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// Copyright 2013 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_HYDROGEN_ENVIRONMENT_LIVENESS_H_
#define V8_HYDROGEN_ENVIRONMENT_LIVENESS_H_
#include "hydrogen.h"
namespace v8 {
namespace internal {
// Trims live ranges of environment slots by doing explicit liveness analysis.
// Values in the environment are kept alive by every subsequent LInstruction
// that is assigned an LEnvironment, which creates register pressure and
// unnecessary spill slot moves. Therefore it is beneficial to trim the
// live ranges of environment slots by zapping them with a constant after
// the last lookup that refers to them.
// Slots are identified by their index and only affected if whitelisted in
// HOptimizedGraphBuilder::IsEligibleForEnvironmentLivenessAnalysis().
class HEnvironmentLivenessAnalysisPhase : public HPhase {
public:
explicit HEnvironmentLivenessAnalysisPhase(HGraph* graph);
void Run();
private:
void ZapEnvironmentSlot(int index, HSimulate* simulate);
void ZapEnvironmentSlotsInSuccessors(HBasicBlock* block, BitVector* live);
void ZapEnvironmentSlotsForInstruction(HEnvironmentMarker* marker);
void UpdateLivenessAtBlockEnd(HBasicBlock* block, BitVector* live);
void UpdateLivenessAtInstruction(HInstruction* instr, BitVector* live);
#ifdef DEBUG
bool VerifyClosures(Handle<JSFunction> a, Handle<JSFunction> b);
#endif
int block_count_;
// Largest number of local variables in any environment in the graph
// (including inlined environments).
int maximum_environment_size_;
// Per-block data. All these lists are indexed by block_id.
ZoneList<BitVector*> live_at_block_start_;
ZoneList<HSimulate*> first_simulate_;
ZoneList<BitVector*> first_simulate_invalid_for_index_;
// List of all HEnvironmentMarker instructions for quick iteration/deletion.
// It is populated during the first pass over the graph, controlled by
// |collect_markers_|.
ZoneList<HEnvironmentMarker*> markers_;
bool collect_markers_;
// Keeps track of the last simulate seen, as well as the environment slots
// for which a new live range has started since (so they must not be zapped
// in that simulate when the end of another live range of theirs is found).
HSimulate* last_simulate_;
BitVector went_live_since_last_simulate_;
DISALLOW_COPY_AND_ASSIGN(HEnvironmentLivenessAnalysisPhase);
};
} } // namespace v8::internal
#endif /* V8_HYDROGEN_ENVIRONMENT_LIVENESS_H_ */
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