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

Review URL: http://codereview.chromium.org/8539008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9965 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/zone-inl.h

@@ -53,6 +53,14 @@ inline void* Zone::New(int size) {
   // 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_;
 

src/zone.h

@@ -86,7 +86,9 @@ class Zone {
   friend class Isolate;
   friend class ZoneScope;
 
-  // All pointers returned from New() have this alignment.
+  // All pointers returned from New() have this alignment.  In addition, if the
+  // object being allocated has a size that is divisible by 8 then its alignment
+  // will be 8.
   static const int kAlignment = kPointerSize;
 
   // Never allocate segments smaller than this size in bytes.