1 /*
2 * Copyright (c) 2014, 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 package org.graalvm.compiler.lir.constopt;
24
25 import java.util.ArrayDeque;
26 import java.util.ArrayList;
27 import java.util.BitSet;
28 import java.util.Deque;
29 import java.util.List;
30
31 import org.graalvm.compiler.core.common.cfg.AbstractBlockBase;
32 import org.graalvm.compiler.debug.Debug;
33 import org.graalvm.compiler.debug.Debug.Scope;
34 import org.graalvm.compiler.debug.Indent;
35 import org.graalvm.compiler.lir.constopt.ConstantTree.Flags;
36 import org.graalvm.compiler.lir.constopt.ConstantTree.NodeCost;
37
38 /**
39 * Analyzes a {@link ConstantTree} and marks potential materialization positions.
40 */
41 public final class ConstantTreeAnalyzer {
42 private final ConstantTree tree;
43 private final BitSet visited;
44
45 @SuppressWarnings("try")
46 public static NodeCost analyze(ConstantTree tree, AbstractBlockBase<?> startBlock) {
47 try (Scope s = Debug.scope("ConstantTreeAnalyzer")) {
48 ConstantTreeAnalyzer analyzer = new ConstantTreeAnalyzer(tree);
49 analyzer.analyzeBlocks(startBlock);
50 return tree.getCost(startBlock);
51 } catch (Throwable e) {
52 throw Debug.handle(e);
53 }
54 }
55
56 private ConstantTreeAnalyzer(ConstantTree tree) {
57 this.tree = tree;
58 this.visited = new BitSet(tree.size());
59 }
60
61 /**
62 * Queues all relevant blocks for {@linkplain #process processing}.
63 *
64 * This is a worklist-style algorithm because a (more elegant) recursive implementation may
65 * cause {@linkplain StackOverflowError stack overflows} on larger graphs.
66 *
67 * @param startBlock The start block of the dominator subtree.
68 */
69 @SuppressWarnings("try")
70 private void analyzeBlocks(AbstractBlockBase<?> startBlock) {
71 Deque<AbstractBlockBase<?>> worklist = new ArrayDeque<>();
72 worklist.offerLast(startBlock);
73 while (!worklist.isEmpty()) {
74 AbstractBlockBase<?> block = worklist.pollLast();
75 try (Indent i = Debug.logAndIndent(Debug.VERBOSE_LEVEL, "analyze: %s", block)) {
76 assert block != null : "worklist is empty!";
77 assert isMarked(block) : "Block not part of the dominator tree: " + block;
78
79 if (isLeafBlock(block)) {
80 Debug.log(Debug.VERBOSE_LEVEL, "leaf block");
81 leafCost(block);
82 continue;
83 }
84
85 if (!visited.get(block.getId())) {
86 // if not yet visited (and not a leaf block) process all children first!
87 Debug.log(Debug.VERBOSE_LEVEL, "not marked");
88 worklist.offerLast(block);
89 AbstractBlockBase<?> dominated = block.getFirstDominated();
90 while (dominated != null) {
91 filteredPush(worklist, dominated);
92 dominated = dominated.getDominatedSibling();
93 }
94 visited.set(block.getId());
95 } else {
96 Debug.log(Debug.VERBOSE_LEVEL, "marked");
97 // otherwise, process block
98 process(block);
99 }
100 }
101 }
102 }
103
104 /**
105 * Calculates the cost of a {@code block}. It is assumed that all {@code children} have already
106 * been {@linkplain #process processed}
107 *
108 * @param block The block to be processed.
109 */
110 private void process(AbstractBlockBase<?> block) {
111 List<UseEntry> usages = new ArrayList<>();
112 double bestCost = 0;
113 int numMat = 0;
114
115 // collect children costs
116 AbstractBlockBase<?> child = block.getFirstDominated();
117 while (child != null) {
118 if (isMarked(child)) {
119 NodeCost childCost = tree.getCost(child);
120 assert childCost != null : "Child with null cost? block: " + child;
121 usages.addAll(childCost.getUsages());
122 numMat += childCost.getNumMaterializations();
123 bestCost += childCost.getBestCost();
124 }
125 child = child.getDominatedSibling();
126 }
127 assert numMat > 0 : "No materialization? " + numMat;
128
129 // choose block
130 List<UseEntry> usagesBlock = tree.getUsages(block);
131 double probabilityBlock = block.probability();
132
133 if (!usagesBlock.isEmpty() || shouldMaterializerInCurrentBlock(probabilityBlock, bestCost, numMat)) {
134 // mark current block as potential materialization position
135 usages.addAll(usagesBlock);
136 bestCost = probabilityBlock;
137 numMat = 1;
138 tree.set(Flags.CANDIDATE, block);
139 } else {
140 // stick with the current solution
141 }
142
143 NodeCost nodeCost = new NodeCost(bestCost, usages, numMat);
144 tree.setCost(block, nodeCost);
145 }
146
147 /**
148 * This is the cost function that decides whether a materialization should be inserted in the
149 * current block.
150 * <p>
151 * Note that this function does not take into account if a materialization is required despite
152 * the probabilities (e.g. there are usages in the current block).
153 *
154 * @param probabilityBlock Probability of the current block.
155 * @param probabilityChildren Accumulated probability of the children.
156 * @param numMat Number of materializations along the subtrees. We use {@code numMat - 1} to
157 * insert materializations as late as possible if the probabilities are the same.
158 */
159 private static boolean shouldMaterializerInCurrentBlock(double probabilityBlock, double probabilityChildren, int numMat) {
160 return probabilityBlock * Math.pow(0.9, numMat - 1) < probabilityChildren;
161 }
162
163 private void filteredPush(Deque<AbstractBlockBase<?>> worklist, AbstractBlockBase<?> block) {
164 if (isMarked(block)) {
165 Debug.log(Debug.VERBOSE_LEVEL, "adding %s to the worklist", block);
166 worklist.offerLast(block);
167 }
168 }
169
170 private void leafCost(AbstractBlockBase<?> block) {
171 tree.set(Flags.CANDIDATE, block);
172 tree.getOrInitCost(block);
173 }
174
175 private boolean isMarked(AbstractBlockBase<?> block) {
176 return tree.isMarked(block);
177 }
178
179 private boolean isLeafBlock(AbstractBlockBase<?> block) {
180 return tree.isLeafBlock(block);
181 }
182
183 }