+            ExprKind::If { .. } |
+            ExprKind::Match { .. } |
+            ExprKind::Call { .. } =>
+                Some(Category::Rvalue(RvalueFunc::Into)),
+
+            ExprKind::Vec { .. } |
+            ExprKind::Tuple { .. } |
+            ExprKind::Adt { .. } |
+            ExprKind::Closure { .. } |
+            ExprKind::Unary { .. } |
+            ExprKind::Binary { .. } |
+            ExprKind::Box { .. } |
+            ExprKind::Cast { .. } |
+            ExprKind::ReifyFnPointer { .. } |
+            ExprKind::UnsafeFnPointer { .. } |
+            ExprKind::Unsize { .. } |
+            ExprKind::Repeat { .. } |
+            ExprKind::Borrow { .. } |
+            ExprKind::Assign { .. } |
+            ExprKind::AssignOp { .. } |
+            ExprKind::InlineAsm { .. } =>
+                Some(Category::Rvalue(RvalueFunc::AsRvalue)),
+
+            ExprKind::Literal { .. } =>
+                Some(Category::Constant),
+
+            ExprKind::Loop { .. } |
+            ExprKind::Block { .. } |
+            ExprKind::Break { .. } |
+            ExprKind::Continue { .. } |
+            ExprKind::Return { .. } =>
+                Some(Category::Rvalue(RvalueFunc::Into)), // TODO
+        }
+    }
+}

src/librustc_mir/build/expr/into.rs

@@ -0,0 +1,282 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! See docs in build/expr/mod.rs
+
+use build::{BlockAnd, Builder};
+use build::expr::category::{Category, RvalueFunc};
+use build::scope::LoopScope;
+use hair::*;
+use repr::*;
+
+impl<H:Hair> Builder<H> {
+    /// Compile `expr`, storing the result into `destination`, which
+    /// is assumed to be uninitialized.
+    pub fn into_expr(&mut self,
+                     destination: &Lvalue<H>,
+                     mut block: BasicBlock,
+                     expr: Expr<H>)
+                     -> BlockAnd<()>
+    {
+        debug!("into_expr(destination={:?}, block={:?}, expr={:?})",
+               destination, block, expr);
+
+        // since we frequently have to reference `self` from within a
+        // closure, where `self` would be shadowed, it's easier to
+        // just use the name `this` uniformly
+        let this = self;
+        let expr_span = expr.span;
+
+        match expr.kind {
+            ExprKind::Scope { extent, value } => {
+                this.in_scope(extent, block, |this| {
+                    this.into(destination, block, value)
+                })
+            }
+            ExprKind::Paren { arg } => {
+                this.into(destination, block, arg)
+            }
+            ExprKind::Block { body: ast_block } => {
+                this.ast_block(destination, block, ast_block)
+            }
+            ExprKind::Match { discriminant, arms } => {
+                this.match_expr(destination, expr_span, block, discriminant, arms)
+            }
+            ExprKind::If { condition: cond_expr, then: then_expr, otherwise: else_expr } => {
+                let operand = unpack!(block = this.as_operand(block, cond_expr));
+
+                let mut then_block = this.cfg.start_new_block();
+                let mut else_block = this.cfg.start_new_block();
+                this.cfg.terminate(block, Terminator::If {
+                    cond: operand,
+                    targets: [then_block, else_block]
+                });
+
+                unpack!(then_block = this.into(destination, then_block, then_expr));
+                unpack!(else_block = this.into(destination, else_block, else_expr));
+
+                let join_block = this.cfg.start_new_block();
+                this.cfg.terminate(then_block, Terminator::Goto { target: join_block });
+                this.cfg.terminate(else_block, Terminator::Goto { target: join_block });
+
+                join_block.unit()
+            }
+            ExprKind::LogicalOp { op, lhs, rhs } => {
+                // And:
+                //
+                // [block: If(lhs)] -true-> [else_block: If(rhs)] -true-> [true_block]
+                //        |                          | (false)
+                //        +----------false-----------+------------------> [false_block]
+                //
+                // Or:
+                //
+                // [block: If(lhs)] -false-> [else_block: If(rhs)] -true-> [true_block]
+                //        |                          | (false)
+                //        +----------true------------+-------------------> [false_block]
+
+                let (true_block, false_block, mut else_block, join_block) =
+                    (this.cfg.start_new_block(), this.cfg.start_new_block(),
+                     this.cfg.start_new_block(), this.cfg.start_new_block());
+
+                let lhs = unpack!(block = this.as_operand(block, lhs));
+                let blocks = match op {
+                    LogicalOp::And => [else_block, false_block],
+                    LogicalOp::Or => [true_block, else_block],
+                };
+                this.cfg.terminate(block, Terminator::If { cond: lhs, targets: blocks });
+
+                let rhs = unpack!(else_block = this.as_operand(else_block, rhs));
+                this.cfg.terminate(else_block, Terminator::If {
+                    cond: rhs,
+                    targets: [true_block, false_block]
+                });
+
+                this.cfg.push_assign_constant(
+                    true_block, expr_span, destination,
+                    Constant {
+                        span: expr_span,
+                        kind: ConstantKind::Literal(Literal::Bool { value: true }),
+                    });
+
+                this.cfg.push_assign_constant(
+                    false_block, expr_span, destination,
+                    Constant {
+                        span: expr_span,
+                        kind: ConstantKind::Literal(Literal::Bool { value: false }),
+                    });
+
+                this.cfg.terminate(true_block, Terminator::Goto { target: join_block });
+                this.cfg.terminate(false_block, Terminator::Goto { target: join_block });
+
+                join_block.unit()
+            }
+            ExprKind::Loop { condition: opt_cond_expr, body } => {
+                // [block] --> [loop_block] ~~> [loop_block_end] -1-> [exit_block]
+                //                  ^                  |
+                //                  |                  0
+                //                  |                  |
+                //                  |                  v
+                //           [body_block_end] <~~~ [body_block]
+                //
+                // If `opt_cond_expr` is `None`, then the graph is somewhat simplified:
+                //
+                // [block] --> [loop_block / body_block ] ~~> [body_block_end]    [exit_block]
+                //                         ^                          |
+                //                         |                          |
+                //                         +--------------------------+
+                //
+
+                let loop_block = this.cfg.start_new_block();
+                let exit_block = this.cfg.start_new_block();
+
+                // start the loop
+                this.cfg.terminate(block, Terminator::Goto { target: loop_block });
+
+                this.in_loop_scope(loop_block, exit_block, |this| {
+                    // conduct the test, if necessary
+                    let body_block;
+                    let opt_cond_expr = opt_cond_expr; // FIXME rustc bug
+                    if let Some(cond_expr) = opt_cond_expr {
+                        let loop_block_end;
+                        let cond = unpack!(loop_block_end = this.as_operand(loop_block, cond_expr));
+                        body_block = this.cfg.start_new_block();
+                        this.cfg.terminate(loop_block_end,
+                                           Terminator::If {
+                                               cond: cond,
+                                               targets: [body_block, exit_block]
+                                           });
+                    } else {
+                        body_block = loop_block;
+                    }
+
+                    // execute the body, branching back to the test
+                    let unit_temp = this.unit_temp.clone();
+                    let body_block_end = unpack!(this.into(&unit_temp, body_block, body));
+                    this.cfg.terminate(body_block_end, Terminator::Goto { target: loop_block });
+
+                    // final point is exit_block
+                    exit_block.unit()
+                })
+            }
+            ExprKind::Assign { lhs, rhs } => {
+                // Note: we evaluate assignments right-to-left. This
+                // is better for borrowck interaction with overloaded
+                // operators like x[j] = x[i].
+                let rhs = unpack!(block = this.as_operand(block, rhs));
+                let lhs = unpack!(block = this.as_lvalue(block, lhs));
+                this.cfg.push_drop(block, expr_span, DropKind::Deep, &lhs);
+                this.cfg.push_assign(block, expr_span, &lhs, Rvalue::Use(rhs));
+                block.unit()
+            }
+            ExprKind::AssignOp { op, lhs, rhs } => {
+                // FIXME(#28160) there is an interesting semantics
+                // question raised here -- should we "freeze" the
+                // value of the lhs here?  I'm inclined to think not,
+                // since it seems closer to the semantics of the
+                // overloaded version, which takes `&mut self`.  This
+                // only affects weird things like `x += {x += 1; x}`
+                // -- is that equal to `x + (x + 1)` or `2*(x+1)`?
+
+                // As above, RTL.
+                let rhs = unpack!(block = this.as_operand(block, rhs));
+                let lhs = unpack!(block = this.as_lvalue(block, lhs));
+
+                // we don't have to drop prior contents or anything
+                // because AssignOp is only legal for Copy types
+                // (overloaded ops should be desugared into a call).
+                this.cfg.push_assign(block, expr_span, &lhs,
+                                     Rvalue::BinaryOp(op,
+                                                      Operand::Consume(lhs.clone()),
+                                                      rhs));
+
+                block.unit()
+            }
+            ExprKind::Continue { label } => {
+                this.break_or_continue(expr_span, label, block,
+                                       |loop_scope| loop_scope.continue_block)
+            }
+            ExprKind::Break { label } => {
+                this.break_or_continue(expr_span, label, block,
+                                       |loop_scope| loop_scope.break_block)
+            }
+            ExprKind::Return { value } => {
+                unpack!(block = this.into(&Lvalue::ReturnPointer, block, value));
+                let extent = this.extent_of_outermost_scope().unwrap();
+                this.exit_scope(expr_span, extent, block, END_BLOCK);
+                this.cfg.start_new_block().unit()
+            }
+            ExprKind::Call { fun, args } => {
+                let fun = unpack!(block = this.as_lvalue(block, fun));
+                let args: Vec<_> =
+                    args.into_iter()
+                        .map(|arg| unpack!(block = this.as_lvalue(block, arg)))
+                        .collect();
+                let success = this.cfg.start_new_block();
+                let panic = this.diverge_cleanup();
+                this.cfg.terminate(block,
+                                   Terminator::Call {
+                                       data: CallData {
+                                           destination: destination.clone(),
+                                           func: fun,
+                                           args: args
+                                       },
+                                       targets: [success, panic]
+                                   });
+                success.unit()
+            }
+
+            // these are the cases that are more naturally handled by some other mode
+            ExprKind::Unary { .. } |
+            ExprKind::Binary { .. } |
+            ExprKind::Box { .. } |
+            ExprKind::Cast { .. } |
+            ExprKind::ReifyFnPointer { .. } |
+            ExprKind::UnsafeFnPointer { .. } |
+            ExprKind::Unsize { .. } |
+            ExprKind::Repeat { .. } |
+            ExprKind::Borrow { .. } |
+            ExprKind::VarRef { .. } |
+            ExprKind::SelfRef |
+            ExprKind::StaticRef { .. } |
+            ExprKind::Vec { .. } |
+            ExprKind::Tuple { .. } |
+            ExprKind::Adt { .. } |
+            ExprKind::Closure { .. } |
+            ExprKind::Index { .. } |
+            ExprKind::Deref { .. } |
+            ExprKind::Literal { .. } |
+            ExprKind::InlineAsm { .. } |
+            ExprKind::Field { .. } => {
+                debug_assert!(match Category::of(&expr.kind).unwrap() {
+                    Category::Rvalue(RvalueFunc::Into) => false,
+                    _ => true,
+                });
+
+                let rvalue = unpack!(block = this.as_rvalue(block, expr));
+                this.cfg.push_assign(block, expr_span, destination, rvalue);
+                block.unit()
+            }
+        }
+    }
+
+    fn break_or_continue<F>(&mut self,
+                            span: H::Span,
+                            label: Option<H::CodeExtent>,
+                            block: BasicBlock,
+                            exit_selector: F)
+                            -> BlockAnd<()>
+        where F: FnOnce(&LoopScope<H>) -> BasicBlock
+    {
+        let loop_scope = self.find_loop_scope(span, label);
+        let exit_block = exit_selector(&loop_scope);
+        self.exit_scope(span, loop_scope.extent, block, exit_block);
+        self.cfg.start_new_block().unit()
+    }
+}

src/librustc_mir/build/expr/mod.rs

@@ -0,0 +1,79 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Translates expressions into MIR. As a caller into this module, you
+//! have many options, but the first thing you have to decide is
+//! whether you are evaluating this expression for its *value*, its
+//! *location*, or as a *constant*.
+//!
+//! Typically, you want the value: e.g., if you are doing `expr_a +
+//! expr_b`, you want the values of those expressions. In that case,
+//! you want one of the following functions. Note that if the expr has
+//! a type that is not `Copy`, then using any of these functions will
+//! "move" the value out of its current home (if any).
+//!
+//! - `into` -- writes the value into a specific location, which
+//!   should be uninitialized
+//! - `as_operand` -- evaluates the value and yields an `Operand`,
+//!   suitable for use as an argument to an `Rvalue`
+//! - `as_temp` -- evaluates into a temporary; this is similar to `as_operand`
+//!   except it always returns a fresh lvalue, even for constants
+//! - `as_rvalue` -- yields an `Rvalue`, suitable for use in an assignment;
+//!   as of this writing, never needed outside of the `expr` module itself
+//!
+//! Sometimes though want the expression's *location*. An example
+//! would be during a match statement, or the operand of the `&`
+//! operator. In that case, you want `as_lvalue`. This will create a
+//! temporary if necessary.
+//!
+//! Finally, if it's a constant you seek, then call
+//! `as_constant`. This creates a `Constant<H>`, but naturally it can
+//! only be used on constant expressions and hence is needed only in
+//! very limited contexts.
+//!
+//! ### Implementation notes
+//!
+//! For any given kind of expression, there is generally one way that
+//! can be translated most naturally. This is specified by the
+//! `Category::of` function in the `category` module. For example, a
+//! struct expression (or other expression that creates a new value)
+//! is typically easiest to write in terms of `as_rvalue` or `into`,
+//! whereas a reference to a field is easiest to write in terms of
+//! `as_lvalue`. (The exception to this is scope and paren
+//! expressions, which have no category.)
+//!
+//! Therefore, the various functions above make use of one another in
+//! a descending fashion. For any given expression, you should pick
+//! the most suitable spot to implement it, and then just let the
+//! other fns cycle around. The handoff works like this:
+//!
+//! - `into(lv)` -> fallback is to create a rvalue with `as_rvalue` and assign it to `lv`
+//! - `as_rvalue` -> fallback is to create an Operand with `as_operand` and use `Rvalue::use`
+//! - `as_operand` -> either invokes `as_constant` or `as_temp`
+//! - `as_constant` -> (no fallback)
+//! - `as_temp` -> creates a temporary and either calls `as_lvalue` or `into`
+//! - `as_lvalue` -> for rvalues, falls back to `as_temp` and returns that
+//!
+//! As you can see, there is a cycle where `into` can (in theory) fallback to `as_temp`
+//! which can fallback to `into`. So if one of the `ExprKind` variants is not, in fact,
+//! implemented in the category where it is supposed to be, there will be a problem.
+//!
+//! Of those fallbacks, the most interesting one is `as_temp`, because
+//! it discriminates based on the category of the expression. This is
+//! basically the point where the "by value" operations are bridged
+//! over to the "by reference" mode (`as_lvalue`).
+
+mod as_constant;
+mod as_lvalue;
+mod as_rvalue;
+mod as_operand;
+mod as_temp;
+mod category;
+mod into;

src/librustc_mir/build/into.rs

@@ -0,0 +1,70 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! In general, there are a number of things for which it's convenient
+//! to just call `builder.into` and have it emit its result into a
+//! given location. This is basically for expressions or things that can be
+//! wrapped up as expressions (e.g. blocks). To make this ergonomic, we use this
+//! latter `EvalInto` trait.
+
+use build::{BlockAnd, Builder};
+use hair::*;
+use repr::*;
+
+pub trait EvalInto<H:Hair> {
+    fn eval_into(self, builder: &mut Builder<H>, destination: &Lvalue<H>,
+                 block: BasicBlock) -> BlockAnd<()>;
+}
+
+impl<H:Hair> Builder<H> {
+    pub fn into<E>(&mut self,
+                   destination: &Lvalue<H>,
+                   block: BasicBlock,
+                   expr: E)
+                   -> BlockAnd<()>
+        where E: EvalInto<H>
+    {
+        expr.eval_into(self, destination, block)
+    }
+}
+
+impl<H:Hair> EvalInto<H> for ExprRef<H> {
+    fn eval_into(self,
+                 builder: &mut Builder<H>,
+                 destination: &Lvalue<H>,
+                 block: BasicBlock)
+                 -> BlockAnd<()> {
+        let expr = builder.hir.mirror(self);
+        builder.into_expr(destination, block, expr)
+    }
+}
+
+impl<H:Hair> EvalInto<H> for Expr<H> {
+    fn eval_into(self,
+                 builder: &mut Builder<H>,
+                 destination: &Lvalue<H>,
+                 block: BasicBlock)
+                 -> BlockAnd<()> {
+        builder.into_expr(destination, block, self)
+    }
+}
+
+impl<H:Hair> EvalInto<H> for Option<ExprRef<H>> {
+    fn eval_into(self,
+                 builder: &mut Builder<H>,
+                 destination: &Lvalue<H>,
+                 block: BasicBlock)
+                 -> BlockAnd<()> {
+        match self {
+            Some(expr) => builder.into(destination, block, expr),
+            None => block.unit()
+        }
+    }
+}

