502 lines
22 KiB
Rust
502 lines
22 KiB
Rust
//! See docs in `build/expr/mod.rs`.
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use rustc_index::vec::Idx;
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use crate::build::expr::as_place::PlaceBase;
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use crate::build::expr::category::{Category, RvalueFunc};
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use crate::build::{BlockAnd, BlockAndExtension, Builder};
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use crate::thir::*;
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use rustc_middle::middle::region;
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use rustc_middle::mir::AssertKind;
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use rustc_middle::mir::Place;
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use rustc_middle::mir::*;
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use rustc_middle::ty::{self, Ty, UpvarSubsts};
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use rustc_span::Span;
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impl<'a, 'tcx> Builder<'a, 'tcx> {
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/// Returns an rvalue suitable for use until the end of the current
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/// scope expression.
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///
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/// The operand returned from this function will *not be valid* after
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/// an ExprKind::Scope is passed, so please do *not* return it from
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/// functions to avoid bad miscompiles.
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crate fn as_local_rvalue(
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&mut self,
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block: BasicBlock,
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expr: &Expr<'_, 'tcx>,
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) -> BlockAnd<Rvalue<'tcx>> {
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let local_scope = self.local_scope();
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self.as_rvalue(block, Some(local_scope), expr)
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}
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/// Compile `expr`, yielding an rvalue.
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crate fn as_rvalue(
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&mut self,
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mut block: BasicBlock,
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scope: Option<region::Scope>,
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expr: &Expr<'_, 'tcx>,
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) -> BlockAnd<Rvalue<'tcx>> {
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debug!("expr_as_rvalue(block={:?}, scope={:?}, expr={:?})", block, scope, expr);
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let this = self;
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let expr_span = expr.span;
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let source_info = this.source_info(expr_span);
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match expr.kind {
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ExprKind::ThreadLocalRef(did) => block.and(Rvalue::ThreadLocalRef(did)),
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ExprKind::Scope { region_scope, lint_level, value } => {
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let region_scope = (region_scope, source_info);
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this.in_scope(region_scope, lint_level, |this| this.as_rvalue(block, scope, value))
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}
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ExprKind::Repeat { value, count } => {
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let value_operand = unpack!(block = this.as_operand(block, scope, value));
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block.and(Rvalue::Repeat(value_operand, count))
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}
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ExprKind::Binary { op, lhs, rhs } => {
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let lhs = unpack!(block = this.as_operand(block, scope, lhs));
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let rhs = unpack!(block = this.as_operand(block, scope, rhs));
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this.build_binary_op(block, op, expr_span, expr.ty, lhs, rhs)
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}
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ExprKind::Unary { op, arg } => {
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let arg = unpack!(block = this.as_operand(block, scope, arg));
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// Check for -MIN on signed integers
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if this.check_overflow && op == UnOp::Neg && expr.ty.is_signed() {
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let bool_ty = this.tcx.types.bool;
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let minval = this.minval_literal(expr_span, expr.ty);
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let is_min = this.temp(bool_ty, expr_span);
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this.cfg.push_assign(
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block,
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source_info,
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is_min,
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Rvalue::BinaryOp(BinOp::Eq, box (arg.to_copy(), minval)),
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);
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block = this.assert(
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block,
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Operand::Move(is_min),
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false,
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AssertKind::OverflowNeg(arg.to_copy()),
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expr_span,
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);
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}
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block.and(Rvalue::UnaryOp(op, arg))
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}
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ExprKind::Box { value } => {
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// The `Box<T>` temporary created here is not a part of the HIR,
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// and therefore is not considered during generator auto-trait
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// determination. See the comment about `box` at `yield_in_scope`.
