1 /*
2 * Copyright (c) 2011, 2015, 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.nodes;
26
27 import static org.graalvm.compiler.nodeinfo.InputType.Association;
28 import static org.graalvm.compiler.nodeinfo.NodeCycles.CYCLES_1;
29 import static org.graalvm.compiler.nodeinfo.NodeCycles.CYCLES_2;
30 import static org.graalvm.compiler.nodeinfo.NodeCycles.CYCLES_UNKNOWN;
31 import static org.graalvm.compiler.nodeinfo.NodeSize.SIZE_1;
32 import static org.graalvm.compiler.nodeinfo.NodeSize.SIZE_2;
33 import static org.graalvm.compiler.nodeinfo.NodeSize.SIZE_UNKNOWN;
34
35 import java.util.Collections;
36
37 import org.graalvm.compiler.graph.Node;
38 import org.graalvm.compiler.graph.NodeClass;
39 import org.graalvm.compiler.nodeinfo.NodeCycles;
40 import org.graalvm.compiler.nodeinfo.NodeInfo;
41 import org.graalvm.compiler.nodeinfo.NodeSize;
42 import org.graalvm.compiler.nodes.spi.NodeLIRBuilderTool;
43
44 /**
45 * LoopEnd nodes represent a loop back-edge. When a LoopEnd is reached, execution continues at the
46 * {@linkplain #loopBegin() loop header}.
47 */
48 @NodeInfo(cycles = CYCLES_1, cyclesRationale = "Backedge jmp", size = SIZE_1, sizeRationale = "Backedge jmp")
49 public final class LoopEndNode extends AbstractEndNode {
50
51 public static final NodeClass<LoopEndNode> TYPE = NodeClass.create(LoopEndNode.class);
52
53 /*
54 * The declared type of the field cannot be LoopBeginNode, because loop explosion during partial
55 * evaluation can temporarily assign a non-loop begin. This node will then be deleted shortly
56 * after - but we still must not have type system violations for that short amount of time.
57 */
58 @Input(Association) AbstractBeginNode loopBegin;
59 protected int endIndex;
60
61 /**
62 * Most loop ends need a safepoint (flag set to true) so that garbage collection can interrupt a
63 * long-running (possibly endless) loop. Safepoints may be disabled for two reasons: 1) Some
64 * code must be safepoint free, i.e., uninterruptible by garbage collection. 2) An optimization
65 * phase determined that the loop already has another safepoint or cannot be endless, so there
66 * is no need for a loop-end safepoint.
67 *
68 * Note that 1) is a hard correctness issue: emitting a safepoint in uninterruptible code is a
69 * bug, i.e., it is not allowed to set the flag back to true once it is false. To ensure that
70 * loop ends that are created late, e.g., during control flow simplifications, have no
71 * safepoints in such cases, the safepoints are actually disabled for the
72 * {@link LoopBeginNode#canEndsSafepoint loop begin}. New loop ends inherit the flag value from
73 * the loop begin.
74 */
75 boolean canSafepoint;
76
77 public LoopEndNode(LoopBeginNode begin) {
78 super(TYPE);
79 int idx = begin.nextEndIndex();
80 assert idx >= 0;
81 this.endIndex = idx;
82 this.loopBegin = begin;
83 this.canSafepoint = begin.canEndsSafepoint;
84 }
85
86 @Override
87 public AbstractMergeNode merge() {
88 return loopBegin();
89 }
90
91 public LoopBeginNode loopBegin() {
92 return (LoopBeginNode) loopBegin;
93 }
94
95 public void setLoopBegin(LoopBeginNode x) {
96 updateUsages(this.loopBegin, x);
97 this.loopBegin = x;
98 }
99
100 /**
101 * Disables safepoints for only this loop end (in contrast to disabling it for
102 * {@link LoopBeginNode#disableSafepoint() the whole loop}.
103 */
104 public void disableSafepoint() {
105 this.canSafepoint = false;
106 }
107
108 public boolean canSafepoint() {
109 assert !canSafepoint || loopBegin().canEndsSafepoint : "When safepoints are disabled for loop begin, safepoints must be disabled for all loop ends";
110 return canSafepoint;
111 }
112
113 @Override
114 public void generate(NodeLIRBuilderTool gen) {
115 gen.visitLoopEnd(this);
116 super.generate(gen);
117 }
118
119 @Override
120 public boolean verify() {
121 assertTrue(loopBegin != null, "must have a loop begin");
122 assertTrue(hasNoUsages(), "LoopEnds can not be used");
123 return super.verify();
124 }
125
126 /**
127 * Returns the index of this loop end amongst its {@link LoopBeginNode}'s loop ends.<br>
128 *
129 * Since a LoopBeginNode also has {@linkplain LoopBeginNode#forwardEnds() forward ends}, this is
130 * <b>not</b> the index into {@link PhiNode} values at the loop begin. Use
131 * {@link LoopBeginNode#phiPredecessorIndex(AbstractEndNode)} for this purpose.
132 *
133 */
134 int endIndex() {
135 return endIndex;
136 }
137
138 void setEndIndex(int idx) {
139 this.endIndex = idx;
140 }
141
142 @Override
143 public Iterable<? extends Node> cfgSuccessors() {
144 return Collections.emptyList();
145 }
146
147 @Override
148 public NodeCycles estimatedNodeCycles() {
149 if (loopBegin() == null) {
150 return CYCLES_UNKNOWN;
151 }
152 if (canSafepoint()) {
153 // jmp+read
154 return CYCLES_2;
155 }
156 return super.estimatedNodeCycles();
157 }
158
159 @Override
160 public NodeSize estimatedNodeSize() {
161 if (loopBegin() == null) {
162 return SIZE_UNKNOWN;
163 }
164 if (canSafepoint()) {
165 return SIZE_2;
166 }
167 return super.estimatedNodeSize();
168 }
169 }