[asm.js] (Re)use temporaries in asm->wasm conversion.

This CL is a prequisite for the stack machine changes, which will need
to use temporaries in various places due to the stack height requirements
on blocks.

R=ahaas@chromium.org,bradnelson@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2280063002
Cr-Commit-Position: refs/heads/master@{#39001}

src/asmjs/asm-wasm-builder.cc

@@ -1099,11 +1099,11 @@ class AsmWasmBuilderImpl final : public AstVisitor<AsmWasmBuilderImpl> {
       }
       case AsmTyper::kMathAbs: {
         if (call_type == kAstI32) {
-          uint32_t tmp = current_function_builder_->AddLocal(kAstI32);
+          WasmTemporary tmp(current_function_builder_, kAstI32);
 
           // if set_local(tmp, x) < 0
           Visit(call->arguments()->at(0));
-          current_function_builder_->EmitSetLocal(tmp);
+          current_function_builder_->EmitSetLocal(tmp.index());
           byte code[] = {WASM_I8(0)};
           current_function_builder_->EmitCode(code, sizeof(code));
           current_function_builder_->Emit(kExprI32LtS);
@@ -1111,12 +1111,12 @@ class AsmWasmBuilderImpl final : public AstVisitor<AsmWasmBuilderImpl> {
 
           // then (0 - tmp)
           current_function_builder_->EmitCode(code, sizeof(code));
-          current_function_builder_->EmitGetLocal(tmp);
+          current_function_builder_->EmitGetLocal(tmp.index());
           current_function_builder_->Emit(kExprI32Sub);
 
           // else tmp
           current_function_builder_->Emit(kExprElse);
-          current_function_builder_->EmitGetLocal(tmp);
+          current_function_builder_->EmitGetLocal(tmp.index());
           // end
           current_function_builder_->Emit(kExprEnd);
 
@@ -1134,25 +1134,25 @@ class AsmWasmBuilderImpl final : public AstVisitor<AsmWasmBuilderImpl> {
       case AsmTyper::kMathMin: {
         // TODO(bradnelson): Change wasm to match Math.min in asm.js mode.
         if (call_type == kAstI32) {
-          uint32_t tmp_x = current_function_builder_->AddLocal(kAstI32);
-          uint32_t tmp_y = current_function_builder_->AddLocal(kAstI32);
+          WasmTemporary tmp_x(current_function_builder_, kAstI32);
+          WasmTemporary tmp_y(current_function_builder_, kAstI32);
 
           // if set_local(tmp_x, x) < set_local(tmp_y, y)
           Visit(call->arguments()->at(0));
-          current_function_builder_->EmitSetLocal(tmp_x);
+          current_function_builder_->EmitSetLocal(tmp_x.index());
 
           Visit(call->arguments()->at(1));
-          current_function_builder_->EmitSetLocal(tmp_y);
+          current_function_builder_->EmitSetLocal(tmp_y.index());
 
           current_function_builder_->Emit(kExprI32LeS);
           current_function_builder_->Emit(kExprIf);
 
           // then tmp_x
-          current_function_builder_->EmitGetLocal(tmp_x);
+          current_function_builder_->EmitGetLocal(tmp_x.index());
 
           // else tmp_y
           current_function_builder_->Emit(kExprElse);
-          current_function_builder_->EmitGetLocal(tmp_y);
+          current_function_builder_->EmitGetLocal(tmp_y.index());
           current_function_builder_->Emit(kExprEnd);
 
         } else if (call_type == kAstF32) {
@@ -1169,26 +1169,26 @@ class AsmWasmBuilderImpl final : public AstVisitor<AsmWasmBuilderImpl> {
       case AsmTyper::kMathMax: {
         // TODO(bradnelson): Change wasm to match Math.max in asm.js mode.
         if (call_type == kAstI32) {
-          uint32_t tmp_x = current_function_builder_->AddLocal(kAstI32);
-          uint32_t tmp_y = current_function_builder_->AddLocal(kAstI32);
+          WasmTemporary tmp_x(current_function_builder_, kAstI32);
+          WasmTemporary tmp_y(current_function_builder_, kAstI32);
 
           // if set_local(tmp_x, x) < set_local(tmp_y, y)
           Visit(call->arguments()->at(0));
 
-          current_function_builder_->EmitSetLocal(tmp_x);
+          current_function_builder_->EmitSetLocal(tmp_x.index());
 
           Visit(call->arguments()->at(1));
-          current_function_builder_->EmitSetLocal(tmp_y);
+          current_function_builder_->EmitSetLocal(tmp_y.index());
 
           current_function_builder_->Emit(kExprI32LeS);
           current_function_builder_->Emit(kExprIf);
 
           // then tmp_y
-          current_function_builder_->EmitGetLocal(tmp_y);
+          current_function_builder_->EmitGetLocal(tmp_y.index());
 
           // else tmp_x
           current_function_builder_->Emit(kExprElse);
-          current_function_builder_->EmitGetLocal(tmp_x);
+          current_function_builder_->EmitGetLocal(tmp_x.index());
           current_function_builder_->Emit(kExprEnd);
 
         } else if (call_type == kAstF32) {

src/wasm/encoder.cc

@@ -56,7 +56,11 @@ WasmFunctionBuilder::WasmFunctionBuilder(WasmModuleBuilder* builder)
       signature_index_(0),
       exported_(0),
       body_(builder->zone()),
-      name_(builder->zone()) {}
+      name_(builder->zone()),
+      i32_temps_(builder->zone()),
+      i64_temps_(builder->zone()),
+      f32_temps_(builder->zone()),
+      f64_temps_(builder->zone()) {}
 
 void WasmFunctionBuilder::EmitVarInt(uint32_t val) {
   byte buffer[8];

src/wasm/encoder.h

@@ -136,12 +136,56 @@ class WasmFunctionBuilder : public ZoneObject {
  private:
   explicit WasmFunctionBuilder(WasmModuleBuilder* builder);
   friend class WasmModuleBuilder;
+  friend class WasmTemporary;
   WasmModuleBuilder* builder_;
   LocalDeclEncoder locals_;
   uint32_t signature_index_;
   bool exported_;
   ZoneVector<uint8_t> body_;
   ZoneVector<char> name_;
+  ZoneVector<uint32_t> i32_temps_;
+  ZoneVector<uint32_t> i64_temps_;
+  ZoneVector<uint32_t> f32_temps_;
+  ZoneVector<uint32_t> f64_temps_;
+};
+
+class WasmTemporary {
+ public:
+  WasmTemporary(WasmFunctionBuilder* builder, LocalType type) {
+    switch (type) {
+      case kAstI32:
+        temporary_ = &builder->i32_temps_;
+        break;
+      case kAstI64:
+        temporary_ = &builder->i64_temps_;
+        break;
+      case kAstF32:
+        temporary_ = &builder->f32_temps_;
+        break;
+      case kAstF64:
+        temporary_ = &builder->f64_temps_;
+        break;
+      default:
+        UNREACHABLE();
+        temporary_ = nullptr;
+    }
+    if (temporary_->size() == 0) {
+      // Allocate a new temporary.
+      index_ = builder->AddLocal(type);
+    } else {
+      // Reuse a previous temporary.
+      index_ = temporary_->back();
+      temporary_->pop_back();
+    }
+  }
+  ~WasmTemporary() {
+    temporary_->push_back(index_);  // return the temporary to the list.
+  }
+  uint32_t index() { return index_; }
+
+ private:
+  ZoneVector<uint32_t>* temporary_;
+  uint32_t index_;
 };
 
 // TODO(titzer): kill!