Mercurial > hg > graal-compiler

comparison graal/GraalCompiler/src/com/sun/c1x/alloc/ControlFlowOptimizer.java @ 2509:16b9a8b5ad39

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Renamings Runtime=>GraalRuntime and Compiler=>GraalCompiler
author Thomas Wuerthinger <thomas@wuerthinger.net>
date Wed, 27 Apr 2011 11:50:44 +0200
parents graal/Compiler/src/com/sun/c1x/alloc/ControlFlowOptimizer.java@9ec15d6914ca
children 4a36a0bd6d18
comparison
equal deleted inserted replaced
2508:fea94949e0a2 2509:16b9a8b5ad39
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.graph.*;
29 import com.sun.c1x.ir.*;
30 import com.sun.c1x.lir.*;
31 import com.sun.c1x.util.*;
32 import com.sun.cri.ci.*;
33
34 /**
35 * This class performs basic optimizations on the control flow graph after LIR generation.
36 *
37 * @author Thomas Wuerthinger
38 */
39 final class ControlFlowOptimizer {
40
41 /**
42 * Performs control flow optimizations on the given IR graph.
43 * @param ir the IR graph that should be optimized
44 */
45 public static void optimize(IR ir) {
46 ControlFlowOptimizer optimizer = new ControlFlowOptimizer(ir);
47 List<BlockBegin> code = ir.linearScanOrder();
48
49 // push the OSR entry block to the end so that we're not jumping over it.
50 BlockBegin osrEntry = ((Base) code.get(0).end()).osrEntry();
51 if (osrEntry != null) {
52 int index = osrEntry.linearScanNumber();
53 assert code.get(index) == osrEntry : "wrong index";
54 code.remove(index);
55 code.add(osrEntry);
56 }
57
58 optimizer.reorderShortLoops(code);
59 optimizer.deleteEmptyBlocks(code);
60 optimizer.deleteUnnecessaryJumps(code);
61 optimizer.deleteJumpsToReturn(code);
62 }
63
64 private final IR ir;
65
66 private ControlFlowOptimizer(IR ir) {
67 this.ir = ir;
68 }
69
70 private void reorderShortLoop(List<BlockBegin> code, BlockBegin headerBlock, int headerIdx) {
71 int i = headerIdx + 1;
72 int maxEnd = Math.min(headerIdx + C1XOptions.MaximumShortLoopSize, code.size());
73 while (i < maxEnd && code.get(i).loopDepth() >= headerBlock.loopDepth()) {
74 i++;
75 }
76
77 if (i == code.size() || code.get(i).loopDepth() < headerBlock.loopDepth()) {
78 int endIdx = i - 1;
79 BlockBegin endBlock = code.get(endIdx);
80
81 if (endBlock.numberOfSux() == 1 && endBlock.suxAt(0) == headerBlock) {
82 // short loop from headerIdx to endIdx found . reorder blocks such that
83 // the headerBlock is the last block instead of the first block of the loop
84
85 for (int j = headerIdx; j < endIdx; j++) {
86 code.set(j, code.get(j + 1));
87 }
88 code.set(endIdx, headerBlock);
89
90 // correct the flags so that any loop alignment occurs in the right place.
91 assert code.get(endIdx).checkBlockFlag(BlockBegin.BlockFlag.BackwardBranchTarget) : "must be backward branch target";
92 code.get(endIdx).clearBlockFlag(BlockBegin.BlockFlag.BackwardBranchTarget);
93 code.get(headerIdx).setBlockFlag(BlockBegin.BlockFlag.BackwardBranchTarget);
94 }
95 }
96 }
97
98 private void reorderShortLoops(List<BlockBegin> code) {
99 for (int i = code.size() - 1; i >= 0; i--) {
100 BlockBegin block = code.get(i);
101
102 if (block.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopHeader)) {
103 reorderShortLoop(code, block, i);
104 }
105 }
106
107 assert verify(code);
108 }
109
110 // only blocks with exactly one successor can be deleted. Such blocks
111 // must always end with an unconditional branch to this successor
112 private boolean canDeleteBlock(BlockBegin block) {
113 if (block.numberOfSux() != 1 ||
114 block.numberOfExceptionHandlers() != 0 ||
115 block == ir.startBlock ||
116 block.isExceptionEntry() ||
117 block.suxAt(0) == block) {
118 return false;
119 }
120
121 List<LIRInstruction> instructions = block.lir().instructionsList();
122
123 assert instructions.size() >= 2 : "block must have label and branch";
124 assert instructions.get(0).code == LIROpcode.Label : "first instruction must always be a label";
125 assert instructions.get(instructions.size() - 1) instanceof LIRBranch : "last instruction must always be a branch";
126 assert ((LIRBranch) instructions.get(instructions.size() - 1)).cond() == Condition.TRUE : "branch must be unconditional";
127 assert ((LIRBranch) instructions.get(instructions.size() - 1)).block() == block.suxAt(0) : "branch target must be the successor";
128
129 // block must have exactly one successor
130
131 return instructions.size() == 2 && instructions.get(instructions.size() - 1).info == null;
132 }
133
134 private void deleteEmptyBlocks(List<BlockBegin> code) {
135 int oldPos = 0;
136 int newPos = 0;
137 int numBlocks = code.size();
138
139 while (oldPos < numBlocks) {
140 BlockBegin block = code.get(oldPos);
141
142 if (canDeleteBlock(block)) {
143 BlockBegin newTarget = block.suxAt(0);
144
145 // propagate backward branch target flag for correct code alignment
146 if (block.checkBlockFlag(BlockBegin.BlockFlag.BackwardBranchTarget)) {
147 newTarget.setBlockFlag(BlockBegin.BlockFlag.BackwardBranchTarget);
148 }
149
150 // update the block references in any branching LIR instructions
151 for (BlockBegin pred : block.predecessors()) {
152 for (LIRInstruction instr : pred.lir().instructionsList()) {
