Mercurial > hg > graal-jvmci-8
comparison graal/Compiler/src/com/sun/c1x/alloc/EdgeMoveOptimizer.java @ 2507:9ec15d6914ca
Pull over of compiler from maxine repository.
author | Thomas Wuerthinger <thomas@wuerthinger.net> |
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date | Wed, 27 Apr 2011 11:43:22 +0200 |
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2506:4a3bf8a5bf41 | 2507:9ec15d6914ca |
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1 /* | |
2 * Copyright (c) 2009, 2011, Oracle and/or its affiliates. All rights reserved. | |
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
4 * | |
5 * This code is free software; you can redistribute it and/or modify it | |
6 * under the terms of the GNU General Public License version 2 only, as | |
7 * published by the Free Software Foundation. | |
8 * | |
9 * This code is distributed in the hope that it will be useful, but WITHOUT | |
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
12 * version 2 for more details (a copy is included in the LICENSE file that | |
13 * accompanied this code). | |
14 * | |
15 * You should have received a copy of the GNU General Public License version | |
16 * 2 along with this work; if not, write to the Free Software Foundation, | |
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
18 * | |
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
20 * or visit www.oracle.com if you need additional information or have any | |
21 * questions. | |
22 */ | |
23 package com.sun.c1x.alloc; | |
24 | |
25 import java.util.*; | |
26 | |
27 import com.sun.c1x.*; | |
28 import com.sun.c1x.ir.*; | |
29 import com.sun.c1x.lir.*; | |
30 | |
31 /** | |
32 * This class optimizes moves, particularly those that result from eliminating SSA form. | |
33 * | |
34 * When a block has more than one predecessor, and all predecessors end with | |
35 * the {@linkplain #same(LIRInstruction, LIRInstruction) same} sequence of | |
36 * {@linkplain LIROpcode#Move move} instructions, then these sequences | |
37 * can be replaced with a single copy of the sequence at the beginning of the block. | |
38 * | |
39 * Similarly, when a block has more than one successor, then same sequences of | |
40 * moves at the beginning of the successors can be placed once at the end of | |
41 * the block. But because the moves must be inserted before all branch | |
42 * instructions, this works only when there is exactly one conditional branch | |
43 * at the end of the block (because the moves must be inserted before all | |
44 * branches, but after all compares). | |
45 * | |
46 * This optimization affects all kind of moves (reg->reg, reg->stack and | |
47 * stack->reg). Because this optimization works best when a block contains only | |
48 * a few moves, it has a huge impact on the number of blocks that are totally | |
49 * empty. | |
50 * | |
51 * @author Christian Wimmer (original HotSpot implementation) | |
52 * @author Thomas Wuerthinger | |
53 * @author Doug Simon | |
54 */ | |
55 final class EdgeMoveOptimizer { | |
56 | |
57 /** | |
58 * Optimizes moves on block edges. | |
59 * | |
60 * @param blockList a list of blocks whose moves should be optimized | |
61 */ | |
62 public static void optimize(List<BlockBegin> blockList) { | |
63 EdgeMoveOptimizer optimizer = new EdgeMoveOptimizer(); | |
64 | |
65 // ignore the first block in the list (index 0 is not processed) | |
66 for (int i = blockList.size() - 1; i >= 1; i--) { | |
67 BlockBegin block = blockList.get(i); | |
68 | |
69 if (block.numberOfPreds() > 1 && !block.checkBlockFlag(BlockBegin.BlockFlag.ExceptionEntry)) { | |
70 optimizer.optimizeMovesAtBlockEnd(block); | |
71 } | |
72 if (block.numberOfSux() == 2) { | |
73 optimizer.optimizeMovesAtBlockBegin(block); | |
74 } | |
75 } | |
76 } | |
77 | |
78 private final List<List<LIRInstruction>> edgeInstructionSeqences; | |
79 | |
80 private EdgeMoveOptimizer() { | |
81 edgeInstructionSeqences = new ArrayList<List<LIRInstruction>>(4); | |
82 } | |
83 | |
84 /** | |
85 * Determines if two operations are both {@linkplain LIROpcode#Move moves} | |
86 * that have the same {@linkplain LIROp1#operand() source} and {@linkplain LIROp1#result() destination} | |
87 * operands and they have the same {@linkplain LIRInstruction#info debug info}. | |
88 * | |
