Merge change 4431 to V8 2.0

src/ia32/macro-assembler-ia32.cc

 // Copyright 2006-2009 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 158 matching lines @@
     cmp(Operand(value), Immediate(ExternalReference::new_space_start()));
     j(equal, &done);
   } else {
     int32_t new_space_start = reinterpret_cast<int32_t>(
         ExternalReference::new_space_start().address());
     lea(value, Operand(object, -new_space_start));
     and_(value, Heap::NewSpaceMask());
     j(equal, &done);
   }
 
-  if ((offset > 0) && (offset < Page::kMaxHeapObjectSize)) {
+  // The offset is relative to a tagged or untagged HeapObject pointer,
+  // so either offset or offset + kHeapObjectTag must be a
+  // multiple of kPointerSize.
+  ASSERT(IsAligned(offset, kPointerSize) ||
+         IsAligned(offset + kHeapObjectTag, kPointerSize));
+
+  // We use optimized write barrier code if the word being written to is not in
+  // a large object chunk or is in the first page of a large object chunk.
+  // We make sure that an offset is inside the right limits whether it is
+  // tagged or untagged.
+  if ((offset > 0) && (offset < Page::kMaxHeapObjectSize - kHeapObjectTag)) {
     // Compute the bit offset in the remembered set, leave it in 'value'.
     lea(value, Operand(object, offset));
     and_(value, Page::kPageAlignmentMask);
     shr(value, kPointerSizeLog2);
 
     // Compute the page address from the heap object pointer, leave it in
     // 'object'.
     and_(object, ~Page::kPageAlignmentMask);
 
     // NOTE: For now, we use the bit-test-and-set (bts) x86 instruction
@@ skipping 1323 matching lines @@
   // Indicate that code has changed.
   CPU::FlushICache(address_, size_);
 
   // Check that the code was patched as expected.
   ASSERT(masm_.pc_ == address_ + size_);
   ASSERT(masm_.reloc_info_writer.pos() == address_ + size_ + Assembler::kGap);
 }
 
 
 } }  // namespace v8::internal