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