Change store buffer overflow check to not rely on the store buffer being (2*Size) aligned.

src/heap/store-buffer.cc

 // Copyright 2011 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/heap/store-buffer.h"
 
 #include <algorithm>
 
 #include "src/counters.h"
 #include "src/heap/incremental-marking.h"
 #include "src/isolate.h"
 #include "src/objects-inl.h"
 #include "src/v8.h"
 
 namespace v8 {
 namespace internal {
 
 StoreBuffer::StoreBuffer(Heap* heap)
     : heap_(heap),
       top_(nullptr),
       start_(nullptr),
       limit_(nullptr),
       virtual_memory_(nullptr) {}
 
 void StoreBuffer::SetUp() {
   // Allocate 3x the buffer size, so that we can start the new store buffer
   // aligned to 2x the size.  This lets us use a bit test to detect the end of
   // the area.
-  virtual_memory_ = new base::VirtualMemory(kStoreBufferSize * 3);
+  virtual_memory_ = new base::VirtualMemory(kStoreBufferSize * 2);
   uintptr_t start_as_int =
       reinterpret_cast<uintptr_t>(virtual_memory_->address());
-  start_ =
-      reinterpret_cast<Address*>(RoundUp(start_as_int, kStoreBufferSize * 2));
+  start_ = reinterpret_cast<Address*>(RoundUp(start_as_int, kStoreBufferSize));
   limit_ = start_ + (kStoreBufferSize / kPointerSize);
 
   DCHECK(reinterpret_cast<Address>(start_) >= virtual_memory_->address());
   DCHECK(reinterpret_cast<Address>(limit_) >= virtual_memory_->address());
   Address* vm_limit = reinterpret_cast<Address*>(
       reinterpret_cast<char*>(virtual_memory_->address()) +
       virtual_memory_->size());
   DCHECK(start_ <= vm_limit);
   DCHECK(limit_ <= vm_limit);
   USE(vm_limit);
-  DCHECK((reinterpret_cast<uintptr_t>(limit_) & kStoreBufferOverflowBit) != 0);
-  DCHECK((reinterpret_cast<uintptr_t>(limit_ - 1) & kStoreBufferOverflowBit) ==
-         0);
+  DCHECK((reinterpret_cast<uintptr_t>(limit_) & kStoreBufferMask) == 0);
 
   if (!virtual_memory_->Commit(reinterpret_cast<Address>(start_),
                                kStoreBufferSize,
                                false)) {  // Not executable.
     V8::FatalProcessOutOfMemory("StoreBuffer::SetUp");
   }
   top_ = start_;
 }
 
 
@@ skipping 15 matching lines @@
     DCHECK(!heap_->code_space()->Contains(*current));
     Address addr = *current;
     Page* page = Page::FromAnyPointerAddress(heap_, addr);
     RememberedSet<OLD_TO_NEW>::Insert(page, addr);
   }
   top_ = start_;
 }
 
 }  // namespace internal
 }  // namespace v8