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comparison graal/Compiler/src/com/sun/c1x/opt/CEEliminator.java @ 2507:9ec15d6914ca

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Pull over of compiler from maxine repository.
author Thomas Wuerthinger <thomas@wuerthinger.net>
date Wed, 27 Apr 2011 11:43:22 +0200
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1 /*
2 * Copyright (c) 2009, 2010, 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.opt;
24
25 import com.sun.c1x.*;
26 import com.sun.c1x.graph.*;
27 import com.sun.c1x.ir.*;
28 import com.sun.c1x.value.*;
29 import com.sun.c1x.value.FrameState.*;
30 import com.sun.cri.ci.*;
31
32 /**
33 * This class implements conditional-expression elimination, which replaces some
34 * simple branching constructs with conditional moves.
35 *
36 * @author Ben L. Titzer
37 */
38 public class CEEliminator implements BlockClosure {
39
40 final IR ir;
41 final InstructionSubstituter subst;
42
43 public CEEliminator(IR ir) {
44 this.ir = ir;
45 this.subst = new InstructionSubstituter(ir);
46 ir.startBlock.iteratePreOrder(this);
47 subst.finish();
48 }
49
50 void adjustExceptionEdges(BlockBegin block, BlockBegin sux) {
51 int e = sux.numberOfExceptionHandlers();
52 for (int i = 0; i < e; i++) {
53 BlockBegin xhandler = sux.exceptionHandlerAt(i);
54 block.addExceptionHandler(xhandler);
55
56 assert xhandler.isPredecessor(sux) : "missing predecessor";
57 if (sux.numberOfPreds() == 0) {
58 // sux is disconnected from graph so disconnect from exception handlers
59 xhandler.removePredecessor(sux);
60 }
61 if (!xhandler.isPredecessor(block)) {
62 xhandler.addPredecessor(block);
63 }
64 }
65 }
66
67 public void apply(BlockBegin block) {
68 // 1) check that block ends with an If
69 if (!(block.end() instanceof If)) {
70 return;
71 }
72 If curIf = (If) block.end();
73
74 // check that the if's operands are of int or object type
75 CiKind ifType = curIf.x().kind;
76 if (!ifType.isInt() && !ifType.isObject()) {
77 return;
78 }
79
80 BlockBegin tBlock = curIf.trueSuccessor();
81 BlockBegin fBlock = curIf.falseSuccessor();
82 Instruction tCur = tBlock.next();
83 Instruction fCur = fBlock.next();
84
85 // one Constant may be present between BlockBegin and BlockEnd
86 Instruction tConst = null;
87 Instruction fConst = null;
88 if (tCur instanceof Constant) {
89 tConst = tCur;
90 tCur = tCur.next();
91 }
92 if (fCur instanceof Constant) {
93 fConst = fCur;
94 fCur = fCur.next();
95 }
96
97 // check that both branches end with a goto
98 if (!(tCur instanceof Goto) || !(fCur instanceof Goto)) {
99 return;
100 }
101 Goto tGoto = (Goto) tCur;
102 Goto fGoto = (Goto) fCur;
103
104 // check that both gotos merge into the same block
105 BlockBegin sux = tGoto.defaultSuccessor();
106 if (sux != fGoto.defaultSuccessor()) {
107 return;
108 }
109
110 // check that at least one word was pushed on suxState
111 FrameState suxState = sux.stateBefore();
112 if (suxState.stackSize() <= curIf.stateAfter().stackSize()) {
113 return;
114 }
115
116 // check that phi function is present at end of successor stack and that
117 // only this phi was pushed on the stack
118 final Value suxPhi = suxState.stackAt(curIf.stateAfter().stackSize());
119 if (suxPhi == null || !(suxPhi instanceof Phi) || ((Phi) suxPhi).block() != sux) {
120 return;
121 }
122 if (suxPhi.kind.sizeInSlots() != suxState.stackSize() - curIf.stateAfter().stackSize()) {
123 return;
124 }
125
126 // get the values that were pushed in the true- and false-branch
127 Value tValue = tGoto.stateAfter().stackAt(curIf.stateAfter().stackSize());
128 Value fValue = fGoto.stateAfter().stackAt(curIf.stateAfter().stackSize());
