Make instruction for write barrier smaller.

R=yangguo@chromium.org
BUG=v8:1495

Review URL: http://codereview.chromium.org/7703007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8978 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/ia32/macro-assembler-ia32.cc

@@ -69,8 +69,8 @@ void MacroAssembler::RecordWriteHelper(Register object,
 
   // Compute number of region covering addr. See Page::GetRegionNumberForAddress
   // method for more details.
-  and_(addr, Page::kPageAlignmentMask);
   shr(addr, Page::kRegionSizeLog2);
+  and_(addr, Page::kPageAlignmentMask >> Page::kRegionSizeLog2);
 
   // Set dirty mark for region.
   // Bit tests with a memory operand should be avoided on Intel processors,