Improve GVN handling of ElementTransitions.

src/hydrogen.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 108 matching lines @@
 
   void SetJoinId(int ast_id);
 
   void Finish(HControlInstruction* last);
   void FinishExit(HControlInstruction* instruction);
   void Goto(HBasicBlock* block, bool drop_extra = false);
 
   int PredecessorIndexOf(HBasicBlock* predecessor) const;
   void AddSimulate(int ast_id) { AddInstruction(CreateSimulate(ast_id)); }
   void AssignCommonDominator(HBasicBlock* other);
+  void AssignLoopSuccessorDominators();
 
   void FinishExitWithDeoptimization(HDeoptimize::UseEnvironment has_uses) {
     FinishExit(CreateDeoptimize(has_uses));
   }
 
   // Add the inlined function exit sequence, adding an HLeaveInlined
   // instruction and updating the bailout environment.
   void AddLeaveInlined(HValue* return_value,
                        HBasicBlock* target,
                        bool drop_extra = false);
 
   // If a target block is tagged as an inline function return, all
   // predecessors should contain the inlined exit sequence:
   //
   // LeaveInlined
   // Simulate (caller's environment)
   // Goto (target block)
   bool IsInlineReturnTarget() const { return is_inline_return_target_; }
   void MarkAsInlineReturnTarget() { is_inline_return_target_ = true; }
 
   bool IsDeoptimizing() const { return is_deoptimizing_; }
   void MarkAsDeoptimizing() { is_deoptimizing_ = true; }
 
+  bool IsLoopSuccessorDominator() const {
+    return dominates_loop_successors_;
+  }
+  void MarkAsLoopSuccessorDominator() {
+    dominates_loop_successors_ = true;
+  }
+
   inline Zone* zone();
 
 #ifdef DEBUG
   void Verify();
 #endif
 
  private:
   void RegisterPredecessor(HBasicBlock* pred);
   void AddDominatedBlock(HBasicBlock* block);
 
@@ skipping 13 matching lines @@
   HEnvironment* last_environment_;
   // Outgoing parameter count at block exit, set during lithium translation.
   int argument_count_;
   // Instruction indices into the lithium code stream.
   int first_instruction_index_;
   int last_instruction_index_;
   ZoneList<int> deleted_phis_;
   HBasicBlock* parent_loop_header_;
   bool is_inline_return_target_;
   bool is_deoptimizing_;
+  bool dominates_loop_successors_;
 };
 
 
+class HPredecessorIterator BASE_EMBEDDED {
+ public:
+  explicit HPredecessorIterator(HBasicBlock* block)
+      : predecessor_list_(block->predecessors()), current_(0) { }
+
+  bool Done() { return current_ >= predecessor_list_->length(); }
+  HBasicBlock* Current() { return predecessor_list_->at(current_); }
+  void Advance() { current_++; }
+
+ private:
+  const ZoneList<HBasicBlock*>* predecessor_list_;
+  int current_;
+};
+
+
 class HLoopInformation: public ZoneObject {
  public:
   explicit HLoopInformation(HBasicBlock* loop_header)
       : back_edges_(4),
         loop_header_(loop_header),
         blocks_(8),
         stack_check_(NULL) {
     blocks_.Add(loop_header);
   }
   virtual ~HLoopInformation() {}
@@ skipping 1077 matching lines @@
   const char* filename_;
   HeapStringAllocator string_allocator_;
   StringStream trace_;
   int indent_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_