src/librustc_mir/build/matches/mod.rs

@@ -0,0 +1,409 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Code related to match expresions. These are sufficiently complex
+//! to warrant their own module and submodules. :) This main module
+//! includes the high-level algorithm, the submodules contain the
+//! details.
+
+use build::{BlockAnd, Builder};
+use repr::*;
+use hair::*;
+
+// helper functions, broken out by category:
+mod simplify;
+mod test;
+mod util;
+
+impl<H:Hair> Builder<H> {
+    pub fn match_expr(&mut self,
+                      destination: &Lvalue<H>,
+                      span: H::Span,
+                      mut block: BasicBlock,
+                      discriminant: ExprRef<H>,
+                      arms: Vec<Arm<H>>)
+                      -> BlockAnd<()>
+    {
+        let discriminant_lvalue =
+            unpack!(block = self.as_lvalue(block, discriminant));
+
+        let arm_blocks: Vec<BasicBlock> =
+            arms.iter()
+                .map(|_| self.cfg.start_new_block())
+                .collect();
+
+        let arm_bodies: Vec<ExprRef<H>> =
+            arms.iter()
+                .map(|arm| arm.body.clone())
+                .collect();
+
+        // assemble a list of candidates: there is one candidate per
+        // pattern, which means there may be more than one candidate
+        // *per arm*. These candidates are kept sorted such that the
+        // highest priority candidate comes last in the list. This the
+        // reverse of the order in which candidates are written in the
+        // source.
+        let candidates: Vec<Candidate<H>> =
+            arms.into_iter()
+                .zip(arm_blocks.iter())
+                .rev() // highest priority comes last
+                .flat_map(|(arm, &arm_block)| {
+                    let guard = arm.guard;
+                    arm.patterns.into_iter()
+                                .rev()
+                                .map(move |pat| (arm_block, pat, guard.clone()))
+                })
+                .map(|(arm_block, pattern, guard)| {
+                    Candidate {
+                        match_pairs: vec![self.match_pair(discriminant_lvalue.clone(), pattern)],
+                        bindings: vec![],
+                        guard: guard,
+                        arm_block: arm_block,
+                    }
+                })
+                .collect();
+
+        // this will generate code to test discriminant_lvalue and
+        // branch to the appropriate arm block
+        let var_extent = self.extent_of_innermost_scope().unwrap();
+        self.match_candidates(span, var_extent, candidates, block);
+
+        // all the arm blocks will rejoin here
+        let end_block = self.cfg.start_new_block();
+
+        for (arm_body, &arm_block) in arm_bodies.into_iter().zip(arm_blocks.iter()) {
+            let mut arm_block = arm_block;
+            unpack!(arm_block = self.into(destination, arm_block, arm_body));
+            self.cfg.terminate(arm_block, Terminator::Goto { target: end_block });
+        }
+
+        end_block.unit()
+    }
+
+    pub fn expr_into_pattern(&mut self,
+                             mut block: BasicBlock,
+                             var_extent: H::CodeExtent,          // lifetime of vars
+                             irrefutable_pat: PatternRef<H>,
+                             initializer: ExprRef<H>)
+                             -> BlockAnd<()>
+    {
+        // optimize the case of `let x = ...`
+        let irrefutable_pat = self.hir.mirror(irrefutable_pat);
+        match irrefutable_pat.kind {
+            PatternKind::Binding { mutability,
+                                   name,
+                                   mode: BindingMode::ByValue,
+                                   var,
+                                   ty,
+                                   subpattern: None } => {
+                let index = self.declare_binding(var_extent, mutability, name,
+                                                 var, ty, irrefutable_pat.span);
+                let lvalue = Lvalue::Var(index);
+                return self.into(&lvalue, block, initializer);
+            }
+            _ => { }
+        }
+        let lvalue = unpack!(block = self.as_lvalue(block, initializer));
+        self.lvalue_into_pattern(block, var_extent,
+                                 PatternRef::Mirror(Box::new(irrefutable_pat)), &lvalue)
+    }
+
+    pub fn lvalue_into_pattern(&mut self,
+                               block: BasicBlock,
+                               var_extent: H::CodeExtent,
+                               irrefutable_pat: PatternRef<H>,
+                               initializer: &Lvalue<H>)
+                               -> BlockAnd<()>
+    {
+        // create a dummy candidate
+        let mut candidate = Candidate::<H> {
+            match_pairs: vec![self.match_pair(initializer.clone(), irrefutable_pat)],
+            bindings: vec![],
+            guard: None,
+            arm_block: block
+        };
+
+        // Simplify the candidate. Since the pattern is irrefutable, this should
+        // always convert all match-pairs into bindings.
+        self.simplify_candidate(&mut candidate);
+
+        if !candidate.match_pairs.is_empty() {
+            self.hir.span_bug(
+                candidate.match_pairs[0].pattern.span,
+                &format!("match pairs {:?} remaining after simplifying irrefutable pattern",
+                         candidate.match_pairs));
+        }
+
+        // now apply the bindings, which will also declare the variables
+        self.bind_matched_candidate(block, var_extent, candidate.bindings);
+
+        block.unit()
+    }
+
+    pub fn declare_uninitialized_variables(&mut self,
+                                           var_extent: H::CodeExtent,
+                                           pattern: PatternRef<H>)
+    {
+        let pattern = self.hir.mirror(pattern);
+        match pattern.kind {
+            PatternKind::Binding { mutability, name, mode: _, var, ty, subpattern } => {
+                self.declare_binding(var_extent, mutability, name, var, ty, pattern.span);
+                if let Some(subpattern) = subpattern {
+                    self.declare_uninitialized_variables(var_extent, subpattern);
+                }
+            }
+            PatternKind::Array { prefix, slice, suffix } |
+            PatternKind::Slice { prefix, slice, suffix } => {
+                for subpattern in prefix.into_iter().chain(slice).chain(suffix) {
+                    self.declare_uninitialized_variables(var_extent, subpattern);
+                }
+            }
+            PatternKind::Constant { .. } | PatternKind::Range { .. } | PatternKind::Wild => {
+            }
+            PatternKind::Deref { subpattern } => {
+                self.declare_uninitialized_variables(var_extent, subpattern);
+            }
+            PatternKind::Leaf { subpatterns } |
+            PatternKind::Variant { subpatterns, .. } => {
+                for subpattern in subpatterns {
+                    self.declare_uninitialized_variables(var_extent, subpattern.pattern);
+                }
+            }
+        }
+    }
+}
+
+#[derive(Clone, Debug)]
+struct Candidate<H:Hair> {
+    // all of these must be satisfied...
+    match_pairs: Vec<MatchPair<H>>,
+
+    // ...these bindings established...
+    bindings: Vec<Binding<H>>,
+
+    // ...and the guard must be evaluated...
+    guard: Option<ExprRef<H>>,
+
+    // ...and then we branch here.
+    arm_block: BasicBlock,
+}
+
+#[derive(Clone, Debug)]
+struct Binding<H:Hair> {
+    span: H::Span,
+    source: Lvalue<H>,
+    name: H::Ident,
+    var_id: H::VarId,
+    var_ty: H::Ty,
+    mutability: Mutability,
+    binding_mode: BindingMode<H>,
+}
+
+#[derive(Clone, Debug)]
+struct MatchPair<H:Hair> {
+    // this lvalue...
+    lvalue: Lvalue<H>,
+
+    // ... must match this pattern.
+    pattern: Pattern<H>,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+enum TestKind<H:Hair> {
+    // test the branches of enum
+    Switch { adt_def: H::AdtDef },
+
+    // test for equality
+    Eq { value: Constant<H>, ty: H::Ty },
+
+    // test whether the value falls within an inclusive range
+    Range { lo: Constant<H>, hi: Constant<H>, ty: H::Ty },
+
+    // test length of the slice is equal to len
+    Len { len: usize, op: BinOp },
+}
+
+#[derive(Debug)]
+struct Test<H:Hair> {
+    span: H::Span,
+
+    // the kind of test to be performed,
+    kind: TestKind<H>,
+
+    // the outcome we expect,
+    outcome: usize,
+
+    // and the match pairs that will result
+    match_pairs: Vec<MatchPair<H>>
+}
+
+///////////////////////////////////////////////////////////////////////////
+// Main matching algorithm
+
+impl<H:Hair> Builder<H> {
+    fn match_candidates(&mut self,
+                        span: H::Span,
+                        var_extent: H::CodeExtent,
+                        mut candidates: Vec<Candidate<H>>,
+                        mut block: BasicBlock)
+    {
+        debug!("matched_candidate(span={:?}, var_extent={:?}, block={:?}, candidates={:?})",
+               span, var_extent, block, candidates);
+
+        // Start by simplifying candidates. Once this process is
+        // complete, all the match pairs which remain require some
+        // form of test, whether it be a switch or pattern comparison.
+        for candidate in &mut candidates {
+            self.simplify_candidate(candidate);
+        }
+
+        // The candidates are inversely sorted by priority. Check to
+        // see whether the candidates in the front of the queue (and
+        // hence back of the vec) have satisfied all their match
+        // pairs.
+        let fully_matched =
+            candidates.iter().rev().take_while(|c| c.match_pairs.is_empty()).count();
+        debug!("match_candidates: {:?} candidates fully matched", fully_matched);
+        for _ in 0..fully_matched {
+            // If so, apply any bindings, test the guard (if any), and
+            // branch to the arm.
+            let candidate = candidates.pop().unwrap();
+            match self.bind_and_guard_matched_candidate(block, var_extent, candidate) {
+                None => { return; }
+                Some(b) => { block = b; }
+            }
+        }
+
+        // If there are no candidates that still need testing, we're done.
+        // Since all matches are exhaustive, execution should never reach this point.
+        if candidates.is_empty() {
+            return self.panic(block);
+        }
+
+        // otherwise, extract the next match pair and construct tests
+        let match_pair = &candidates.last().unwrap().match_pairs[0];
+        let test = self.test(match_pair);
+        debug!("match_candidates: test={:?} match_pair={:?}", test, match_pair);
+        let target_blocks = self.perform_test(block, &match_pair.lvalue, &test);
+
+        for (outcome, target_block) in target_blocks.into_iter().enumerate() {
+            let applicable_candidates: Vec<Candidate<H>> =
+                candidates.iter()
+                          .filter_map(|candidate| {
+                              self.candidate_under_assumption(&match_pair.lvalue,
+                                                              &test.kind,
+                                                              outcome,
+                                                              candidate)
+                          })
+                          .collect();
+            self.match_candidates(span, var_extent, applicable_candidates, target_block);
+        }
+    }
+
+    /// Initializes each of the bindings from the candidate by
+    /// moving/copying/ref'ing the source as appropriate. Tests the
+    /// guard, if any, and then branches to the arm. Returns the block
+    /// for the case where the guard fails.
+    ///
+    /// Note: we check earlier that if there is a guard, there cannot
+    /// be move bindings.  This isn't really important for the
+    /// self-consistency of this fn, but the reason for it should be
+    /// clear: after we've done the assignments, if there were move
+    /// bindings, further tests would be a use-after-move (which would
+    /// in turn be detected by the borrowck code that runs on the
+    /// MIR).
+    fn bind_and_guard_matched_candidate(&mut self,
+                                        mut block: BasicBlock,
+                                        var_extent: H::CodeExtent,
+                                        candidate: Candidate<H>)
+                                        -> Option<BasicBlock> {
+        debug!("bind_and_guard_matched_candidate(block={:?}, var_extent={:?}, candidate={:?})",
+               block, var_extent, candidate);
+
+        debug_assert!(candidate.match_pairs.is_empty());
+
+        self.bind_matched_candidate(block, var_extent, candidate.bindings);
+
+        if let Some(guard) = candidate.guard {
+            // the block to branch to if the guard fails; if there is no
+            // guard, this block is simply unreachable
+            let cond = unpack!(block = self.as_operand(block, guard));
+            let otherwise = self.cfg.start_new_block();
+            self.cfg.terminate(block, Terminator::If { cond: cond,
+                                                       targets: [candidate.arm_block, otherwise]});
+            Some(otherwise)
+        } else {
+            self.cfg.terminate(block, Terminator::Goto { target: candidate.arm_block });
+            None
+        }
+    }
+
+    fn bind_matched_candidate(&mut self,
+                              block: BasicBlock,
+                              var_extent: H::CodeExtent,
+                              bindings: Vec<Binding<H>>) {
+        debug!("bind_matched_candidate(block={:?}, var_extent={:?}, bindings={:?})",
+               block, var_extent, bindings);
+
+        // Assign each of the bindings. This may trigger moves out of the candidate.
+        for binding in bindings {
+            // Create a variable for the `var_id` being bound. In the
+            // case where there are multiple patterns for a single
+            // arm, it may already exist.
+            let var_index = if !self.var_indices.contains_key(&binding.var_id) {
+                self.declare_binding(var_extent,
+                                     binding.mutability,
+                                     binding.name,
+                                     binding.var_id,
+                                     binding.var_ty,
+                                     binding.span)
+            } else {
+                self.var_indices[&binding.var_id]
+            };
+
+            let rvalue = match binding.binding_mode {
+                BindingMode::ByValue =>
+                    Rvalue::Use(Operand::Consume(binding.source)),
+                BindingMode::ByRef(region, borrow_kind) =>
+                    Rvalue::Ref(region, borrow_kind, binding.source),
+            };
+
+            self.cfg.push_assign(block, binding.span, &Lvalue::Var(var_index), rvalue);
+        }
+    }
+
+    fn declare_binding(&mut self,
+                       var_extent: H::CodeExtent,
+                       mutability: Mutability,
+                       name: H::Ident,
+                       var_id: H::VarId,
+                       var_ty: H::Ty,
+                       span: H::Span)
+                       -> u32
+    {
+        debug!("declare_binding(var_id={:?}, name={:?}, var_ty={:?}, var_extent={:?}, span={:?})",
+               var_id, name, var_ty, var_extent, span);
+
+        let index = self.var_decls.len();
+        self.var_decls.push(VarDecl::<H> {
+            mutability: mutability,
+            name: name,
+            ty: var_ty.clone(),
+        });
+        let index = index as u32;
+        self.schedule_drop(span, var_extent, DropKind::Deep, &Lvalue::Var(index), var_ty);
+        self.var_indices.insert(var_id, index);
+
+        debug!("declare_binding: index={:?}", index);
+
+        index
+    }
+}
+

src/librustc_mir/build/matches/simplify.rs

@@ -0,0 +1,127 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Simplifying Candidates
+//!
+//! *Simplifying* a match pair `lvalue @ pattern` means breaking it down
+//! into bindings or other, simpler match pairs. For example:
+//!
+//! - `lvalue @ (P1, P2)` can be simplified to `[lvalue.0 @ P1, lvalue.1 @ P2]`
+//! - `lvalue @ x` can be simplified to `[]` by binding `x` to `lvalue`
+//!
+//! The `simplify_candidate` routine just repeatedly applies these
+//! sort of simplifications until there is nothing left to
+//! simplify. Match pairs cannot be simplified if they require some
+//! sort of test: for example, testing which variant an enum is, or
+//! testing a value against a constant.
+
+use build::Builder;
+use build::matches::{Binding, MatchPair, Candidate};
+use hair::*;
+use repr::*;
+
+use std::mem;
+
+impl<H:Hair> Builder<H> {
+    pub fn simplify_candidate(&mut self,
+                              candidate: &mut Candidate<H>)
+    {
+        // repeatedly simplify match pairs until fixed point is reached
+        loop {
+            let match_pairs = mem::replace(&mut candidate.match_pairs, vec![]);
+            let mut progress = match_pairs.len(); // count how many were simplified
+            for match_pair in match_pairs {
+                if let Err(match_pair) = self.simplify_match_pair(match_pair, candidate) {
+                    candidate.match_pairs.push(match_pair);
+                    progress -= 1; // this one was not simplified
+                }
+            }
+            if progress == 0 {
+                return; // if we were not able to simplify any, done.
+            }
+        }
+    }
+
+    /// Tries to simplify `match_pair`, returning true if
+    /// successful. If successful, new match pairs and bindings will
+    /// have been pushed into the candidate. On failure (if false is
+    /// returned), no changes are made to candidate.
+    fn simplify_match_pair(&mut self,
+                           match_pair: MatchPair<H>,
+                           candidate: &mut Candidate<H>)
+                           -> Result<(), MatchPair<H>> // returns Err() if cannot simplify
+    {
+        match match_pair.pattern.kind {
+            PatternKind::Wild(..) => {
+                // nothing left to do
+                Ok(())
+            }
+
+            PatternKind::Binding { name, mutability, mode, var, ty, subpattern } => {
+                candidate.bindings.push(Binding {
+                    name: name,
+                    mutability: mutability,
+                    span: match_pair.pattern.span,
+                    source: match_pair.lvalue.clone(),
+                    var_id: var,
+                    var_ty: ty,
+                    binding_mode: mode,
+                });
+
+                if let Some(subpattern) = subpattern {
+                    // this is the `x @ P` case; have to keep matching against `P` now
+                    let subpattern = self.hir.mirror(subpattern);
+                    candidate.match_pairs.push(MatchPair::new(match_pair.lvalue, subpattern));
+                }
+
+                Ok(())
+            }
+
+            PatternKind::Constant { .. } => {
+                // FIXME normalize patterns when possible
+                Err(match_pair)
+            }
+
+            PatternKind::Array { prefix, slice: None, suffix } => {
+                self.append_prefix_suffix_pairs(
+                    &mut candidate.match_pairs, match_pair.lvalue.clone(), prefix, suffix);
+                Ok(())
+            }
+
+            PatternKind::Array { prefix: _, slice: Some(_), suffix: _ } => {
+                self.hir.span_bug(
+                    match_pair.pattern.span,
+                    &format!("slice patterns not implemented in MIR"));
+            }
+
+            PatternKind::Slice { .. } |
+            PatternKind::Range { .. } |
+            PatternKind::Variant { .. } => {
+                // cannot simplify, test is required
+                Err(match_pair)
+            }
+
+            PatternKind::Leaf { subpatterns } => {
+                // tuple struct, match subpats (if any)
+                candidate.match_pairs.extend(
+                    self.field_match_pairs(match_pair.lvalue, subpatterns));
+                Ok(())
+            }
+
+            PatternKind::Deref { subpattern } => {
+                let lvalue = match_pair.lvalue.deref();
+                let subpattern = self.hir.mirror(subpattern);
+                candidate.match_pairs.push(MatchPair::new(lvalue, subpattern));
+                Ok(())
+            }
+        }
+    }
+}
+

src/librustc_mir/build/matches/test.rs

@@ -0,0 +1,301 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Testing candidates
+//
+// After candidates have been simplified, the only match pairs that
+// remain are those that require some sort of test. The functions here
+// identify what tests are needed, perform the tests, and then filter
+// the candidates based on the result.
+
+use build::Builder;
+use build::matches::{Candidate, MatchPair, Test, TestKind};
+use hair::*;
+use repr::*;
+
+impl<H:Hair> Builder<H> {
+    /// Identifies what test is needed to decide if `match_pair` is applicable.
+    ///
+    /// It is a bug to call this with a simplifyable pattern.
+    pub fn test(&mut self, match_pair: &MatchPair<H>) -> Test<H> {
+        match match_pair.pattern.kind.clone() {
+            PatternKind::Variant { adt_def, variant_index, subpatterns } => {
+                let elem = ProjectionElem::Downcast(adt_def, variant_index);
+                let downcast_lvalue = match_pair.lvalue.clone().elem(elem);
+
+                let consequent_match_pairs =
+                    subpatterns.into_iter()
+                               .map(|subpattern| {
+                                   let lvalue =
+                                       downcast_lvalue.clone().field(
+                                           subpattern.field);
+                                   self.match_pair(lvalue, subpattern.pattern)
+                               })
+                               .collect();
+
+                Test {
+                    span: match_pair.pattern.span,
+                    kind: TestKind::Switch { adt_def: adt_def },
+                    outcome: variant_index,
+                    match_pairs: consequent_match_pairs,
+                }
+            }
+
+            PatternKind::Constant { expr } => {
+                let expr = self.as_constant(expr);
+                Test {
+                    span: match_pair.pattern.span,
+                    kind: TestKind::Eq { value: expr,
+                                         ty: match_pair.pattern.ty.clone() },
+                    outcome: 0, // 0 == true, of course. :)
+                    match_pairs: vec![]
+                }
+            }
+
+            PatternKind::Range { lo, hi } => {
+                let lo = self.as_constant(lo);
+                let hi = self.as_constant(hi);
+                Test {
+                    span: match_pair.pattern.span,
+                    kind: TestKind::Range { lo: lo,
+                                            hi: hi,
+                                            ty: match_pair.pattern.ty.clone() },
+                    outcome: 0, // 0 == true, of course. :)
+                    match_pairs: vec![]
+                }
+            }
+
+            PatternKind::Slice { prefix, slice: None, suffix } => {
+                let len = prefix.len() + suffix.len();
+                let mut consequent_match_pairs = vec![];
+                self.append_prefix_suffix_pairs(
+                    &mut consequent_match_pairs, match_pair.lvalue.clone(), prefix, suffix);
+                Test {
+                    span: match_pair.pattern.span,
+                    kind: TestKind::Len { len: len, op: BinOp::Eq },
+                    outcome: 0, // 0 == true, of course. :)
+                    match_pairs: consequent_match_pairs
+                }
+            }
+
+            PatternKind::Slice { prefix: _, slice: Some(_), suffix: _ } => {
+                self.hir.span_bug(
+                    match_pair.pattern.span,
+                    &format!("slice patterns not implemented in MIR"));
+            }
+
+            PatternKind::Array { .. } |
+            PatternKind::Wild |
+            PatternKind::Binding { .. } |
+            PatternKind::Leaf { .. } |
+            PatternKind::Deref { .. } => {
+                self.error_simplifyable(match_pair)
+            }
+        }
+    }
+
+    /// Generates the code to perform a test.
+    pub fn perform_test(&mut self,
+                        block: BasicBlock,
+                        lvalue: &Lvalue<H>,
+                        test: &Test<H>)
+                        -> Vec<BasicBlock> {
+        match test.kind.clone() {
+            TestKind::Switch { adt_def } => {
+                let num_enum_variants = self.hir.num_variants(adt_def);
+                let target_blocks: Vec<_> =
+                    (0..num_enum_variants).map(|_| self.cfg.start_new_block())
+                                          .collect();
+                self.cfg.terminate(block, Terminator::Switch {
+                    discr: lvalue.clone(),
+                    targets: target_blocks.clone()
+                });
+                target_blocks
+            }
+
+            TestKind::Eq { value, ty } => {
+                // call PartialEq::eq(discrim, constant)
+                let constant = self.push_constant(block, test.span, ty.clone(), value);
+                let item_ref = self.hir.partial_eq(ty);
+                self.call_comparison_fn(block, test.span, item_ref, lvalue.clone(), constant)
+            }
+
+            TestKind::Range { lo, hi, ty } => {
+                // Test `v` by computing `PartialOrd::le(lo, v) && PartialOrd::le(v, hi)`.
+                let lo = self.push_constant(block, test.span, ty.clone(), lo);
+                let hi = self.push_constant(block, test.span, ty.clone(), hi);
+                let item_ref = self.hir.partial_le(ty);
+
+                let lo_blocks =
+                    self.call_comparison_fn(block, test.span, item_ref.clone(), lo, lvalue.clone());
+
+                let hi_blocks =
+                    self.call_comparison_fn(lo_blocks[0], test.span, item_ref, lvalue.clone(), hi);
+
+                let failure = self.cfg.start_new_block();
+                self.cfg.terminate(lo_blocks[1], Terminator::Goto { target: failure });
+                self.cfg.terminate(hi_blocks[1], Terminator::Goto { target: failure });
+
+                vec![hi_blocks[0], failure]
+            }
+
+            TestKind::Len { len, op } => {
+                let (usize_ty, bool_ty) = (self.hir.usize_ty(), self.hir.bool_ty());
+                let (actual, result) = (self.temp(usize_ty), self.temp(bool_ty));
+
+                // actual = len(lvalue)
+                self.cfg.push_assign(
+                    block, test.span,
+                    &actual, Rvalue::Len(lvalue.clone()));
+
+                // expected = <N>
+                let expected =
+                    self.push_usize(block, test.span, len);
+
+                // result = actual == expected OR result = actual < expected
+                self.cfg.push_assign(
+                    block, test.span,
+                    &result, Rvalue::BinaryOp(op,
+                                              Operand::Consume(actual),
+                                              Operand::Consume(expected)));
+
+                // branch based on result
+                let target_blocks: Vec<_> = vec![self.cfg.start_new_block(),
+                                                 self.cfg.start_new_block()];
+                self.cfg.terminate(block, Terminator::If {
+                    cond: Operand::Consume(result),
+                    targets: [target_blocks[0], target_blocks[1]]
+                });
+
+                target_blocks
+            }
+        }
+    }
+
+    fn call_comparison_fn(&mut self,
+                          block: BasicBlock,
+                          span: H::Span,
+                          item_ref: ItemRef<H>,
+                          lvalue1: Lvalue<H>,
+                          lvalue2: Lvalue<H>)
+                          -> Vec<BasicBlock> {
+        let target_blocks = vec![self.cfg.start_new_block(),
+                                 self.cfg.start_new_block()];
+
+        let bool_ty = self.hir.bool_ty();
+        let eq_result = self.temp(bool_ty);
+        let func = self.push_item_ref(block, span, item_ref);
+        let call_blocks = [self.cfg.start_new_block(), self.diverge_cleanup()];
+        self.cfg.terminate(block,
+                           Terminator::Call {
+                               data: CallData {
+                                   destination: eq_result.clone(),
+                                   func: func,
+                                   args: vec![lvalue1, lvalue2],
+                               },
+                               targets: call_blocks,
+                           });
+
+        // check the result
+        self.cfg.terminate(call_blocks[0],
+                           Terminator::If {
+                               cond: Operand::Consume(eq_result),
+                               targets: [target_blocks[0], target_blocks[1]]
+                           });
+
+        target_blocks
+    }
+
+    /// Given a candidate and the outcome of a test we have performed,
+    /// transforms the candidate into a new candidate that reflects
+    /// further tests still needed. Returns `None` if this candidate
+    /// has now been ruled out.
+    ///
+    /// For example, if a candidate included the patterns `[x.0 @
+    /// Ok(P1), x.1 @ 22]`, and we did a switch test on `x.0` and
+    /// found the variant `Err` (as indicated by the `test_outcome`
+    /// parameter), we would return `None`. But if the test_outcome
+    /// were `Ok`, we would return `Some([x.0.downcast<Ok>.0 @ P1, x.1
+    /// @ 22])`.
+    pub fn candidate_under_assumption(&mut self,
+                                      test_lvalue: &Lvalue<H>,
+                                      test_kind: &TestKind<H>,
+                                      test_outcome: usize,
+                                      candidate: &Candidate<H>)
+                                      -> Option<Candidate<H>> {
+        let candidate = candidate.clone();
+        let match_pairs = candidate.match_pairs;
+        match self.match_pairs_under_assumption(test_lvalue, test_kind, test_outcome, match_pairs) {
+            Some(match_pairs) => Some(Candidate { match_pairs: match_pairs, ..candidate }),
+            None => None
+        }
+    }
+
+    /// Helper for candidate_under_assumption that does the actual
+    /// work of transforming the list of match pairs.
+    fn match_pairs_under_assumption(&mut self,
+                                    test_lvalue: &Lvalue<H>,
+                                    test_kind: &TestKind<H>,
+                                    test_outcome: usize,
+                                    match_pairs: Vec<MatchPair<H>>)
+                                    -> Option<Vec<MatchPair<H>>> {
+        let mut result = vec![];
+        for match_pair in match_pairs {
+            // if the match pair is testing a different lvalue, it
+            // is unaffected by this test.
+            if match_pair.lvalue != *test_lvalue {
+                result.push(match_pair);
+                continue;
+            }
+
+            let desired_test = self.test(&match_pair);
+
+            if *test_kind != desired_test.kind {
+                // if the match pair wants to (e.g.) test for
+                // equality against some particular constant, but
+                // we did a switch, then we can't say whether it
+                // matches or not, so we still have to include it
+                // as a possibility.
+                //
+                // For example, we have a constant `FOO:
+                // Option<i32> = Some(22)`, and `match_pair` is `x
+                // @ FOO`, but we did a switch on the variant
+                // (`Some` vs `None`). (OK, in principle this
+                // could tell us something, but we're not that
+                // smart yet to actually dig into the constant
+                // itself)
+                result.push(match_pair);
+                continue;
+            }
+
+            if test_outcome != desired_test.outcome {
+                // if we did the right kind of test, but it had the
+                // wrong outcome, then this *entire candidate* can no
+                // longer apply, huzzah! Therefore, we can stop this
+                // iteration and just return `None` to our caller.
+                return None;
+            }
+
+            // otherwise, the test passed, so we now have to include the
+            // "unlocked" set of match pairs. For example, if we had `x @
+            // Some(P1)`, and here we `test_kind==Switch` and
+            // `outcome=Some`, then we would return `x.downcast<Some>.0 @
+            // P1`.
+            result.extend(desired_test.match_pairs);
+        }
+        Some(result)
+    }
+
+    fn error_simplifyable(&mut self, match_pair: &MatchPair<H>) -> ! {
+        self.hir.span_bug(
+            match_pair.pattern.span,
+            &format!("simplifyable pattern found: {:?}", match_pair.pattern))
+    }
+}

