1 /* 2 * Copyright (c) 2012, 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 com.oracle.graal.replacements.nodes; 24 25 import com.oracle.graal.api.code.*; 26 import com.oracle.graal.api.meta.*; 27 import com.oracle.graal.compiler.common.type.*; 28 import com.oracle.graal.graph.spi.*; 29 import com.oracle.graal.nodeinfo.*; 30 import com.oracle.graal.nodes.*; 31 import com.oracle.graal.nodes.calc.*; 32 import com.oracle.graal.nodes.spi.*; 33 34 /** 35 * Determines the index of the most significant "1" bit. Note that the result is undefined if the 36 * input is zero. 37 */ 38 @NodeInfo 39 public class BitScanReverseNode extends UnaryNode implements LIRLowerable { 40 41 public static BitScanReverseNode create(ValueNode value) { 42 return new BitScanReverseNode(value); 43 } 44 45 protected BitScanReverseNode(ValueNode value) { 46 super(StampFactory.forInteger(Kind.Int, 0, ((PrimitiveStamp) value.stamp()).getBits()), value); 47 assert value.getKind() == Kind.Int || value.getKind() == Kind.Long; 48 } 49 50 @Override 51 public boolean inferStamp() { 52 IntegerStamp valueStamp = (IntegerStamp) getValue().stamp(); 53 int min; 54 int max; 55 long mask = CodeUtil.mask(valueStamp.getBits()); 56 int lastAlwaysSetBit = scan(valueStamp.downMask() & mask); 57 if (lastAlwaysSetBit == -1) { 58 min = -1; 59 } else { 60 min = lastAlwaysSetBit; 61 } 62 int lastMaybeSetBit = scan(valueStamp.upMask() & mask); 63 max = lastMaybeSetBit; 64 return updateStamp(StampFactory.forInteger(Kind.Int, min, max)); 65 } 66 67 @Override 68 public ValueNode canonical(CanonicalizerTool tool, ValueNode forValue) { 69 if (forValue.isConstant()) { 70 JavaConstant c = forValue.asJavaConstant(); 71 if (c.asLong() != 0) { 72 return ConstantNode.forInt(forValue.getKind() == Kind.Int ? scan(c.asInt()) : scan(c.asLong())); 73 } 74 } 75 return this; 76 } 77 78 /** 79 * Utility method with defined return value for 0. 80 * 81 * @param v 82 * @return index of first set bit or -1 if {@code v} == 0. 83 */ 84 public static int scan(long v) { 85 return 63 - Long.numberOfLeadingZeros(v); 86 } 87 88 /** 89 * Utility method with defined return value for 0. 90 * 91 * @param v 92 * @return index of first set bit or -1 if {@code v} == 0. 93 */ 94 public static int scan(int v) { 95 return 31 - Integer.numberOfLeadingZeros(v); 96 } 97 98 /** 99 * Raw intrinsic for bsr instruction. 100 * 101 * @param v 102 * @return index of first set bit or an undefined value if {@code v} == 0. 103 */ 104 @NodeIntrinsic 105 public static native int unsafeScan(int v); 106 107 /** 108 * Raw intrinsic for bsr instruction. 109 * 110 * @param v 111 * @return index of first set bit or an undefined value if {@code v} == 0. 112 */ 113 @NodeIntrinsic 114 public static native int unsafeScan(long v); 115 116 @Override 117 public void generate(NodeLIRBuilderTool gen) { 118 Value result = gen.getLIRGeneratorTool().emitBitScanReverse(gen.operand(getValue())); 119 gen.setResult(this, result); 120 } 121 122 }