1 /*
2 * Copyright (c) 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.phases.graph;
26
27 import static org.graalvm.compiler.nodes.cfg.ControlFlowGraph.multiplyProbabilities;
28
29 import java.util.function.ToDoubleFunction;
30
31 import jdk.internal.vm.compiler.collections.EconomicMap;
32 import jdk.internal.vm.compiler.collections.Equivalence;
33 import org.graalvm.compiler.debug.CounterKey;
34 import org.graalvm.compiler.debug.DebugContext;
35 import org.graalvm.compiler.graph.Node;
36 import org.graalvm.compiler.graph.NodeInputList;
37 import org.graalvm.compiler.nodes.AbstractBeginNode;
38 import org.graalvm.compiler.nodes.AbstractEndNode;
39 import org.graalvm.compiler.nodes.AbstractMergeNode;
40 import org.graalvm.compiler.nodes.ControlSplitNode;
41 import org.graalvm.compiler.nodes.EndNode;
42 import org.graalvm.compiler.nodes.FixedNode;
43 import org.graalvm.compiler.nodes.LoopBeginNode;
44 import org.graalvm.compiler.nodes.StartNode;
45
46 /**
47 * Compute probabilities for fixed nodes on the fly and cache them at {@link AbstractBeginNode}s.
48 */
49 public class FixedNodeProbabilityCache implements ToDoubleFunction<FixedNode> {
50
51 private static final CounterKey computeNodeProbabilityCounter = DebugContext.counter("ComputeNodeProbability");
52
53 private final EconomicMap<FixedNode, Double> cache = EconomicMap.create(Equivalence.IDENTITY);
54
55 /**
56 * <p>
57 * Given a {@link FixedNode} this method finds the most immediate {@link AbstractBeginNode}
58 * preceding it that either:
59 * <ul>
60 * <li>has no predecessor (ie, the begin-node is a merge, in particular a loop-begin, or the
61 * start-node)</li>
62 * <li>has a control-split predecessor</li>
63 * </ul>
64 * </p>
65 *
66 * <p>
67 * The thus found {@link AbstractBeginNode} is equi-probable with the {@link FixedNode} it was
68 * obtained from. When computed for the first time (afterwards a cache lookup returns it) that
69 * probability is computed as follows, again depending on the begin-node's predecessor:
70 * <ul>
71 * <li>No predecessor. In this case the begin-node is either:</li>
72 * <ul>
73 * <li>a merge-node, whose probability adds up those of its forward-ends</li>
74 * <li>a loop-begin, with probability as above multiplied by the loop-frequency</li>
75 * </ul>
76 * <li>Control-split predecessor: probability of the branch times that of the control-split</li>
77 * </ul>
78 * </p>
79 *
80 * <p>
81 * As an exception to all the above, a probability of 1 is assumed for a {@link FixedNode} that
82 * appears to be dead-code (ie, lacks a predecessor).
83 * </p>
84 *
85 */
86 @Override
87 public double applyAsDouble(FixedNode node) {
88 assert node != null;
89 computeNodeProbabilityCounter.increment(node.getDebug());
90
91 FixedNode current = findBegin(node);
92 if (current == null) {
93 // this should only appear for dead code
94 return 1D;
95 }
96
97 assert current instanceof AbstractBeginNode;
98 Double cachedValue = cache.get(current);
99 if (cachedValue != null) {
100 return cachedValue;
101 }
102
103 double probability = 0.0;
104 if (current.predecessor() == null) {
105 if (current instanceof AbstractMergeNode) {
106 probability = handleMerge(current, probability);
107 } else {
108 assert current instanceof StartNode;
109 probability = 1D;
110 }
111 } else {
112 ControlSplitNode split = (ControlSplitNode) current.predecessor();
113 probability = multiplyProbabilities(split.probability((AbstractBeginNode) current), applyAsDouble(split));
114 }
115 assert !Double.isNaN(probability) && !Double.isInfinite(probability) : current + " " + probability;
116 cache.put(current, probability);
117 return probability;
118 }
119
120 private double handleMerge(FixedNode current, double probability) {
121 double result = probability;
122 AbstractMergeNode currentMerge = (AbstractMergeNode) current;
123 NodeInputList<EndNode> currentForwardEnds = currentMerge.forwardEnds();
124 /*
125 * Use simple iteration instead of streams, since the stream infrastructure adds many frames
126 * which causes the recursion to overflow the stack earlier than it would otherwise.
127 */
128 for (AbstractEndNode endNode : currentForwardEnds) {
129 result += applyAsDouble(endNode);
130 }
131 if (current instanceof LoopBeginNode) {
132 result = multiplyProbabilities(result, ((LoopBeginNode) current).loopFrequency());
133 }
134 return result;
135 }
136
137 private static FixedNode findBegin(FixedNode node) {
138 FixedNode current = node;
139 while (true) {
140 assert current != null;
141 Node predecessor = current.predecessor();
142 if (current instanceof AbstractBeginNode) {
143 if (predecessor == null) {
144 break;
145 } else if (predecessor.successors().count() != 1) {
146 assert predecessor instanceof ControlSplitNode : "a FixedNode with multiple successors needs to be a ControlSplitNode: " + current + " / " + predecessor;
147 break;
148 }
149 } else if (predecessor == null) {
150 current = null;
151 break;
152 }
153 current = (FixedNode) predecessor;
154 }
155 return current;
156 }
157 }