Rescan cells at the end of mark-sweep. This means they don't need a

src/ia32/stub-cache-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 2504 matching lines @@
 
   // Check that the value in the cell is not the hole. If it is, this
   // cell could have been deleted and reintroducing the global needs
   // to update the property details in the property dictionary of the
   // global object. We bail out to the runtime system to do that.
   __ cmp(cell_operand, factory()->the_hole_value());
   __ j(equal, &miss);
 
   // Store the value in the cell.
   __ mov(cell_operand, eax);
-  Label done;
-  __ test(eax, Immediate(kSmiTagMask));
-  __ j(zero, &done);
-
-  __ mov(ecx, eax);
-  __ lea(edx, cell_operand);
-  // Cells are always in the remembered set.
-  __ RecordWrite(ebx,  // Object.
-                 edx,  // Address.
-                 ecx,  // Value.
-                 kDontSaveFPRegs,
-                 OMIT_REMEMBERED_SET,
-                 OMIT_SMI_CHECK);
+  // No write barrier here, because cells are always rescanned.
 
   // Return the value (register eax).
-  __ bind(&done);
-
   Counters* counters = isolate()->counters();
   __ IncrementCounter(counters->named_store_global_inline(), 1);
   __ ret(0);
 
   // Handle store cache miss.
   __ bind(&miss);
   __ IncrementCounter(counters->named_store_global_inline_miss(), 1);
   Handle<Code> ic = isolate()->builtins()->StoreIC_Miss();
   __ jmp(ic, RelocInfo::CODE_TARGET);
 
@@ skipping 1293 matching lines @@
   Handle<Code> ic_miss = masm->isolate()->builtins()->KeyedStoreIC_Miss();
   __ jmp(ic_miss, RelocInfo::CODE_TARGET);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32