1 /* 2 * Copyright (c) 2013, 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 package org.graalvm.compiler.phases.graph; 24 25 import org.graalvm.compiler.core.common.type.ObjectStamp; 26 import org.graalvm.compiler.graph.Node; 27 import org.graalvm.compiler.nodes.StructuredGraph; 28 import org.graalvm.compiler.nodes.ValueNode; 29 import org.graalvm.compiler.nodes.ValuePhiNode; 30 31 public class InferStamps { 32 33 /** 34 * Infer the stamps for all Object nodes in the graph, to make the stamps as precise as 35 * possible. For example, this propagates the word-type through phi functions. To handle phi 36 * functions at loop headers, the stamp inference is called until a fix point is reached. 37 * <p> 38 * This method can be used when it is needed that stamps are inferred before the first run of 39 * the canonicalizer. For example, word type rewriting must run before the first run of the 40 * canonicalizer because many nodes are not prepared to see the word type during 41 * canonicalization. 42 */ 43 public static void inferStamps(StructuredGraph graph) { 44 /* 45 * We want to make the stamps more precise. For cyclic phi functions, this means we have to 46 * ignore the initial stamp because the imprecise stamp would always propagate around the 47 * cycle. We therefore set the stamp to an illegal stamp, which is automatically ignored 48 * when the phi function performs the "meet" operator on its input stamps. 49 */ 50 for (Node n : graph.getNodes()) { 51 if (n instanceof ValuePhiNode) { 52 ValueNode node = (ValueNode) n; 53 if (node.stamp() instanceof ObjectStamp) { 54 assert node.stamp().hasValues() : "We assume all Phi and Proxy stamps are legal before the analysis"; 55 node.setStamp(node.stamp().empty()); 56 } 57 } 58 } 59 60 boolean stampChanged; 61 // The algorithm is not guaranteed to reach a stable state. 62 int z = 0; 63 do { 64 stampChanged = false; 65 /* 66 * We could use GraphOrder.forwardGraph() to process the nodes in a defined order and 67 * propagate long def-use chains in fewer iterations. However, measurements showed that 68 * we have few iterations anyway, and the overhead of computing the order is much higher 69 * than the benefit. 70 */ 71 for (Node n : graph.getNodes()) { 72 if (n instanceof ValueNode) { 73 ValueNode node = (ValueNode) n; 74 if (node.stamp() instanceof ObjectStamp) { 75 stampChanged |= node.inferStamp(); 76 } 77 } 78 } 79 ++z; 80 } while (stampChanged && z < 10000); 81 82 /* 83 * Check that all the illegal stamps we introduced above are correctly replaced with real 84 * stamps again. 85 */ 86 assert checkNoEmptyStamp(graph); 87 } 88 89 private static boolean checkNoEmptyStamp(StructuredGraph graph) { 90 for (Node n : graph.getNodes()) { 91 if (n instanceof ValuePhiNode) { 92 ValueNode node = (ValueNode) n; 93 assert node.stamp().hasValues() : "Stamp is empty after analysis. This is not necessarily an error, but a condition that we want to investigate (and then maybe relax or remove the assertion)."; 94 } 95 } 96 return true; 97 } 98 }