Implement fixpoint iteration for escape analysis.

src/hydrogen-escape-analysis.h

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@@ skipping 22 matching lines @@
 
 namespace v8 {
 namespace internal {
 
 
 class HEscapeAnalysisPhase : public HPhase {
  public:
   explicit HEscapeAnalysisPhase(HGraph* graph)
       : HPhase("H_Escape analysis", graph),
         captured_(0, zone()),
+        maybe_more_work_(true),
         number_of_objects_(0),
         number_of_values_(0),
         cumulative_values_(0),
         block_states_(graph->blocks()->length(), zone()) { }
 
   void Run() {

[titzer, 2013/08/30 11:19:29]

I would move this method into the .cc file and make the "more_work" variable
into the return value of the CollectCapturedValues() method--then you don't need
a field.

[Michael Starzinger, 2013/09/17 13:47:13]

Done. After rebasing I can just check for "captured.is_empty()", much simpler
now with the latest version.

-    CollectCapturedValues();
-    PerformScalarReplacement();
+    for (int i = 0; i < kMaxFixpointIterationCount && maybe_more_work_; i++) {
+      CollectCapturedValues();
+      PerformScalarReplacement();
+    }
   }
 
  private:
   void CollectCapturedValues();
   void CollectIfNoEscapingUses(HInstruction* instr);
   void PerformScalarReplacement();
   void AnalyzeDataFlow(HInstruction* instr);
 
   HCapturedObject* NewState(HInstruction* prev);
   HCapturedObject* NewStateForAllocation(HInstruction* prev);
   HCapturedObject* NewStateForLoopHeader(HInstruction* prev, HCapturedObject*);
   HCapturedObject* NewStateCopy(HInstruction* prev, HCapturedObject* state);
 
   HPhi* NewPhiAndInsert(HBasicBlock* block, HValue* incoming_value, int index);
 
   HCapturedObject* StateAt(HBasicBlock* block) {
     return block_states_.at(block->block_id());
   }
 
   void SetStateAt(HBasicBlock* block, HCapturedObject* state) {
     block_states_.Set(block->block_id(), state);
   }
 
+  // Maximum number of escape analysis iterations.
+  static const int kMaxFixpointIterationCount = 2;
+
   // List of allocations captured during collection phase.
   ZoneList<HInstruction*> captured_;
 
+  // Indicates another iteration might discover new captured objects.
+  bool maybe_more_work_;
+
   // Number of captured objects on which scalar replacement was done.
   int number_of_objects_;
 
   // Number of scalar values tracked during scalar replacement phase.
   int number_of_values_;
   int cumulative_values_;
 
   // Map of block IDs to the data-flow state at block entry during the
   // scalar replacement phase.
   ZoneList<HCapturedObject*> block_states_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_ESCAPE_ANALYSIS_H_