1 /* 2 * Copyright (c) 2011, 2020, 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 24 25 package org.graalvm.compiler.virtual.phases.ea; 26 27 import static org.graalvm.compiler.core.common.GraalOptions.EscapeAnalyzeOnly; 28 29 import org.graalvm.compiler.nodes.StructuredGraph; 30 import org.graalvm.compiler.nodes.StructuredGraph.ScheduleResult; 31 import org.graalvm.compiler.nodes.cfg.ControlFlowGraph; 32 import org.graalvm.compiler.nodes.spi.CoreProviders; 33 import org.graalvm.compiler.phases.common.CanonicalizerPhase; 34 import org.graalvm.compiler.phases.graph.ReentrantBlockIterator; 35 import jdk.internal.vm.compiler.word.LocationIdentity; 36 37 /** 38 * This phase performs read and (simple) write elimination on a graph. It operates on multiple 39 * granularities, i.e., before and after high-tier lowering. The phase iterates the graph in a 40 * reverse-post-order fashion {@linkplain ReentrantBlockIterator} and tracks the currently active 41 * value for a specific {@linkplain LocationIdentity}, which allows the removal of subsequent reads 42 * if no writes happen in between, etc. if the value read from memory is in a virtual register 43 * (node). 44 * 45 * A trivial example for read elimination can be seen below: 46 * 47 * <pre> 48 * int i = object.fieldValue; 49 * // code not changing object.fieldValue but using i 50 * consume(object.fieldValue); 51 * </pre> 52 * 53 * Read elimination will transform this piece of code to the code below and remove the second, 54 * unnecessary, memory read of the field: 55 * 56 * <pre> 57 * int i = object.fieldValue; 58 * // code not changing object.fieldValue but using i 59 * consume(i); 60 * </pre> 61 */ 62 public class EarlyReadEliminationPhase extends EffectsPhase<CoreProviders> { 63 64 protected final boolean considerGuards; 65 EarlyReadEliminationPhase(CanonicalizerPhase canonicalizer)66 public EarlyReadEliminationPhase(CanonicalizerPhase canonicalizer) { 67 super(1, canonicalizer, true); 68 this.considerGuards = true; 69 } 70 EarlyReadEliminationPhase(CanonicalizerPhase canonicalizer, boolean considerGuards)71 public EarlyReadEliminationPhase(CanonicalizerPhase canonicalizer, boolean considerGuards) { 72 super(1, canonicalizer, true); 73 this.considerGuards = considerGuards; 74 } 75 76 @Override run(StructuredGraph graph, CoreProviders context)77 protected void run(StructuredGraph graph, CoreProviders context) { 78 if (VirtualUtil.matches(graph, EscapeAnalyzeOnly.getValue(graph.getOptions()))) { 79 runAnalysis(graph, context); 80 } 81 } 82 83 @Override createEffectsClosure(CoreProviders context, ScheduleResult schedule, ControlFlowGraph cfg)84 protected Closure<?> createEffectsClosure(CoreProviders context, ScheduleResult schedule, ControlFlowGraph cfg) { 85 assert schedule == null; 86 return new ReadEliminationClosure(cfg, considerGuards); 87 } 88 89 @Override codeSizeIncrease()90 public float codeSizeIncrease() { 91 return 2f; 92 } 93 } 94