[Interpreter] Enable assignments in expressions.

src/interpreter/bytecode-array-builder.cc

Index: src/interpreter/bytecode-array-builder.cc
diff --git a/src/interpreter/bytecode-array-builder.cc b/src/interpreter/bytecode-array-builder.cc
index 87c61358e884a45884b4a08ec636d66c541015fa..0dfa58f660cd706b15591adcf326a10dc344b184 100644
--- a/src/interpreter/bytecode-array-builder.cc
+++ b/src/interpreter/bytecode-array-builder.cc
@@ -282,11 +282,23 @@ 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());
   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) {