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

src/wasm/encoder.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_WASM_ENCODER_H_
 #define V8_WASM_ENCODER_H_
 
 #include "src/signature.h"
 #include "src/zone-containers.h"
 
@@ skipping 118 matching lines @@
   bool exported() { return exported_; }
 
   // Writing methods.
   void WriteSignature(ZoneBuffer& buffer) const;
   void WriteExport(ZoneBuffer& buffer, uint32_t func_index) const;
   void WriteBody(ZoneBuffer& buffer) const;
 
  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!
 class WasmDataSegmentEncoder : public ZoneObject {
  public:
   WasmDataSegmentEncoder(Zone* zone, const byte* data, uint32_t size,
                          uint32_t dest);
   void Write(ZoneBuffer& buffer) const;
 
  private:
@@ skipping 41 matching lines @@
   ZoneVector<std::pair<LocalType, bool>> globals_;
   SignatureMap signature_map_;
   int start_function_index_;
 };
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_ENCODER_H_