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 org.graalvm.compiler.lir; 24 25 import static org.graalvm.compiler.lir.LIR.verifyBlocks; 26 27 import java.util.List; 28 29 import org.graalvm.compiler.core.common.cfg.AbstractBlockBase; 30 import org.graalvm.compiler.debug.Debug; 31 import org.graalvm.compiler.debug.DebugCounter; 32 import org.graalvm.compiler.lir.gen.LIRGenerationResult; 33 import org.graalvm.compiler.lir.phases.PostAllocationOptimizationPhase; 34 35 import jdk.vm.ci.code.TargetDescription; 36 37 /** 38 * This class performs basic optimizations on the control flow graph after LIR generation. 39 */ 40 public final class ControlFlowOptimizer extends PostAllocationOptimizationPhase { 41 42 /** 43 * Performs control flow optimizations on the given LIR graph. 44 */ 45 @Override 46 protected void run(TargetDescription target, LIRGenerationResult lirGenRes, PostAllocationOptimizationContext context) { 47 LIR lir = lirGenRes.getLIR(); 48 new Optimizer(lir).deleteEmptyBlocks(lir.codeEmittingOrder()); 49 } 50 51 private static final class Optimizer { 52 53 private final LIR lir; 54 55 private Optimizer(LIR lir) { 56 this.lir = lir; 57 } 58 59 private static final DebugCounter BLOCKS_DELETED = Debug.counter("BlocksDeleted"); 60 61 /** 62 * Checks whether a block can be deleted. Only blocks with exactly one successor and an 63 * unconditional branch to this successor are eligable. 64 * 65 * @param block the block checked for deletion 66 * @return whether the block can be deleted 67 */ 68 private boolean canDeleteBlock(AbstractBlockBase<?> block) { 69 if (block == null || block.getSuccessorCount() != 1 || block.getPredecessorCount() == 0 || block.getSuccessors()[0] == block) { 70 return false; 71 } 72 73 List<LIRInstruction> instructions = lir.getLIRforBlock(block); 74 75 assert instructions.size() >= 2 : "block must have label and branch"; 76 assert instructions.get(0) instanceof StandardOp.LabelOp : "first instruction must always be a label"; 77 assert instructions.get(instructions.size() - 1) instanceof StandardOp.JumpOp : "last instruction must always be a branch"; 78 assert ((StandardOp.JumpOp) instructions.get(instructions.size() - 1)).destination().label() == ((StandardOp.LabelOp) lir.getLIRforBlock(block.getSuccessors()[0]).get( 79 0)).getLabel() : "branch target must be the successor"; 80 81 // Block must have exactly one successor. 82 return instructions.size() == 2 && !instructions.get(instructions.size() - 1).hasState() && !block.isExceptionEntry(); 83 } 84 85 private void alignBlock(AbstractBlockBase<?> block) { 86 if (!block.isAligned()) { 87 block.setAlign(true); 88 List<LIRInstruction> instructions = lir.getLIRforBlock(block); 89 assert instructions.get(0) instanceof StandardOp.LabelOp : "first instruction must always be a label"; 90 StandardOp.LabelOp label = (StandardOp.LabelOp) instructions.get(0); 91 instructions.set(0, new StandardOp.LabelOp(label.getLabel(), true)); 92 } 93 } 94 95 private void deleteEmptyBlocks(AbstractBlockBase<?>[] blocks) { 96 assert verifyBlocks(lir, blocks); 97 for (int i = 0; i < blocks.length; i++) { 98 AbstractBlockBase<?> block = blocks[i]; 99 if (canDeleteBlock(block)) { 100 101 block.delete(); 102 // adjust successor and predecessor lists 103 AbstractBlockBase<?> other = block.getSuccessors()[0]; 104 if (block.isAligned()) { 105 alignBlock(other); 106 } 107 108 BLOCKS_DELETED.increment(); 109 blocks[i] = null; 110 } 111 } 112 assert verifyBlocks(lir, blocks); 113 } 114 } 115 }