8-byte align zone allocations of objects that may require it.

src/zone-inl.h

 // Copyright 2011 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 35 matching lines @@
   Isolate::Current()->set_zone_allow_allocation(prev_);
 }
 
 
 inline void* Zone::New(int size) {
   ASSERT(Isolate::Current()->zone_allow_allocation());
   ASSERT(ZoneScope::nesting() > 0);
   // Round up the requested size to fit the alignment.
   size = RoundUp(size, kAlignment);
 
+  // If the allocation size is divisible by 8 then we return an 8-byte aligned
+  // address.
+  if (kPointerSize == 4 && kAlignment == 4) {
+    position_ += ((~size) & 4) & (reinterpret_cast<intptr_t>(position_) & 4);
+  } else {
+    ASSERT(kAlignment >= kPointerSize);
+  }
+
   // Check if the requested size is available without expanding.
   Address result = position_;
 
   if (size > limit_ - position_) {
      result = NewExpand(size);
   } else {
      position_ += size;
   }
 
   // Check that the result has the proper alignment and return it.
@@ skipping 70 matching lines @@
 
 
 int ZoneScope::nesting() {
   return Isolate::Current()->zone()->scope_nesting_;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ZONE_INL_H_