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
24
25 package org.graalvm.compiler.lir.constopt;
26
27 import java.util.ArrayDeque;
28 import java.util.ArrayList;
29 import java.util.BitSet;
30 import java.util.Deque;
31 import java.util.List;
32
33 import org.graalvm.compiler.core.common.cfg.AbstractBlockBase;
34 import org.graalvm.compiler.debug.DebugContext;
35 import org.graalvm.compiler.debug.Indent;
36 import org.graalvm.compiler.lir.constopt.ConstantTree.Flags;
37 import org.graalvm.compiler.lir.constopt.ConstantTree.NodeCost;
38
39 /**
40 * Analyzes a {@link ConstantTree} and marks potential materialization positions.
41 */
42 public final class ConstantTreeAnalyzer {
43 private final ConstantTree tree;
44 private final BitSet visited;
45
46 @SuppressWarnings("try")
47 public static NodeCost analyze(DebugContext debug, ConstantTree tree, AbstractBlockBase<?> startBlock) {
48 try (DebugContext.Scope s = debug.scope("ConstantTreeAnalyzer")) {
49 ConstantTreeAnalyzer analyzer = new ConstantTreeAnalyzer(tree);
50 analyzer.analyzeBlocks(debug, startBlock);
51 return tree.getCost(startBlock);
52 } catch (Throwable e) {
53 throw debug.handle(e);
54 }
55 }
56
57 private ConstantTreeAnalyzer(ConstantTree tree) {
58 this.tree = tree;
59 this.visited = new BitSet(tree.size());
60 }
61
62 /**
63 * Queues all relevant blocks for {@linkplain #process processing}.
64 *
65 * This is a worklist-style algorithm because a (more elegant) recursive implementation may
66 * cause {@linkplain StackOverflowError stack overflows} on larger graphs.
67 *
68 * @param startBlock The start block of the dominator subtree.
69 */
70 @SuppressWarnings("try")
71 private void analyzeBlocks(DebugContext debug, AbstractBlockBase<?> startBlock) {
72 Deque<AbstractBlockBase<?>> worklist = new ArrayDeque<>();
73 worklist.offerLast(startBlock);
74 while (!worklist.isEmpty()) {
75 AbstractBlockBase<?> block = worklist.pollLast();
76 try (Indent i = debug.logAndIndent(DebugContext.VERBOSE_LEVEL, "analyze: %s", block)) {
77 assert block != null : "worklist is empty!";
78 assert isMarked(block) : "Block not part of the dominator tree: " + block;
79
80 if (isLeafBlock(block)) {
81 debug.log(DebugContext.VERBOSE_LEVEL, "leaf block");
82 leafCost(block);
83 continue;
84 }
85
86 if (!visited.get(block.getId())) {
87 // if not yet visited (and not a leaf block) process all children first!
88 debug.log(DebugContext.VERBOSE_LEVEL, "not marked");
89 worklist.offerLast(block);
90 AbstractBlockBase<?> dominated = block.getFirstDominated();
91 while (dominated != null) {
92 filteredPush(debug, worklist, dominated);
93 dominated = dominated.getDominatedSibling();
94 }
95 visited.set(block.getId());
96 } else {
97 debug.log(DebugContext.VERBOSE_LEVEL, "marked");
98 // otherwise, process block
99 process(block);
100 }
101 }
102 }
103 }
104
105 /**
106 * Calculates the cost of a {@code block}. It is assumed that all {@code children} have already
107 * been {@linkplain #process processed}
108 *
109 * @param block The block to be processed.
110 */
111 private void process(AbstractBlockBase<?> block) {
112 List<UseEntry> usages = new ArrayList<>();
113 double bestCost = 0;
114 int numMat = 0;
115
116 // collect children costs
117 AbstractBlockBase<?> child = block.getFirstDominated();
118 while (child != null) {
119 if (isMarked(child)) {
120 NodeCost childCost = tree.getCost(child);
121 assert childCost != null : "Child with null cost? block: " + child;
122 usages.addAll(childCost.getUsages());
123 numMat += childCost.getNumMaterializations();
124 bestCost += childCost.getBestCost();
125 }
126 child = child.getDominatedSibling();
127 }
128 assert numMat > 0 : "No materialization? " + numMat;
129
130 // choose block
131 List<UseEntry> usagesBlock = tree.getUsages(block);
132 double probabilityBlock = block.getRelativeFrequency();
133
134 if (!usagesBlock.isEmpty() || shouldMaterializerInCurrentBlock(probabilityBlock, bestCost, numMat)) {
135 // mark current block as potential materialization position
136 usages.addAll(usagesBlock);
137 bestCost = probabilityBlock;
138 numMat = 1;
139 tree.set(Flags.CANDIDATE, block);
140 } else {
141 // stick with the current solution
142 }
143
144 NodeCost nodeCost = new NodeCost(bestCost, usages, numMat);
145 tree.setCost(block, nodeCost);
146 }
147
148 /**
149 * This is the cost function that decides whether a materialization should be inserted in the
150 * current block.
151 * <p>
152 * Note that this function does not take into account if a materialization is required despite
153 * the probabilities (e.g. there are usages in the current block).
154 *
155 * @param probabilityBlock Probability of the current block.
156 * @param probabilityChildren Accumulated probability of the children.
157 * @param numMat Number of materializations along the subtrees. We use {@code numMat - 1} to
158 * insert materializations as late as possible if the probabilities are the same.
159 */
160 private static boolean shouldMaterializerInCurrentBlock(double probabilityBlock, double probabilityChildren, int numMat) {
161 return probabilityBlock * Math.pow(0.9, numMat - 1) < probabilityChildren;
162 }
163
164 private void filteredPush(DebugContext debug, Deque<AbstractBlockBase<?>> worklist, AbstractBlockBase<?> block) {
165 if (isMarked(block)) {
166 debug.log(DebugContext.VERBOSE_LEVEL, "adding %s to the worklist", block);
167 worklist.offerLast(block);
168 }
169 }
170
171 private void leafCost(AbstractBlockBase<?> block) {
172 tree.set(Flags.CANDIDATE, block);
173 tree.getOrInitCost(block);
174 }
175
176 private boolean isMarked(AbstractBlockBase<?> block) {
177 return tree.isMarked(block);
178 }
179
180 private boolean isLeafBlock(AbstractBlockBase<?> block) {
181 return tree.isLeafBlock(block);
182 }
183
184 }