src/librustc_mir/build/matches/util.rs

@@ -0,0 +1,82 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use build::Builder;
+use build::matches::MatchPair;
+use hair::*;
+use repr::*;
+use std::u32;
+
+impl<H:Hair> Builder<H> {
+    pub fn field_match_pairs(&mut self,
+                             lvalue: Lvalue<H>,
+                             subpatterns: Vec<FieldPatternRef<H>>)
+                             -> Vec<MatchPair<H>> {
+        subpatterns.into_iter()
+                   .map(|fieldpat| {
+                       let lvalue = lvalue.clone().field(fieldpat.field);
+                       self.match_pair(lvalue, fieldpat.pattern)
+                   })
+                   .collect()
+    }
+
+    pub fn match_pair(&mut self, lvalue: Lvalue<H>, pattern: PatternRef<H>) -> MatchPair<H> {
+        let pattern = self.hir.mirror(pattern);
+        MatchPair::new(lvalue, pattern)
+    }
+
+    pub fn append_prefix_suffix_pairs(&mut self,
+                                      match_pairs: &mut Vec<MatchPair<H>>,
+                                      lvalue: Lvalue<H>,
+                                      prefix: Vec<PatternRef<H>>,
+                                      suffix: Vec<PatternRef<H>>)
+    {
+        let min_length = prefix.len() + suffix.len();
+        assert!(min_length < u32::MAX as usize);
+        let min_length = min_length as u32;
+
+        let prefix_pairs: Vec<_> =
+            prefix.into_iter()
+                  .enumerate()
+                  .map(|(idx, subpattern)| {
+                      let elem = ProjectionElem::ConstantIndex {
+                          offset: idx as u32,
+                          min_length: min_length,
+                          from_end: false,
+                      };
+                      let lvalue = lvalue.clone().elem(elem);
+                      self.match_pair(lvalue, subpattern)
+                  })
+                  .collect();
+
+        let suffix_pairs: Vec<_> =
+            suffix.into_iter()
+                  .rev()
+                  .enumerate()
+                  .map(|(idx, subpattern)| {
+                      let elem = ProjectionElem::ConstantIndex {
+                          offset: (idx+1) as u32,
+                          min_length: min_length,
+                          from_end: true,
+                      };
+                      let lvalue = lvalue.clone().elem(elem);
+                      self.match_pair(lvalue, subpattern)
+                  })
+                  .collect();
+
+        match_pairs.extend(prefix_pairs.into_iter().chain(suffix_pairs));
+    }
+}
+
+impl<H:Hair> MatchPair<H> {
+    pub fn new(lvalue: Lvalue<H>, pattern: Pattern<H>) -> MatchPair<H> {
+        MatchPair { lvalue: lvalue, pattern: pattern }
+    }
+}

src/librustc_mir/build/misc.rs

@@ -0,0 +1,78 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Miscellaneous builder routines that are not specific to building any particular
+//! kind of thing.
+
+use build::Builder;
+use hair::*;
+use repr::*;
+
+use std::u32;
+
+impl<H:Hair> Builder<H> {
+    /// Add a new temporary value of type `ty` storing the result of
+    /// evaluating `expr`.
+    ///
+    /// NB: **No cleanup is scheduled for this temporary.** You should
+    /// call `schedule_drop` once the temporary is initialized.
+    pub fn temp(&mut self, ty: H::Ty) -> Lvalue<H> {
+        let index = self.temp_decls.len();
+        self.temp_decls.push(TempDecl { ty: ty });
+        assert!(index < (u32::MAX) as usize);
+        let lvalue = Lvalue::Temp(index as u32);
+        debug!("temp: created temp {:?} with type {:?}",
+               lvalue, self.temp_decls.last().unwrap().ty);
+        lvalue
+    }
+
+    pub fn push_constant(&mut self,
+                         block: BasicBlock,
+                         span: H::Span,
+                         ty: H::Ty,
+                         constant: Constant<H>)
+                         -> Lvalue<H> {
+        let temp = self.temp(ty);
+        self.cfg.push_assign_constant(block, span, &temp, constant);
+        temp
+    }
+
+    pub fn push_usize(&mut self,
+                      block: BasicBlock,
+                      span: H::Span,
+                      value: usize)
+                      -> Lvalue<H> {
+        let usize_ty = self.hir.usize_ty();
+        let temp = self.temp(usize_ty);
+        self.cfg.push_assign_constant(
+            block, span, &temp,
+            Constant {
+                span: span,
+                kind: ConstantKind::Literal(Literal::Uint { bits: IntegralBits::BSize,
+                                                            value: value as u64 }),
+            });
+        temp
+    }
+
+    pub fn push_item_ref(&mut self,
+                         block: BasicBlock,
+                         span: H::Span,
+                         item_ref: ItemRef<H>)
+                         -> Lvalue<H> {
+        let constant = Constant {
+            span: span,
+            kind: ConstantKind::Literal(Literal::Item {
+                def_id: item_ref.def_id,
+                substs: item_ref.substs
+            })
+        };
+        self.push_constant(block, span, item_ref.ty, constant)
+    }
+}

src/librustc_mir/build/mod.rs

@@ -0,0 +1,174 @@
+// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use hair::{self, Hair};
+use rustc_data_structures::fnv::FnvHashMap;
+use repr::*;
+
+struct Builder<H:Hair> {
+    hir: H,
+    extents: FnvHashMap<H::CodeExtent, Vec<GraphExtent>>,
+    cfg: CFG<H>,
+    scopes: Vec<scope::Scope<H>>,
+    loop_scopes: Vec<scope::LoopScope<H>>,
+    unit_temp: Lvalue<H>,
+    var_decls: Vec<VarDecl<H>>,
+    var_indices: FnvHashMap<H::VarId, u32>,
+    temp_decls: Vec<TempDecl<H>>,
+}
+
+struct CFG<H:Hair> {
+    basic_blocks: Vec<BasicBlockData<H>>
+}
+
+///////////////////////////////////////////////////////////////////////////
+// The `BlockAnd` "monad" packages up the new basic block along with a
+// produced value (sometimes just unit, of course). The `unpack!`
+// macro (and methods below) makes working with `BlockAnd` much more
+// convenient.
+
+#[must_use] // if you don't use one of these results, you're leaving a dangling edge
+struct BlockAnd<T>(BasicBlock, T);
+
+impl BasicBlock {
+    fn and<T>(self, v: T) -> BlockAnd<T> {
+        BlockAnd(self, v)
+    }
+
+    fn unit(self) -> BlockAnd<()> {
+        BlockAnd(self, ())
+    }
+}
+
+/// Update a block pointer and return the value.
+/// Use it like `let x = unpack!(block = self.foo(block, foo))`.
+macro_rules! unpack {
+    ($x:ident = $c:expr) => {
+        {
+            let BlockAnd(b, v) = $c;
+            $x = b;
+            v
+        }
+    };
+
+    ($c:expr) => {
+        {
+            let BlockAnd(b, ()) = $c;
+            b
+        }
+    };
+}
+
+///////////////////////////////////////////////////////////////////////////
+// construct() -- the main entry point for building MIR for a function
+
+pub fn construct<H:Hair>(mut hir: H,
+                        _span: H::Span,
+                        implicit_arguments: Vec<H::Ty>,
+                        explicit_arguments: Vec<(H::Ty, H::Pattern)>,
+                        argument_extent: H::CodeExtent,
+                        ast_block: H::Block)
+                        -> Mir<H> {
+    let cfg = CFG { basic_blocks: vec![] };
+
+    // it's handy to have a temporary of type `()` sometimes, so make
+    // one from the start and keep it available
+    let temp_decls = vec![TempDecl::<H> { ty: hir.unit_ty() }];
+    let unit_temp = Lvalue::Temp(0);
+
+    let mut builder = Builder {
+        hir: hir,
+        cfg: cfg,
+        extents: FnvHashMap(),
+        scopes: vec![],
+        loop_scopes: vec![],
+        temp_decls: temp_decls,
+        var_decls: vec![],
+        var_indices: FnvHashMap(),
+        unit_temp: unit_temp,
+    };
+
+    assert_eq!(builder.cfg.start_new_block(), START_BLOCK);
+    assert_eq!(builder.cfg.start_new_block(), END_BLOCK);
+    assert_eq!(builder.cfg.start_new_block(), DIVERGE_BLOCK);
+
+    let mut block = START_BLOCK;
+    let arg_decls = unpack!(block = builder.args_and_body(block,
+                                                          implicit_arguments,
+                                                          explicit_arguments,
+                                                          argument_extent,
+                                                          ast_block));
+
+    builder.cfg.terminate(block, Terminator::Goto { target: END_BLOCK });
+    builder.cfg.terminate(END_BLOCK, Terminator::Return);
+
+    Mir  {
+        basic_blocks: builder.cfg.basic_blocks,
+        extents: builder.extents,
+        var_decls: builder.var_decls,
+        arg_decls: arg_decls,
+        temp_decls: builder.temp_decls,
+    }
+}
+
+impl<H:Hair> Builder<H> {
+    fn args_and_body(&mut self,
+                     mut block: BasicBlock,
+                     implicit_arguments: Vec<H::Ty>,
+                     explicit_arguments: Vec<(H::Ty, H::Pattern)>,
+                     argument_extent: H::CodeExtent,
+                     ast_block: H::Block)
+                     -> BlockAnd<Vec<ArgDecl<H>>>
+    {
+        self.in_scope(argument_extent, block, |this| {
+            let arg_decls = {
+                let implicit_arg_decls = implicit_arguments.into_iter()
+                                                           .map(|ty| ArgDecl { ty: ty });
+
+                // to start, translate the argument patterns and collect the
+                // argument types.
+                let explicit_arg_decls =
+                    explicit_arguments
+                    .into_iter()
+                    .enumerate()
+                    .map(|(index, (ty, pattern))| {
+                        let lvalue = Lvalue::Arg(index as u32);
+                        unpack!(block = this.lvalue_into_pattern(block,
+                                                                 argument_extent,
+                                                                 hair::PatternRef::Hair(pattern),
+                                                                 &lvalue));
+                        ArgDecl { ty: ty }
+                    });
+
+                implicit_arg_decls.chain(explicit_arg_decls).collect()
+            };
+
+            // start the first basic block and translate the body
+            unpack!(block = this.ast_block(&Lvalue::ReturnPointer, block, ast_block));
+
+            block.and(arg_decls)
+        })
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////
+// Builder methods are broken up into modules, depending on what kind
+// of thing is being translated. Note that they use the `unpack` macro
+// above extensively.
+
+mod block;
+mod cfg;
+mod expr;
+mod into;
+mod matches;
+mod misc;
+mod scope;
+mod stmt;
+

src/librustc_mir/build/scope.rs

@@ -0,0 +1,304 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+/*!
+Managing the scope stack. The scopes are tied to lexical scopes, so as
+we descend the HAIR, we push a scope on the stack, translate ite
+contents, and then pop it off. Every scope is named by a
+`H::CodeExtent`.
+
+### SEME Regions
+
+When pushing a new scope, we record the current point in the graph (a
+basic block); this marks the entry to the scope. We then generate more
+stuff in the control-flow graph. Whenever the scope is exited, either
+via a `break` or `return` or just by fallthrough, that marks an exit
+from the scope. Each lexical scope thus corresponds to a single-entry,
+multiple-exit (SEME) region in the control-flow graph.
+
+For now, we keep a mapping from each `H::CodeExtent` to its
+corresponding SEME region for later reference (see caveat in next
+paragraph). This is because region scopes are tied to
+them. Eventually, when we shift to non-lexical lifetimes, three should
+be no need to remember this mapping.
+
+There is one additional wrinkle, actually, that I wanted to hide from
+you but duty compels me to mention. In the course of translating
+matches, it sometimes happen that certain code (namely guards) gets
+executed multiple times. This means that the scope lexical scope may
+in fact correspond to multiple, disjoint SEME regions. So in fact our
+mapping os from one scope to a vector of SEME regions.
+
+### Drops
+
+The primary purpose for scopes is to insert drops: while translating
+the contents, we also accumulate lvalues that need to be dropped upon
+exit from each scope. This is done by calling `schedule_drop`. Once a
+drop is scheduled, whenever we branch out we will insert drops of all
+those lvalues onto the outgoing edge. Note that we don't know the full
+set of scheduled drops up front, and so whenever we exit from the
+scope we only drop the values scheduled thus far. For example, consider
+the scope S corresponding to this loop:
+
+```
+loop {
+    let x = ...;
+    if cond { break; }
+    let y = ...;
+}
+```
+
+When processing the `let x`, we will add one drop to the scope for
+`x`.  The break will then insert a drop for `x`. When we process `let
+y`, we will add another drop (in fact, to a subscope, but let's ignore
+that for now); any later drops would also drop `y`.
+
+### Early exit
+
+There are numerous "normal" ways to early exit a scope: `break`,
+`continue`, `return` (panics are handled separately). Whenever an
+early exit occurs, the method `exit_scope` is called. It is given the
+current point in execution where the early exit occurs, as well as the
+scope you want to branch to (note that all early exits from to some
+other enclosing scope). `exit_scope` will record thid exit point and
+also add all drops.
+
+Panics are handled in a similar fashion, except that a panic always
+returns out to the `DIVERGE_BLOCK`. To trigger a panic, simply call
+`panic(p)` with the current point `p`. Or else you can call
+`diverge_cleanup`, which will produce a block that you can branch to
+which does the appropriate cleanup and then diverges. `panic(p)`
+simply calls `diverge_cleanup()` and adds an edge from `p` to the
+result.
+
+### Loop scopes
+
+In addition to the normal scope stack, we track a loop scope stack
+that contains only loops. It tracks where a `break` and `continue`
+should go to.
+
+*/
+
+use build::{BlockAnd, Builder, CFG};
+use hair::Hair;
+use repr::*;
+
+pub struct Scope<H:Hair> {
+    extent: H::CodeExtent,
+    exits: Vec<ExecutionPoint>,
+    drops: Vec<(DropKind, H::Span, Lvalue<H>)>,
+    cached_block: Option<BasicBlock>,
+}
+
+#[derive(Clone, Debug)]
+pub struct LoopScope<H:Hair> {
+    pub extent: H::CodeExtent,      // extent of the loop
+    pub continue_block: BasicBlock, // where to go on a `loop`
+    pub break_block: BasicBlock,    // where to go on a `break
+}
+
+impl<H:Hair> Builder<H> {
+    /// Start a loop scope, which tracks where `continue` and `break`
+    /// should branch to. See module comment for more details.
+    pub fn in_loop_scope<F,R>(&mut self,
+                              loop_block: BasicBlock,
+                              break_block: BasicBlock,
+                              f: F)
+                              -> BlockAnd<R>
+        where F: FnOnce(&mut Builder<H>) -> BlockAnd<R>
+    {
+        let extent = self.extent_of_innermost_scope().unwrap();
+        let loop_scope = LoopScope::<H> { extent: extent.clone(),
+                                          continue_block: loop_block,
+                                          break_block: break_block };
+        self.loop_scopes.push(loop_scope);
+        let r = f(self);
+        assert!(self.loop_scopes.pop().unwrap().extent == extent);
+        r
+    }
+
+    /// Start a scope. The closure `f` should translate the contents
+    /// of the scope. See module comment for more details.
+    pub fn in_scope<F,R>(&mut self,
+                         extent: H::CodeExtent,
+                         block: BasicBlock,
+                         f: F)
+                         -> BlockAnd<R>
+        where F: FnOnce(&mut Builder<H>) -> BlockAnd<R>
+    {
+        debug!("in_scope(extent={:?}, block={:?})", extent, block);
+
+        let start_point = self.cfg.end_point(block);
+
+        // push scope, execute `f`, then pop scope again
+        self.scopes.push(Scope {
+            extent: extent.clone(),
+            drops: vec![],
+            exits: vec![],
+            cached_block: None,
+        });
+        let BlockAnd(fallthrough_block, rv) = f(self);
+        let mut scope = self.scopes.pop().unwrap();
+
+        // add in any drops needed on the fallthrough path (any other
+        // exiting paths, such as those that arise from `break`, will
+        // have drops already)
+        for (kind, span, lvalue) in scope.drops {
+            self.cfg.push_drop(fallthrough_block, span, kind, &lvalue);
+        }
+
+        // add the implicit fallthrough edge
+        scope.exits.push(self.cfg.end_point(fallthrough_block));
+
+        // compute the extent from start to finish and store it in the graph
+        let graph_extent = self.graph_extent(start_point, scope.exits);
+        self.extents.entry(extent)
+                    .or_insert(vec![])
+                    .push(graph_extent);
+
+        debug!("in_scope: exiting extent={:?} fallthrough_block={:?}", extent, fallthrough_block);
+        fallthrough_block.and(rv)
+    }
+
+    /// Creates a graph extent (SEME region) from an entry point and
+    /// exit points.
+    fn graph_extent(&self, entry: ExecutionPoint, exits: Vec<ExecutionPoint>) -> GraphExtent {
+        if exits.len() == 1 && entry.block == exits[0].block {
+            GraphExtent { entry: entry, exit: GraphExtentExit::Statement(exits[0].statement) }
+        } else {
+            GraphExtent { entry: entry, exit: GraphExtentExit::Points(exits) }
+        }
+    }
+
+    /// Finds the loop scope for a given label. This is used for
+    /// resolving `break` and `continue`.
+    pub fn find_loop_scope(&mut self,
+                           span: H::Span,
+                           label: Option<H::CodeExtent>)
+                           -> LoopScope<H> {
+        let loop_scope =
+            match label {
+                None => {
+                    // no label? return the innermost loop scope
+                    self.loop_scopes.iter()
+                                    .rev()
+                                    .next()
+                }
+                Some(label) => {
+                    // otherwise, find the loop-scope with the correct id
+                    self.loop_scopes.iter()
+                                    .rev()
+                                    .filter(|loop_scope| loop_scope.extent == label)
+                                    .next()
+                }
+            };
+
+        match loop_scope {
+            Some(loop_scope) => loop_scope.clone(),
+            None => self.hir.span_bug(span, "no enclosing loop scope found?")
+        }
+    }
+
+    /// Branch out of `block` to `target`, exiting all scopes up to
+    /// and including `extent`.  This will insert whatever drops are
+    /// needed, as well as tracking this exit for the SEME region. See
+    /// module comment for details.
+    pub fn exit_scope(&mut self,
+                      span: H::Span,
+                      extent: H::CodeExtent,
+                      block: BasicBlock,
+                      target: BasicBlock) {
+        let popped_scopes =
+            match self.scopes.iter().rev().position(|scope| scope.extent == extent) {
+                Some(p) => p + 1,
+                None => self.hir.span_bug(span, &format!("extent {:?} does not enclose",
+                                                              extent)),
+            };
+
+        for scope in self.scopes.iter_mut().rev().take(popped_scopes) {
+            for &(kind, drop_span, ref lvalue) in &scope.drops {
+                self.cfg.push_drop(block, drop_span, kind, lvalue);
+            }
+
+            scope.exits.push(self.cfg.end_point(block));
+        }
+
+        self.cfg.terminate(block, Terminator::Goto { target: target });
+    }
+
+    /// Creates a path that performs all required cleanup for
+    /// unwinding. This path terminates in DIVERGE. Returns the start
+    /// of the path. See module comment for more details.
+    pub fn diverge_cleanup(&mut self) -> BasicBlock {
+        diverge_cleanup_helper(&mut self.cfg, &mut self.scopes)
+    }
+
+    /// Create diverge cleanup and branch to it from `block`.
+    pub fn panic(&mut self, block: BasicBlock) {
+        let cleanup = self.diverge_cleanup();
+        self.cfg.terminate(block, Terminator::Panic { target: cleanup });
+    }
+
+    /// Indicates that `lvalue` should be dropped on exit from
+    /// `extent`.
+    pub fn schedule_drop(&mut self,
+                         span: H::Span,
+                         extent: H::CodeExtent,
+                         kind: DropKind,
+                         lvalue: &Lvalue<H>,
+                         lvalue_ty: H::Ty)
+    {
+        if self.hir.needs_drop(lvalue_ty, span) {
+            match self.scopes.iter_mut().rev().find(|s| s.extent == extent) {
+                Some(scope) => {
+                    scope.drops.push((kind, span, lvalue.clone()));
+                    scope.cached_block = None;
+                }
+                None => self.hir.span_bug(span, &format!("extent {:?} not in scope to drop {:?}",
+                                                         extent, lvalue)),
+            }
+        }
+    }
+
+    pub fn extent_of_innermost_scope(&self) -> Option<H::CodeExtent> {
+        self.scopes.last().map(|scope| scope.extent)
+    }
+
+    pub fn extent_of_outermost_scope(&self) -> Option<H::CodeExtent> {
+        self.scopes.first().map(|scope| scope.extent)
+    }
+}
+
+fn diverge_cleanup_helper<H:Hair>(cfg: &mut CFG<H>,
+                                 scopes: &mut [Scope<H>])
+                                 -> BasicBlock {
+    let len = scopes.len();
+
+    if len == 0 {
+        return DIVERGE_BLOCK;
+    }
+
+    let (remaining, scope) = scopes.split_at_mut(len - 1);
+    let scope = &mut scope[0];
+
+    if let Some(b) = scope.cached_block {
+        return b;
+    }
+
+    let block = cfg.start_new_block();
+    for &(kind, span, ref lvalue) in &scope.drops {
+        cfg.push_drop(block, span, kind, lvalue);
+    }
+    scope.cached_block = Some(block);
+
+    let remaining_cleanup_block = diverge_cleanup_helper(cfg, remaining);
+    cfg.terminate(block, Terminator::Goto { target: remaining_cleanup_block });
+    block
+}