89 * @param op1 the first instruction to compare | |
90 * @param op2 the second instruction to compare | |
91 * @return {@code true} if {@code op1} and {@code op2} are the same by the above algorithm | |
92 */ | |
93 private boolean same(LIRInstruction op1, LIRInstruction op2) { | |
94 assert op1 != null; | |
95 assert op2 != null; | |
96 | |
97 if (op1.code == LIROpcode.Move && op2.code == LIROpcode.Move) { | |
98 assert op1 instanceof LIROp1 : "move must be LIROp1"; | |
99 assert op2 instanceof LIROp1 : "move must be LIROp1"; | |
100 LIROp1 move1 = (LIROp1) op1; | |
101 LIROp1 move2 = (LIROp1) op2; | |
102 if (move1.info == move2.info && move1.operand().equals(move2.operand()) && move1.result().equals(move2.result())) { | |
103 // these moves are exactly equal and can be optimized | |
104 return true; | |
105 } | |
106 } | |
107 return false; | |
108 } | |
109 | |
110 /** | |
111 * Moves the longest {@linkplain #same common} subsequence at the end all | |
112 * predecessors of {@code block} to the start of {@code block}. | |
113 */ | |
114 private void optimizeMovesAtBlockEnd(BlockBegin block) { | |
115 if (block.isPredecessor(block)) { | |
116 // currently we can't handle this correctly. | |
117 return; | |
118 } | |
119 | |
120 // clear all internal data structures | |
121 edgeInstructionSeqences.clear(); | |
122 | |
123 int numPreds = block.numberOfPreds(); | |
124 assert numPreds > 1 : "do not call otherwise"; | |
125 assert !block.checkBlockFlag(BlockBegin.BlockFlag.ExceptionEntry) : "exception handlers not allowed"; | |
126 | |
127 // setup a list with the LIR instructions of all predecessors | |
128 for (int i = 0; i < numPreds; i++) { | |
129 BlockBegin pred = block.predAt(i); | |
130 List<LIRInstruction> predInstructions = pred.lir().instructionsList(); | |
131 | |
132 if (pred.numberOfSux() != 1) { | |
133 // this can happen with switch-statements where multiple edges are between | |
134 // the same blocks. | |
135 return; | |
136 } | |
137 | |
138 assert pred.suxAt(0) == block : "invalid control flow"; | |
139 assert predInstructions.get(predInstructions.size() - 1).code == LIROpcode.Branch : "block with successor must end with branch"; | |
140 assert predInstructions.get(predInstructions.size() - 1) instanceof LIRBranch : "branch must be LIROpBranch"; | |
141 assert ((LIRBranch) predInstructions.get(predInstructions.size() - 1)).cond() == Condition.TRUE : "block must end with unconditional branch"; | |
142 | |
143 if (predInstructions.get(predInstructions.size() - 1).info != null) { | |
144 // can not optimize instructions that have debug info | |
145 return; | |
146 } | |
147 | |
148 // ignore the unconditional branch at the end of the block | |
149 List<LIRInstruction> seq = predInstructions.subList(0, predInstructions.size() - 1); | |
150 edgeInstructionSeqences.add(seq); | |
151 } | |
152 | |
153 // process lir-instructions while all predecessors end with the same instruction | |
154 while (true) { | |
155 List<LIRInstruction> seq = edgeInstructionSeqences.get(0); | |
156 if (seq.isEmpty()) { | |
157 return; | |
158 } | |
159 | |
160 LIRInstruction op = last(seq); | |
161 for (int i = 1; i < numPreds; ++i) { | |
162 List<LIRInstruction> otherSeq = edgeInstructionSeqences.get(i); | |
163 if (otherSeq.isEmpty() || !same(op, last(otherSeq))) { | |
164 return; | |
165 } | |
166 } | |
167 | |
168 // insert the instruction at the beginning of the current block | |
169 block.lir().insertBefore(1, op); | |
170 | |
171 // delete the instruction at the end of all predecessors | |
172 for (int i = 0; i < numPreds; i++) { | |
173 seq = edgeInstructionSeqences.get(i); | |
174 removeLast(seq); | |
175 } | |
176 } | |
177 } | |
178 | |
179 /** | |
180 * Moves the longest {@linkplain #same common} subsequence at the start of all | |
181 * successors of {@code block} to the end of {@code block} just prior to the | |
182 * branch instruction ending {@code block}. | |
183 */ | |
184 private void optimizeMovesAtBlockBegin(BlockBegin block) { | |
185 | |
186 edgeInstructionSeqences.clear(); | |
187 int numSux = block.numberOfSux(); | |
188 | |
189 List<LIRInstruction> instructions = block.lir().instructionsList(); | |
190 | |
191 assert numSux == 2 : "method should not be called otherwise"; | |