153 if (instr instanceof LIRBranch) {
154 ((LIRBranch) instr).substitute(block, newTarget);
155 } else if (instr instanceof LIRTableSwitch) {
156 ((LIRTableSwitch) instr).substitute(block, newTarget);
157 }
158 }
159 }
160
161 // adjust successor and predecessor lists
162 ir.replaceBlock(block, newTarget);
163 C1XMetrics.BlocksDeleted++;
164 } else {
165 // adjust position of this block in the block list if blocks before
166 // have been deleted
167 if (newPos != oldPos) {
168 code.set(newPos, code.get(oldPos));
169 }
170 newPos++;
171 }
172 oldPos++;
173 }
174 Util.truncate(code, newPos);
175
176 assert verify(code);
177 }
178
179 private void deleteUnnecessaryJumps(List<BlockBegin> code) {
180 // skip the last block because there a branch is always necessary
181 for (int i = code.size() - 2; i >= 0; i--) {
182 BlockBegin block = code.get(i);
183 List<LIRInstruction> instructions = block.lir().instructionsList();
184
185 LIRInstruction lastOp = instructions.get(instructions.size() - 1);
186 if (lastOp.code == LIROpcode.Branch) {
187 assert lastOp instanceof LIRBranch : "branch must be of type LIRBranch";
188 LIRBranch lastBranch = (LIRBranch) lastOp;
189
190 assert lastBranch.block() != null : "last branch must always have a block as target";
191 assert lastBranch.label() == lastBranch.block().label() : "must be equal";
192
193 if (lastBranch.info == null) {
194 if (lastBranch.block() == code.get(i + 1)) {
195 // delete last branch instruction
196 Util.truncate(instructions, instructions.size() - 1);
197
198 } else {
199 LIRInstruction prevOp = instructions.get(instructions.size() - 2);
200 if (prevOp.code == LIROpcode.Branch || prevOp.code == LIROpcode.CondFloatBranch) {
201 assert prevOp instanceof LIRBranch : "branch must be of type LIRBranch";
202 LIRBranch prevBranch = (LIRBranch) prevOp;
203
204 if (prevBranch.block() == code.get(i + 1) && prevBranch.info == null) {
205 // eliminate a conditional branch to the immediate successor
206 prevBranch.changeBlock(lastBranch.block());
207 prevBranch.negateCondition();
208 Util.truncate(instructions, instructions.size() - 1);
209 }
210 }
211 }
212 }
213 }
214 }
215
216 assert verify(code);
217 }
218
219 private void deleteJumpsToReturn(List<BlockBegin> code) {
220 for (int i = code.size() - 1; i >= 0; i--) {
221 BlockBegin block = code.get(i);
222 List<LIRInstruction> curInstructions = block.lir().instructionsList();
223 LIRInstruction curLastOp = curInstructions.get(curInstructions.size() - 1);
224
225 assert curInstructions.get(0).code == LIROpcode.Label : "first instruction must always be a label";
226 if (curInstructions.size() == 2 && curLastOp.code == LIROpcode.Return) {
227 // the block contains only a label and a return
228 // if a predecessor ends with an unconditional jump to this block, then the jump
229 // can be replaced with a return instruction
230 //
231 // Note: the original block with only a return statement cannot be deleted completely
232 // because the predecessors might have other (conditional) jumps to this block.
233 // this may lead to unnecesary return instructions in the final code
234
235 assert curLastOp.info == null : "return instructions do not have debug information";
236
237 assert curLastOp instanceof LIROp1 : "return must be LIROp1";
238 CiValue returnOpr = ((LIROp1) curLastOp).operand();
239
240 for (int j = block.numberOfPreds() - 1; j >= 0; j--) {
241 BlockBegin pred = block.predAt(j);
242 List<LIRInstruction> predInstructions = pred.lir().instructionsList();
243 LIRInstruction predLastOp = predInstructions.get(predInstructions.size() - 1);
244
245 if (predLastOp.code == LIROpcode.Branch) {
246 assert predLastOp instanceof LIRBranch : "branch must be LIRBranch";
247 LIRBranch predLastBranch = (LIRBranch) predLastOp;
248
249 if (predLastBranch.block() == block && predLastBranch.cond() == Condition.TRUE && predLastBranch.info == null) {
250 // replace the jump to a return with a direct return
251 // Note: currently the edge between the blocks is not deleted
252 predInstructions.set(predInstructions.size() - 1, new LIROp1(LIROpcode.Return, returnOpr));
253 }
254 }
255 }
256 }
257 }
258 }
259
260 private boolean verify(List<BlockBegin> code) {
261 for (BlockBegin block : code) {
262 List<LIRInstruction> instructions = block.lir().instructionsList();
263
264 for (LIRInstruction instr : instructions) {
265 if (instr instanceof LIRBranch) {
266 LIRBranch opBranch = (LIRBranch) instr;
267 assert opBranch.block() == null || code.contains(opBranch.block()) : "missing successor branch from: " + block + " to: " + opBranch.block();
268 assert opBranch.unorderedBlock() == null || code.contains(opBranch.unorderedBlock()) : "missing successor branch from: " + block + " to: " + opBranch.unorderedBlock();
269 }
270 }
271
272 for (BlockBegin sux : block.end().successors()) {
273 assert code.contains(sux) : "missing successor from: " + block + "to: " + sux;
274 }
275
276 for (BlockBegin pred : block.predecessors()) {
277 assert code.contains(pred) : "missing predecessor from: " + block + "to: " + pred;
278 }
279 }
280
281 return true;
282 }
283 }