v8/src/hydrogen-gvn.h

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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 {

// 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();
      // TODO(danno): Turn this into a fixpoint iteration.
    }
  }

 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.
  BitVector visited_on_paths_;

  DISALLOW_COPY_AND_ASSIGN(HGlobalValueNumberingPhase);
};


} }  // namespace v8::internal

#endif  // V8_HYDROGEN_GVN_H_