Optimize write barrier of map-only elements transitions

src/ia32/macro-assembler-ia32.h

Index: src/ia32/macro-assembler-ia32.h
diff --git a/src/ia32/macro-assembler-ia32.h b/src/ia32/macro-assembler-ia32.h
index c71cad897fa0438e3dbd06519acac8a186d79320..5b7358fdf04cab0276ef9e1bf4631ec968c9689b 100644
--- a/src/ia32/macro-assembler-ia32.h
+++ b/src/ia32/macro-assembler-ia32.h
@@ -90,6 +90,12 @@ class MacroAssembler: public Assembler {
                      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,
@@ -194,6 +200,16 @@ class MacroAssembler: public Assembler {
       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