New hydrogen instruction to reduce cost of growing an array on keyed stores.

src/x64/macro-assembler-x64.cc

 // Copyright 2012 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/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
@@ skipping 907 matching lines @@
   if (value == 0) {
     xorl(kScratchRegister, kScratchRegister);
     return kScratchRegister;
   }
   LoadSmiConstant(kScratchRegister, source);
   return kScratchRegister;
 }
 
 
 void MacroAssembler::LoadSmiConstant(Register dst, Smi* source) {
+  // Special-casing 0 here to use xorl seems to make things slower, so we don't
+  // do it.
   Move(dst, source, Assembler::RelocInfoNone());
 }
 
 
 void MacroAssembler::Integer32ToSmi(Register dst, Register src) {
   STATIC_ASSERT(kSmiTag == 0);
   if (!dst.is(src)) {
     movl(dst, src);
   }
   shlp(dst, Immediate(kSmiShift));
@@ skipping 4152 matching lines @@
   if (mag.shift > 0) sarl(rdx, Immediate(mag.shift));
   movl(rax, dividend);
   shrl(rax, Immediate(31));
   addl(rdx, rax);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64