ssa_phi_elimination.h revision 7c3952f423b8213083d60596a5f0bf4237ca3f7b 
1/*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef ART_COMPILER_OPTIMIZING_SSA_PHI_ELIMINATION_H_
18#define ART_COMPILER_OPTIMIZING_SSA_PHI_ELIMINATION_H_
19
20#include "nodes.h"
21#include "optimization.h"
22
23namespace art {
24
25/**
26 * Optimization phase that removes dead phis from the graph. Dead phis are unused
27 * phis, or phis only used by other phis.
28 */
29class SsaDeadPhiElimination : public HOptimization {
30 public:
31  explicit SsaDeadPhiElimination(HGraph* graph)
32      : HOptimization(graph, true, kSsaDeadPhiEliminationPassName),
33        worklist_(graph->GetArena(), kDefaultWorklistSize) {}
34
35  void Run() OVERRIDE;
36
37  void MarkDeadPhis();
38  void EliminateDeadPhis();
39
40  static constexpr const char* kSsaDeadPhiEliminationPassName = "dead_phi_elimination";
41
42 private:
43  GrowableArray<HPhi*> worklist_;
44
45  static constexpr size_t kDefaultWorklistSize = 8;
46
47  DISALLOW_COPY_AND_ASSIGN(SsaDeadPhiElimination);
48};
49
50/**
51 * Removes redundant phis that may have been introduced when doing SSA conversion.
52 * For example, when entering a loop, we create phis for all live registers. These
53 * registers might be updated with the same value, or not updated at all. We can just
54 * replace the phi with the value when entering the loop.
55 */
56class SsaRedundantPhiElimination : public HOptimization {
57 public:
58  explicit SsaRedundantPhiElimination(HGraph* graph)
59      : HOptimization(graph, true, kSsaRedundantPhiEliminationPassName),
60        worklist_(graph->GetArena(), kDefaultWorklistSize) {}
61
62  void Run() OVERRIDE;
63
64  static constexpr const char* kSsaRedundantPhiEliminationPassName = "redundant_phi_elimination";
65
66 private:
67  GrowableArray<HPhi*> worklist_;
68
69  static constexpr size_t kDefaultWorklistSize = 8;
70
71  DISALLOW_COPY_AND_ASSIGN(SsaRedundantPhiElimination);
72};
73
74}  // namespace art
75
76#endif  // ART_COMPILER_OPTIMIZING_SSA_PHI_ELIMINATION_H_
77