[Interpreter] Reduce temporary register usage in generated bytecode.

src/interpreter/bytecode-generator.h

Index: src/interpreter/bytecode-generator.h
diff --git a/src/interpreter/bytecode-generator.h b/src/interpreter/bytecode-generator.h
index 3ce65322cc4314c81798e37397b6531d70583451..802e6e1fc8d04a6c2fd3433384392ac8602c0123 100644
--- a/src/interpreter/bytecode-generator.h
+++ b/src/interpreter/bytecode-generator.h
@@ -30,6 +30,9 @@ class BytecodeGenerator : public AstVisitor {
  private:
   class ControlScope;
   class ControlScopeForIteration;
+  class ExpressionResultScope;
+  class AccumulatorResultScope;
+  class RegisterResultScope;
 
   DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
 
@@ -43,6 +46,13 @@ class BytecodeGenerator : public AstVisitor {
   void VisitTypeOf(UnaryOperation* expr);
   void VisitNot(UnaryOperation* expr);
 
+  void VisitForAccumulatorValue(Expression* expression);

[rmcilroy, 2015/10/08 16:54:26]

Could we have some comments on when these are expected to be used.

[oth, 2015/10/09 12:50:48]

Done.

+  void VisitForRegisterValue(Expression* expression,

[rmcilroy, 2015/10/08 16:54:26]

Could VisitForRegisterValue just return the Register (with MUST_USE_RESULT)
rather than having a separate GetResultRegister? Also, would it make sense to
have the register stored in the RegisterResultScope instead of in the
BytecodeGenerator?

[oth, 2015/10/09 12:50:48]

Done.

[rmcilroy, 2015/10/09 13:02:56]

What did you think of storing the register in the RegisterResultScope  instead
of in the BytecodeGenerator? Doesn't seem to be done. It would allow the removal
of GetResultRegister and ResultRegisterIsEmpty functions.

+                             TemporaryRegisterScope* temporary_register_scope);
+  MUST_USE_RESULT Register GetResultRegister();
+  void DropResultRegister();

[rmcilroy, 2015/10/08 16:54:26]

Doesn't look like this is necessary as a seperate function since it's only used
by GetResultRegister

[oth, 2015/10/09 12:50:48]

Done. Right there was an intermediate step that also used this, but that
disappeared before the CL.

+  void SetResultRegister(Register reg);
+
   inline BytecodeArrayBuilder* builder() { return &builder_; }
   inline Scope* scope() const { return scope_; }
   inline void set_scope(Scope* scope) { scope_ = scope; }
@@ -51,6 +61,12 @@ class BytecodeGenerator : public AstVisitor {
   inline CompilationInfo* info() const { return info_; }
   inline void set_info(CompilationInfo* info) { info_ = info; }
   ZoneVector<Handle<Object>>* globals() { return &globals_; }
+  inline void set_result_scope(ExpressionResultScope* result_scope) {
+    result_scope_ = result_scope;
+  }
+  inline ExpressionResultScope* result_scope() const {
+    return result_scope_;
+  }
 
   LanguageMode language_mode() const;
   Strength language_mode_strength() const;
@@ -65,6 +81,8 @@ class BytecodeGenerator : public AstVisitor {
 
   // TODO(rmcilroy): Encapsulate this in an environment object.
   Register current_context_;
+  ExpressionResultScope* result_scope_;
+  Maybe<Register> result_register_;
 };
 
 }  // namespace interpreter