1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
|
/*
* Copyright (C) 2007 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.dx.ssa.back;
import com.android.dx.rop.code.BasicBlock;
import com.android.dx.rop.code.BasicBlockList;
import com.android.dx.rop.code.CstInsn;
import com.android.dx.rop.code.Insn;
import com.android.dx.rop.code.InsnList;
import com.android.dx.rop.code.RegOps;
import com.android.dx.rop.code.RopMethod;
import com.android.dx.rop.code.SwitchInsn;
import com.android.dx.util.IntList;
import java.util.BitSet;
/**
* Searches for basic blocks that all have the same successor and insns
* but different predecessors. These blocks are then combined into a single
* block and the now-unused blocks are deleted. These identical blocks
* frequently are created when catch blocks are edge-split.
*/
public class IdenticalBlockCombiner {
private final RopMethod ropMethod;
private final BasicBlockList blocks;
private final BasicBlockList newBlocks;
/**
* Constructs instance. Call {@code process()} to run.
*
* @param rm {@code non-null;} instance to process
*/
public IdenticalBlockCombiner(RopMethod rm) {
ropMethod = rm;
blocks = ropMethod.getBlocks();
newBlocks = blocks.getMutableCopy();
}
/**
* Runs algorithm. TODO: This is n^2, and could be made linear-ish with
* a hash. In particular, hash the contents of each block and only
* compare blocks with the same hash.
*
* @return {@code non-null;} new method that has been processed
*/
public RopMethod process() {
int szBlocks = blocks.size();
// indexed by label
BitSet toDelete = new BitSet(blocks.getMaxLabel());
// For each non-deleted block...
for (int bindex = 0; bindex < szBlocks; bindex++) {
BasicBlock b = blocks.get(bindex);
if (toDelete.get(b.getLabel())) {
// doomed block
continue;
}
IntList preds = ropMethod.labelToPredecessors(b.getLabel());
// ...look at all of it's predecessors that have only one succ...
int szPreds = preds.size();
for (int i = 0; i < szPreds; i++) {
int iLabel = preds.get(i);
BasicBlock iBlock = blocks.labelToBlock(iLabel);
if (toDelete.get(iLabel)
|| iBlock.getSuccessors().size() > 1
|| iBlock.getFirstInsn().getOpcode().getOpcode() ==
RegOps.MOVE_RESULT) {
continue;
}
IntList toCombine = new IntList();
// ...and see if they can be combined with any other preds...
for (int j = i + 1; j < szPreds; j++) {
int jLabel = preds.get(j);
BasicBlock jBlock = blocks.labelToBlock(jLabel);
if (jBlock.getSuccessors().size() == 1
&& compareInsns(iBlock, jBlock)) {
toCombine.add(jLabel);
toDelete.set(jLabel);
}
}
combineBlocks(iLabel, toCombine);
}
}
for (int i = szBlocks - 1; i >= 0; i--) {
if (toDelete.get(newBlocks.get(i).getLabel())) {
newBlocks.set(i, null);
}
}
newBlocks.shrinkToFit();
newBlocks.setImmutable();
return new RopMethod(newBlocks, ropMethod.getFirstLabel());
}
/**
* Helper method to compare the contents of two blocks.
*
* @param a {@code non-null;} a block to compare
* @param b {@code non-null;} another block to compare
* @return {@code true} iff the two blocks' instructions are the same
*/
private static boolean compareInsns(BasicBlock a, BasicBlock b) {
return a.getInsns().contentEquals(b.getInsns());
}
/**
* Combines blocks proven identical into one alpha block, re-writing
* all of the successor links that point to the beta blocks to point
* to the alpha block instead.
*
* @param alphaLabel block that will replace all the beta block
* @param betaLabels label list of blocks to combine
*/
private void combineBlocks(int alphaLabel, IntList betaLabels) {
int szBetas = betaLabels.size();
for (int i = 0; i < szBetas; i++) {
int betaLabel = betaLabels.get(i);
BasicBlock bb = blocks.labelToBlock(betaLabel);
IntList preds = ropMethod.labelToPredecessors(bb.getLabel());
int szPreds = preds.size();
for (int j = 0; j < szPreds; j++) {
BasicBlock predBlock = newBlocks.labelToBlock(preds.get(j));
replaceSucc(predBlock, betaLabel, alphaLabel);
}
}
}
/**
* Replaces one of a block's successors with a different label. Constructs
* an updated BasicBlock instance and places it in {@code newBlocks}.
*
* @param block block to replace
* @param oldLabel label of successor to replace
* @param newLabel label of new successor
*/
private void replaceSucc(BasicBlock block, int oldLabel, int newLabel) {
IntList newSuccessors = block.getSuccessors().mutableCopy();
int newPrimarySuccessor;
newSuccessors.set(newSuccessors.indexOf(oldLabel), newLabel);
newPrimarySuccessor = block.getPrimarySuccessor();
if (newPrimarySuccessor == oldLabel) {
newPrimarySuccessor = newLabel;
}
newSuccessors.setImmutable();
BasicBlock newBB = new BasicBlock(block.getLabel(),
block.getInsns(), newSuccessors, newPrimarySuccessor);
newBlocks.set(newBlocks.indexOfLabel(block.getLabel()), newBB);
}
}
|
