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27
28#ifndef V8_HYDROGEN_ENVIRONMENT_LIVENESS_H_
29#define V8_HYDROGEN_ENVIRONMENT_LIVENESS_H_
30
31
32#include "hydrogen.h"
33
34namespace v8 {
35namespace internal {
36
37
38// Trims live ranges of environment slots by doing explicit liveness analysis.
39// Values in the environment are kept alive by every subsequent LInstruction
40// that is assigned an LEnvironment, which creates register pressure and
41// unnecessary spill slot moves. Therefore it is beneficial to trim the
42// live ranges of environment slots by zapping them with a constant after
43// the last lookup that refers to them.
44// Slots are identified by their index and only affected if whitelisted in
45// HOptimizedGraphBuilder::IsEligibleForEnvironmentLivenessAnalysis().
46class HEnvironmentLivenessAnalysisPhase : public HPhase {
47 public:
48  explicit HEnvironmentLivenessAnalysisPhase(HGraph* graph);
49
50  void Run();
51
52 private:
53  void ZapEnvironmentSlot(int index, HSimulate* simulate);
54  void ZapEnvironmentSlotsInSuccessors(HBasicBlock* block, BitVector* live);
55  void ZapEnvironmentSlotsForInstruction(HEnvironmentMarker* marker);
56  void UpdateLivenessAtBlockEnd(HBasicBlock* block, BitVector* live);
57  void UpdateLivenessAtInstruction(HInstruction* instr, BitVector* live);
58
59  int block_count_;
60
61  // Largest number of local variables in any environment in the graph
62  // (including inlined environments).
63  int maximum_environment_size_;
64
65  // Per-block data. All these lists are indexed by block_id.
66  ZoneList<BitVector*> live_at_block_start_;
67  ZoneList<HSimulate*> first_simulate_;
68  ZoneList<BitVector*> first_simulate_invalid_for_index_;
69
70  // List of all HEnvironmentMarker instructions for quick iteration/deletion.
71  // It is populated during the first pass over the graph, controlled by
72  // |collect_markers_|.
73  ZoneList<HEnvironmentMarker*> markers_;
74  bool collect_markers_;
75
76  // Keeps track of the last simulate seen, as well as the environment slots
77  // for which a new live range has started since (so they must not be zapped
78  // in that simulate when the end of another live range of theirs is found).
79  HSimulate* last_simulate_;
80  BitVector went_live_since_last_simulate_;
81
82  DISALLOW_COPY_AND_ASSIGN(HEnvironmentLivenessAnalysisPhase);
83};
84
85
86} }  // namespace v8::internal
87
88#endif /* V8_HYDROGEN_ENVIRONMENT_LIVENESS_H_ */
89