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let result = this.local_decls.push(LocalDecl::new(expr.ty, expr_span).internal());
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this.cfg.push(
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block,
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Statement { source_info, kind: StatementKind::StorageLive(result) },
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);
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if let Some(scope) = scope {
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// schedule a shallow free of that memory, lest we unwind:
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this.schedule_drop_storage_and_value(expr_span, scope, result);
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}
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// malloc some memory of suitable type (thus far, uninitialized):
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let box_ = Rvalue::NullaryOp(NullOp::Box, value.ty);
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this.cfg.push_assign(block, source_info, Place::from(result), box_);
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// initialize the box contents:
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unpack!(
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block = this.expr_into_dest(
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this.tcx.mk_place_deref(Place::from(result)),
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block,
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value
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)
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);
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block.and(Rvalue::Use(Operand::Move(Place::from(result))))
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}
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ExprKind::Cast { source } => {
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let source = unpack!(block = this.as_operand(block, scope, source));
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block.and(Rvalue::Cast(CastKind::Misc, source, expr.ty))
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}
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ExprKind::Pointer { cast, source } => {
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let source = unpack!(block = this.as_operand(block, scope, source));
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block.and(Rvalue::Cast(CastKind::Pointer(cast), source, expr.ty))
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}
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ExprKind::Array { fields } => {
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// (*) We would (maybe) be closer to codegen if we
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// handled this and other aggregate cases via
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// `into()`, not `as_rvalue` -- in that case, instead
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// of generating
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//
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// let tmp1 = ...1;
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// let tmp2 = ...2;
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// dest = Rvalue::Aggregate(Foo, [tmp1, tmp2])
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//
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// we could just generate
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//
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// dest.f = ...1;
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// dest.g = ...2;
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//
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// The problem is that then we would need to:
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//
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// (a) have a more complex mechanism for handling
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// partial cleanup;
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// (b) distinguish the case where the type `Foo` has a
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// destructor, in which case creating an instance
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// as a whole "arms" the destructor, and you can't
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// write individual fields; and,
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// (c) handle the case where the type Foo has no
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// fields. We don't want `let x: ();` to compile
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// to the same MIR as `let x = ();`.
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// first process the set of fields
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let el_ty = expr.ty.sequence_element_type(this.tcx);
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let fields: Vec<_> = fields
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.into_iter()
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.map(|f| unpack!(block = this.as_operand(block, scope, f)))
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.collect();
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block.and(Rvalue::Aggregate(box AggregateKind::Array(el_ty), fields))
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}
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ExprKind::Tuple { fields } => {
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// see (*) above
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// first process the set of fields
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let fields: Vec<_> = fields
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.into_iter()
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.map(|f| unpack!(block = this.as_operand(block, scope, f)))
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.collect();
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block.and(Rvalue::Aggregate(box AggregateKind::Tuple, fields))
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}
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ExprKind::Closure { closure_id, substs, upvars, movability, ref fake_reads } => {
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// Convert the closure fake reads, if any, from `ExprRef` to mir `Place`
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// and push the fake reads.
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// This must come before creating the operands. This is required in case
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// there is a fake read and a borrow of the same path, since otherwise the
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// fake read might interfere with the borrow. Consider an example like this
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// one:
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// ```
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// let mut x = 0;
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// let c = || {
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// &mut x; // mutable borrow of `x`
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// match x { _ => () } // fake read of `x`
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// };
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// ```
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// FIXME(RFC2229): Remove feature gate once diagnostics are improved
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if this.tcx.features().capture_disjoint_fields {
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for (thir_place, cause, hir_id) in fake_reads.into_iter() {
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let place_builder =
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unpack!(block = this.as_place_builder(block, thir_place));
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if let Ok(place_builder_resolved) =
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place_builder.try_upvars_resolved(this.tcx, this.typeck_results)
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{
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let mir_place =
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place_builder_resolved.into_place(this.tcx, this.typeck_results);
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this.cfg.push_fake_read(
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block,
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this.source_info(this.tcx.hir().span(*hir_id)),
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*cause,
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mir_place,
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);
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}
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}
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}
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// see (*) above
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let operands: Vec<_> = upvars
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.into_iter()
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.map(|upvar| {
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match Category::of(&upvar.kind) {
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// Use as_place to avoid creating a temporary when
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// moving a variable into a closure, so that
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// borrowck knows which variables to mark as being
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// used as mut. This is OK here because the upvar
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// expressions have no side effects and act on
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// disjoint places.
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// This occurs when capturing by copy/move, while
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// by reference captures use as_operand
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Some(Category::Place) => {
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let place = unpack!(block = this.as_place(block, upvar));
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this.consume_by_copy_or_move(place)
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}
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_ => {
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// Turn mutable borrow captures into unique
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// borrow captures when capturing an immutable
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// variable. This is sound because the mutation
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// that caused the capture will cause an error.
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match upvar.kind {
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ExprKind::Borrow {
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borrow_kind:
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BorrowKind::Mut { allow_two_phase_borrow: false },
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arg,
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} => unpack!(
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block = this.limit_capture_mutability(
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upvar.span, upvar.ty, scope, block, arg,
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)
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),
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_ => unpack!(block = this.as_operand(block, scope, upvar)),
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}
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}
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}
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})
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.collect();
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let result = match substs {
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UpvarSubsts::Generator(substs) => {
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// We implicitly set the discriminant to 0. See
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// librustc_mir/transform/deaggregator.rs for details.