192 assert instructions.get(instructions.size() - 1).code == LIROpcode.Branch : "block with successor must end with branch"; | |
193 assert instructions.get(instructions.size() - 1) instanceof LIRBranch : "branch must be LIROpBranch"; | |
194 assert ((LIRBranch) instructions.get(instructions.size() - 1)).cond() == Condition.TRUE : "block must end with unconditional branch"; | |
195 | |
196 if (instructions.get(instructions.size() - 1).info != null) { | |
197 // cannot optimize instructions when debug info is needed | |
198 return; | |
199 } | |
200 | |
201 LIRInstruction branch = instructions.get(instructions.size() - 2); | |
202 if (branch.info != null || (branch.code != LIROpcode.Branch && branch.code != LIROpcode.CondFloatBranch)) { | |
203 // not a valid case for optimization | |
204 // currently, only blocks that end with two branches (conditional branch followed | |
205 // by unconditional branch) are optimized | |
206 return; | |
207 } | |
208 | |
209 // now it is guaranteed that the block ends with two branch instructions. | |
210 // the instructions are inserted at the end of the block before these two branches | |
211 int insertIdx = instructions.size() - 2; | |
212 | |
213 if (C1XOptions.DetailedAsserts) { | |
214 for (int i = insertIdx - 1; i >= 0; i--) { | |
215 LIRInstruction op = instructions.get(i); | |
216 if ((op.code == LIROpcode.Branch || op.code == LIROpcode.CondFloatBranch) && ((LIRBranch) op).block() != null) { | |
217 throw new Error("block with two successors can have only two branch instructions"); | |
218 } | |
219 } | |
220 } | |
221 | |
222 // setup a list with the lir-instructions of all successors | |
223 for (int i = 0; i < numSux; i++) { | |
224 BlockBegin sux = block.suxAt(i); | |
225 List<LIRInstruction> suxInstructions = sux.lir().instructionsList(); | |
226 | |
227 assert suxInstructions.get(0).code == LIROpcode.Label : "block must start with label"; | |
228 | |
229 if (sux.numberOfPreds() != 1) { | |
230 // this can happen with switch-statements where multiple edges are between | |
231 // the same blocks. | |
232 return; | |
233 } | |
234 assert sux.predAt(0) == block : "invalid control flow"; | |
235 assert !sux.checkBlockFlag(BlockBegin.BlockFlag.ExceptionEntry) : "exception handlers not allowed"; | |
236 | |
237 // ignore the label at the beginning of the block | |
238 List<LIRInstruction> seq = suxInstructions.subList(1, suxInstructions.size()); | |
239 edgeInstructionSeqences.add(seq); | |
240 } | |
241 | |
242 // process LIR instructions while all successors begin with the same instruction | |
243 while (true) { | |
244 List<LIRInstruction> seq = edgeInstructionSeqences.get(0); | |
245 if (seq.isEmpty()) { | |
246 return; | |
247 } | |
248 | |
249 LIRInstruction op = first(seq); | |
250 for (int i = 1; i < numSux; i++) { | |
251 List<LIRInstruction> otherSeq = edgeInstructionSeqences.get(i); | |
252 if (otherSeq.isEmpty() || !same(op, first(otherSeq))) { | |
253 // these instructions are different and cannot be optimized . | |
254 // no further optimization possible | |
255 return; | |
256 } | |
257 } | |
258 | |
259 // insert instruction at end of current block | |
260 block.lir().insertBefore(insertIdx, op); | |
261 insertIdx++; | |
262 | |
263 // delete the instructions at the beginning of all successors | |
264 for (int i = 0; i < numSux; i++) { | |
265 seq = edgeInstructionSeqences.get(i); | |
266 removeFirst(seq); | |
267 } | |
268 } | |
269 } | |
270 | |
271 /** | |
272 * Gets the first element from a LIR instruction sequence. | |
273 */ | |
274 private static LIRInstruction first(List<LIRInstruction> seq) { | |
275 return seq.get(0); | |
276 } | |
277 | |
278 /** | |
279 * Gets the last element from a LIR instruction sequence. | |
280 */ | |
281 private static LIRInstruction last(List<LIRInstruction> seq) { | |
282 return seq.get(seq.size() - 1); | |
283 } | |
284 | |
285 /** | |
286 * Removes the first element from a LIR instruction sequence. | |
287 */ | |
288 private static void removeFirst(List<LIRInstruction> seq) { | |
289 seq.remove(0); | |
290 } | |
291 | |
292 /** | |
293 * Removes the last element from a LIR instruction sequence. | |
294 */ | |
295 private static void removeLast(List<LIRInstruction> seq) { | |
296 seq.remove(seq.size() - 1); | |
297 } | |
298 } |