Provide a tagged allocation top pointer.

src/crankshaft/x64/lithium-codegen-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.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/crankshaft/x64/lithium-codegen-x64.h"
 
 #include "src/base/bits.h"
 #include "src/code-factory.h"
@@ skipping 5231 matching lines @@
     AllocationFlags allocation_flags = NO_ALLOCATION_FLAGS;
     if (instr->hydrogen()->IsOldSpaceAllocation()) {
       DCHECK(!instr->hydrogen()->IsNewSpaceAllocation());
       allocation_flags = static_cast<AllocationFlags>(flags | PRETENURE);
     }
     // If the allocation folding dominator allocate triggered a GC, allocation
     // happend in the runtime. We have to reset the top pointer to virtually
     // undo the allocation.
     ExternalReference allocation_top =
         AllocationUtils::GetAllocationTopReference(isolate(), allocation_flags);
-    __ subp(rax, Immediate(kHeapObjectTag));
     __ Store(allocation_top, rax);
-    __ addp(rax, Immediate(kHeapObjectTag));
   }
 }
 
 
 void LCodeGen::DoTypeof(LTypeof* instr) {
   DCHECK(ToRegister(instr->context()).is(rsi));
   DCHECK(ToRegister(instr->value()).is(rbx));
   Label end, do_call;
   Register value_register = ToRegister(instr->value());
   __ JumpIfNotSmi(value_register, &do_call);
@@ skipping 349 matching lines @@
   __ bind(deferred->exit());
   __ bind(&done);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64