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let movability = movability.unwrap();
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box AggregateKind::Generator(closure_id, substs, movability)
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}
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UpvarSubsts::Closure(substs) => box AggregateKind::Closure(closure_id, substs),
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};
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block.and(Rvalue::Aggregate(result, operands))
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}
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ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => {
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block = unpack!(this.stmt_expr(block, expr, None));
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block.and(Rvalue::Use(Operand::Constant(box Constant {
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span: expr_span,
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user_ty: None,
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literal: ty::Const::zero_sized(this.tcx, this.tcx.types.unit).into(),
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})))
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}
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ExprKind::Yield { .. }
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| ExprKind::Literal { .. }
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| ExprKind::ConstBlock { .. }
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| ExprKind::StaticRef { .. }
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| ExprKind::Block { .. }
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| ExprKind::Match { .. }
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| ExprKind::If { .. }
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| ExprKind::NeverToAny { .. }
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| ExprKind::Use { .. }
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| ExprKind::Borrow { .. }
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| ExprKind::AddressOf { .. }
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| ExprKind::Adt { .. }
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| ExprKind::Loop { .. }
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| ExprKind::LogicalOp { .. }
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| ExprKind::Call { .. }
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| ExprKind::Field { .. }
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| ExprKind::Deref { .. }
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| ExprKind::Index { .. }
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| ExprKind::VarRef { .. }
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| ExprKind::UpvarRef { .. }
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| ExprKind::Break { .. }
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| ExprKind::Continue { .. }
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| ExprKind::Return { .. }
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| ExprKind::InlineAsm { .. }
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| ExprKind::LlvmInlineAsm { .. }
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| ExprKind::PlaceTypeAscription { .. }
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| ExprKind::ValueTypeAscription { .. } => {
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// these do not have corresponding `Rvalue` variants,
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// so make an operand and then return that
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debug_assert!(!matches!(
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Category::of(&expr.kind),
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Some(Category::Rvalue(RvalueFunc::AsRvalue))
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));
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let operand = unpack!(block = this.as_operand(block, scope, expr));
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block.and(Rvalue::Use(operand))
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}
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}
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}
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crate fn build_binary_op(
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&mut self,
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mut block: BasicBlock,
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op: BinOp,
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span: Span,
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ty: Ty<'tcx>,
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lhs: Operand<'tcx>,
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rhs: Operand<'tcx>,
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) -> BlockAnd<Rvalue<'tcx>> {
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let source_info = self.source_info(span);
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let bool_ty = self.tcx.types.bool;
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if self.check_overflow && op.is_checkable() && ty.is_integral() {
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let result_tup = self.tcx.intern_tup(&[ty, bool_ty]);
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let result_value = self.temp(result_tup, span);
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self.cfg.push_assign(
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block,
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source_info,
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result_value,
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Rvalue::CheckedBinaryOp(op, box (lhs.to_copy(), rhs.to_copy())),
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);
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let val_fld = Field::new(0);
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let of_fld = Field::new(1);
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let tcx = self.tcx;
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let val = tcx.mk_place_field(result_value, val_fld, ty);
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let of = tcx.mk_place_field(result_value, of_fld, bool_ty);
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let err = AssertKind::Overflow(op, lhs, rhs);
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block = self.assert(block, Operand::Move(of), false, err, span);
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block.and(Rvalue::Use(Operand::Move(val)))
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} else {
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if ty.is_integral() && (op == BinOp::Div || op == BinOp::Rem) {
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// Checking division and remainder is more complex, since we 1. always check
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// and 2. there are two possible failure cases, divide-by-zero and overflow.
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let zero_err = if op == BinOp::Div {
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AssertKind::DivisionByZero(lhs.to_copy())
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} else {
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AssertKind::RemainderByZero(lhs.to_copy())
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};
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let overflow_err = AssertKind::Overflow(op, lhs.to_copy(), rhs.to_copy());
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// Check for / 0
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let is_zero = self.temp(bool_ty, span);
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let zero = self.zero_literal(span, ty);
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self.cfg.push_assign(
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block,
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source_info,
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is_zero,
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Rvalue::BinaryOp(BinOp::Eq, box (rhs.to_copy(), zero)),
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);
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block = self.assert(block, Operand::Move(is_zero), false, zero_err, span);
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// We only need to check for the overflow in one case:
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// MIN / -1, and only for signed values.
