Improve GVN handling of ElementTransitions.

src/hydrogen.h

Index: src/hydrogen.h
diff --git a/src/hydrogen.h b/src/hydrogen.h
index 7e09505d7261c6710d24c2e5fd268316c37c5992..8a41f66c36539f819cf3f5f4effccedb5ee0cb92 100644
--- a/src/hydrogen.h
+++ b/src/hydrogen.h
@@ -126,6 +126,7 @@ class HBasicBlock: public ZoneObject {
   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));
@@ -149,6 +150,13 @@ class HBasicBlock: public ZoneObject {
   bool IsDeoptimizing() const { return is_deoptimizing_; }
   void MarkAsDeoptimizing() { is_deoptimizing_ = true; }
 
+  bool IsLoopSuccessorDominator() const {
+    return dominates_loop_successors_;
+  }
+  void MarkAsLoopSuccessorDominator() {

[fschneider, 2012/02/02 14:59:50]

Please add output to --trace-hydrogen so that you can identify the marked blocks
in the visualizer.

[danno, 2012/02/06 16:54:57]

Done.

+    dominates_loop_successors_ = true;
+  }
+
   inline Zone* zone();
 
 #ifdef DEBUG
@@ -182,6 +190,7 @@ class HBasicBlock: public ZoneObject {
   HBasicBlock* parent_loop_header_;
   bool is_inline_return_target_;
   bool is_deoptimizing_;
+  bool dominates_loop_successors_;
 };