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 "base/arena_containers.h"
21 #include "nodes.h"
22 #include "optimization.h"
23 
24 namespace art {
25 
26 /**
27  * Optimization phase that removes dead phis from the graph. Dead phis are unused
28  * phis, or phis only used by other phis.
29  */
30 class SsaDeadPhiElimination : public HOptimization {
31  public:
SsaDeadPhiElimination(HGraph * graph)32   explicit SsaDeadPhiElimination(HGraph* graph)
33       : HOptimization(graph, kSsaDeadPhiEliminationPassName),
34         worklist_(graph->GetArena()->Adapter(kArenaAllocSsaPhiElimination)) {
35     worklist_.reserve(kDefaultWorklistSize);
36   }
37 
38   void Run() OVERRIDE;
39 
40   void MarkDeadPhis();
41   void EliminateDeadPhis();
42 
43   static constexpr const char* kSsaDeadPhiEliminationPassName = "dead_phi_elimination";
44 
45  private:
46   ArenaVector<HPhi*> worklist_;
47 
48   static constexpr size_t kDefaultWorklistSize = 8;
49 
50   DISALLOW_COPY_AND_ASSIGN(SsaDeadPhiElimination);
51 };
52 
53 /**
54  * Removes redundant phis that may have been introduced when doing SSA conversion.
55  * For example, when entering a loop, we create phis for all live registers. These
56  * registers might be updated with the same value, or not updated at all. We can just
57  * replace the phi with the value when entering the loop.
58  */
59 class SsaRedundantPhiElimination : public HOptimization {
60  public:
SsaRedundantPhiElimination(HGraph * graph)61   explicit SsaRedundantPhiElimination(HGraph* graph)
62       : HOptimization(graph, kSsaRedundantPhiEliminationPassName),
63         worklist_(graph->GetArena()->Adapter(kArenaAllocSsaPhiElimination)) {
64     worklist_.reserve(kDefaultWorklistSize);
65   }
66 
67   void Run() OVERRIDE;
68 
69   static constexpr const char* kSsaRedundantPhiEliminationPassName = "redundant_phi_elimination";
70 
71  private:
72   ArenaVector<HPhi*> worklist_;
73 
74   static constexpr size_t kDefaultWorklistSize = 8;
75 
76   DISALLOW_COPY_AND_ASSIGN(SsaRedundantPhiElimination);
77 };
78 
79 }  // namespace art
80 
81 #endif  // ART_COMPILER_OPTIMIZING_SSA_PHI_ELIMINATION_H_
82