Add basic ssa analyzer

Cargo.lock

@@ -409,6 +409,7 @@ name = "rustc_codegen_cranelift"
 version = "0.1.0"
 dependencies = [
  "ar 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "bitflags 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "cranelift 0.18.1 (git+https://github.com/CraneStation/cranelift.git)",
  "cranelift-faerie 0.18.1 (git+https://github.com/CraneStation/cranelift.git)",
  "cranelift-module 0.18.1 (git+https://github.com/CraneStation/cranelift.git)",

Cargo.toml

@@ -23,3 +23,4 @@ target-lexicon = "0.0.3"
 #goblin = "0.0.17"
 faerie = "0.4.4"
 ar = "0.6.0"
+bitflags = "1.0.3"

src/abi.rs

@@ -186,17 +186,15 @@ impl<'a, 'tcx: 'a> FunctionCx<'a, 'tcx> {
 }
 
 pub fn codegen_fn_prelude<'a, 'tcx: 'a>(fx: &mut FunctionCx<'a, 'tcx>, start_ebb: Ebb) {
+    let ssa_analyzed = crate::analyze::analyze(fx);
+    fx.tcx.sess.warn(&format!("ssa {:?}", ssa_analyzed));
+
     match fx.self_sig().abi {
         Abi::Rust | Abi::RustCall => {}
         _ => unimplemented!("declared function with non \"rust\" or \"rust-call\" abi"),
     }
 
     let ret_param = fx.bcx.append_ebb_param(start_ebb, types::I64);
-    let _ = fx.bcx.create_stack_slot(StackSlotData {
-        kind: StackSlotKind::ExplicitSlot,
-        size: 0,
-        offset: None,
-    }); // Dummy stack slot for debugging
 
     enum ArgKind {
         Normal(Value),
@@ -237,6 +235,17 @@ pub fn codegen_fn_prelude<'a, 'tcx: 'a>(fx: &mut FunctionCx<'a, 'tcx>, start_ebb
 
     for (local, arg_kind, ty) in func_params {
         let layout = fx.layout_of(ty);
+
+        if let ArgKind::Normal(ebb_param) = arg_kind {
+            if !ssa_analyzed.get(&local).unwrap().contains(crate::analyze::Flags::NOT_SSA) {
+                let var = Variable(local);
+                fx.bcx.declare_var(var, fx.cton_type(ty).unwrap());
+                fx.bcx.def_var(var, ebb_param);
+                fx.local_map.insert(local, CPlace::Var(var, layout));
+                continue;
+            }
+        }
+
         let stack_slot = fx.bcx.create_stack_slot(StackSlotData {
             kind: StackSlotKind::ExplicitSlot,
             size: layout.size.bytes() as u32,
@@ -270,12 +279,20 @@ pub fn codegen_fn_prelude<'a, 'tcx: 'a>(fx: &mut FunctionCx<'a, 'tcx>, start_ebb
     for local in fx.mir.vars_and_temps_iter() {
         let ty = fx.mir.local_decls[local].ty;
         let layout = fx.layout_of(ty);
-        let stack_slot = fx.bcx.create_stack_slot(StackSlotData {
-            kind: StackSlotKind::ExplicitSlot,
-            size: layout.size.bytes() as u32,
-            offset: None,
-        });
-        let place = CPlace::from_stack_slot(fx, stack_slot, ty);
+
+        let place = if ssa_analyzed.get(&local).unwrap().contains(crate::analyze::Flags::NOT_SSA) {
+            let stack_slot = fx.bcx.create_stack_slot(StackSlotData {
+                kind: StackSlotKind::ExplicitSlot,
+                size: layout.size.bytes() as u32,
+                offset: None,
+            });
+            CPlace::from_stack_slot(fx, stack_slot, ty)
+        } else {
+            let var = Variable(local);
+            fx.bcx.declare_var(var, fx.cton_type(ty).unwrap());
+            CPlace::Var(var, layout)
+        };
+
         fx.local_map.insert(local, place);
     }
 }

src/analyze.rs

@@ -0,0 +1,52 @@
+use crate::prelude::*;
+
+use rustc::mir::{StatementKind::*};
+
+bitflags! {
+    pub struct Flags: u8 {
+        const NOT_SSA = 0b00000001;
+    }
+}
+
+pub fn analyze<'a, 'tcx: 'a>(fx: &FunctionCx<'a, 'tcx>) -> HashMap<Local, Flags> {
+    let mut flag_map = HashMap::new();
+
+    for local in fx.mir.local_decls.indices() {
+        flag_map.insert(local, Flags::empty());
+    }
+
+    not_ssa(&mut flag_map, RETURN_PLACE);
+
+    for (local, local_decl) in fx.mir.local_decls.iter_enumerated() {
+        if fx.cton_type(local_decl.ty).is_none() {
+            not_ssa(&mut flag_map, local);
+        }
+    }
+
+    for bb in fx.mir.basic_blocks().iter() {
+        for stmt in bb.statements.iter() {
+            match &stmt.kind {
+                Assign(_, Rvalue::Ref(_, _, place)) => analyze_non_ssa_place(&mut flag_map, place),
+                _ => {}
+            }
+        }
+
+        match &bb.terminator().kind {
+            TerminatorKind::Call { destination: Some((place, _)), .. } => analyze_non_ssa_place(&mut flag_map, place),
+            _ => {}
+        }
+    }
+
+    flag_map
+}
+
+fn analyze_non_ssa_place(flag_map: &mut HashMap<Local, Flags>, place: &Place) {
+    match place {
+        Place::Local(local) => not_ssa(flag_map, local),
+        _ => {}
+    }
+}
+
+fn not_ssa<L: ::std::borrow::Borrow<Local>>(flag_map: &mut HashMap<Local, Flags>, local: L) {
+    *flag_map.get_mut(local.borrow()).unwrap() |= Flags::NOT_SSA;
+}

src/common.rs

@@ -9,7 +9,7 @@ use crate::prelude::*;
 pub type CurrentBackend = ::cranelift_simplejit::SimpleJITBackend;
 
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
-pub struct Variable(Local);
+pub struct Variable(pub Local);
 
 impl EntityRef for Variable {
     fn new(u: usize) -> Self {

src/lib.rs

@@ -12,6 +12,8 @@ extern crate rustc_target;
 extern crate rustc_data_structures;
 
 extern crate ar;
+#[macro_use]
+extern crate bitflags;
 extern crate faerie;
 //extern crate goblin;
 extern crate cranelift;
@@ -49,6 +51,7 @@ macro_rules! unimpl {
 }
 
 mod abi;
+mod analyze;
 mod base;
 mod common;
 mod constant;