src/librustc_mir/build/stmt.rs

@@ -0,0 +1,61 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use build::{BlockAnd, Builder};
+use hair::*;
+use repr::*;
+
+impl<H:Hair> Builder<H> {
+    pub fn stmts(&mut self, mut block: BasicBlock, stmts: Vec<StmtRef<H>>) -> BlockAnd<()> {
+        for stmt in stmts {
+            unpack!(block = self.stmt(block, stmt));
+        }
+        block.unit()
+    }
+
+    pub fn stmt(&mut self, mut block: BasicBlock, stmt: StmtRef<H>) -> BlockAnd<()> {
+        let this = self;
+        let Stmt { span, kind } = this.hir.mirror(stmt);
+        match kind {
+            StmtKind::Let { remainder_scope,
+                            init_scope,
+                            pattern,
+                            initializer: Some(initializer),
+                            stmts } => {
+                this.in_scope(remainder_scope, block, |this| {
+                    unpack!(block = this.in_scope(init_scope, block, |this| {
+                        this.expr_into_pattern(block, remainder_scope, pattern, initializer)
+                    }));
+                    this.stmts(block, stmts)
+                })
+            }
+
+            StmtKind::Let { remainder_scope, init_scope, pattern, initializer: None, stmts } => {
+                this.in_scope(remainder_scope, block, |this| {
+                    unpack!(block = this.in_scope(init_scope, block, |this| {
+                        this.declare_uninitialized_variables(remainder_scope, pattern);
+                        block.unit()
+                    }));
+                    this.stmts(block, stmts)
+                })
+            }
+
+            StmtKind::Expr { scope, expr } => {
+                this.in_scope(scope, block, |this| {
+                    let expr = this.hir.mirror(expr);
+                    let temp = this.temp(expr.ty.clone());
+                    unpack!(block = this.into(&temp, block, expr));
+                    this.cfg.push_drop(block, span, DropKind::Deep, &temp);
+                    block.unit()
+                })
+            }
+        }
+    }
+}

src/librustc_mir/dump.rs

@@ -0,0 +1,225 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! An experimental pass that scources for `#[rustc_mir]` attributes,
+//! builds the resulting MIR, and dumps it out into a file for inspection.
+//!
+//! The attribute formats that are currently accepted are:
+//!
+//! - `#[rustc_mir(graphviz="file.gv")]`
+//! - `#[rustc_mir(pretty="file.mir")]`
+
+extern crate syntax;
+extern crate rustc;
+extern crate rustc_front;
+
+use build;
+use dot;
+use repr::Mir;
+use std::fs::File;
+use tcx::{PatNode, Cx};
+
+use self::rustc::middle::def_id::DefId;
+use self::rustc::middle::infer;
+use self::rustc::middle::region::CodeExtentData;
+use self::rustc::middle::ty::{self, Ty};
+use self::rustc::util::common::ErrorReported;
+use self::rustc_front::hir;
+use self::rustc_front::attr::{AttrMetaMethods};
+use self::rustc_front::visit;
+use self::syntax::ast;
+use self::syntax::codemap::Span;
+
+pub fn dump_crate(tcx: &ty::ctxt) {
+    let mut dump = OuterDump { tcx: tcx };
+    visit::walk_crate(&mut dump, tcx.map.krate());
+}
+
+///////////////////////////////////////////////////////////////////////////
+// OuterDump -- walks a crate, looking for fn items and methods to build MIR from
+
+struct OuterDump<'a,'tcx:'a> {
+    tcx: &'a ty::ctxt<'tcx>,
+}
+
+impl<'a, 'tcx> OuterDump<'a, 'tcx> {
+    fn visit_mir<OP>(&self, attributes: &'tcx [hir::Attribute], mut walk_op: OP)
+        where OP: FnMut(&mut InnerDump<'a,'tcx>)
+    {
+        let mut built_mir = false;
+
+        for attr in attributes {
+            if attr.check_name("rustc_mir") {
+                let mut closure_dump = InnerDump { tcx: self.tcx, attr: Some(attr) };
+                walk_op(&mut closure_dump);
+                built_mir = true;
+            }
+        }
+
+        let always_build_mir = self.tcx.sess.opts.always_build_mir;
+        if !built_mir && always_build_mir {
+            let mut closure_dump = InnerDump { tcx: self.tcx, attr: None };
+            walk_op(&mut closure_dump);
+        }
+    }
+}
+
+
+impl<'a, 'tcx> visit::Visitor<'tcx> for OuterDump<'a, 'tcx> {
+    fn visit_item(&mut self, item: &'tcx hir::Item) {
+        self.visit_mir(&item.attrs, |c| visit::walk_item(c, item));
+        visit::walk_item(self, item);
+    }
+
+    fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
+        match trait_item.node {
+            hir::MethodTraitItem(_, Some(_)) => {
+                self.visit_mir(&trait_item.attrs, |c| visit::walk_trait_item(c, trait_item));
+            }
+            _ => { }
+        }
+        visit::walk_trait_item(self, trait_item);
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////
+// InnerDump -- dumps MIR for a single fn and its contained closures
+
+struct InnerDump<'a,'tcx:'a> {
+    tcx: &'a ty::ctxt<'tcx>,
+    attr: Option<&'a hir::Attribute>,
+}
+
+impl<'a, 'tcx> visit::Visitor<'tcx> for InnerDump<'a,'tcx> {
+    fn visit_item(&mut self, _: &'tcx hir::Item) {
+        // ignore nested items; they need their own graphviz annotation
+    }
+
+    fn visit_fn(&mut self,
+                fk: visit::FnKind<'tcx>,
+                decl: &'tcx hir::FnDecl,
+                body: &'tcx hir::Block,
+                span: Span,
+                id: ast::NodeId) {
+        let (prefix, implicit_arg_tys) = match fk {
+            visit::FnKind::Closure =>
+                (format!("{}-", id), vec![closure_self_ty(&self.tcx, id, body.id)]),
+            _ =>
+                (format!(""), vec![]),
+        };
+
+        let param_env =
+            ty::ParameterEnvironment::for_item(self.tcx, id);
+
+        let infcx =
+            infer::new_infer_ctxt(self.tcx,
+                                  &self.tcx.tables,
+                                  Some(param_env),
+                                  true);
+
+        match build_mir(Cx::new(&infcx), implicit_arg_tys, id, span, decl, body) {
+            Ok(mir) => {
+                let meta_item_list =
+                    self.attr.iter()
+                             .flat_map(|a| a.meta_item_list())
+                             .flat_map(|l| l.iter());
+                for item in meta_item_list {
+                    if item.check_name("graphviz") {
+                        match item.value_str() {
+                            Some(s) => {
+                                match
+                                    File::create(format!("{}{}", prefix, s))
+                                    .and_then(|ref mut output| dot::render(&mir, output))
+                                {
+                                    Ok(()) => { }
+                                    Err(e) => {
+                                        self.tcx.sess.span_fatal(
+                                            item.span,
+                                            &format!("Error writing graphviz \
+                                                      results to `{}`: {}",
+                                                     s, e));
+                                    }
+                                }
+                            }
+                            None => {
+                                self.tcx.sess.span_err(
+                                    item.span,
+                                    &format!("graphviz attribute requires a path"));
+                            }
+                        }
+                    }
+                }
+            }
+            Err(ErrorReported) => { }
+        }
+
+        visit::walk_fn(self, fk, decl, body, span);
+    }
+}
+
+fn build_mir<'a,'tcx:'a>(cx: Cx<'a,'tcx>,
+                         implicit_arg_tys: Vec<Ty<'tcx>>,
+                         fn_id: ast::NodeId,
+                         span: Span,
+                         decl: &'tcx hir::FnDecl,
+                         body: &'tcx hir::Block)
+                         -> Result<Mir<Cx<'a,'tcx>>, ErrorReported> {
+    let arguments =
+        decl.inputs
+            .iter()
+            .map(|arg| {
+                let ty = cx.tcx.node_id_to_type(arg.id);
+                (ty, PatNode::irrefutable(&arg.pat))
+            })
+            .collect();
+
+    let parameter_scope =
+        cx.tcx.region_maps.lookup_code_extent(
+            CodeExtentData::ParameterScope { fn_id: fn_id, body_id: body.id });
+    Ok(build::construct(cx,
+                        span,
+                        implicit_arg_tys,
+                        arguments,
+                        parameter_scope,
+                        body))
+}
+
+fn closure_self_ty<'a,'tcx>(tcx: &ty::ctxt<'tcx>,
+                            closure_expr_id: ast::NodeId,
+                            body_id: ast::NodeId)
+                            -> Ty<'tcx>
+{
+    let closure_ty = tcx.node_id_to_type(closure_expr_id);
+
+    // We're just hard-coding the idea that the signature will be
+    // &self or &mut self and hence will have a bound region with
+    // number 0, hokey.
+    let region =
+        ty::Region::ReFree(
+            ty::FreeRegion {
+                scope: tcx.region_maps.item_extent(body_id),
+                bound_region: ty::BoundRegion::BrAnon(0)
+            });
+    let region =
+        tcx.mk_region(region);
+
+    match tcx.closure_kind(DefId::local(closure_expr_id)) {
+        ty::ClosureKind::FnClosureKind =>
+            tcx.mk_ref(region,
+                       ty::TypeAndMut { ty: closure_ty,
+                                        mutbl: hir::MutImmutable }),
+        ty::ClosureKind::FnMutClosureKind =>
+            tcx.mk_ref(region,
+                       ty::TypeAndMut { ty: closure_ty,
+                                        mutbl: hir::MutMutable }),
+        ty::ClosureKind::FnOnceClosureKind =>
+            closure_ty
+    }
+}

src/librustc_mir/graphviz/mod.rs

@@ -0,0 +1,157 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use dot;
+use hair::Hair;
+use repr::*;
+use std::borrow::IntoCow;
+
+#[derive(Copy, Clone, PartialEq, Eq)]
+pub struct EdgeIndex {
+    source: BasicBlock,
+    target: BasicBlock,
+    index: usize,
+}
+
+impl<'a,H:Hair> dot::Labeller<'a, BasicBlock, EdgeIndex> for Mir<H> {
+    fn graph_id(&'a self) -> dot::Id<'a> {
+        dot::Id::new("Mir").unwrap()
+    }
+
+    fn node_id(&'a self, n: &BasicBlock) -> dot::Id<'a> {
+        dot::Id::new(format!("BB{}", n.index())).unwrap()
+    }
+
+    fn node_shape(&'a self, _: &BasicBlock) -> Option<dot::LabelText<'a>> {
+        Some(dot::LabelText::label("none"))
+    }
+
+    fn node_label(&'a self, &n: &BasicBlock) -> dot::LabelText<'a> {
+        let mut buffer = String::new();
+        buffer.push_str("<TABLE ALIGN=\"LEFT\">");
+
+        buffer.push_str("<TR><TD>");
+        buffer.push_str(&format!("{:?}", n));
+        buffer.push_str("</TD></TR>");
+
+        let data = self.basic_block_data(n);
+        for statement in &data.statements {
+            buffer.push_str("<TR><TD>");
+            buffer.push_str(&escape(format!("{:?}", statement)));
+            buffer.push_str("</TD></TR>");
+        }
+
+        buffer.push_str("<TR><TD>");
+        buffer.push_str(&escape(format!("{:?}", &data.terminator)));
+        buffer.push_str("</TD></TR>");
+
+        buffer.push_str("</TABLE>");
+
+        dot::LabelText::html(buffer)
+    }
+
+    fn edge_label(&'a self, edge: &EdgeIndex) -> dot::LabelText<'a> {
+        dot::LabelText::label(format!("{}", edge.index))
+    }
+}
+
+impl<'a,H:Hair> dot::GraphWalk<'a, BasicBlock, EdgeIndex> for Mir<H> {
+    fn nodes(&'a self) -> dot::Nodes<'a, BasicBlock> {
+        self.all_basic_blocks().into_cow()
+    }
+
+    fn edges(&'a self) -> dot::Edges<'a, EdgeIndex> {
+        self.all_basic_blocks()
+            .into_iter()
+            .flat_map(|source| {
+                self.basic_block_data(source).terminator
+                                             .successors()
+                                             .iter()
+                                             .enumerate()
+                                             .map(move |(index, &target)| {
+                                                 EdgeIndex { source: source,
+                                                             target: target,
+                                                             index: index }
+                                             })
+            })
+            .collect::<Vec<_>>()
+            .into_cow()
+    }
+
+    fn source(&'a self, edge: &EdgeIndex) -> BasicBlock {
+        edge.source
+    }
+
+    fn target(&'a self, edge: &EdgeIndex) -> BasicBlock {
+        edge.target
+    }
+}
+
+fn escape(text: String) -> String {
+    let text = dot::escape_html(&text);
+    let text = all_to_subscript("Temp", text);
+    let text = all_to_subscript("Var", text);
+    let text = all_to_subscript("Arg", text);
+    let text = all_to_subscript("BB", text);
+    text
+}
+
+/// A call like `all_to_subscript("Temp", "Temp(123)")` will convert
+/// to `Temp₁₂₃`.
+fn all_to_subscript(header: &str, mut text: String) -> String {
+    let mut offset = 0;
+    while offset < text.len() {
+        if let Some(text1) = to_subscript1(header, &text, &mut offset) {
+            text = text1;
+        }
+    }
+    return text;
+
+    /// Looks for `Foo(\d*)` where `header=="Foo"` and replaces the `\d` with subscripts.
+    /// Updates `offset` to point to the next location where we might want to search.
+    /// Returns an updated string if changes were made, else None.
+    fn to_subscript1(header: &str, text: &str, offset: &mut usize) -> Option<String> {
+        let a = match text[*offset..].find(header) {
+            None => { *offset = text.len(); return None; }
+            Some(a) => a + *offset,
+        };
+
+        // Example:
+        //
+        // header: "Foo"
+        // text:   ....Foo(123)...
+        //             ^  ^
+        //             a  b
+
+        let b = a + header.len();
+        *offset = b;
+
+        let mut chars = text[b..].chars();
+        if Some('(') != chars.next() {
+            return None;
+        }
+
+        let mut result = String::new();
+        result.push_str(&text[..b]);
+
+        while let Some(c) = chars.next() {
+            if c == ')' { break; }
+            if !c.is_digit(10) { return None; }
+
+            // 0x208 is _0 in unicode, 0x209 is _1, etc
+            const SUBSCRIPTS: &'static str = "₀₁₂₃₄₅₆₇₈₉";
+            let n = (c as usize) - ('0' as usize);
+            result.extend(SUBSCRIPTS.chars().skip(n).take(1));
+        }
+
+        result.extend(chars);
+        return Some(result);
+    }
+}

src/librustc_mir/hair.rs

@@ -0,0 +1,382 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! The MIR is translated from some high-level abstract IR
+//! (HAIR). This section defines the HAIR along with a trait for
+//! accessing it. The intention is to allow MIR construction to be
+//! unit-tested and separated from the Rust source and compiler data
+//! structures.
+
+use repr::{BinOp, BorrowKind, Field, Literal, Mutability, UnOp};
+use std::fmt::Debug;
+use std::hash::Hash;
+
+pub trait Hair: Sized+Debug+Clone+Eq+Hash { // (*)
+
+    // (*) the `Sized` and Debug` bounds are the only ones that really
+    // make sense.  The rest are just there so that we can
+    // `#[derive(Clone)]` on things that are parameterized over
+    // `H:HAIR`. It's kind of lame.
+
+    type VarId: Copy+Debug+Eq+Hash;                              // e.g., NodeId for a variable
+    type DefId: Copy+Debug+Eq+Hash;                              // e.g., DefId
+    type AdtDef: Copy+Debug+Eq+Hash;                             // e.g., AdtDef<'tcx>
+    type Name: Copy+Debug+Eq+Hash;                               // e.g., ast::Name
+    type Ident: Copy+Debug+Eq+Hash;                              // e.g., ast::Ident
+    type InternedString: Clone+Debug+Eq+Hash;                    // e.g., InternedString
+    type Bytes: Clone+Debug+Eq+Hash;                             // e.g., Rc<Vec<u8>>
+    type Span: Copy+Debug+Eq;                                    // e.g., syntax::codemap::Span
+    type Projection: Clone+Debug+Eq;                             // e.g., ty::ProjectionTy<'tcx>
+    type Substs: Clone+Debug+Eq;                                 // e.g., substs::Substs<'tcx>
+    type ClosureSubsts: Clone+Debug+Eq;                          // e.g., ty::ClosureSubsts<'tcx>
+    type Ty: Clone+Debug+Eq;                                     // e.g., ty::Ty<'tcx>
+    type Region: Copy+Debug;                                     // e.g., ty::Region
+    type CodeExtent: Copy+Debug+Hash+Eq;                         // e.g., region::CodeExtent
+    type Pattern: Clone+Debug+Mirror<Self,Output=Pattern<Self>>; // e.g., &P<ast::Pat>
+    type Expr: Clone+Debug+Mirror<Self,Output=Expr<Self>>;       // e.g., &P<ast::Expr>
+    type Stmt: Clone+Debug+Mirror<Self,Output=Stmt<Self>>;       // e.g., &P<ast::Stmt>
+    type Block: Clone+Debug+Mirror<Self,Output=Block<Self>>;     // e.g., &P<ast::Block>
+    type InlineAsm: Clone+Debug+Eq+Hash;                         // e.g., ast::InlineAsm
+
+    /// Normalizes `ast` into the appropriate `mirror` type.
+    fn mirror<M:Mirror<Self>>(&mut self, ast: M) -> M::Output {
+        ast.make_mirror(self)
+    }
+
+    /// Returns the unit type `()`
+    fn unit_ty(&mut self) -> Self::Ty;
+
+    /// Returns the type `usize`.
+    fn usize_ty(&mut self) -> Self::Ty;
+
+    /// Returns the type `bool`.
+    fn bool_ty(&mut self) -> Self::Ty;
+
+    /// Returns a reference to `PartialEq::<T,T>::eq`
+    fn partial_eq(&mut self, ty: Self::Ty) -> ItemRef<Self>;
+
+    /// Returns a reference to `PartialOrd::<T,T>::le`
+    fn partial_le(&mut self, ty: Self::Ty) -> ItemRef<Self>;
+
+    /// Returns the number of variants for the given enum
+    fn num_variants(&mut self, adt: Self::AdtDef) -> usize;
+
+    fn fields(&mut self, adt: Self::AdtDef, variant_index: usize) -> Vec<Field<Self>>;
+
+    /// true if a value of type `ty` (may) need to be dropped; this
+    /// may return false even for non-Copy types if there is no
+    /// destructor to execute. If correct result is not known, may be
+    /// approximated by returning `true`; this will result in more
+    /// drops but not incorrect code.
+    fn needs_drop(&mut self, ty: Self::Ty, span: Self::Span) -> bool;
+
+    /// Report an internal inconsistency.
+    fn span_bug(&mut self, span: Self::Span, message: &str) -> !;
+}
+
+#[derive(Clone, Debug)]
+pub struct ItemRef<H:Hair> {
+    pub ty: H::Ty,
+    pub def_id: H::DefId,
+    pub substs: H::Substs,
+}
+
+#[derive(Clone, Debug)]
+pub struct Block<H:Hair> {
+    pub extent: H::CodeExtent,
+    pub span: H::Span,
+    pub stmts: Vec<StmtRef<H>>,
+    pub expr: Option<ExprRef<H>>,
+}
+
+#[derive(Clone, Debug)]
+pub enum StmtRef<H:Hair> {
+    Hair(H::Stmt),
+    Mirror(Box<Stmt<H>>),
+}
+
+#[derive(Clone, Debug)]
+pub struct Stmt<H:Hair> {
+    pub span: H::Span,
+    pub kind: StmtKind<H>,
+}
+
+#[derive(Clone, Debug)]
+pub enum StmtKind<H:Hair> {
+    Expr {
+        /// scope for this statement; may be used as lifetime of temporaries
+        scope: H::CodeExtent,
+
+        /// expression being evaluated in this statement
+        expr: ExprRef<H>
+    },
+
+    Let {
+        /// scope for variables bound in this let; covers this and
+        /// remaining statements in block
+        remainder_scope: H::CodeExtent,
+
+        /// scope for the initialization itself; might be used as
+        /// lifetime of temporaries
+        init_scope: H::CodeExtent,
+
+        /// let <PAT> = ...
+        pattern: PatternRef<H>,
+
+        /// let pat = <INIT> ...
+        initializer: Option<ExprRef<H>>,
+
+        /// let pat = init; <STMTS>
+        stmts: Vec<StmtRef<H>>
+    },
+}
+
+// The Hair trait implementor translates their expressions (`H::Expr`)
+// into instances of this `Expr` enum. This translation can be done
+// basically as lazilly or as eagerly as desired: every recursive
+// reference to an expression in this enum is an `ExprRef<H>`, which
+// may in turn be another instance of this enum (boxed), or else an
+// untranslated `H::Expr`. Note that instances of `Expr` are very
+// shortlived. They are created by `Hair::to_expr`, analyzed and
+// converted into MIR, and then discarded.
+//
+// If you compare `Expr` to the full compiler AST, you will see it is
+// a good bit simpler. In fact, a number of the more straight-forward
+// MIR simplifications are already done in the impl of `Hair`. For
+// example, method calls and overloaded operators are absent: they are
+// expected to be converted into `Expr::Call` instances.
+#[derive(Clone, Debug)]
+pub struct Expr<H:Hair> {
+    // type of this expression
+    pub ty: H::Ty,
+
+    // lifetime of this expression if it should be spilled into a
+    // temporary; should be None only if in a constant context
+    pub temp_lifetime: Option<H::CodeExtent>,
+
+    // span of the expression in the source
+    pub span: H::Span,
+
+    // kind of expression
+    pub kind: ExprKind<H>,
+}
+
+#[derive(Clone, Debug)]
+pub enum ExprKind<H:Hair> {
+    Scope { extent: H::CodeExtent, value: ExprRef<H> },
+    Paren { arg: ExprRef<H> }, // ugh. should be able to remove this!
+    Box { place: Option<ExprRef<H>>, value: ExprRef<H> },
+    Call { fun: ExprRef<H>, args: Vec<ExprRef<H>> },
+    Deref { arg: ExprRef<H> }, // NOT overloaded!
+    Binary { op: BinOp, lhs: ExprRef<H>, rhs: ExprRef<H> }, // NOT overloaded!
+    LogicalOp { op: LogicalOp, lhs: ExprRef<H>, rhs: ExprRef<H> },
+    Unary { op: UnOp, arg: ExprRef<H> }, // NOT overloaded!
+    Cast { source: ExprRef<H> },
+    ReifyFnPointer { source: ExprRef<H> },
+    UnsafeFnPointer { source: ExprRef<H> },
+    Unsize { source: ExprRef<H> },
+    If { condition: ExprRef<H>, then: ExprRef<H>, otherwise: Option<ExprRef<H>> },
+    Loop { condition: Option<ExprRef<H>>, body: ExprRef<H>, },
+    Match { discriminant: ExprRef<H>, arms: Vec<Arm<H>> },
+    Block { body: H::Block },
+    Assign { lhs: ExprRef<H>, rhs: ExprRef<H> },
+    AssignOp { op: BinOp, lhs: ExprRef<H>, rhs: ExprRef<H> },
+    Field { lhs: ExprRef<H>, name: Field<H> },
+    Index { lhs: ExprRef<H>, index: ExprRef<H> },
+    VarRef { id: H::VarId },
+    SelfRef, // first argument, used for self in a closure
+    StaticRef { id: H::DefId },
+    Borrow { region: H::Region, borrow_kind: BorrowKind, arg: ExprRef<H> },
+    Break { label: Option<H::CodeExtent> },
+    Continue { label: Option<H::CodeExtent> },
+    Return { value: Option<ExprRef<H>> },
+    Repeat { value: ExprRef<H>, count: ExprRef<H> },
+    Vec { fields: Vec<ExprRef<H>> },
+    Tuple { fields: Vec<ExprRef<H>> },
+    Adt { adt_def: H::AdtDef,
+          variant_index: usize,
+          substs: H::Substs,
+          fields: Vec<FieldExprRef<H>>,
+          base: Option<ExprRef<H>> },
+    Closure { closure_id: H::DefId, substs: H::ClosureSubsts,
+              upvars: Vec<ExprRef<H>> },
+    Literal { literal: Literal<H> },
+    InlineAsm { asm: H::InlineAsm },
+}
+
+#[derive(Clone, Debug)]
+pub enum ExprRef<H:Hair> {
+    Hair(H::Expr),
+    Mirror(Box<Expr<H>>),
+}
+
+#[derive(Clone, Debug)]
+pub struct FieldExprRef<H:Hair> {
+    pub name: Field<H>,
+    pub expr: ExprRef<H>,
+}
+
+#[derive(Clone, Debug)]
+pub struct Arm<H:Hair> {
+    pub patterns: Vec<PatternRef<H>>,
+    pub guard: Option<ExprRef<H>>,
+    pub body: ExprRef<H>,
+}
+
+#[derive(Clone, Debug)]
+pub struct Pattern<H:Hair> {
+    pub ty: H::Ty,
+    pub span: H::Span,
+    pub kind: PatternKind<H>,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub enum LogicalOp {
+    And,
+    Or
+}
+
+#[derive(Clone, Debug)]
+pub enum PatternKind<H:Hair> {
+    Wild,
+
+    // x, ref x, x @ P, etc
+    Binding { mutability: Mutability,
+              name: H::Ident,
+              mode: BindingMode<H>,
+              var: H::VarId,
+              ty: H::Ty,
+              subpattern: Option<PatternRef<H>> },
+
+    // Foo(...) or Foo{...} or Foo, where `Foo` is a variant name from an adt with >1 variants
+    Variant { adt_def: H::AdtDef, variant_index: usize, subpatterns: Vec<FieldPatternRef<H>> },
+
+    // (...), Foo(...), Foo{...}, or Foo, where `Foo` is a variant name from an adt with 1 variant
+    Leaf { subpatterns: Vec<FieldPatternRef<H>> },
+
+    Deref { subpattern: PatternRef<H> }, // box P, &P, &mut P, etc
+
+    Constant { expr: ExprRef<H> },
+
+    Range { lo: ExprRef<H>, hi: ExprRef<H> },
+
+    // matches against a slice, checking the length and extracting elements
+    Slice { prefix: Vec<PatternRef<H>>,
+            slice: Option<PatternRef<H>>,
+            suffix: Vec<PatternRef<H>> },
+
+    // fixed match against an array, irrefutable
+    Array { prefix: Vec<PatternRef<H>>,
+            slice: Option<PatternRef<H>>,
+            suffix: Vec<PatternRef<H>> },
+}
+
+#[derive(Copy, Clone, Debug)]
+pub enum BindingMode<H:Hair> {
+    ByValue,
+    ByRef(H::Region, BorrowKind),
+}
+
+#[derive(Clone, Debug)]
+pub enum PatternRef<H:Hair> {
+    Hair(H::Pattern),
+    Mirror(Box<Pattern<H>>),
+}
+
+#[derive(Clone, Debug)]
+pub struct FieldPatternRef<H:Hair> {
+    pub field: Field<H>,
+    pub pattern: PatternRef<H>,
+}
+
+///////////////////////////////////////////////////////////////////////////
+// The Mirror trait
+
+/// "Mirroring" is the process of converting from a Hair type into one
+/// of the types in this file. For example, the mirror of a `H::Expr`
+/// is an `Expr<H>`. Mirroring is the point at which the actual IR is
+/// converting into the more idealized representation described in
+/// this file. Mirroring is gradual: when you mirror an outer
+/// expression like `e1 + e2`, the references to the inner expressions
+/// `e1` and `e2` are `ExprRef<H>` instances, and they may or may not
+/// be eagerly mirrored.  This allows a single AST node from the
+/// compiler to expand into one or more Hair nodes, which lets the Hair
+/// nodes be simpler.
+pub trait Mirror<H:Hair> {
+    type Output;
+
+    fn make_mirror(self, hir: &mut H) -> Self::Output;
+}
+
+impl<H:Hair> Mirror<H> for Expr<H> {
+    type Output = Expr<H>;
+
+    fn make_mirror(self, _: &mut H) -> Expr<H> {
+        self
+    }
+}
+
+impl<H:Hair> Mirror<H> for ExprRef<H> {
+    type Output = Expr<H>;
+
+    fn make_mirror(self, hir: &mut H) -> Expr<H> {
+        match self {
+            ExprRef::Hair(h) => h.make_mirror(hir),
+            ExprRef::Mirror(m) => *m,
+        }
+    }
+}
+
+impl<H:Hair> Mirror<H> for Stmt<H> {
+    type Output = Stmt<H>;
+
+    fn make_mirror(self, _: &mut H) -> Stmt<H> {
+        self
+    }
+}
+
+impl<H:Hair> Mirror<H> for StmtRef<H> {
+    type Output = Stmt<H>;
+
+    fn make_mirror(self, hir: &mut H) -> Stmt<H> {
+        match self {
+            StmtRef::Hair(h) => h.make_mirror(hir),
+            StmtRef::Mirror(m) => *m,
+        }
+    }
+}
+
+impl<H:Hair> Mirror<H> for Pattern<H> {
+    type Output = Pattern<H>;
+
+    fn make_mirror(self, _: &mut H) -> Pattern<H> {
+        self
+    }
+}
+
+impl<H:Hair> Mirror<H> for PatternRef<H> {
+    type Output = Pattern<H>;
+
+    fn make_mirror(self, hir: &mut H) -> Pattern<H> {
+        match self {
+            PatternRef::Hair(h) => h.make_mirror(hir),
+            PatternRef::Mirror(m) => *m,
+        }
+    }
+}
+
+impl<H:Hair> Mirror<H> for Block<H> {
+    type Output = Block<H>;
+
+    fn make_mirror(self, _: &mut H) -> Block<H> {
+        self
+    }
+}
+

