Provide tagged allocation top pointer

src/code-stub-assembler.cc

 // Copyright 2016 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/code-stub-assembler.h"
 #include "src/code-factory.h"
 
 namespace v8 {
 namespace internal {
 
@@ skipping 326 matching lines @@
   Node* runtime_result = CallRuntime(Runtime::kAllocateInTargetSpace, context,
                                      SmiTag(size_in_bytes), runtime_flags);
   result.Bind(runtime_result);
   Goto(&merge_runtime);
 
   // When there is enough space, return `top' and bump it up.
   Bind(&no_runtime_call);
   Node* no_runtime_result = top;
   StoreNoWriteBarrier(MachineType::PointerRepresentation(), top_address,
                       new_top);
-  no_runtime_result = BitcastWordToTagged(
-      IntPtrAdd(no_runtime_result, IntPtrConstant(kHeapObjectTag)));
   result.Bind(no_runtime_result);
   Goto(&merge_runtime);
 
   Bind(&merge_runtime);
   return result.value();
 }
 
 Node* CodeStubAssembler::AllocateRawAligned(Node* size_in_bytes,
                                             AllocationFlags flags,
                                             Node* top_address,
                                             Node* limit_address) {
   Node* top = Load(MachineType::Pointer(), top_address);
   Node* limit = Load(MachineType::Pointer(), limit_address);
   Variable adjusted_size(this, MachineType::PointerRepresentation());
   adjusted_size.Bind(size_in_bytes);
   if (flags & kDoubleAlignment) {
     // TODO(epertoso): Simd128 alignment.
     Label aligned(this), not_aligned(this), merge(this, &adjusted_size);
-    Branch(WordAnd(top, IntPtrConstant(kDoubleAlignmentMask)), &not_aligned,
-           &aligned);
+    Branch(WordAnd(top, IntPtrConstant(kDoubleAlignmentMask - kHeapObjectTag)),
+           &not_aligned, &aligned);
 
     Bind(&not_aligned);
     Node* not_aligned_size =
         IntPtrAdd(size_in_bytes, IntPtrConstant(kPointerSize));
     adjusted_size.Bind(not_aligned_size);
     Goto(&merge);

[Michael Lippautz, 2016/04/28 16:58:08]

I have the feeling that we should've written a tag here ;) Bug?

 
     Bind(&aligned);
     Goto(&merge);
 
     Bind(&merge);
   }
 
   Variable address(this, MachineRepresentation::kTagged);
   address.Bind(AllocateRawUnaligned(adjusted_size.value(), kNone, top, limit));
 
@@ skipping 750 matching lines @@
 }
 
 Node* CodeStubAssembler::BitFieldDecode(Node* word32, uint32_t shift,
                                         uint32_t mask) {
   return Word32Shr(Word32And(word32, Int32Constant(mask)),
                    Int32Constant(shift));
 }
 
 }  // namespace internal
 }  // namespace v8