Optimize write barrier of map-only elements transitions

src/ia32/macro-assembler-ia32.h

 // Copyright 2012 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 72 matching lines @@
                            SaveFPRegsMode save_fp,
                            RememberedSetFinalAction and_then);
 
   void CheckPageFlag(Register object,
                      Register scratch,
                      int mask,
                      Condition cc,
                      Label* condition_met,
                      Label::Distance condition_met_distance = Label::kFar);
 
+  void CheckPageFlag(Handle<Map> map,

[Michael Starzinger, 2012/06/06 09:41:17]

I am not sure if we should rename this to CheckPageFlagForMap, I'll leave that
up to you.

[danno, 2012/06/06 10:58:28]

Done.

+                     int mask,
+                     Condition cc,
+                     Label* condition_met,
+                     Label::Distance condition_met_distance = Label::kFar);
+
   // Check if object is in new space.  Jumps if the object is not in new space.
   // The register scratch can be object itself, but scratch will be clobbered.
   void JumpIfNotInNewSpace(Register object,
                            Register scratch,
                            Label* branch,
                            Label::Distance distance = Label::kFar) {
     InNewSpace(object, scratch, zero, branch, distance);
   }
 
   // Check if object is in new space.  Jumps if the object is in new space.
@@ skipping 84 matching lines @@
   // operation. RecordWrite filters out smis so it does not update the
   // write barrier if the value is a smi.
   void RecordWrite(
       Register object,
       Register address,
       Register value,
       SaveFPRegsMode save_fp,
       RememberedSetAction remembered_set_action = EMIT_REMEMBERED_SET,
       SmiCheck smi_check = INLINE_SMI_CHECK);
 
+  // For page containing |object| mark the region covering the object's map
+  // dirty. |object| is the object being stored into, |map| is the Map object
+  // that was stored.
+  void RecordWriteForMap(
+      Register object,
+      Handle<Map> map,
+      Register scratch1,
+      Register scratch2,
+      SaveFPRegsMode save_fp);
+  
 #ifdef ENABLE_DEBUGGER_SUPPORT
   // ---------------------------------------------------------------------------
   // Debugger Support
 
   void DebugBreak();
 #endif
 
   // Enter specific kind of exit frame. Expects the number of
   // arguments in register eax and sets up the number of arguments in
   // register edi and the pointer to the first argument in register
@@ skipping 763 matching lines @@
   }                                                                       \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_IA32_MACRO_ASSEMBLER_IA32_H_