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27
28#ifndef V8_HYDROGEN_GVN_H_
29#define V8_HYDROGEN_GVN_H_
30
31#include "hydrogen.h"
32#include "hydrogen-instructions.h"
33#include "compiler.h"
34#include "zone.h"
35
36namespace v8 {
37namespace internal {
38
39// Perform common subexpression elimination and loop-invariant code motion.
40class HGlobalValueNumberingPhase : public HPhase {
41 public:
42  explicit HGlobalValueNumberingPhase(HGraph* graph);
43
44  void Run() {
45    Analyze();
46    // Trigger a second analysis pass to further eliminate duplicate values
47    // that could only be discovered by removing side-effect-generating
48    // instructions during the first pass.
49    if (FLAG_smi_only_arrays && removed_side_effects_) {
50      Analyze();
51      // TODO(danno): Turn this into a fixpoint iteration.
52    }
53  }
54
55 private:
56  void Analyze();
57  GVNFlagSet CollectSideEffectsOnPathsToDominatedBlock(
58      HBasicBlock* dominator,
59      HBasicBlock* dominated);
60  void AnalyzeGraph();
61  void ComputeBlockSideEffects();
62  void LoopInvariantCodeMotion();
63  void ProcessLoopBlock(HBasicBlock* block,
64                        HBasicBlock* before_loop,
65                        GVNFlagSet loop_kills,
66                        GVNFlagSet* accumulated_first_time_depends,
67                        GVNFlagSet* accumulated_first_time_changes);
68  bool AllowCodeMotion();
69  bool ShouldMove(HInstruction* instr, HBasicBlock* loop_header);
70
71  bool removed_side_effects_;
72
73  // A map of block IDs to their side effects.
74  ZoneList<GVNFlagSet> block_side_effects_;
75
76  // A map of loop header block IDs to their loop's side effects.
77  ZoneList<GVNFlagSet> loop_side_effects_;
78
79  // Used when collecting side effects on paths from dominator to
80  // dominated.
81  BitVector visited_on_paths_;
82
83  DISALLOW_COPY_AND_ASSIGN(HGlobalValueNumberingPhase);
84};
85
86
87} }  // namespace v8::internal
88
89#endif  // V8_HYDROGEN_GVN_H_
90