src/librustc_mir/lib.rs

@@ -0,0 +1,34 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+/*!
+
+Rust MIR: a lowered representation of Rust. Also: an experiment!
+
+*/
+
+#![crate_name = "rustc_mir"]
+#![crate_type = "rlib"]
+#![crate_type = "dylib"]
+
+#![feature(ref_slice)]
+#![feature(rustc_private)]
+#![feature(into_cow)]
+
+#[macro_use] extern crate log;
+extern crate graphviz as dot;
+extern crate rustc_data_structures;
+
+pub mod build;
+pub mod dump;
+pub mod hair;
+pub mod repr;
+mod graphviz;
+mod tcx;

src/librustc_mir/repr.rs

@@ -0,0 +1,676 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use hair::Hair;
+use rustc_data_structures::fnv::FnvHashMap;
+use std::fmt::{Debug, Formatter, Error};
+use std::slice;
+use std::u32;
+
+/// Lowered representation of a single function.
+pub struct Mir<H:Hair> {
+    pub basic_blocks: Vec<BasicBlockData<H>>,
+
+    // for every node id
+    pub extents: FnvHashMap<H::CodeExtent, Vec<GraphExtent>>,
+
+    pub var_decls: Vec<VarDecl<H>>,
+    pub arg_decls: Vec<ArgDecl<H>>,
+    pub temp_decls: Vec<TempDecl<H>>,
+}
+
+/// where execution begins
+pub const START_BLOCK: BasicBlock = BasicBlock(0);
+
+/// where execution ends, on normal return
+pub const END_BLOCK: BasicBlock = BasicBlock(1);
+
+/// where execution ends, on panic
+pub const DIVERGE_BLOCK: BasicBlock = BasicBlock(2);
+
+impl<H:Hair> Mir<H> {
+    pub fn all_basic_blocks(&self) -> Vec<BasicBlock> {
+        (0..self.basic_blocks.len())
+            .map(|i| BasicBlock::new(i))
+            .collect()
+    }
+
+    pub fn basic_block_data(&self, bb: BasicBlock) -> &BasicBlockData<H> {
+        &self.basic_blocks[bb.index()]
+    }
+
+    pub fn basic_block_data_mut(&mut self, bb: BasicBlock) -> &mut BasicBlockData<H> {
+        &mut self.basic_blocks[bb.index()]
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////
+// Mutability and borrow kinds
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum Mutability {
+    Mut,
+    Not,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum BorrowKind {
+    /// Data must be immutable and is aliasable.
+    Shared,
+
+    /// Data must be immutable but not aliasable.  This kind of borrow
+    /// cannot currently be expressed by the user and is used only in
+    /// implicit closure bindings. It is needed when you the closure
+    /// is borrowing or mutating a mutable referent, e.g.:
+    ///
+    ///    let x: &mut isize = ...;
+    ///    let y = || *x += 5;
+    ///
+    /// If we were to try to translate this closure into a more explicit
+    /// form, we'd encounter an error with the code as written:
+    ///
+    ///    struct Env { x: & &mut isize }
+    ///    let x: &mut isize = ...;
+    ///    let y = (&mut Env { &x }, fn_ptr);  // Closure is pair of env and fn
+    ///    fn fn_ptr(env: &mut Env) { **env.x += 5; }
+    ///
+    /// This is then illegal because you cannot mutate a `&mut` found
+    /// in an aliasable location. To solve, you'd have to translate with
+    /// an `&mut` borrow:
+    ///
+    ///    struct Env { x: & &mut isize }
+    ///    let x: &mut isize = ...;
+    ///    let y = (&mut Env { &mut x }, fn_ptr); // changed from &x to &mut x
+    ///    fn fn_ptr(env: &mut Env) { **env.x += 5; }
+    ///
+    /// Now the assignment to `**env.x` is legal, but creating a
+    /// mutable pointer to `x` is not because `x` is not mutable. We
+    /// could fix this by declaring `x` as `let mut x`. This is ok in
+    /// user code, if awkward, but extra weird for closures, since the
+    /// borrow is hidden.
+    ///
+    /// So we introduce a "unique imm" borrow -- the referent is
+    /// immutable, but not aliasable. This solves the problem. For
+    /// simplicity, we don't give users the way to express this
+    /// borrow, it's just used when translating closures.
+    Unique,
+
+    /// Data is mutable and not aliasable.
+    Mut
+}
+
+///////////////////////////////////////////////////////////////////////////
+// Variables and temps
+
+// A "variable" is a binding declared by the user as part of the fn
+// decl, a let, etc.
+pub struct VarDecl<H:Hair> {
+    pub mutability: Mutability,
+    pub name: H::Ident,
+    pub ty: H::Ty,
+}
+
+// A "temp" is a temporary that we place on the stack. They are
+// anonymous, always mutable, and have only a type.
+pub struct TempDecl<H:Hair> {
+    pub ty: H::Ty,
+}
+
+// A "arg" is one of the function's formal arguments. These are
+// anonymous and distinct from the bindings that the user declares.
+//
+// For example, in this function:
+//
+// ```
+// fn foo((x, y): (i32, u32)) { ... }
+// ```
+//
+// there is only one argument, of type `(i32, u32)`, but two bindings
+// (`x` and `y`).
+pub struct ArgDecl<H:Hair> {
+    pub ty: H::Ty,
+}
+
+///////////////////////////////////////////////////////////////////////////
+// Graph extents
+
+/// A moment in the flow of execution. It corresponds to a point in
+/// between two statements:
+///
+///    BB[block]:
+///                          <--- if statement == 0
+///        STMT[0]
+///                          <--- if statement == 1
+///        STMT[1]
+///        ...
+///                          <--- if statement == n-1
+///        STMT[n-1]
+///                          <--- if statement == n
+///
+/// where the block has `n` statements.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct ExecutionPoint {
+    pub block: BasicBlock,
+    pub statement: u32,
+}
+
+/// A single-entry-multiple-exit region in the graph. We build one of
+/// these for every node-id during MIR construction. By construction
+/// we are assured that the entry dominates all points within, and
+/// that, for every interior point X, it is postdominated by some exit.
+pub struct GraphExtent {
+    pub entry: ExecutionPoint,
+    pub exit: GraphExtentExit,
+}
+
+pub enum GraphExtentExit {
+    /// `Statement(X)`: a very common special case covering a span
+    /// that is local to a single block. It starts at the entry point
+    /// and extends until the start of statement `X` (non-inclusive).
+    Statement(u32),
+
+    /// The more general case where the exits are a set of points.
+    Points(Vec<ExecutionPoint>),
+}
+
+///////////////////////////////////////////////////////////////////////////
+// BasicBlock
+
+/// The index of a particular basic block. The index is into the `basic_blocks`
+/// list of the `Mir`.
+///
+/// (We use a `u32` internally just to save memory.)
+#[derive(Copy, Clone, PartialEq, Eq)]
+pub struct BasicBlock(u32);
+
+impl BasicBlock {
+    pub fn new(index: usize) -> BasicBlock {
+        assert!(index < (u32::MAX as usize));
+        BasicBlock(index as u32)
+    }
+
+    /// Extract the index.
+    pub fn index(self) -> usize {
+        self.0 as usize
+    }
+}
+
+impl Debug for BasicBlock {
+    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
+        write!(fmt, "BB({})", self.0)
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////
+// BasicBlock and Terminator
+
+#[derive(Debug)]
+pub struct BasicBlockData<H:Hair> {
+    pub statements: Vec<Statement<H>>,
+    pub terminator: Terminator<H>,
+}
+
+pub enum Terminator<H:Hair> {
+    /// block should have one successor in the graph; we jump there
+    Goto { target: BasicBlock },
+
+    /// block should initiate unwinding; should be one successor
+    /// that does cleanup and branches to DIVERGE_BLOCK
+    Panic { target: BasicBlock },
+
+    /// jump to branch 0 if this lvalue evaluates to true
+    If { cond: Operand<H>, targets: [BasicBlock; 2] },
+
+    /// lvalue evaluates to some enum; jump depending on the branch
+    Switch { discr: Lvalue<H>, targets: Vec<BasicBlock> },
+
+    /// Indicates that the last statement in the block panics, aborts,
+    /// etc. No successors. This terminator appears on exactly one
+    /// basic block which we create in advance. However, during
+    /// construction, we use this value as a sentinel for "terminator
+    /// not yet assigned", and assert at the end that only the
+    /// well-known diverging block actually diverges.
+    Diverge,
+
+    /// Indicates a normal return. The ReturnPointer lvalue should
+    /// have been filled in by now. This should only occur in the
+    /// `END_BLOCK`.
+    Return,
+
+    /// block ends with a call; it should have two successors. The
+    /// first successor indicates normal return. The second indicates
+    /// unwinding.
+    Call { data: CallData<H>, targets: [BasicBlock; 2] },
+}
+
+impl<H:Hair> Terminator<H> {
+    pub fn successors(&self) -> &[BasicBlock] {
+        use self::Terminator::*;
+        match *self {
+            Goto { target: ref b } => slice::ref_slice(b),
+            Panic { target: ref b } => slice::ref_slice(b),
+            If { cond: _, targets: ref b } => b,
+            Switch { discr: _, targets: ref b } => b,
+            Diverge => &[],
+            Return => &[],
+            Call { data: _, targets: ref b } => b,
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct CallData<H:Hair> {
+    /// where the return value is written to
+    pub destination: Lvalue<H>,
+
+    /// the fn being called
+    pub func: Lvalue<H>,
+
+    /// the arguments
+    pub args: Vec<Lvalue<H>>,
+}
+
+impl<H:Hair> BasicBlockData<H> {
+    pub fn new(terminator: Terminator<H>) -> BasicBlockData<H> {
+        BasicBlockData {
+            statements: vec![],
+            terminator: terminator,
+        }
+    }
+}
+
+impl<H:Hair> Debug for Terminator<H> {
+    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
+        use self::Terminator::*;
+        match *self {
+            Goto { target } =>
+                write!(fmt, "goto -> {:?}", target),
+            Panic { target } =>
+                write!(fmt, "panic -> {:?}", target),
+            If { cond: ref lv, ref targets } =>
+                write!(fmt, "if({:?}) -> {:?}", lv, targets),
+            Switch { discr: ref lv, ref targets } =>
+                write!(fmt, "switch({:?}) -> {:?}", lv, targets),
+            Diverge =>
+                write!(fmt, "diverge"),
+            Return =>
+                write!(fmt, "return"),
+            Call { data: ref c, targets } => {
+                try!(write!(fmt, "{:?} = {:?}(", c.destination, c.func));
+                for (index, arg) in c.args.iter().enumerate() {
+                    if index > 0 { try!(write!(fmt, ", ")); }
+                    try!(write!(fmt, "{:?}", arg));
+                }
+                write!(fmt, ") -> {:?}", targets)
+            }
+        }
+    }
+}
+
+
+///////////////////////////////////////////////////////////////////////////
+// Statements
+
+pub struct Statement<H:Hair> {
+    pub span: H::Span,
+    pub kind: StatementKind<H>,
+}
+
+#[derive(Debug)]
+pub enum StatementKind<H:Hair> {
+    Assign(Lvalue<H>, Rvalue<H>),
+    Drop(DropKind, Lvalue<H>),
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum DropKind {
+    Shallow,
+    Deep
+}
+
+impl<H:Hair> Debug for Statement<H> {
+    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
+        use self::StatementKind::*;
+        match self.kind {
+            Assign(ref lv, ref rv) => write!(fmt, "{:?} = {:?}", lv, rv),
+            Drop(DropKind::Shallow, ref lv) => write!(fmt, "shallow_drop {:?}", lv),
+            Drop(DropKind::Deep, ref lv) => write!(fmt, "drop {:?}", lv),
+        }
+    }
+}
+///////////////////////////////////////////////////////////////////////////
+// Lvalues
+
+/// A path to a value; something that can be evaluated without
+/// changing or disturbing program state.
+#[derive(Clone, PartialEq)]
+pub enum Lvalue<H:Hair> {
+    /// local variable declared by the user
+    Var(u32),
+
+    /// temporary introduced during lowering into MIR
+    Temp(u32),
+
+    /// formal parameter of the function; note that these are NOT the
+    /// bindings that the user declares, which are vars
+    Arg(u32),
+
+    /// static or static mut variable
+    Static(H::DefId),
+
+    /// the return pointer of the fn
+    ReturnPointer,
+
+    /// projection out of an lvalue (access a field, deref a pointer, etc)
+    Projection(Box<LvalueProjection<H>>)
+}
+
+/// The `Projection` data structure defines things of the form `B.x`
+/// or `*B` or `B[index]`. Note that it is parameterized because it is
+/// shared between `Constant` and `Lvalue`. See the aliases
+/// `LvalueProjection` etc below.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Projection<H:Hair,B,V> {
+    pub base: B,
+    pub elem: ProjectionElem<H,V>,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum ProjectionElem<H:Hair,V> {
+    Deref,
+    Field(Field<H>),
+    Index(V),
+
+    // These indices are generated by slice patterns. Easiest to explain
+    // by example:
+    //
+    // ```
+    // [X, _, .._, _, _] => { offset: 0, min_length: 4, from_end: false },
+    // [_, X, .._, _, _] => { offset: 1, min_length: 4, from_end: false },
+    // [_, _, .._, X, _] => { offset: 2, min_length: 4, from_end: true },
+    // [_, _, .._, _, X] => { offset: 1, min_length: 4, from_end: true },
+    // ```
+    ConstantIndex {
+        offset: u32,      // index or -index (in Python terms), depending on from_end
+        min_length: u32,  // thing being indexed must be at least this long
+        from_end: bool,   // counting backwards from end?
+    },
+
+    // "Downcast" to a variant of an ADT. Currently, we only introduce
+    // this for ADTs with more than one variant. It may be better to
+    // just introduce it always, or always for enums.
+    Downcast(H::AdtDef, usize),
+}
+
+/// Alias for projections as they appear in lvalues, where the base is an lvalue
+/// and the index is an operand.
+pub type LvalueProjection<H> =
+    Projection<H,Lvalue<H>,Operand<H>>;
+
+/// Alias for projections as they appear in lvalues, where the base is an lvalue
+/// and the index is an operand.
+pub type LvalueElem<H> =
+    ProjectionElem<H,Operand<H>>;
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub enum Field<H:Hair> {
+    Named(H::Name),
+    Indexed(usize),
+}
+
+impl<H:Hair> Lvalue<H> {
+    pub fn field(self, f: Field<H>) -> Lvalue<H> {
+        self.elem(ProjectionElem::Field(f))
+    }
+
+    pub fn deref(self) -> Lvalue<H> {
+        self.elem(ProjectionElem::Deref)
+    }
+
+    pub fn index(self, index: Operand<H>) -> Lvalue<H> {
+        self.elem(ProjectionElem::Index(index))
+    }
+
+    pub fn elem(self, elem: LvalueElem<H>) -> Lvalue<H> {
+        Lvalue::Projection(Box::new(LvalueProjection { base: self, elem: elem }))
+    }
+}
+
+impl<H:Hair> Debug for Lvalue<H> {
+    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
+        use self::Lvalue::*;
+
+        match *self {
+            Var(id) =>
+                write!(fmt,"Var({:?})", id),
+            Arg(id) =>
+                write!(fmt,"Arg({:?})", id),
+            Temp(id) =>
+                write!(fmt,"Temp({:?})", id),
+            Static(id) =>
+                write!(fmt,"Static({:?})", id),
+            ReturnPointer =>
+                write!(fmt,"ReturnPointer"),
+            Projection(ref data) =>
+                match data.elem {
+                    ProjectionElem::Downcast(_, variant_index) =>
+                        write!(fmt,"({:?} as {:?})", data.base, variant_index),
+                    ProjectionElem::Deref =>
+                        write!(fmt,"(*{:?})", data.base),
+                    ProjectionElem::Field(Field::Named(name)) =>
+                        write!(fmt,"{:?}.{:?}", data.base, name),
+                    ProjectionElem::Field(Field::Indexed(index)) =>
+                        write!(fmt,"{:?}.{:?}", data.base, index),
+                    ProjectionElem::Index(ref index) =>
+                        write!(fmt,"{:?}[{:?}]", data.base, index),
+                    ProjectionElem::ConstantIndex { offset, min_length, from_end: false } =>
+                        write!(fmt,"{:?}[{:?}; {:?}]", data.base, offset, min_length),
+                    ProjectionElem::ConstantIndex { offset, min_length, from_end: true } =>
+                        write!(fmt,"{:?}[-{:?}; {:?}]", data.base, offset, min_length),
+                },
+        }
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////
+// Operands
+//
+// These are values that can appear inside an rvalue (or an index
+// lvalue). They are intentionally limited to prevent rvalues from
+// being nested in one another.
+
+#[derive(Clone, PartialEq)]
+pub enum Operand<H:Hair> {
+    Consume(Lvalue<H>),
+    Constant(Constant<H>),
+}
+
+impl<H:Hair> Debug for Operand<H> {
+    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
+        use self::Operand::*;
+        match *self {
+            Constant(ref a) => write!(fmt, "{:?}", a),
+            Consume(ref lv) => write!(fmt, "{:?}", lv),
+        }
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////
+// Rvalues
+
+#[derive(Clone)]
+pub enum Rvalue<H:Hair> {
+    // x (either a move or copy, depending on type of x)
+    Use(Operand<H>),
+
+    // [x; 32]
+    Repeat(Operand<H>, Operand<H>),
+
+    // &x or &mut x
+    Ref(H::Region, BorrowKind, Lvalue<H>),
+
+    // length of a [X] or [X;n] value
+    Len(Lvalue<H>),
+
+    Cast(CastKind, Operand<H>, H::Ty),
+
+    BinaryOp(BinOp, Operand<H>, Operand<H>),
+
+    UnaryOp(UnOp, Operand<H>),
+
+    // Creates an *uninitialized* Box
+    Box(H::Ty),
+
+    // Create an aggregate value, like a tuple or struct.  This is
+    // only needed because we want to distinguish `dest = Foo { x:
+    // ..., y: ... }` from `dest.x = ...; dest.y = ...;` in the case
+    // that `Foo` has a destructor. These rvalues can be optimized
+    // away after type-checking and before lowering.
+    Aggregate(AggregateKind<H>, Vec<Operand<H>>),
+
+    InlineAsm(H::InlineAsm),
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum CastKind {
+    Misc,
+
+    /// Convert unique, zero-sized type for a fn to fn()
+    ReifyFnPointer,
+
+    /// Convert safe fn() to unsafe fn()
+    UnsafeFnPointer,
+
+    /// "Unsize" -- convert a thin-or-fat pointer to a fat pointer.
+    /// trans must figure out the details once full monomorphization
+    /// is known. For example, this could be used to cast from a
+    /// `&[i32;N]` to a `&[i32]`, or a `Box<T>` to a `Box<Trait>`
+    /// (presuming `T: Trait`).
+    Unsize,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum AggregateKind<H:Hair> {
+    Vec,
+    Tuple,
+    Adt(H::AdtDef, usize, H::Substs),
+    Closure(H::DefId, H::ClosureSubsts),
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum BinOp {
+    /// The `+` operator (addition)
+    Add,
+    /// The `-` operator (subtraction)
+    Sub,
+    /// The `*` operator (multiplication)
+    Mul,
+    /// The `/` operator (division)
+    Div,
+    /// The `%` operator (modulus)
+    Rem,
+    /// The `^` operator (bitwise xor)
+    BitXor,
+    /// The `&` operator (bitwise and)
+    BitAnd,
+    /// The `|` operator (bitwise or)
+    BitOr,
+    /// The `<<` operator (shift left)
+    Shl,
+    /// The `>>` operator (shift right)
+    Shr,
+    /// The `==` operator (equality)
+    Eq,
+    /// The `<` operator (less than)
+    Lt,
+    /// The `<=` operator (less than or equal to)
+    Le,
+    /// The `!=` operator (not equal to)
+    Ne,
+    /// The `>=` operator (greater than or equal to)
+    Ge,
+    /// The `>` operator (greater than)
+    Gt,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum UnOp {
+    /// The `!` operator for logical inversion
+    Not,
+    /// The `-` operator for negation
+    Neg
+}
+
+impl<H:Hair> Debug for Rvalue<H> {
+    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
+        use self::Rvalue::*;
+
+        match *self {
+            Use(ref lvalue) => write!(fmt, "{:?}", lvalue),
+            Repeat(ref a, ref b) => write!(fmt, "[{:?}; {:?}]", a, b),
+            Ref(ref a, bk, ref b) => write!(fmt, "&{:?} {:?} {:?}", a, bk, b),
+            Len(ref a) => write!(fmt, "LEN({:?})", a),
+            Cast(ref kind, ref lv, ref ty) => write!(fmt, "{:?} as {:?} ({:?}", lv, ty, kind),
+            BinaryOp(ref op, ref a, ref b) => write!(fmt, "{:?}({:?},{:?})", op, a, b),
+            UnaryOp(ref op, ref a) => write!(fmt, "{:?}({:?})", op, a),
+            Box(ref t) => write!(fmt, "Box {:?}", t),
+            Aggregate(ref kind, ref lvs) => write!(fmt, "Aggregate<{:?}>({:?})", kind, lvs),
+            InlineAsm(ref asm) => write!(fmt, "InlineAsm({:?})", asm),
+        }
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////
+// Constants
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct Constant<H:Hair> {
+    pub span: H::Span,
+    pub kind: ConstantKind<H>
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum ConstantKind<H:Hair> {
+    Literal(Literal<H>),
+    Aggregate(AggregateKind<H>, Vec<Constant<H>>),
+    Call(Box<Constant<H>>, Vec<Constant<H>>),
+    Cast(Box<Constant<H>>, H::Ty),
+    Repeat(Box<Constant<H>>, Box<Constant<H>>),
+    Ref(BorrowKind, Box<Constant<H>>),
+    BinaryOp(BinOp, Box<Constant<H>>, Box<Constant<H>>),
+    UnaryOp(UnOp, Box<Constant<H>>),
+    Projection(Box<ConstantProjection<H>>)
+}
+
+pub type ConstantProjection<H> =
+    Projection<H,Constant<H>,Constant<H>>;
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Literal<H:Hair> {
+    Item { def_id: H::DefId, substs: H::Substs },
+    Projection { projection: H::Projection },
+    Int { bits: IntegralBits, value: i64 },
+    Uint { bits: IntegralBits, value: u64 },
+    Float { bits: FloatBits, value: f64 },
+    Char { c: char },
+    Bool { value: bool },
+    Bytes { value: H::Bytes },
+    String { value: H::InternedString },
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, PartialOrd)]
+pub enum IntegralBits {
+    B8, B16, B32, B64, BSize
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, PartialOrd)]
+pub enum FloatBits {
+    F32, F64
+}

