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

src/ia32/code-stubs-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 4635 matching lines @@
     // function without changing the state.
     __ cmp(ecx, edi);
     __ j(equal, &call, Label::kNear);
     __ cmp(ecx, Immediate(MegamorphicSentinel(isolate)));
     __ j(equal, &call, Label::kNear);
 
     // A monomorphic miss (i.e, here the cache is not uninitialized) goes
     // megamorphic.
     __ cmp(ecx, Immediate(UninitializedSentinel(isolate)));
     __ j(equal, &initialize, Label::kNear);
-    // MegamorphicSentinel is a root so no write-barrier is needed.
+    // MegamorphicSentinel is an immortal immovable object (undefined) so no
+    // write-barrier is needed.
     __ mov(FieldOperand(ebx, JSGlobalPropertyCell::kValueOffset),
            Immediate(MegamorphicSentinel(isolate)));
     __ jmp(&call, Label::kNear);
 
     // An uninitialized cache is patched with the function.
     __ bind(&initialize);
     __ mov(FieldOperand(ebx, JSGlobalPropertyCell::kValueOffset), edi);
-    __ mov(ecx, edi);
-    __ RecordWriteField(ebx,
-                        JSGlobalPropertyCell::kValueOffset,
-                        ecx,
-                        edx,
-                        kDontSaveFPRegs,
-                        OMIT_REMEMBERED_SET,  // Cells are rescanned.
-                        OMIT_SMI_CHECK);
+    // No need for a write barrier here - cells are rescanned.
 
     __ bind(&call);
   }
 
   // Fast-case: Just invoke the function.
   ParameterCount actual(argc_);
 
   if (ReceiverMightBeImplicit()) {
     Label call_as_function;
     __ cmp(eax, isolate->factory()->the_hole_value());
@@ skipping 11 matching lines @@
                     NullCallWrapper(),
                     CALL_AS_FUNCTION);
 
   // Slow-case: Non-function called.
   __ bind(&slow);
   if (RecordCallTarget()) {
     // If there is a call target cache, mark it megamorphic in the
     // non-function case.
     __ mov(ebx, Operand(esp, 0));
     __ mov(ebx, Operand(ebx, 1));
+    // MegamorphicSentinel is an immortal immovable object (undefined) so no
+    // write barrier is needed.
     __ mov(FieldOperand(ebx, JSGlobalPropertyCell::kValueOffset),
            Immediate(MegamorphicSentinel(isolate)));
   }
   // Check for function proxy.
   __ CmpInstanceType(ecx, JS_FUNCTION_PROXY_TYPE);
   __ j(not_equal, &non_function);
   __ pop(ecx);
   __ push(edi);  // put proxy as additional argument under return address
   __ push(ecx);
   __ Set(eax, Immediate(argc_ + 1));
@@ skipping 2571 matching lines @@
                                  false);
   __ pop(edx);
   __ ret(0);
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32