129
130 assert tValue.kind == fValue.kind : "incompatible types";
131
132 if (tValue.kind.isFloat() || tValue.kind.isDouble()) {
133 // backend does not support conditional moves on floats
134 return;
135 }
136
137 // check that successor has no other phi functions but suxPhi
138 // this can happen when tBlock or fBlock contained additional stores to local variables
139 // that are no longer represented by explicit instructions
140 boolean suxHasOtherPhi = sux.stateBefore().forEachPhi(sux, new PhiProcedure() {
141 public boolean doPhi(Phi phi) {
142 return phi == suxPhi;
143 }
144 });
145 if (suxHasOtherPhi) {
146 return;
147 }
148
149 // check that true and false blocks don't have phis
150 if (tBlock.stateBefore().hasPhis() || fBlock.stateBefore().hasPhis()) {
151 return;
152 }
153
154 // 2) cut off the original if and replace with constants and a Goto
155 // cut curIf away and get node before
156 Instruction ifPrev = curIf.prev(block);
157 int bci = curIf.bci();
158
159 // append constants of true- and false-block if necessary
160 // clone constants because original block must not be destroyed
161 assert (tValue != fConst && fValue != tConst) || tConst == fConst : "mismatch";
162 if (tValue == tConst) {
163 Constant tc = new Constant(tConst.asConstant());
164 tValue = tc;
165 ifPrev = ifPrev.setNext(tc, bci);
166 }
167 if (fValue == fConst) {
168 Constant fc = new Constant(fConst.asConstant());
169 fValue = fc;
170 ifPrev = ifPrev.setNext(fc, bci);
171 }
172
173 Value result;
174 if (tValue == fValue) {
175 // conditional chooses the same value regardless
176 result = tValue;
177 C1XMetrics.RedundantConditionals++;
178 } else {
179 // it is very unlikely that the condition can be statically decided
180 // (this was checked previously by the Canonicalizer), so always
181 // append IfOp
182 result = new IfOp(curIf.x(), curIf.condition(), curIf.y(), tValue, fValue);
183 ifPrev = ifPrev.setNext((Instruction) result, bci);
184 }
185
186 // append Goto to successor
187 FrameState stateBefore = curIf.isSafepoint() ? curIf.stateAfter() : null;
188 Goto newGoto = new Goto(sux, stateBefore, curIf.isSafepoint() || tGoto.isSafepoint() || fGoto.isSafepoint());
189
190 // prepare state for Goto
191 FrameState tempGotoState = curIf.stateAfter();
192 while (suxState.scope() != tempGotoState.scope()) {
193 tempGotoState = tempGotoState.popScope();
194 assert tempGotoState != null : "states do not match up";
195 }
196 MutableFrameState gotoState = tempGotoState.copy();
197 gotoState.push(result.kind, result);
198 assert gotoState.isSameAcrossScopes(suxState) : "states must match now";
199 // ATTN: assumption: last use of gotoState, else add .immutableCopy()
200 newGoto.setStateAfter(gotoState);
201
202 // Steal the bci for the goto from the sux
203 ifPrev = ifPrev.setNext(newGoto, sux.bci());
204
205 // update block end (will remove this block from tBlock and fBlock predecessors)
206 block.setEnd(newGoto);
207
208 // remove blocks if they became unreachable
209 tryRemove(tBlock);
210 tryRemove(fBlock);
211
212 // substitute the phi if possible
213 Phi suxAsPhi = (Phi) suxPhi;
214 if (suxAsPhi.inputCount() == 1) {
215 // if the successor block now has only one predecessor
216 assert suxAsPhi.inputAt(0) == result : "screwed up phi";
217 subst.setSubst(suxPhi, result);
218
219 // 3) successfully eliminated a conditional expression
220 C1XMetrics.ConditionalEliminations++;
221 }
222 }
223
224 private void tryRemove(BlockBegin succ) {
225 if (succ.numberOfPreds() == 0) {
226 // block just became unreachable
227 for (BlockBegin s : succ.end().successors()) {
228 s.predecessors().remove(succ);
229 }
230 }
231 }
232 }