Allow map check hoisting in GVN for stable maps.

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 1539 matching lines @@
   HCompareMap(HValue* value,
               Handle<Map> map,
               CompilationInfo* info,
               HBasicBlock* true_target = NULL,
               HBasicBlock* false_target = NULL)
       : HUnaryControlInstruction(value, true_target, false_target),
         known_successor_index_(kNoKnownSuccessorIndex), map_(Unique<Map>(map)) {
     ASSERT(!map.is_null());
     is_stable_ = map->is_stable();
 
-    if (FLAG_check_elimination && is_stable_) {
+    if (is_stable_) {
       map->AddDependentCompilationInfo(
           DependentCode::kPrototypeCheckGroup, info);
     }
   }
 
   int known_successor_index_;
   bool is_stable_;
   Unique<Map> map_;
 };
 
@@ skipping 1122 matching lines @@
   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, CompilationInfo* info, Zone* zone) {
     map_set_.Add(Unique<Map>(map), zone);
     is_stable_ = is_stable_ && map->is_stable();
-
-    if (FLAG_check_elimination && is_stable_) {
+    if (is_stable_) {
       map->AddDependentCompilationInfo(
           DependentCode::kPrototypeCheckGroup, info);
+    } else {
+      SetDependsOnFlag(kMaps);
+      SetDependsOnFlag(kElementsKind);
     }
 
     if (!has_migration_target_ && map->is_migration_target()) {
       has_migration_target_ = true;
       SetChangesFlag(kNewSpacePromotion);
     }
   }
 
   // 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), is_stable_(true) {
     SetOperandAt(0, value);
     // Use the object value for the dependency if NULL is passed.
     SetOperandAt(1, typecheck != NULL ? typecheck : value);
     set_representation(Representation::Tagged());
     SetFlag(kUseGVN);
     SetFlag(kTrackSideEffectDominators);
-    SetDependsOnFlag(kMaps);
-    SetDependsOnFlag(kElementsKind);
   }
 
   bool omit_;
   bool has_migration_target_;
   bool is_stable_;
   UniqueSet<Map> map_set_;
 };
 
 
 class HCheckValue V8_FINAL : public HUnaryOperation {
@@ skipping 3762 matching lines @@
   void SetTransition(HConstant* map_constant, CompilationInfo* info) {
     ASSERT(!has_transition());  // Only set once.
     Handle<Map> map = Handle<Map>::cast(map_constant->handle(info->isolate()));
     if (map->CanBeDeprecated()) {
       map->AddDependentCompilationInfo(DependentCode::kTransitionGroup, info);
     }
     SetOperandAt(2, map_constant);
     has_transition_ = true;
     is_stable_ = map->is_stable();
 
-    if (FLAG_check_elimination && is_stable_) {
+    if (is_stable_) {
       map->AddDependentCompilationInfo(
           DependentCode::kPrototypeCheckGroup, info);
     }
   }
 
   bool is_stable() const {
     return is_stable_;
   }
 
   bool NeedsWriteBarrier() {
@@ skipping 935 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_