Make instruction for write barrier smaller.

src/ia32/macro-assembler-ia32.cc

 // 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 51 matching lines @@
     Abort("new-space object passed to RecordWriteHelper");
     bind(&not_in_new_space);
   }
 
   // Compute the page start address from the heap object pointer, and reuse
   // the 'object' register for it.
   and_(object, ~Page::kPageAlignmentMask);
 
   // 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,
   // as they usually have long latency and multiple uops. We load the bit base
   // operand to a register at first and store it back after bit set.
   mov(scratch, Operand(object, Page::kDirtyFlagOffset));
   bts(Operand(scratch), addr);
   mov(Operand(object, Page::kDirtyFlagOffset), scratch);
 }
 
@@ skipping 2164 matching lines @@
 
   // 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
 
 #endif  // V8_TARGET_ARCH_IA32