Perform string add in generated code on X64 platform...

src/ia32/macro-assembler-ia32.cc

 // Copyright 2006-2009 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 816 matching lines @@
 
 void MacroAssembler::AllocateTwoByteString(Register result,
                                            Register length,
                                            Register scratch1,
                                            Register scratch2,
                                            Register scratch3,
                                            Label* gc_required) {
   // Calculate the number of bytes needed for the characters in the string while
   // observing object alignment.
   ASSERT((SeqTwoByteString::kHeaderSize & kObjectAlignmentMask) == 0);
-  mov(scratch1, length);
   ASSERT(kShortSize == 2);
-  shl(scratch1, 1);
-  add(Operand(scratch1), Immediate(kObjectAlignmentMask));
+  // scratch1 = length * 2 + kObjectAlignmentMask.
+  lea(scratch1, Operand(length, length, times_1, kObjectAlignmentMask));
   and_(Operand(scratch1), Immediate(~kObjectAlignmentMask));
 
   // Allocate two byte string in new space.
   AllocateInNewSpace(SeqTwoByteString::kHeaderSize,
                      times_1,
                      scratch1,
                      result,
                      scratch2,
                      scratch3,
                      gc_required,
@@ skipping 567 matching lines @@
   // Indicate that code has changed.
   CPU::FlushICache(address_, size_);
 
   // Check that the code was patched as expected.
   ASSERT(masm_.pc_ == address_ + size_);
   ASSERT(masm_.reloc_info_writer.pos() == address_ + size_ + Assembler::kGap);
 }
 
 
 } }  // namespace v8::internal