[x86] Support immediate indices for StoreWriteBarrier.

src/compiler/ia32/code-generator-ia32.cc

Index: src/compiler/ia32/code-generator-ia32.cc
diff --git a/src/compiler/ia32/code-generator-ia32.cc b/src/compiler/ia32/code-generator-ia32.cc
index 7ec7eba8111f51012561545c8547822258134412..586d5488e906c6c3777b8b2704b974671c32c205 100644
--- a/src/compiler/ia32/code-generator-ia32.cc
+++ b/src/compiler/ia32/code-generator-ia32.cc
@@ -790,13 +790,20 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
       break;
     case kIA32StoreWriteBarrier: {
       Register object = i.InputRegister(0);
-      Register index = i.InputRegister(1);
       Register value = i.InputRegister(2);
-      __ mov(Operand(object, index, times_1, 0), value);
-      __ lea(index, Operand(object, index, times_1, 0));
       SaveFPRegsMode mode =
           frame()->DidAllocateDoubleRegisters() ? kSaveFPRegs : kDontSaveFPRegs;
-      __ RecordWrite(object, index, value, mode);
+      if (HasImmediateInput(instr, 1)) {
+        int index = i.InputInt32(1);
+        Register scratch = i.TempRegister(1);
+        __ mov(Operand(object, index), value);
+        __ RecordWriteContextSlot(object, index, value, scratch, mode);
+      } else {
+        Register index = i.InputRegister(1);
+        __ mov(Operand(object, index, times_1, 0), value);
+        __ lea(index, Operand(object, index, times_1, 0));
+        __ RecordWrite(object, index, value, mode);
+      }
       break;
     }
     case kCheckedLoadInt8: