Mark CheckMaps that can cause migration with ChangesNewSpacePromotion.

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 2535 matching lines @@
 
 class HCheckMaps: public HTemplateInstruction<2> {
  public:
   static HCheckMaps* New(Zone* zone, HValue* context, HValue* value,
                          Handle<Map> map, CompilationInfo* info,
                          HValue *typecheck = NULL);
   static HCheckMaps* New(Zone* zone, HValue* context,
                          HValue* value, SmallMapList* maps,
                          HValue *typecheck = NULL) {
     HCheckMaps* check_map = new(zone) HCheckMaps(value, zone, typecheck);
+    bool has_migration_target = false;
     for (int i = 0; i < maps->length(); i++) {
       check_map->map_set_.Add(maps->at(i), zone);

[danno, 2013/08/13 09:17:41]

Why not choke-point the Add method, looking for maps with the migration target
flag set, that way the "has_migration_target" logic be handled in the
constructor, I think it's a little cleaner than in the New method

-      check_map->has_migration_target_ |= maps->at(i)->is_migration_target();
+      has_migration_target |= maps->at(i)->is_migration_target();
     }
+    if (has_migration_target) check_map->MarkMigrationTarget();
     check_map->map_set_.Sort();
     return check_map;
   }
 
   bool CanOmitMapChecks() { return omit_; }
 
   virtual bool HasEscapingOperandAt(int index) { return false; }
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::Tagged();
   }
@@ skipping 22 matching lines @@
     }
     for (int i = 0; i < map_unique_ids_.length(); i++) {
       if (map_unique_ids_.at(i) != b->map_unique_ids_.at(i)) {
         return false;
       }
     }
     return true;
   }
 
  private:
+  void MarkMigrationTarget() {
+    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), map_unique_ids_(0, zone) {
     SetOperandAt(0, value);
     // Use the object value for the dependency if NULL is passed.
     // TODO(titzer): do GVN flags already express this dependency?
     SetOperandAt(1, typecheck != NULL ? typecheck : value);
     set_representation(Representation::Tagged());
     SetFlag(kUseGVN);
@@ skipping 4154 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_