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if ty.is_signed() {
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let neg_1 = self.neg_1_literal(span, ty);
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let min = self.minval_literal(span, ty);
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let is_neg_1 = self.temp(bool_ty, span);
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let is_min = self.temp(bool_ty, span);
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let of = self.temp(bool_ty, span);
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// this does (rhs == -1) & (lhs == MIN). It could short-circuit instead
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self.cfg.push_assign(
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block,
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source_info,
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is_neg_1,
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Rvalue::BinaryOp(BinOp::Eq, box (rhs.to_copy(), neg_1)),
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);
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self.cfg.push_assign(
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block,
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source_info,
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is_min,
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Rvalue::BinaryOp(BinOp::Eq, box (lhs.to_copy(), min)),
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);
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let is_neg_1 = Operand::Move(is_neg_1);
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let is_min = Operand::Move(is_min);
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self.cfg.push_assign(
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block,
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source_info,
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of,
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Rvalue::BinaryOp(BinOp::BitAnd, box (is_neg_1, is_min)),
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);
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block = self.assert(block, Operand::Move(of), false, overflow_err, span);
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}
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}
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block.and(Rvalue::BinaryOp(op, box (lhs, rhs)))
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}
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}
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fn limit_capture_mutability(
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&mut self,
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upvar_span: Span,
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upvar_ty: Ty<'tcx>,
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temp_lifetime: Option<region::Scope>,
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mut block: BasicBlock,
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arg: &Expr<'_, 'tcx>,
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) -> BlockAnd<Operand<'tcx>> {
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let this = self;
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let source_info = this.source_info(upvar_span);
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let temp = this.local_decls.push(LocalDecl::new(upvar_ty, upvar_span));
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this.cfg.push(block, Statement { source_info, kind: StatementKind::StorageLive(temp) });
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let arg_place_builder = unpack!(block = this.as_place_builder(block, arg));
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let mutability = match arg_place_builder.base() {
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// We are capturing a path that starts off a local variable in the parent.
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// The mutability of the current capture is same as the mutability
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// of the local declaration in the parent.
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PlaceBase::Local(local) => this.local_decls[local].mutability,
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// Parent is a closure and we are capturing a path that is captured
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// by the parent itself. The mutability of the current capture
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// is same as that of the capture in the parent closure.
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PlaceBase::Upvar { .. } => {
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let enclosing_upvars_resolved =
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arg_place_builder.clone().into_place(this.tcx, this.typeck_results);
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match enclosing_upvars_resolved.as_ref() {
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PlaceRef {
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local,
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projection: &[ProjectionElem::Field(upvar_index, _), ..],
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}
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| PlaceRef {
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local,
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projection:
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&[ProjectionElem::Deref, ProjectionElem::Field(upvar_index, _), ..],
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} => {
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// Not in a closure
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debug_assert!(
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local == Local::new(1),
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"Expected local to be Local(1), found {:?}",
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local
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);
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// Not in a closure
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debug_assert!(
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this.upvar_mutbls.len() > upvar_index.index(),
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"Unexpected capture place, upvar_mutbls={:#?}, upvar_index={:?}",
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this.upvar_mutbls,
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upvar_index
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);
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this.upvar_mutbls[upvar_index.index()]
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}
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_ => bug!("Unexpected capture place"),
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}
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}
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};
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let borrow_kind = match mutability {
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Mutability::Not => BorrowKind::Unique,
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Mutability::Mut => BorrowKind::Mut { allow_two_phase_borrow: false },
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};
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let arg_place = arg_place_builder.into_place(this.tcx, this.typeck_results);
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this.cfg.push_assign(
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block,
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source_info,
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Place::from(temp),
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Rvalue::Ref(this.tcx.lifetimes.re_erased, borrow_kind, arg_place),
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);
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// See the comment in `expr_as_temp` and on the `rvalue_scopes` field for why
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// this can be `None`.
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if let Some(temp_lifetime) = temp_lifetime {
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this.schedule_drop_storage_and_value(upvar_span, temp_lifetime, temp);
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|
}
|
|
|
|
block.and(Operand::Move(Place::from(temp)))
|
|
}
|
|
|
|
// Helper to get a `-1` value of the appropriate type
|
|
fn neg_1_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
|
|
let param_ty = ty::ParamEnv::empty().and(ty);
|
|
let bits = self.tcx.layout_of(param_ty).unwrap().size.bits();
|
|
let n = (!0u128) >> (128 - bits);
|
|
let literal = ty::Const::from_bits(self.tcx, n, param_ty);
|
|
|
|
self.literal_operand(span, literal)
|
|
}
|
|
|
|
// Helper to get the minimum value of the appropriate type
|
|
fn minval_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
|
|
assert!(ty.is_signed());
|
|
let param_ty = ty::ParamEnv::empty().and(ty);
|
|
let bits = self.tcx.layout_of(param_ty).unwrap().size.bits();
|
|
let n = 1 << (bits - 1);
|
|
let literal = ty::Const::from_bits(self.tcx, n, param_ty);
|
|
|
|
self.literal_operand(span, literal)
|
|
}
|
|
}
|