1 /*
   2  * Copyright (c) 2011, 2014, 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.java;
  26 
  27 import static org.graalvm.compiler.nodes.cfg.ControlFlowGraph.multiplyRelativeFrequencies;
  28 
  29 import java.util.List;
  30 
  31 import jdk.internal.vm.compiler.collections.EconomicMap;
  32 import org.graalvm.compiler.nodes.AbstractBeginNode;
  33 import org.graalvm.compiler.nodes.AbstractMergeNode;
  34 import org.graalvm.compiler.nodes.ControlSplitNode;
  35 import org.graalvm.compiler.nodes.FixedNode;
  36 import org.graalvm.compiler.nodes.LoopBeginNode;
  37 import org.graalvm.compiler.nodes.LoopExitNode;
  38 import org.graalvm.compiler.nodes.StructuredGraph;
  39 import org.graalvm.compiler.nodes.cfg.ControlFlowGraph;
  40 import org.graalvm.compiler.phases.Phase;
  41 import org.graalvm.compiler.phases.graph.ReentrantNodeIterator;
  42 
  43 public final class ComputeLoopFrequenciesClosure extends ReentrantNodeIterator.NodeIteratorClosure<Double> {
  44 
  45     private static final ComputeLoopFrequenciesClosure INSTANCE = new ComputeLoopFrequenciesClosure();
  46 
  47     private ComputeLoopFrequenciesClosure() {
  48         // nothing to do
  49     }
  50 
  51     @Override
  52     protected Double processNode(FixedNode node, Double currentState) {
  53         // normal nodes never change the probability of a path
  54         return currentState;
  55     }
  56 
  57     @Override
  58     protected Double merge(AbstractMergeNode merge, List<Double> states) {
  59         // a merge has the sum of all predecessor probabilities
  60         double result = 0.0;
  61         for (double d : states) {
  62             result += d;
  63         }
  64         return result;
  65     }
  66 
  67     @Override
  68     protected Double afterSplit(AbstractBeginNode node, Double oldState) {
  69         // a control split splits up the probability
  70         ControlSplitNode split = (ControlSplitNode) node.predecessor();
  71         return oldState * split.probability(node);
  72     }
  73 
  74     @Override
  75     protected EconomicMap<LoopExitNode, Double> processLoop(LoopBeginNode loop, Double initialState) {
  76         EconomicMap<LoopExitNode, Double> exitStates = ReentrantNodeIterator.processLoop(this, loop, 1D).exitStates;
  77 
  78         double exitRelativeFrequency = 0.0;
  79         for (double d : exitStates.getValues()) {
  80             exitRelativeFrequency += d;
  81         }
  82         exitRelativeFrequency = Math.min(1.0, exitRelativeFrequency);
  83         exitRelativeFrequency = Math.max(ControlFlowGraph.MIN_RELATIVE_FREQUENCY, exitRelativeFrequency);
  84         double loopFrequency = 1.0 / exitRelativeFrequency;
  85         loop.setLoopFrequency(loopFrequency);
  86 
  87         double adjustmentFactor = initialState * loopFrequency;
  88         exitStates.replaceAll((exitNode, frequency) -> multiplyRelativeFrequencies(frequency, adjustmentFactor));
  89 
  90         return exitStates;
  91     }
  92 
  93     /**
  94      * Computes the frequencies of all loops in the given graph. This is done by performing a
  95      * reverse postorder iteration and computing the probability of all fixed nodes. The combined
  96      * probability of all exits of a loop can be used to compute the loop's expected frequency.
  97      */
  98     public static void compute(StructuredGraph graph) {
  99         if (graph.hasLoops()) {
 100             ReentrantNodeIterator.apply(INSTANCE, graph.start(), 1D);
 101         }
 102     }
 103 
 104     public static class ComputeLoopFrequencyPhase extends Phase {
 105 
 106         @Override
 107         protected void run(StructuredGraph graph) {
 108             compute(graph);
 109         }
 110     }
 111 
 112     public static final ComputeLoopFrequencyPhase PHASE_INSTANCE = new ComputeLoopFrequencyPhase();
 113 
 114 }