src/hydrogen-gvn.h

// Copyright 2013 the V8 project authors. All rights reserved.
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#ifndef V8_HYDROGEN_GVN_H_
#define V8_HYDROGEN_GVN_H_

#include "hydrogen.h"
#include "hydrogen-instructions.h"
#include "compiler.h"
#include "zone.h"

namespace v8 {
namespace internal {

// Simple sparse set with O(1) add, contains, and clear.
class SparseSet {
 public:
  SparseSet(Zone* zone, int capacity)
      : capacity_(capacity),
        length_(0),
        dense_(zone->NewArray<int>(capacity)),
        sparse_(zone->NewArray<int>(capacity)) {
#ifndef NVALGRIND
    // Initialize the sparse array to make valgrind happy.
    memset(sparse_, 0, sizeof(sparse_[0]) * capacity);
#endif
  }

  bool Contains(int n) const {
    ASSERT(0 <= n && n < capacity_);
    int d = sparse_[n];
    return 0 <= d && d < length_ && dense_[d] == n;
  }

  bool Add(int n) {
    if (Contains(n)) return false;
    dense_[length_] = n;
    sparse_[n] = length_;
    ++length_;
    return true;
  }

  void Clear() { length_ = 0; }

 private:
  int capacity_;
  int length_;
  int* dense_;
  int* sparse_;

  DISALLOW_COPY_AND_ASSIGN(SparseSet);
};


// 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_) {
      Analyze();
      ASSERT(!removed_side_effects_);
    }
  }

 private:
  void Analyze();
  GVNFlagSet CollectSideEffectsOnPathsToDominatedBlock(
      HBasicBlock* dominator,
      HBasicBlock* dominated);
  void AnalyzeGraph();
  void ComputeBlockSideEffects();
  void LoopInvariantCodeMotion();
  void ProcessLoopBlock(HBasicBlock* block,
                        HBasicBlock* before_loop,
                        GVNFlagSet loop_kills,
                        GVNFlagSet* accumulated_first_time_depends,
                        GVNFlagSet* accumulated_first_time_changes);
  bool AllowCodeMotion();
  bool ShouldMove(HInstruction* instr, HBasicBlock* loop_header);

  bool removed_side_effects_;

  // A map of block IDs to their side effects.
  ZoneList<GVNFlagSet> block_side_effects_;

  // A map of loop header block IDs to their loop's side effects.
  ZoneList<GVNFlagSet> loop_side_effects_;

  // Used when collecting side effects on paths from dominator to
  // dominated.
  SparseSet visited_on_paths_;

  DISALLOW_COPY_AND_ASSIGN(HGlobalValueNumberingPhase);
};


} }  // namespace v8::internal

#endif  // V8_HYDROGEN_GVN_H_