001 /*
002 * This file is part of the Jikes RVM project (http://jikesrvm.org).
003 *
004 * This file is licensed to You under the Eclipse Public License (EPL);
005 * You may not use this file except in compliance with the License. You
006 * may obtain a copy of the License at
007 *
008 * http://www.opensource.org/licenses/eclipse-1.0.php
009 *
010 * See the COPYRIGHT.txt file distributed with this work for information
011 * regarding copyright ownership.
012 */
013 package org.jikesrvm.compilers.opt.regalloc;
014
015 import java.util.Enumeration;
016 import java.util.HashSet;
017
018 import org.jikesrvm.compilers.opt.DefUse;
019 import org.jikesrvm.compilers.opt.OptOptions;
020 import org.jikesrvm.compilers.opt.driver.CompilerPhase;
021 import org.jikesrvm.compilers.opt.ir.IR;
022 import org.jikesrvm.compilers.opt.ir.Instruction;
023 import org.jikesrvm.compilers.opt.ir.Move;
024 import org.jikesrvm.compilers.opt.ir.Register;
025 import org.jikesrvm.compilers.opt.ir.operand.Operand;
026 import org.jikesrvm.compilers.opt.liveness.LiveAnalysis;
027
028 /**
029 * Coalesce registers in move instructions where possible.
030 */
031 public class CoalesceMoves extends CompilerPhase {
032
033 /**
034 * verbose debugging flag
035 */
036 static final boolean DEBUG = false;
037
038 /**
039 * Return this instance of this phase. This phase contains no
040 * per-compilation instance fields.
041 * @param ir not used
042 * @return this
043 */
044 @Override
045 public CompilerPhase newExecution(IR ir) {
046 return this;
047 }
048
049 /**
050 * Should we perform this phase?
051 * @return <code>true</code> iff move instructions should be
052 * coalesced after leaving SSA
053 */
054 @Override
055 public final boolean shouldPerform(OptOptions options) {
056 return options.SSA_COALESCE_AFTER;
057 }
058
059 /**
060 * Return a string name for this phase.
061 * @return "Coalesce Moves"
062 */
063 @Override
064 public final String getName() {
065 return "Coalesce Moves";
066 }
067
068 @Override
069 public final void perform(IR ir) {
070 // Compute liveness.
071 LiveAnalysis live = new LiveAnalysis(false /* GC Maps */, false /* don't skip local
072 propagation */);
073 live.perform(ir);
074
075 // Compute def-use information.
076 DefUse.computeDU(ir);
077
078 // Number the instructions
079 ir.numberInstructions();
080
081 // Maintain a set of dead move instructions.
082 HashSet<Instruction> dead = new HashSet<Instruction>(5);
083
084 // for each Move instruction ...
085 for (Enumeration<Instruction> e = ir.forwardInstrEnumerator(); e.hasMoreElements();) {
086 Instruction s = e.nextElement();
087 if (s.operator.isMove()) {
088 Register r = Move.getResult(s).asRegister().getRegister();
089 if (r.isSymbolic()) {
090 Operand val = Move.getVal(s);
091 if (val != null && val.isRegister()) {
092 Register r2 = val.asRegister().getRegister();
093 if (r2.isSymbolic()) {
094 if (Coalesce.attempt(ir, live, r, r2)) {
095 if (DEBUG) System.out.println("COALESCED " + r + " " + r2);
096 dead.add(s);
097 }
098 }
099 }
100 }
101 }
102 }
103
104 // Now remove all dead Move instructions.
105 for (Instruction s : dead) {
106 DefUse.removeInstructionAndUpdateDU(s);
107 }
108 }
109 }