src/librustc_mir/tcx/block.rs

@@ -0,0 +1,114 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use hair::*;
+
+use tcx::Cx;
+use tcx::pattern::PatNode;
+use tcx::rustc::middle::region::{BlockRemainder, CodeExtentData};
+use tcx::rustc_front::hir;
+use tcx::syntax::ast;
+use tcx::syntax::ptr::P;
+use tcx::to_ref::ToRef;
+
+impl<'a,'tcx:'a> Mirror<Cx<'a,'tcx>> for &'tcx hir::Block {
+    type Output = Block<Cx<'a,'tcx>>;
+
+    fn make_mirror(self, cx: &mut Cx<'a,'tcx>) -> Block<Cx<'a,'tcx>> {
+        // We have to eagerly translate the "spine" of the statements
+        // in order to get the lexical scoping correctly.
+        let stmts = mirror_stmts(cx, self.id, self.stmts.iter().enumerate());
+        Block {
+            extent: cx.tcx.region_maps.node_extent(self.id),
+            span: self.span,
+            stmts: stmts,
+            expr: self.expr.to_ref()
+        }
+    }
+}
+
+impl<'a,'tcx:'a> Mirror<Cx<'a,'tcx>> for &'tcx hir::Stmt {
+    type Output = Stmt<Cx<'a,'tcx>>;
+
+    fn make_mirror(self, _cx: &mut Cx<'a,'tcx>) -> Stmt<Cx<'a,'tcx>> {
+        // In order to get the scoping correct, we eagerly mirror
+        // statements when we translate the enclosing block, so we
+        // should in fact never get to this point.
+        panic!("statements are eagerly mirrored");
+    }
+}
+
+fn mirror_stmts<'a,'tcx:'a,STMTS>(cx: &mut Cx<'a,'tcx>,
+                                  block_id: ast::NodeId,
+                                  mut stmts: STMTS)
+                                  -> Vec<StmtRef<Cx<'a,'tcx>>>
+    where STMTS: Iterator<Item=(usize, &'tcx P<hir::Stmt>)>
+{
+    let mut result = vec![];
+    while let Some((index, stmt)) = stmts.next() {
+        match stmt.node {
+            hir::StmtExpr(ref expr, id) | hir::StmtSemi(ref expr, id) =>
+                result.push(
+                    StmtRef::Mirror(
+                        Box::new(Stmt { span: stmt.span,
+                                        kind: StmtKind::Expr {
+                                            scope: cx.tcx.region_maps.node_extent(id),
+                                            expr: expr.to_ref() } }))),
+
+            hir::StmtDecl(ref decl, id) => {
+                match decl.node {
+                    hir::DeclItem(..) => { /* ignore for purposes of the MIR */ }
+                    hir::DeclLocal(ref local) => {
+                        let remainder_extent = CodeExtentData::Remainder(BlockRemainder {
+                            block: block_id,
+                            first_statement_index: index as u32
+                        });
+                        let remainder_extent =
+                            cx.tcx.region_maps.lookup_code_extent(remainder_extent);
+
+                        // pull in all following statements, since
+                        // they are within the scope of this let:
+                        let following_stmts = mirror_stmts(cx, block_id, stmts);
+
+                        result.push(
+                            StmtRef::Mirror(
+                                Box::new(Stmt {
+                                    span: stmt.span,
+                                    kind: StmtKind::Let {
+                                        remainder_scope: remainder_extent,
+                                        init_scope: cx.tcx.region_maps.node_extent(id),
+                                        pattern: PatNode::irrefutable(&local.pat).to_ref(),
+                                        initializer: local.init.to_ref(),
+                                        stmts: following_stmts
+                                    }
+                                })));
+
+                        return result;
+                    }
+                }
+            }
+        }
+    }
+    return result;
+}
+
+pub fn to_expr_ref<'a,'tcx:'a>(cx: &mut Cx<'a,'tcx>,
+                               block: &'tcx hir::Block)
+                               -> ExprRef<Cx<'a, 'tcx>> {
+    let block_ty = cx.tcx.node_id_to_type(block.id);
+    let temp_lifetime = cx.tcx.region_maps.temporary_scope(block.id);
+    let expr = Expr {
+        ty: block_ty,
+        temp_lifetime: temp_lifetime,
+        span: block.span,
+        kind: ExprKind::Block { body: block }
+    };
+    expr.to_ref()
+}

