Do deferred migration of maps after deoptimizing once.

src/hydrogen-instructions.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 2805 matching lines @@
  protected:
   virtual bool DataEquals(HValue* other) V8_OVERRIDE {
     return this->map_set_.Equals(&HCheckMaps::cast(other)->map_set_);
   }
 
   virtual int RedefinedOperandIndex() { return 0; }
 
  private:
   void Add(Handle<Map> map, Zone* zone) {
     map_set_.Add(Unique<Map>(map), zone);
-    if (!has_migration_target_ && map->is_migration_target()) {
+    if (!has_migration_target_ &&
+        map->is_migration_target() &&
+        map->has_migrated()) {

[Toon Verwaest, 2013/11/20 10:45:54]

The map cannot both be a migration target and have migrated. Currently this
disables the feature entirely. I think what you want is limit the scope in which
"is_migration_target" is set to true; eg only if the map was ever used in a
migration.

       has_migration_target_ = true;
       SetGVNFlag(kChangesNewSpacePromotion);
     }
   }
 
   // Clients should use one of the static New* methods above.
   HCheckMaps(HValue* value, Zone *zone, HValue* typecheck)
       : HTemplateInstruction<2>(value->type()),
         omit_(false), has_migration_target_(false) {
     SetOperandAt(0, value);
@@ skipping 4621 matching lines @@
   virtual bool IsDeletable() const V8_OVERRIDE { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_