[Interpreter] Enable assignments in expressions.

src/interpreter/bytecode-array-builder.cc

 // 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.
 
 #include "src/interpreter/bytecode-array-builder.h"
 
 namespace v8 {
 namespace internal {
 namespace interpreter {
 
@@ skipping 270 matching lines @@
     Register reg) {
   if (!IsRegisterInAccumulator(reg)) {
     Output(Bytecode::kLdar, reg.ToOperand());
   }
   return *this;
 }
 
 
 BytecodeArrayBuilder& BytecodeArrayBuilder::StoreAccumulatorInRegister(
     Register reg) {
+  // TODO(oth): Avoid storing the accumulator in the register if the
+  // previous bytecode loaded the accumulator with the same register.
+  //
+  // TODO(oth): If the previous bytecode is a MOV into this register,
+  // the previous instruction can be removed. The logic for determining
+  // these redundant MOVs appears complex.
+  Output(Bytecode::kStar, reg.ToOperand());
   if (!IsRegisterInAccumulator(reg)) {
     Output(Bytecode::kStar, reg.ToOperand());
   }
   return *this;
 }
 
 
+BytecodeArrayBuilder& BytecodeArrayBuilder::MoveRegister(Register from,
+                                                         Register to) {
+  DCHECK(from != to);
+  Output(Bytecode::kMov, from.ToOperand(), to.ToOperand());
+  return *this;
+}
+
+
 BytecodeArrayBuilder& BytecodeArrayBuilder::LoadGlobal(
     size_t name_index, int feedback_slot, LanguageMode language_mode,
     TypeofMode typeof_mode) {
   // TODO(rmcilroy): Potentially store language and typeof information in an
   // operand rather than having extra bytecodes.
   Bytecode bytecode = BytecodeForLoadGlobal(language_mode, typeof_mode);
   if (FitsInIdx8Operand(name_index) && FitsInIdx8Operand(feedback_slot)) {
     Output(bytecode, static_cast<uint8_t>(name_index),
            static_cast<uint8_t>(feedback_slot));
   } else if (FitsInIdx16Operand(name_index) &&
@@ skipping 1007 matching lines @@
   DCHECK_GT(next_consecutive_count_, 0);
   builder_->BorrowConsecutiveTemporaryRegister(next_consecutive_register_);
   allocated_.push_back(next_consecutive_register_);
   next_consecutive_count_--;
   return Register(next_consecutive_register_++);
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8