src/librustc_mir/tcx/expr.rs

@@ -0,0 +1,870 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use hair::*;
+use repr::*;
+use rustc_data_structures::fnv::FnvHashMap;
+use std::rc::Rc;
+use tcx::Cx;
+use tcx::block;
+use tcx::pattern::PatNode;
+use tcx::rustc::front::map;
+use tcx::rustc::middle::def;
+use tcx::rustc::middle::def_id::DefId;
+use tcx::rustc::middle::region::CodeExtent;
+use tcx::rustc::middle::pat_util;
+use tcx::rustc::middle::ty::{self, Ty};
+use tcx::rustc_front::hir;
+use tcx::rustc_front::util as hir_util;
+use tcx::syntax::codemap::Span;
+use tcx::syntax::parse::token;
+use tcx::syntax::ptr::P;
+use tcx::to_ref::ToRef;
+
+impl<'a,'tcx:'a> Mirror<Cx<'a,'tcx>> for &'tcx hir::Expr {
+    type Output = Expr<Cx<'a,'tcx>>;
+
+    fn make_mirror(self, cx: &mut Cx<'a,'tcx>) -> Expr<Cx<'a,'tcx>> {
+        debug!("Expr::make_mirror(): id={}, span={:?}", self.id, self.span);
+
+        let expr_ty = cx.tcx.expr_ty(self); // note: no adjustments (yet)!
+
+        let kind = match self.node {
+            // Here comes the interesting stuff:
+
+            hir::ExprMethodCall(_, _, ref args) => {
+                // Rewrite a.b(c) into UFCS form like Trait::b(a, c)
+                let expr = method_callee(cx, self, ty::MethodCall::expr(self.id));
+                let args = args.iter()
+                               .map(|e| e.to_ref())
+                               .collect();
+                ExprKind::Call {
+                    fun: expr.to_ref(),
+                    args: args
+                }
+            }
+
+            hir::ExprAddrOf(mutbl, ref expr) => {
+                let region = match expr_ty.sty {
+                    ty::TyRef(r, _) => r,
+                    _ => cx.tcx.sess.span_bug(expr.span, "type of & not region")
+                };
+                ExprKind::Borrow { region: *region,
+                                   borrow_kind: to_borrow_kind(mutbl),
+                                   arg: expr.to_ref() }
+            }
+
+            hir::ExprBlock(ref blk) => {
+                ExprKind::Block {
+                    body: &**blk
+                }
+            }
+
+            hir::ExprAssign(ref lhs, ref rhs) => {
+                ExprKind::Assign {
+                    lhs: lhs.to_ref(),
+                    rhs: rhs.to_ref(),
+                }
+            }
+
+            hir::ExprAssignOp(op, ref lhs, ref rhs) => {
+                let op = bin_op(op.node);
+                ExprKind::AssignOp {
+                    op: op,
+                    lhs: lhs.to_ref(),
+                    rhs: rhs.to_ref(),
+                }
+            }
+
+            hir::ExprLit(ref lit) => {
+                let literal = convert_literal(cx, self.span, expr_ty, lit);
+                ExprKind::Literal { literal: literal }
+            }
+
+            hir::ExprBinary(op, ref lhs, ref rhs) => {
+                if cx.tcx.is_method_call(self.id) {
+                    let pass_args = if hir_util::is_by_value_binop(op.node) {
+                        PassArgs::ByValue
+                    } else {
+                        PassArgs::ByRef
+                    };
+                    overloaded_operator(cx, self, ty::MethodCall::expr(self.id),
+                                        pass_args, lhs.to_ref(), vec![rhs])
+                } else {
+                    // FIXME overflow
+                    match op.node {
+                        hir::BinOp_::BiAnd => {
+                            ExprKind::LogicalOp { op: LogicalOp::And,
+                                                  lhs: lhs.to_ref(),
+                                                  rhs: rhs.to_ref() }
+                        }
+                        hir::BinOp_::BiOr => {
+                            ExprKind::LogicalOp { op: LogicalOp::Or,
+                                                  lhs: lhs.to_ref(),
+                                                  rhs: rhs.to_ref() }
+                        }
+                        _ => {
+                            let op = bin_op(op.node);
+                            ExprKind::Binary { op: op,
+                                               lhs: lhs.to_ref(),
+                                               rhs: rhs.to_ref() }
+                        }
+                    }
+                }
+            }
+
+            hir::ExprIndex(ref lhs, ref index) => {
+                if cx.tcx.is_method_call(self.id) {
+                    overloaded_lvalue(cx, self, ty::MethodCall::expr(self.id),
+                                      PassArgs::ByValue, lhs.to_ref(), vec![index])
+                } else {
+                    ExprKind::Index { lhs: lhs.to_ref(),
+                                      index: index.to_ref() }
+                }
+            }
+
+            hir::ExprUnary(hir::UnOp::UnDeref, ref arg) => {
+                if cx.tcx.is_method_call(self.id) {
+                    overloaded_lvalue(cx, self, ty::MethodCall::expr(self.id),
+                                      PassArgs::ByValue, arg.to_ref(), vec![])
+                } else {
+                    ExprKind::Deref { arg: arg.to_ref() }
+                }
+            }
+
+            hir::ExprUnary(hir::UnOp::UnUniq, ref arg) => {
+                assert!(!cx.tcx.is_method_call(self.id));
+                ExprKind::Box { place: None, value: arg.to_ref() }
+            }
+
+            hir::ExprUnary(op, ref arg) => {
+                if cx.tcx.is_method_call(self.id) {
+                    overloaded_operator(cx, self, ty::MethodCall::expr(self.id),
+                                        PassArgs::ByValue, arg.to_ref(), vec![])
+                } else {
+                    // FIXME overflow
+                    let op = match op {
+                        hir::UnOp::UnNot => UnOp::Not,
+                        hir::UnOp::UnNeg => UnOp::Neg,
+                        hir::UnOp::UnUniq | hir::UnOp::UnDeref => {
+                            cx.tcx.sess.span_bug(
+                                self.span,
+                                &format!("operator should have been handled elsewhere {:?}", op));
+                        }
+                    };
+                    ExprKind::Unary { op: op, arg: arg.to_ref() }
+                }
+            }
+
+            hir::ExprStruct(_, ref fields, ref base) => {
+                match expr_ty.sty {
+                    ty::TyStruct(adt, substs) => {
+                        ExprKind::Adt {
+                            adt_def: adt,
+                            variant_index: 0,
+                            substs: substs,
+                            fields: fields.to_ref(),
+                            base: base.to_ref(),
+                        }
+                    }
+                    ty::TyEnum(adt, substs) => {
+                        match cx.tcx.def_map.borrow()[&self.id].full_def() {
+                            def::DefVariant(enum_id, variant_id, true) => {
+                                debug_assert!(adt.did == enum_id);
+                                let index = adt.variant_index_with_id(variant_id);
+                                ExprKind::Adt {
+                                    adt_def: adt,
+                                    variant_index: index,
+                                    substs: substs,
+                                    fields: fields.to_ref(),
+                                    base: base.to_ref(),
+                                }
+                            }
+                            ref def => {
+                                cx.tcx.sess.span_bug(
+                                    self.span,
+                                    &format!("unexpected def: {:?}", def));
+                            }
+                        }
+                    }
+                    _ => {
+                        cx.tcx.sess.span_bug(
+                            self.span,
+                            &format!("unexpected type for struct literal: {:?}", expr_ty));
+                    }
+                }
+            }
+
+            hir::ExprClosure(..) => {
+                let closure_ty = cx.tcx.expr_ty(self);
+                let (def_id, substs) = match closure_ty.sty {
+                    ty::TyClosure(def_id, ref substs) => (def_id, substs),
+                    _ => {
+                        cx.tcx.sess.span_bug(self.span,
+                                          &format!("closure expr w/o closure type: {:?}",
+                                                   closure_ty));
+                    }
+                };
+                let upvars = cx.tcx.with_freevars(self.id, |freevars| {
+                    freevars.iter()
+                            .enumerate()
+                            .map(|(i, fv)| capture_freevar(cx, self, fv, substs.upvar_tys[i]))
+                            .collect()
+                });
+                ExprKind::Closure {
+                    closure_id: def_id,
+                    substs: &**substs,
+                    upvars: upvars,
+                }
+            }
+
+            hir::ExprRange(ref start, ref end) => {
+                let range_ty = cx.tcx.expr_ty(self);
+                let (adt_def, substs) = match range_ty.sty {
+                    ty::TyStruct(adt_def, substs) => (adt_def, substs),
+                    _ => {
+                        cx.tcx.sess.span_bug(
+                            self.span,
+                            &format!("unexpanded ast"));
+                    }
+                };
+
+                let field_expr_ref = |s: &'tcx P<hir::Expr>, nm: &str| {
+                    FieldExprRef { name: Field::Named(token::intern(nm)),
+                                   expr: s.to_ref() }
+                };
+
+                let start_field = start.as_ref()
+                                       .into_iter()
+                                       .map(|s| field_expr_ref(s, "start"));
+
+                let end_field = end.as_ref()
+                                   .into_iter()
+                                   .map(|e| field_expr_ref(e, "end"));
+
+                ExprKind::Adt { adt_def: adt_def,
+                                variant_index: 0,
+                                substs: substs,
+                                fields: start_field.chain(end_field).collect(),
+                                base: None }
+            }
+
+            hir::ExprPath(..) => {
+                convert_path_expr(cx, self)
+            }
+
+            hir::ExprInlineAsm(ref asm) => {
+                ExprKind::InlineAsm { asm: asm }
+            }
+
+            // Now comes the rote stuff:
+
+            hir::ExprParen(ref p) =>
+                ExprKind::Paren { arg: p.to_ref() },
+            hir::ExprRepeat(ref v, ref c) =>
+                ExprKind::Repeat { value: v.to_ref(), count: c.to_ref() },
+            hir::ExprRet(ref v) =>
+                ExprKind::Return { value: v.to_ref() },
+            hir::ExprBreak(label) =>
+                ExprKind::Break { label: label.map(|_| loop_label(cx, self)) },
+            hir::ExprAgain(label) =>
+                ExprKind::Continue { label: label.map(|_| loop_label(cx, self)) },
+            hir::ExprMatch(ref discr, ref arms, _) =>
+                ExprKind::Match { discriminant: discr.to_ref(),
+                                  arms: arms.iter().map(|a| convert_arm(cx, a)).collect() },
+            hir::ExprIf(ref cond, ref then, ref otherwise) =>
+                ExprKind::If { condition: cond.to_ref(),
+                               then: block::to_expr_ref(cx, then),
+                               otherwise: otherwise.to_ref() },
+            hir::ExprWhile(ref cond, ref body, _) =>
+                ExprKind::Loop { condition: Some(cond.to_ref()),
+                                 body: block::to_expr_ref(cx, body) },
+            hir::ExprLoop(ref body, _) =>
+                ExprKind::Loop { condition: None,
+                                 body: block::to_expr_ref(cx, body) },
+            hir::ExprField(ref source, ident) =>
+                ExprKind::Field { lhs: source.to_ref(),
+                                  name: Field::Named(ident.node.name) },
+            hir::ExprTupField(ref source, ident) =>
+                ExprKind::Field { lhs: source.to_ref(),
+                                  name: Field::Indexed(ident.node) },
+            hir::ExprCast(ref source, _) =>
+                ExprKind::Cast { source: source.to_ref() },
+            hir::ExprBox(ref place, ref value) =>
+                ExprKind::Box { place: place.to_ref(), value: value.to_ref() },
+            hir::ExprVec(ref fields) =>
+                ExprKind::Vec { fields: fields.to_ref() },
+            hir::ExprTup(ref fields) =>
+                ExprKind::Tuple { fields: fields.to_ref() },
+            hir::ExprCall(ref fun, ref args) =>
+                ExprKind::Call { fun: fun.to_ref(), args: args.to_ref() },
+        };
+
+        let temp_lifetime = cx.tcx.region_maps.temporary_scope(self.id);
+        let expr_extent = cx.tcx.region_maps.node_extent(self.id);
+
+        let mut expr = Expr {
+            temp_lifetime: temp_lifetime,
+            ty: expr_ty,
+            span: self.span,
+            kind: kind,
+        };
+
+        // Now apply adjustments, if any.
+        match cx.tcx.tables.borrow().adjustments.get(&self.id) {
+            None => { }
+            Some(&ty::AdjustReifyFnPointer) => {
+                let adjusted_ty = cx.tcx.expr_ty_adjusted(self);
+                expr = Expr {
+                    temp_lifetime: temp_lifetime,
+                    ty: adjusted_ty,
+                    span: self.span,
+                    kind: ExprKind::ReifyFnPointer { source: expr.to_ref() },
+                };
+            }
+            Some(&ty::AdjustUnsafeFnPointer) => {
+                let adjusted_ty = cx.tcx.expr_ty_adjusted(self);
+                expr = Expr {
+                    temp_lifetime: temp_lifetime,
+                    ty: adjusted_ty,
+                    span: self.span,
+                    kind: ExprKind::UnsafeFnPointer { source: expr.to_ref() },
+                };
+            }
+            Some(&ty::AdjustDerefRef(ref adj)) => {
+                for i in 0..adj.autoderefs {
+                    let i = i as u32;
+                    let adjusted_ty =
+                        expr.ty.adjust_for_autoderef(
+                            cx.tcx,
+                            self.id,
+                            self.span,
+                            i,
+                            |mc| cx.tcx.tables.borrow().method_map.get(&mc).map(|m| m.ty));
+                    let kind = if cx.tcx.is_overloaded_autoderef(self.id, i) {
+                        overloaded_lvalue(cx, self, ty::MethodCall::autoderef(self.id, i),
+                                          PassArgs::ByValue, expr.to_ref(), vec![])
+                    } else {
+                        ExprKind::Deref { arg: expr.to_ref() }
+                    };
+                    expr = Expr {
+                        temp_lifetime: temp_lifetime,
+                        ty: adjusted_ty,
+                        span: self.span,
+                        kind: kind
+                    };
+                }
+
+                if let Some(target) = adj.unsize {
+                    expr = Expr {
+                        temp_lifetime: temp_lifetime,
+                        ty: target,
+                        span: self.span,
+                        kind: ExprKind::Unsize { source: expr.to_ref() }
+                    };
+                } else if let Some(autoref) = adj.autoref {
+                    let adjusted_ty = expr.ty.adjust_for_autoref(cx.tcx, Some(autoref));
+                    match autoref {
+                        ty::AutoPtr(r, m) => {
+                            expr = Expr {
+                                temp_lifetime: temp_lifetime,
+                                ty: adjusted_ty,
+                                span: self.span,
+                                kind: ExprKind::Borrow { region: *r,
+                                                         borrow_kind: to_borrow_kind(m),
+                                                         arg: expr.to_ref() }
+                            };
+                        }
+                        ty::AutoUnsafe(m) => {
+                            // Convert this to a suitable `&foo` and
+                            // then an unsafe coercion. Limit the region to be just this
+                            // expression.
+                            let region = ty::ReScope(expr_extent);
+                            let region = cx.tcx.mk_region(region);
+                            expr = Expr {
+                                temp_lifetime: temp_lifetime,
+                                ty: cx.tcx.mk_ref(region, ty::TypeAndMut { ty: expr.ty, mutbl: m }),
+                                span: self.span,
+                                kind: ExprKind::Borrow { region: *region,
+                                                         borrow_kind: to_borrow_kind(m),
+                                                         arg: expr.to_ref() }
+                            };
+                            expr = Expr {
+                                temp_lifetime: temp_lifetime,
+                                ty: adjusted_ty,
+                                span: self.span,
+                                kind: ExprKind::Cast { source: expr.to_ref() }
+                            };
+                        }
+                    }
+                }
+            }
+        }
+
+        // Next, wrap this up in the expr's scope.
+        expr = Expr {
+            temp_lifetime: temp_lifetime,
+            ty: expr.ty,
+            span: self.span,
+            kind: ExprKind::Scope { extent: expr_extent,
+                                    value: expr.to_ref() }
+        };
+
+        // Finally, create a destruction scope, if any.
+        if let Some(extent) = cx.tcx.region_maps.opt_destruction_extent(self.id) {
+            expr = Expr {
+                temp_lifetime: temp_lifetime,
+                ty: expr.ty,
+                span: self.span,
+                kind: ExprKind::Scope { extent: extent, value: expr.to_ref() }
+            };
+        }
+
+        // OK, all done!
+        expr
+    }
+}
+
+fn method_callee<'a,'tcx:'a>(cx: &mut Cx<'a,'tcx>,
+                             expr: &hir::Expr,
+                             method_call: ty::MethodCall)
+                             -> Expr<Cx<'a,'tcx>> {
+    let tables = cx.tcx.tables.borrow();
+    let callee = &tables.method_map[&method_call];
+    let temp_lifetime = cx.tcx.region_maps.temporary_scope(expr.id);
+    Expr {
+        temp_lifetime: temp_lifetime,
+        ty: callee.ty,
+        span: expr.span,
+        kind: ExprKind::Literal {
+            literal: Literal::Item {
+                def_id: callee.def_id,
+                substs: callee.substs,
+            }
+        }
+    }
+}
+
+fn to_borrow_kind(m: hir::Mutability) -> BorrowKind {
+    match m {
+        hir::MutMutable => BorrowKind::Mut,
+        hir::MutImmutable => BorrowKind::Shared,
+    }
+}
+
+fn convert_literal<'a,'tcx:'a>(cx: &mut Cx<'a,'tcx>,
+                               expr_span: Span,
+                               expr_ty: Ty<'tcx>,
+                               literal: &hir::Lit)
+                               -> Literal<Cx<'a,'tcx>>
+{
+    use repr::IntegralBits::*;
+    match (&literal.node, &expr_ty.sty) {
+        (&hir::LitStr(ref text, _), _) =>
+            Literal::String { value: text.clone() },
+        (&hir::LitByteStr(ref bytes), _) =>
+            Literal::Bytes { value: bytes.clone() },
+        (&hir::LitByte(c), _) =>
+            Literal::Uint { bits: B8, value: c as u64 },
+        (&hir::LitChar(c), _) =>
+            Literal::Char { c: c },
+        (&hir::LitInt(v, _), &ty::TyUint(hir::TyU8)) =>
+            Literal::Uint { bits: B8, value: v },
+        (&hir::LitInt(v, _), &ty::TyUint(hir::TyU16)) =>
+            Literal::Uint { bits: B16, value: v },
+        (&hir::LitInt(v, _), &ty::TyUint(hir::TyU32)) =>
+            Literal::Uint { bits: B32, value: v },
+        (&hir::LitInt(v, _), &ty::TyUint(hir::TyU64)) =>
+            Literal::Uint { bits: B64, value: v },
+        (&hir::LitInt(v, _), &ty::TyUint(hir::TyUs)) =>
+            Literal::Uint { bits: BSize, value: v },
+        (&hir::LitInt(v, hir::SignedIntLit(_, hir::Sign::Minus)), &ty::TyInt(hir::TyI8)) =>
+            Literal::Int { bits: B8, value: -(v as i64) },
+        (&hir::LitInt(v, hir::SignedIntLit(_, hir::Sign::Minus)), &ty::TyInt(hir::TyI16)) =>
+            Literal::Int { bits: B16, value: -(v as i64) },
+        (&hir::LitInt(v, hir::SignedIntLit(_, hir::Sign::Minus)), &ty::TyInt(hir::TyI32)) =>
+            Literal::Int { bits: B32, value: -(v as i64) },
+        (&hir::LitInt(v, hir::SignedIntLit(_, hir::Sign::Minus)), &ty::TyInt(hir::TyI64)) =>
+            Literal::Int { bits: B64, value: -(v as i64) },
+        (&hir::LitInt(v, hir::SignedIntLit(_, hir::Sign::Minus)), &ty::TyInt(hir::TyIs)) =>
+            Literal::Int { bits: BSize, value: -(v as i64) },
+        (&hir::LitInt(v, _), &ty::TyInt(hir::TyI8)) =>
+            Literal::Int { bits: B8, value: v as i64 },
+        (&hir::LitInt(v, _), &ty::TyInt(hir::TyI16)) =>
+            Literal::Int { bits: B16, value: v as i64 },
+        (&hir::LitInt(v, _), &ty::TyInt(hir::TyI32)) =>
+            Literal::Int { bits: B32, value: v as i64 },
+        (&hir::LitInt(v, _), &ty::TyInt(hir::TyI64)) =>
+            Literal::Int { bits: B64, value: v as i64 },
+        (&hir::LitInt(v, _), &ty::TyInt(hir::TyIs)) =>
+            Literal::Int { bits: BSize, value: v as i64 },
+        (&hir::LitFloat(ref v, _), &ty::TyFloat(hir::TyF32)) |
+        (&hir::LitFloatUnsuffixed(ref v), &ty::TyFloat(hir::TyF32)) =>
+            Literal::Float { bits: FloatBits::F32, value: v.parse::<f64>().unwrap() },
+        (&hir::LitFloat(ref v, _), &ty::TyFloat(hir::TyF64)) |
+        (&hir::LitFloatUnsuffixed(ref v), &ty::TyFloat(hir::TyF64)) =>
+            Literal::Float { bits: FloatBits::F64, value: v.parse::<f64>().unwrap() },
+        (&hir::LitBool(v), _) =>
+            Literal::Bool { value: v },
+        (ref l, ref t) =>
+            cx.tcx.sess.span_bug(
+                expr_span,
+                &format!("Invalid literal/type combination: {:?},{:?}", l, t))
+    }
+}
+
+fn convert_arm<'a,'tcx:'a>(cx: &Cx<'a,'tcx>, arm: &'tcx hir::Arm) -> Arm<Cx<'a,'tcx>> {
+    let map = if arm.pats.len() == 1 {
+        None
+    } else {
+        let mut map = FnvHashMap();
+        pat_util::pat_bindings(&cx.tcx.def_map, &arm.pats[0], |_, p_id, _, path| {
+            map.insert(path.node, p_id);
+        });
+        Some(Rc::new(map))
+    };
+
+    Arm { patterns: arm.pats.iter().map(|p| PatNode::new(p, map.clone()).to_ref()).collect(),
+          guard: arm.guard.to_ref(),
+          body: arm.body.to_ref() }
+}
+
+fn convert_path_expr<'a,'tcx:'a>(cx: &mut Cx<'a,'tcx>,
+                                 expr: &'tcx hir::Expr)
+                                 -> ExprKind<Cx<'a,'tcx>>
+{
+    let substs = cx.tcx.mk_substs(cx.tcx.node_id_item_substs(expr.id).substs);
+    match cx.tcx.def_map.borrow()[&expr.id].full_def() {
+        def::DefVariant(_, def_id, false) |
+        def::DefStruct(def_id) |
+        def::DefFn(def_id, _) |
+        def::DefConst(def_id) |
+        def::DefMethod(def_id) |
+        def::DefAssociatedConst(def_id) =>
+            ExprKind::Literal {
+                literal: Literal::Item { def_id: def_id, substs: substs }
+            },
+
+        def::DefStatic(node_id, _) =>
+            ExprKind::StaticRef {
+                id: node_id,
+            },
+
+        def @ def::DefLocal(..) |
+        def @ def::DefUpvar(..) =>
+            convert_var(cx, expr, def),
+
+        def =>
+            cx.tcx.sess.span_bug(
+                expr.span,
+                &format!("def `{:?}` not yet implemented", def)),
+    }
+}
+
+fn convert_var<'a,'tcx:'a>(cx: &mut Cx<'a,'tcx>,
+                           expr: &'tcx hir::Expr,
+                           def: def::Def)
+                           -> ExprKind<Cx<'a,'tcx>>
+{
+    let temp_lifetime = cx.tcx.region_maps.temporary_scope(expr.id);
+
+    match def {
+        def::DefLocal(node_id) => {
+            ExprKind::VarRef {
+                id: node_id,
+            }
+        }
+
+        def::DefUpvar(id_var, index, closure_expr_id) => {
+            debug!("convert_var(upvar({:?}, {:?}, {:?}))", id_var, index, closure_expr_id);
+            let var_ty = cx.tcx.node_id_to_type(id_var);
+
+            let body_id = match cx.tcx.map.find(closure_expr_id) {
+                Some(map::NodeExpr(expr)) => {
+                    match expr.node {
+                        hir::ExprClosure(_, _, ref body) => body.id,
+                        _ => {
+                            cx.tcx.sess.span_bug(expr.span,
+                                              &format!("closure expr is not a closure expr"));
+                        }
+                    }
+                }
+                _ => {
+                    cx.tcx.sess.span_bug(expr.span,
+                                      &format!("ast-map has garbage for closure expr"));
+                }
+            };
+
+            // FIXME free regions in closures are not right
+            let closure_ty =
+                cx.tcx.node_id_to_type(closure_expr_id);
+
+            // FIXME we're just hard-coding the idea that the
+            // signature will be &self or &mut self and hence will
+            // have a bound region with number 0
+            let region =
+                ty::Region::ReFree(
+                    ty::FreeRegion {
+                        scope: cx.tcx.region_maps.node_extent(body_id),
+                        bound_region: ty::BoundRegion::BrAnon(0)
+                    });
+            let region =
+                cx.tcx.mk_region(region);
+
+            let self_expr = match cx.tcx.closure_kind(DefId::local(closure_expr_id)) {
+                ty::ClosureKind::FnClosureKind => {
+                    let ref_closure_ty =
+                        cx.tcx.mk_ref(region,
+                                   ty::TypeAndMut { ty: closure_ty,
+                                                    mutbl: hir::MutImmutable });
+                    Expr {
+                        ty: closure_ty,
+                        temp_lifetime: temp_lifetime,
+                        span: expr.span,
+                        kind: ExprKind::Deref {
+                            arg: Expr {
+                                ty: ref_closure_ty,
+                                temp_lifetime: temp_lifetime,
+                                span: expr.span,
+                                kind: ExprKind::SelfRef
+                            }.to_ref()
+                        }
+                    }
+                }
+                ty::ClosureKind::FnMutClosureKind => {
+                    let ref_closure_ty =
+                        cx.tcx.mk_ref(region,
+                                   ty::TypeAndMut { ty: closure_ty,
+                                                    mutbl: hir::MutMutable });
+                    Expr {
+                        ty: closure_ty,
+                        temp_lifetime: temp_lifetime,
+                        span: expr.span,
+                        kind: ExprKind::Deref {
+                            arg: Expr {
+                                ty: ref_closure_ty,
+                                temp_lifetime: temp_lifetime,
+                                span: expr.span,
+                                kind: ExprKind::SelfRef
+                            }.to_ref()
+                        }
+                    }
+                }
+                ty::ClosureKind::FnOnceClosureKind => {
+                    Expr {
+                        ty: closure_ty,
+                        temp_lifetime: temp_lifetime,
+                        span: expr.span,
+                        kind: ExprKind::SelfRef
+                    }
+                }
+            };
+
+            // at this point we have `self.n`, which loads up the upvar
+            let field_kind =
+                ExprKind::Field { lhs: self_expr.to_ref(),
+                                  name: Field::Indexed(index) };
+
+            // ...but the upvar might be an `&T` or `&mut T` capture, at which
+            // point we need an implicit deref
+            let upvar_id = ty::UpvarId { var_id: id_var, closure_expr_id: closure_expr_id };
+            let upvar_capture = match cx.tcx.upvar_capture(upvar_id) {
+                Some(c) => c,
+                None => {
+                    cx.tcx.sess.span_bug(
+                        expr.span,
+                        &format!("no upvar_capture for {:?}", upvar_id));
+                }
+            };
+            match upvar_capture {
+                ty::UpvarCapture::ByValue => field_kind,
+                ty::UpvarCapture::ByRef(_) => {
+                    ExprKind::Deref {
+                        arg: Expr {
+                            temp_lifetime: temp_lifetime,
+                            ty: var_ty,
+                            span: expr.span,
+                            kind: field_kind,
+                        }.to_ref()
+                    }
+                }
+            }
+        }
+
+        _ => cx.tcx.sess.span_bug(expr.span, "type of & not region")
+    }
+}
+
+
+fn bin_op(op: hir::BinOp_) -> BinOp {
+    match op {
+        hir::BinOp_::BiAdd => BinOp::Add,
+        hir::BinOp_::BiSub => BinOp::Sub,
+        hir::BinOp_::BiMul => BinOp::Mul,
+        hir::BinOp_::BiDiv => BinOp::Div,
+        hir::BinOp_::BiRem => BinOp::Rem,
+        hir::BinOp_::BiBitXor => BinOp::BitXor,
+        hir::BinOp_::BiBitAnd => BinOp::BitAnd,
+        hir::BinOp_::BiBitOr => BinOp::BitOr,
+        hir::BinOp_::BiShl => BinOp::Shl,
+        hir::BinOp_::BiShr => BinOp::Shr,
+        hir::BinOp_::BiEq => BinOp::Eq,
+        hir::BinOp_::BiLt => BinOp::Lt,
+        hir::BinOp_::BiLe => BinOp::Le,
+        hir::BinOp_::BiNe => BinOp::Ne,
+        hir::BinOp_::BiGe => BinOp::Ge,
+        hir::BinOp_::BiGt => BinOp::Gt,
+        _ => panic!("no equivalent for ast binop {:?}", op)
+    }
+}
+
+enum PassArgs {
+    ByValue,
+    ByRef
+}
+
+fn overloaded_operator<'a,'tcx:'a>(cx: &mut Cx<'a,'tcx>,
+                                   expr: &'tcx hir::Expr,
+                                   method_call: ty::MethodCall,
+                                   pass_args: PassArgs,
+                                   receiver: ExprRef<Cx<'a,'tcx>>,
+                                   args: Vec<&'tcx P<hir::Expr>>)
+                                   -> ExprKind<Cx<'a,'tcx>>
+{
+    // the receiver has all the adjustments that are needed, so we can
+    // just push a reference to it
+    let mut argrefs = vec![receiver];
+
+    // the arguments, unfortunately, do not, so if this is a ByRef
+    // operator, we have to gin up the autorefs (but by value is easy)
+    match pass_args {
+        PassArgs::ByValue => {
+            argrefs.extend(
+                args.iter()
+                    .map(|arg| arg.to_ref()))
+        }
+
+        PassArgs::ByRef => {
+            let scope = cx.tcx.region_maps.node_extent(expr.id);
+            let region = cx.tcx.mk_region(ty::ReScope(scope));
+            let temp_lifetime = cx.tcx.region_maps.temporary_scope(expr.id);
+            argrefs.extend(
+                args.iter()
+                    .map(|arg| {
+                        let arg_ty = cx.tcx.expr_ty_adjusted(arg);
+                        let adjusted_ty =
+                            cx.tcx.mk_ref(region,
+                                       ty::TypeAndMut { ty: arg_ty,
+                                                        mutbl: hir::MutImmutable });
+                        Expr {
+                            temp_lifetime: temp_lifetime,
+                            ty: adjusted_ty,
+                            span: expr.span,
+                            kind: ExprKind::Borrow { region: *region,
+                                                     borrow_kind: BorrowKind::Shared,
+                                                     arg: arg.to_ref() }
+                        }.to_ref()
+                    }))
+        }
+    }
+
+    // now create the call itself
+    let fun = method_callee(cx, expr, method_call);
+    ExprKind::Call {
+        fun: fun.to_ref(),
+        args: argrefs,
+    }
+}
+
+fn overloaded_lvalue<'a,'tcx:'a>(cx: &mut Cx<'a,'tcx>,
+                                 expr: &'tcx hir::Expr,
+                                 method_call: ty::MethodCall,
+                                 pass_args: PassArgs,
+                                 receiver: ExprRef<Cx<'a,'tcx>>,
+                                 args: Vec<&'tcx P<hir::Expr>>)
+                                 -> ExprKind<Cx<'a,'tcx>>
+{
+    // For an overloaded *x or x[y] expression of type T, the method
+    // call returns an &T and we must add the deref so that the types
+    // line up (this is because `*x` and `x[y]` represent lvalues):
+
+    // to find the type &T of the content returned by the method;
+    let tables = cx.tcx.tables.borrow();
+    let callee = &tables.method_map[&method_call];
+    let ref_ty = callee.ty.fn_ret();
+    let ref_ty = cx.tcx.no_late_bound_regions(&ref_ty).unwrap().unwrap();
+    //                                              1~~~~~   2~~~~~
+    // (1) callees always have all late-bound regions fully instantiated,
+    // (2) overloaded methods don't return `!`
+
+    // construct the complete expression `foo()` for the overloaded call,
+    // which will yield the &T type
+    let temp_lifetime = cx.tcx.region_maps.temporary_scope(expr.id);
+    let ref_kind = overloaded_operator(cx, expr, method_call, pass_args, receiver, args);
+    let ref_expr = Expr {
+        temp_lifetime: temp_lifetime,
+        ty: ref_ty,
+        span: expr.span,
+        kind: ref_kind,
+    };
+
+    // construct and return a deref wrapper `*foo()`
+    ExprKind::Deref { arg: ref_expr.to_ref() }
+}
+
+fn capture_freevar<'a,'tcx:'a>(cx: &mut Cx<'a,'tcx>,
+                               closure_expr: &'tcx hir::Expr,
+                               freevar: &ty::Freevar,
+                               freevar_ty: Ty<'tcx>)
+                               -> ExprRef<Cx<'a,'tcx>> {
+    let id_var = freevar.def.def_id().node;
+    let upvar_id = ty::UpvarId { var_id: id_var, closure_expr_id: closure_expr.id };
+    let upvar_capture = cx.tcx.upvar_capture(upvar_id).unwrap();
+    let temp_lifetime = cx.tcx.region_maps.temporary_scope(closure_expr.id);
+    let var_ty = cx.tcx.node_id_to_type(id_var);
+    let captured_var = Expr { temp_lifetime: temp_lifetime,
+                              ty: var_ty,
+                              span: closure_expr.span,
+                              kind: convert_var(cx, closure_expr, freevar.def) };
+    match upvar_capture {
+        ty::UpvarCapture::ByValue => {
+            captured_var.to_ref()
+        }
+        ty::UpvarCapture::ByRef(upvar_borrow) => {
+            let borrow_kind = match upvar_borrow.kind {
+                ty::BorrowKind::ImmBorrow => BorrowKind::Shared,
+                ty::BorrowKind::UniqueImmBorrow => BorrowKind::Unique,
+                ty::BorrowKind::MutBorrow => BorrowKind::Mut,
+            };
+            Expr {
+                temp_lifetime: temp_lifetime,
+                ty: freevar_ty,
+                span: closure_expr.span,
+                kind: ExprKind::Borrow { region: upvar_borrow.region,
+                                         borrow_kind: borrow_kind,
+                                         arg: captured_var.to_ref() }
+            }.to_ref()
+        }
+    }
+}
+
+fn loop_label<'a,'tcx:'a>(cx: &mut Cx<'a,'tcx>,
+                          expr: &'tcx hir::Expr)
+                          -> CodeExtent
+{
+    match cx.tcx.def_map.borrow().get(&expr.id).map(|d| d.full_def()) {
+        Some(def::DefLabel(loop_id)) => cx.tcx.region_maps.node_extent(loop_id),
+        d => {
+            cx.tcx.sess.span_bug(
+                expr.span,
+                &format!("loop scope resolved to {:?}", d));
+        }
+    }
+}

