Perform a fix point iteration for GVN.

src/hydrogen-gvn.h

 // Copyright 2013 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 24 matching lines @@
 
 namespace v8 {
 namespace internal {
 
 // Perform common subexpression elimination and loop-invariant code motion.
 class HGlobalValueNumberingPhase : public HPhase {
  public:
   explicit HGlobalValueNumberingPhase(HGraph* graph);
 
   void Run() {
-    Analyze();
-    // Trigger a second analysis pass to further eliminate duplicate values
-    // that could only be discovered by removing side-effect-generating
-    // instructions during the first pass.
-    if (FLAG_smi_only_arrays && removed_side_effects_) {
+    int max_fixpoint_iteration_count = FLAG_gvn_iterations;
+    for (int i = 0; i < max_fixpoint_iteration_count; i++) {
       Analyze();
-      // TODO(danno): Turn this into a fixpoint iteration.
+      if (!removed_side_effects_) break;
+      Reset();
     }
   }
 
  private:
+  void Reset();
   void Analyze();
   GVNFlagSet CollectSideEffectsOnPathsToDominatedBlock(
       HBasicBlock* dominator,
       HBasicBlock* dominated);
   void AnalyzeGraph();
   void ComputeBlockSideEffects();
   void LoopInvariantCodeMotion();
   void ProcessLoopBlock(HBasicBlock* block,
                         HBasicBlock* before_loop,
                         GVNFlagSet loop_kills,
@@ skipping 14 matching lines @@
   // dominated.
   BitVector visited_on_paths_;
 
   DISALLOW_COPY_AND_ASSIGN(HGlobalValueNumberingPhase);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_GVN_H_