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 
23 namespace 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  */
29 class SsaDeadPhiElimination : public HOptimization {
30  public:
SsaDeadPhiElimination(HGraph * graph)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  */
56 class SsaRedundantPhiElimination : public HOptimization {
57  public:
SsaRedundantPhiElimination(HGraph * graph)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