Fix DoubleStackSlot-to-DoubleStackSlot moves on ia32. Unify platform-independent code.

src/x64/lithium-codegen-x64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 446 matching lines @@
   HConstant* constant = chunk_->LookupConstant(op);
   ASSERT(chunk_->LookupLiteralRepresentation(op).IsTagged());
   return constant->handle();
 }
 
 
 Operand LCodeGen::ToOperand(LOperand* op) const {
   // Does not handle registers. In X64 assembler, plain registers are not
   // representable as an Operand.
   ASSERT(op->IsStackSlot() || op->IsDoubleStackSlot());
-  int index = op->index();
-  if (index >= 0) {
-    // Local or spill slot. Skip the frame pointer, function, and
-    // context in the fixed part of the frame.
-    return Operand(rbp, -(index + 3) * kPointerSize);
-  } else {
-    // Incoming parameter. Skip the return address.
-    return Operand(rbp, -(index - 1) * kPointerSize);
-  }
+  return Operand(rbp, StackSlotOffset(op->index()));
 }
 
 
 void LCodeGen::WriteTranslation(LEnvironment* environment,
                                 Translation* translation,
                                 int* arguments_index,
                                 int* arguments_count) {
   if (environment == NULL) return;
 
   // The translation includes one command per value in the environment.
@@ skipping 5256 matching lines @@
                                FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64