[x86] Support immediate indices for StoreWriteBarrier.

src/compiler/x64/code-generator-x64.cc

 // Copyright 2013 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/compiler/code-generator.h"
 
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/gap-resolver.h"
 #include "src/compiler/node-matchers.h"
 #include "src/scopes.h"
@@ skipping 1087 matching lines @@
       } else {
         if (instr->InputAt(0)->IsRegister()) {
           __ pushq(i.InputRegister(0));
         } else {
           __ pushq(i.InputOperand(0));
         }
       }
       break;
     case kX64StoreWriteBarrier: {
       Register object = i.InputRegister(0);
-      Register index = i.InputRegister(1);
       Register value = i.InputRegister(2);
-      __ movq(Operand(object, index, times_1, 0), value);
-      __ leaq(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);
+        __ movq(Operand(object, index), value);
+        __ RecordWriteContextSlot(object, index, value, scratch, mode);
+      } else {
+        Register index = i.InputRegister(1);
+        __ movq(Operand(object, index, times_1, 0), value);
+        __ leaq(index, Operand(object, index, times_1, 0));
+        __ RecordWrite(object, index, value, mode);
+      }
       break;
     }
     case kCheckedLoadInt8:
       ASSEMBLE_CHECKED_LOAD_INTEGER(movsxbl);
       break;
     case kCheckedLoadUint8:
       ASSEMBLE_CHECKED_LOAD_INTEGER(movzxbl);
       break;
     case kCheckedLoadInt16:
       ASSEMBLE_CHECKED_LOAD_INTEGER(movsxwl);
@@ skipping 474 matching lines @@
     }
   }
   MarkLazyDeoptSite();
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace compiler
 }  // namespace v8