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annotate graal/com.oracle.graal.lir/src/com/oracle/graal/lir/ControlFlowOptimizer.java @ 7530:5e3d1a68664e

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applied mx eclipseformat to all Java files
author Doug Simon <doug.simon@oracle.com>
date Wed, 23 Jan 2013 16:34:57 +0100
parents ca3e5df0e6cf
children 68b964b6dc8e
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1 /*
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2 * Copyright (c) 2009, 2011, Oracle and/or its affiliates. All rights reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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20 * or visit www.oracle.com if you need additional information or have any
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21 * questions.
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22 */
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23 package com.oracle.graal.lir;
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24
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25 import java.util.*;
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26
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27 import com.oracle.graal.debug.*;
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28 import com.oracle.graal.nodes.cfg.*;
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29
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30 /**
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31 * This class performs basic optimizations on the control flow graph after LIR generation.
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32 */
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33 public final class ControlFlowOptimizer {
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34
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35 /**
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36 * Performs control flow optimizations on the given LIR graph.
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37 */
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38 public static void optimize(LIR ir) {
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39 List<Block> blocks = ir.codeEmittingOrder();
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40 ControlFlowOptimizer.deleteEmptyBlocks(ir, blocks);
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41 ControlFlowOptimizer.deleteUnnecessaryJumps(ir, blocks);
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42 }
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43
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44 private ControlFlowOptimizer() {
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45 }
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46
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47 /**
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48 * Checks whether a block can be deleted. Only blocks with exactly one successor and an
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49 * unconditional branch to this successor are eligable.
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50 *
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51 * @param block the block checked for deletion
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52 * @return whether the block can be deleted
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53 */
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54 private static boolean canDeleteBlock(LIR ir, Block block) {
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55 if (block.getSuccessorCount() != 1 || block.getPredecessorCount() == 0 || block.getFirstSuccessor() == block) {
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56 return false;
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57 }
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58
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59 List<LIRInstruction> instructions = ir.lir(block);
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60
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61 assert instructions.size() >= 2 : "block must have label and branch";
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62 assert instructions.get(0) instanceof StandardOp.LabelOp : "first instruction must always be a label";
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63 assert instructions.get(instructions.size() - 1) instanceof StandardOp.JumpOp : "last instruction must always be a branch";
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64 assert ((StandardOp.JumpOp) instructions.get(instructions.size() - 1)).destination().label() == ((StandardOp.LabelOp) ir.lir(block.getFirstSuccessor()).get(0)).getLabel() : "branch target must be the successor";
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65
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66 // Block must have exactly one successor.
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67 return instructions.size() == 2 && !instructions.get(instructions.size() - 1).hasState();
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68 }
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69
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70 private static void deleteEmptyBlocks(LIR ir, List<Block> blocks) {
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71 assert verify(blocks);
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72 Iterator<Block> iterator = blocks.iterator();
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73 while (iterator.hasNext()) {
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74 Block block = iterator.next();
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75 if (canDeleteBlock(ir, block)) {
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76 // adjust successor and predecessor lists
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77 Block other = block.getFirstSuccessor();
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78 for (Block pred : block.getPredecessors()) {
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79 Collections.replaceAll(pred.getSuccessors(), block, other);
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80 }
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81 for (int i = 0; i < other.getPredecessorCount(); i++) {
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82 if (other.getPredecessors().get(i) == block) {
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83 other.getPredecessors().remove(i);
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84 other.getPredecessors().addAll(i, block.getPredecessors());
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85 }
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86 }
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87 block.getSuccessors().clear();
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88 block.getPredecessors().clear();
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89 Debug.metric("BlocksDeleted").increment();
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90 iterator.remove();
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91 }
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92 }
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93 assert verify(blocks);
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94 }
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95
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96 private static void deleteUnnecessaryJumps(LIR ir, List<Block> blocks) {
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97 // skip the last block because there a branch is always necessary
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98 for (int i = blocks.size() - 2; i >= 0; i--) {
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99 Block block = blocks.get(i);
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100 List<LIRInstruction> instructions = ir.lir(block);
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101
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102 LIRInstruction lastOp = instructions.get(instructions.size() - 1);
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103 if (lastOp instanceof StandardOp.JumpOp) {
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104 StandardOp.JumpOp lastJump = (StandardOp.JumpOp) lastOp;
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105
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106 if (!lastOp.hasState()) {
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107 if (lastJump.destination().label() == ((StandardOp.LabelOp) ir.lir(blocks.get(i + 1)).get(0)).getLabel()) {
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108 // delete last branch instruction
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109 instructions.remove(instructions.size() - 1);
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110 } else {
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111 LIRInstruction prevOp = instructions.get(instructions.size() - 2);
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112 if (prevOp instanceof StandardOp.BranchOp) {
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113 StandardOp.BranchOp prevBranch = (StandardOp.BranchOp) prevOp;
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114
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115 if (prevBranch.destination().label() == ((StandardOp.LabelOp) ir.lir(blocks.get(i + 1)).get(0)).getLabel() && !prevOp.hasState()) {
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116 // eliminate a conditional branch to the immediate successor
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117 prevBranch.negate(lastJump.destination());
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118 instructions.remove(instructions.size() - 1);
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119 }
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120 }
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121 }
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122 }
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123 }
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124 }
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125 assert verify(blocks);
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126 }
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127
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128 private static boolean verify(List<Block> code) {
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129 for (Block block : code) {
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130 for (Block sux : block.getSuccessors()) {
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131 assert code.contains(sux) : "missing successor from: " + block + "to: " + sux;
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132 }
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133 for (Block pred : block.getPredecessors()) {
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134 assert code.contains(pred) : "missing predecessor from: " + block + "to: " + pred;
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135 }
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136 }
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137
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138 return true;
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139 }
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140 }