src/librustc_mir/tcx/mod.rs

@@ -0,0 +1,184 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use hair::*;
+use repr::*;
+use std::fmt::{Debug, Formatter, Error};
+use std::hash::{Hash, Hasher};
+use std::rc::Rc;
+
+use self::rustc::middle::def_id::DefId;
+use self::rustc::middle::infer::InferCtxt;
+use self::rustc::middle::region::CodeExtent;
+use self::rustc::middle::subst::{self, Subst, Substs};
+use self::rustc::middle::ty::{self, Ty};
+use self::rustc_front::hir;
+use self::syntax::ast;
+use self::syntax::codemap::Span;
+use self::syntax::parse::token::{self, special_idents, InternedString};
+
+extern crate rustc;
+extern crate rustc_front;
+extern crate syntax;
+
+#[derive(Copy, Clone)]
+pub struct Cx<'a,'tcx:'a> {
+    pub tcx: &'a ty::ctxt<'tcx>,
+    pub infcx: &'a InferCtxt<'a,'tcx>,
+}
+
+impl<'a,'tcx> Cx<'a,'tcx> {
+    pub fn new(infcx: &'a InferCtxt<'a,'tcx>) -> Cx<'a,'tcx> {
+        Cx { tcx: infcx.tcx, infcx: infcx }
+    }
+}
+
+pub use self::pattern::PatNode;
+
+impl<'a,'tcx:'a> Hair for Cx<'a, 'tcx> {
+    type VarId = ast::NodeId;
+    type DefId = DefId;
+    type AdtDef = ty::AdtDef<'tcx>;
+    type Name = ast::Name;
+    type Ident = ast::Ident;
+    type InternedString = InternedString;
+    type Bytes = Rc<Vec<u8>>;
+    type Span = Span;
+    type Projection = ty::ProjectionTy<'tcx>;
+    type Substs = &'tcx subst::Substs<'tcx>;
+    type ClosureSubsts = &'tcx ty::ClosureSubsts<'tcx>;
+    type Ty = Ty<'tcx>;
+    type Region = ty::Region;
+    type CodeExtent = CodeExtent;
+    type Pattern = PatNode<'tcx>;
+    type Expr = &'tcx hir::Expr;
+    type Stmt = &'tcx hir::Stmt;
+    type Block = &'tcx hir::Block;
+    type InlineAsm = &'tcx hir::InlineAsm;
+
+    fn unit_ty(&mut self) -> Ty<'tcx> {
+        self.tcx.mk_nil()
+    }
+
+    fn usize_ty(&mut self) -> Ty<'tcx> {
+        self.tcx.types.usize
+    }
+
+    fn bool_ty(&mut self) -> Ty<'tcx> {
+        self.tcx.types.bool
+    }
+
+    fn partial_eq(&mut self, ty: Ty<'tcx>) -> ItemRef<Self> {
+        let eq_def_id = self.tcx.lang_items.eq_trait().unwrap();
+        self.cmp_method_ref(eq_def_id, "eq", ty)
+    }
+
+    fn partial_le(&mut self, ty: Ty<'tcx>) -> ItemRef<Self> {
+        let ord_def_id = self.tcx.lang_items.ord_trait().unwrap();
+        self.cmp_method_ref(ord_def_id, "le", ty)
+    }
+
+    fn num_variants(&mut self, adt_def: ty::AdtDef<'tcx>) -> usize {
+        adt_def.variants.len()
+    }
+
+    fn fields(&mut self, adt_def: ty::AdtDef<'tcx>, variant_index: usize) -> Vec<Field<Self>> {
+        adt_def.variants[variant_index]
+            .fields
+            .iter()
+            .enumerate()
+            .map(|(index, field)| {
+                if field.name == special_idents::unnamed_field.name {
+                    Field::Indexed(index)
+                } else {
+                    Field::Named(field.name)
+                }
+            })
+            .collect()
+    }
+
+    fn needs_drop(&mut self, ty: Ty<'tcx>, span: Self::Span) -> bool {
+        if self.infcx.type_moves_by_default(ty, span) {
+            // TODO we should do an add'l check here to determine if
+            // any dtor will execute, but the relevant fn
+            // (`type_needs_drop`) is currently factored into
+            // `librustc_trans`, so we can't easily do so.
+            true
+        } else {
+            // if type implements Copy, cannot require drop
+            false
+        }
+    }
+
+    fn span_bug(&mut self, span: Self::Span, message: &str) -> ! {
+        self.tcx.sess.span_bug(span, message)
+    }
+}
+
+impl<'a,'tcx:'a> Cx<'a,'tcx> {
+    fn cmp_method_ref(&mut self,
+                      trait_def_id: DefId,
+                      method_name: &str,
+                      arg_ty: Ty<'tcx>)
+                      -> ItemRef<Cx<'a,'tcx>> {
+        let method_name = token::intern(method_name);
+        let substs = Substs::new_trait(vec![arg_ty], vec![], arg_ty);
+        for trait_item in self.tcx.trait_items(trait_def_id).iter() {
+            match *trait_item {
+                ty::ImplOrTraitItem::MethodTraitItem(ref method) => {
+                    if method.name == method_name {
+                        let method_ty = self.tcx.lookup_item_type(method.def_id);
+                        let method_ty = method_ty.ty.subst(self.tcx, &substs);
+                        return ItemRef {
+                            ty: method_ty,
+                            def_id: method.def_id,
+                            substs: self.tcx.mk_substs(substs),
+                        };
+                    }
+                }
+                ty::ImplOrTraitItem::ConstTraitItem(..) |
+                ty::ImplOrTraitItem::TypeTraitItem(..) => {
+                }
+            }
+        }
+
+        self.tcx.sess.bug(
+            &format!("found no method `{}` in `{:?}`", method_name, trait_def_id));
+    }
+}
+
+// We only need this impl so that we do deriving for things that are
+// defined relative to the `Hair` trait. See `Hair` trait for more
+// details.
+impl<'a,'tcx> PartialEq for Cx<'a,'tcx> {
+    fn eq(&self, _: &Cx<'a,'tcx>) -> bool {
+        panic!("Cx should never ACTUALLY be compared for equality")
+    }
+}
+
+impl<'a,'tcx> Eq for Cx<'a,'tcx> { }
+
+impl<'a,'tcx> Hash for Cx<'a,'tcx> {
+    fn hash<H: Hasher>(&self, _: &mut H) {
+        panic!("Cx should never ACTUALLY be hashed")
+    }
+}
+
+impl<'a,'tcx> Debug for Cx<'a,'tcx> {
+    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
+        write!(fmt, "Tcx")
+    }
+}
+
+mod block;
+mod expr;
+mod pattern;
+mod to_ref;
+

src/librustc_mir/tcx/pattern.rs

@@ -0,0 +1,291 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use hair::*;
+use repr::*;
+
+use rustc_data_structures::fnv::FnvHashMap;
+use std::rc::Rc;
+use tcx::Cx;
+use tcx::rustc::middle::const_eval::lookup_const_by_id;
+use tcx::rustc::middle::def;
+use tcx::rustc::middle::pat_util::{pat_is_resolved_const, pat_is_binding};
+use tcx::rustc::middle::ty::{self, Ty};
+use tcx::rustc_front::hir;
+use tcx::syntax::ast;
+use tcx::syntax::ptr::P;
+use tcx::to_ref::ToRef;
+
+/// When there are multiple patterns in a single arm, each one has its
+/// own node-ids for the bindings.  References to the variables always
+/// use the node-ids from the first pattern in the arm, so we just
+/// remap the ids for all subsequent bindings to the first one.
+///
+/// Example:
+/// ```
+/// match foo {
+///    Test1(flavor /* def 1 */) |
+///    Test2(flavor /* def 2 */) if flavor /* ref 1 */.is_tasty() => { ... }
+///    _ => { ... }
+/// }
+/// ```
+#[derive(Clone, Debug)]
+pub struct PatNode<'tcx> {
+    pat: &'tcx hir::Pat,
+    binding_map: Option<Rc<FnvHashMap<ast::Ident, ast::NodeId>>>
+}
+
+impl<'tcx> PatNode<'tcx> {
+    pub fn new(pat: &'tcx hir::Pat,
+               binding_map: Option<Rc<FnvHashMap<ast::Ident, ast::NodeId>>>)
+               -> PatNode<'tcx> {
+        PatNode {
+            pat: pat,
+            binding_map: binding_map,
+        }
+    }
+
+    pub fn irrefutable(pat: &'tcx hir::Pat)
+                       -> PatNode<'tcx> {
+        PatNode::new(pat, None)
+    }
+
+    fn pat_ref<'a>(&self, pat: &'tcx hir::Pat) -> PatternRef<Cx<'a,'tcx>> {
+        PatNode::new(pat, self.binding_map.clone()).to_ref()
+    }
+
+    fn pat_refs<'a>(&self, pats: &'tcx Vec<P<hir::Pat>>) -> Vec<PatternRef<Cx<'a,'tcx>>> {
+        pats.iter().map(|p| self.pat_ref(p)).collect()
+    }
+
+    fn opt_pat_ref<'a>(&self, pat: &'tcx Option<P<hir::Pat>>) -> Option<PatternRef<Cx<'a,'tcx>>> {
+        pat.as_ref().map(|p| self.pat_ref(p))
+    }
+
+    fn slice_or_array_pattern<'a>(&self,
+                                  cx: &mut Cx<'a, 'tcx>,
+                                  ty: Ty<'tcx>,
+                                  prefix: &'tcx Vec<P<hir::Pat>>,
+                                  slice: &'tcx Option<P<hir::Pat>>,
+                                  suffix: &'tcx Vec<P<hir::Pat>>)
+                                  -> PatternKind<Cx<'a,'tcx>>
+    {
+        match ty.sty {
+            ty::TySlice(..) =>
+                // matching a slice or fixed-length array
+                PatternKind::Slice {
+                    prefix: self.pat_refs(prefix),
+                    slice: self.opt_pat_ref(slice),
+                    suffix: self.pat_refs(suffix),
+                },
+
+            ty::TyArray(_, len) => {
+                // fixed-length array
+                assert!(len >= prefix.len() + suffix.len());
+                PatternKind::Array {
+                    prefix: self.pat_refs(prefix),
+                    slice: self.opt_pat_ref(slice),
+                    suffix: self.pat_refs(suffix),
+                }
+            }
+
+            _ => {
+                cx.tcx.sess.span_bug(
+                    self.pat.span,
+                    "unexpanded macro or bad constant etc");
+            }
+        }
+    }
+
+    fn variant_or_leaf<'a>(&self,
+                           cx: &mut Cx<'a, 'tcx>,
+                           subpatterns: Vec<FieldPatternRef<Cx<'a,'tcx>>>)
+                           -> PatternKind<Cx<'a,'tcx>>
+    {
+        let def = cx.tcx.def_map.borrow().get(&self.pat.id).unwrap().full_def();
+        match def {
+            def::DefVariant(enum_id, variant_id, _) => {
+                let adt_def = cx.tcx.lookup_adt_def(enum_id);
+                if adt_def.variants.len() > 1 {
+                    PatternKind::Variant { adt_def: adt_def,
+                                           variant_index: adt_def.variant_index_with_id(variant_id),
+                                           subpatterns: subpatterns }
+                } else {
+                    PatternKind::Leaf { subpatterns: subpatterns }
+                }
+            }
+
+            // NB: resolving to DefStruct means the struct *constructor*,
+            // not the struct as a type.
+            def::DefStruct(..) | def::DefTy(..) => {
+                PatternKind::Leaf { subpatterns: subpatterns }
+            }
+
+            _ => {
+                cx.tcx.sess.span_bug(
+                    self.pat.span,
+                    &format!("inappropriate def for pattern: {:?}", def));
+            }
+        }
+    }
+}
+
+impl<'a,'tcx:'a> Mirror<Cx<'a,'tcx>> for PatNode<'tcx> {
+    type Output = Pattern<Cx<'a,'tcx>>;
+
+    fn make_mirror(self, cx: &mut Cx<'a,'tcx>) -> Pattern<Cx<'a,'tcx>> {
+        let kind = match self.pat.node {
+            hir::PatWild(..) =>
+                PatternKind::Wild,
+
+            hir::PatLit(ref lt) =>
+                PatternKind::Constant { expr: lt.to_ref() },
+
+            hir::PatRange(ref begin, ref end) =>
+                PatternKind::Range { lo: begin.to_ref(),
+                                     hi: end.to_ref() },
+
+            hir::PatEnum(..) | hir::PatIdent(..) | hir::PatQPath(..)
+                if pat_is_resolved_const(&cx.tcx.def_map, self.pat) =>
+            {
+                let def = cx.tcx.def_map.borrow().get(&self.pat.id).unwrap().full_def();
+                match def {
+                    def::DefConst(def_id) | def::DefAssociatedConst(def_id) =>
+                        match lookup_const_by_id(cx.tcx, def_id, Some(self.pat.id)) {
+                            Some(const_expr) =>
+                                PatternKind::Constant { expr: const_expr.to_ref() },
+                            None =>
+                                cx.tcx.sess.span_bug(
+                                    self.pat.span,
+                                    &format!("cannot eval constant: {:?}", def_id)),
+                        },
+                    _ =>
+                        cx.tcx.sess.span_bug(
+                            self.pat.span,
+                            &format!("def not a constant: {:?}", def)),
+                }
+            }
+
+            hir::PatRegion(ref subpattern, _) |
+            hir::PatBox(ref subpattern) => {
+                PatternKind::Deref { subpattern: self.pat_ref(subpattern) }
+            }
+
+            hir::PatVec(ref prefix, ref slice, ref suffix) => {
+                let ty = cx.tcx.node_id_to_type(self.pat.id);
+                match ty.sty {
+                    ty::TyRef(_, mt) =>
+                        PatternKind::Deref {
+                            subpattern: Pattern {
+                                ty: mt.ty,
+                                span: self.pat.span,
+                                kind: self.slice_or_array_pattern(cx, mt.ty, prefix,
+                                                                  slice, suffix),
+                            }.to_ref()
+                        },
+
+                    ty::TySlice(..) |
+                    ty::TyArray(..) =>
+                        self.slice_or_array_pattern(cx, ty, prefix, slice, suffix),
+
+                    ref sty =>
+                        cx.tcx.sess.span_bug(
+                            self.pat.span,
+                            &format!("unexpanded type for vector pattern: {:?}", sty)),
+                }
+            }
+
+            hir::PatTup(ref subpatterns) => {
+                let subpatterns =
+                    subpatterns.iter()
+                               .enumerate()
+                               .map(|(i, subpattern)| FieldPatternRef {
+                                   field: Field::Indexed(i),
+                                   pattern: self.pat_ref(subpattern),
+                               })
+                               .collect();
+
+                PatternKind::Leaf { subpatterns: subpatterns }
+            }
+
+            hir::PatIdent(bm, ref ident, ref sub)
+                if pat_is_binding(&cx.tcx.def_map, self.pat) =>
+            {
+                let id = match self.binding_map {
+                    None => self.pat.id,
+                    Some(ref map) => map[&ident.node],
+                };
+                let var_ty = cx.tcx.node_id_to_type(self.pat.id);
+                let region = match var_ty.sty {
+                    ty::TyRef(&r, _) => Some(r),
+                    _ => None,
+                };
+                let (mutability, mode) = match bm {
+                    hir::BindByValue(hir::MutMutable) =>
+                        (Mutability::Mut, BindingMode::ByValue),
+                    hir::BindByValue(hir::MutImmutable) =>
+                        (Mutability::Not, BindingMode::ByValue),
+                    hir::BindByRef(hir::MutMutable) =>
+                        (Mutability::Not, BindingMode::ByRef(region.unwrap(), BorrowKind::Mut)),
+                    hir::BindByRef(hir::MutImmutable) =>
+                        (Mutability::Not, BindingMode::ByRef(region.unwrap(), BorrowKind::Shared)),
+                };
+                PatternKind::Binding {
+                    mutability: mutability,
+                    mode: mode,
+                    name: ident.node,
+                    var: id,
+                    ty: var_ty,
+                    subpattern: self.opt_pat_ref(sub),
+                }
+            }
+
+            hir::PatIdent(..) => {
+                self.variant_or_leaf(cx, vec![])
+            }
+
+            hir::PatEnum(_, ref opt_subpatterns) => {
+                let subpatterns =
+                    opt_subpatterns.iter()
+                                   .flat_map(|v| v.iter())
+                                   .enumerate()
+                                   .map(|(i, field)| FieldPatternRef {
+                                       field: Field::Indexed(i),
+                                       pattern: self.pat_ref(field),
+                                   })
+                                   .collect();
+                self.variant_or_leaf(cx, subpatterns)
+            }
+
+            hir::PatStruct(_, ref fields, _) => {
+                let subpatterns =
+                    fields.iter()
+                          .map(|field| FieldPatternRef {
+                              field: Field::Named(field.node.ident.name),
+                              pattern: self.pat_ref(&field.node.pat),
+                          })
+                          .collect();
+                self.variant_or_leaf(cx, subpatterns)
+            }
+
+            hir::PatQPath(..) => {
+                cx.tcx.sess.span_bug(
+                    self.pat.span,
+                    "unexpanded macro or bad constant etc");
+            }
+        };
+
+        let ty = cx.tcx.node_id_to_type(self.pat.id);
+
+        Pattern { span: self.pat.span,
+                  ty: ty,
+                  kind: kind }
+    }
+}

src/librustc_mir/tcx/to_ref.rs

@@ -0,0 +1,94 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use hair::*;
+use repr::*;
+
+use tcx::Cx;
+use tcx::pattern::PatNode;
+use tcx::rustc_front::hir;
+use tcx::syntax::ptr::P;
+
+pub trait ToRef<H> {
+    type Output;
+    fn to_ref(self) -> Self::Output;
+}
+
+impl<'a,'tcx:'a> ToRef<Cx<'a,'tcx>> for &'tcx hir::Expr {
+    type Output = ExprRef<Cx<'a,'tcx>>;
+
+    fn to_ref(self) -> ExprRef<Cx<'a,'tcx>> {
+        ExprRef::Hair(self)
+    }
+}
+
+impl<'a,'tcx:'a> ToRef<Cx<'a,'tcx>> for &'tcx P<hir::Expr> {
+    type Output = ExprRef<Cx<'a,'tcx>>;
+
+    fn to_ref(self) -> ExprRef<Cx<'a,'tcx>> {
+        ExprRef::Hair(&**self)
+    }
+}
+
+impl<'a,'tcx:'a> ToRef<Cx<'a,'tcx>> for Expr<Cx<'a,'tcx>> {
+    type Output = ExprRef<Cx<'a,'tcx>>;
+
+    fn to_ref(self) -> ExprRef<Cx<'a,'tcx>> {
+        ExprRef::Mirror(Box::new(self))
+    }
+}
+
+impl<'a,'tcx:'a> ToRef<Cx<'a,'tcx>> for PatNode<'tcx> {
+    type Output = PatternRef<Cx<'a,'tcx>>;
+
+    fn to_ref(self) -> PatternRef<Cx<'a,'tcx>> {
+        PatternRef::Hair(self)
+    }
+}
+
+impl<'a,'tcx:'a> ToRef<Cx<'a,'tcx>> for Pattern<Cx<'a,'tcx>> {
+    type Output = PatternRef<Cx<'a,'tcx>>;
+
+    fn to_ref(self) -> PatternRef<Cx<'a,'tcx>> {
+        PatternRef::Mirror(Box::new(self))
+    }
+}
+
+impl<'a,'tcx:'a,T,U> ToRef<Cx<'a,'tcx>> for &'tcx Option<T>
+    where &'tcx T: ToRef<Cx<'a,'tcx>, Output=U>
+{
+    type Output = Option<U>;
+
+    fn to_ref(self) -> Option<U> {
+        self.as_ref().map(|expr| expr.to_ref())
+    }
+}
+
+impl<'a,'tcx:'a,T,U> ToRef<Cx<'a,'tcx>> for &'tcx Vec<T>
+    where &'tcx T: ToRef<Cx<'a,'tcx>, Output=U>
+{
+    type Output = Vec<U>;
+
+    fn to_ref(self) -> Vec<U> {
+        self.iter().map(|expr| expr.to_ref()).collect()
+    }
+}
+
+impl<'a,'tcx:'a> ToRef<Cx<'a,'tcx>> for &'tcx hir::Field {
+    type Output = FieldExprRef<Cx<'a,'tcx>>;
+
+    fn to_ref(self) -> FieldExprRef<Cx<'a,'tcx>> {
+        FieldExprRef {
+            name: Field::Named(self.ident.node.name),
+            expr: self.expr.to_ref()
+        }
+    }
+}
+

src/libsyntax/feature_gate.rs

@@ -272,13 +272,20 @@ pub const KNOWN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeGat
                                        feature")),
     ("rustc_variance", Normal, Gated("rustc_attrs",
                                      "the `#[rustc_variance]` attribute \
-                                      is an experimental feature")),
+                                      is just used for rustc unit tests \
+                                      and will never be stable")),
     ("rustc_error", Whitelisted, Gated("rustc_attrs",
                                        "the `#[rustc_error]` attribute \
-                                        is an experimental feature")),
+                                        is just used for rustc unit tests \
+                                        and will never be stable")),
     ("rustc_move_fragments", Normal, Gated("rustc_attrs",
                                            "the `#[rustc_move_fragments]` attribute \
-                                            is an experimental feature")),
+                                            is just used for rustc unit tests \
+                                            and will never be stable")),
+    ("rustc_mir", Normal, Gated("rustc_attrs",
+                                "the `#[rustc_mir]` attribute \
+                                 is just used for rustc unit tests \
+                                 and will never be stable")),
 
     ("allow_internal_unstable", Normal, Gated("allow_internal_unstable",
                                               EXPLAIN_ALLOW_INTERNAL_UNSTABLE)),

src/test/compile-fail/feature-gate-rustc-attrs.rs

@@ -14,7 +14,7 @@
 
 #[rustc_variance] //~ ERROR the `#[rustc_variance]` attribute is just used for rustc unit tests and will never be stable
 #[rustc_error] //~ ERROR the `#[rustc_error]` attribute is just used for rustc unit tests and will never be stable
-#[rustc_move_fragments] //~ ERROR the `#[rustc_move_fragments]` attribute is an experimental feature
+#[rustc_move_fragments] //~ ERROR the `#[rustc_move_fragments]` attribute is just used for rustc unit tests and will never be stable
 #[rustc_foo]
 //~^ ERROR unless otherwise specified, attributes with the prefix `rustc_` are reserved for internal compiler diagnostics