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 least significant "1" bit. Note that the result is undefined if the 36 * input is zero. 37 */ 38 @NodeInfo 39 public class BitScanForwardNode extends UnaryNode implements LIRLowerable { 40 41 public static BitScanForwardNode create(ValueNode value) { 42 return new BitScanForwardNode(value); 43 } 44 45 protected BitScanForwardNode(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 firstAlwaysSetBit = scan(valueStamp.downMask() & mask); 57 if (firstAlwaysSetBit == -1) { 58 int lastMaybeSetBit = BitScanReverseNode.scan(valueStamp.upMask() & mask); 59 min = -1; 60 max = lastMaybeSetBit; 61 } else { 62 int firstMaybeSetBit = scan(valueStamp.upMask() & mask); 63 min = firstMaybeSetBit; 64 max = firstAlwaysSetBit; 65 } 66 return updateStamp(StampFactory.forInteger(Kind.Int, min, max)); 67 } 68 69 @Override 70 public ValueNode canonical(CanonicalizerTool tool, ValueNode forValue) { 71 if (forValue.isConstant()) { 72 JavaConstant c = forValue.asJavaConstant(); 73 if (c.asLong() != 0) { 74 return ConstantNode.forInt(forValue.getKind() == Kind.Int ? scan(c.asInt()) : scan(c.asLong())); 75 } 76 } 77 return this; 78 } 79 80 /** 81 * Utility method with defined return value for 0. 82 * 83 * @param v 84 * @return number of trailing zeros or -1 if {@code v} == 0. 85 */ 86 public static int scan(long v) { 87 if (v == 0) { 88 return -1; 89 } 90 return Long.numberOfTrailingZeros(v); 91 } 92 93 /** 94 * Utility method with defined return value for 0. 95 * 96 * @param v 97 * @return number of trailing zeros or -1 if {@code v} == 0. 98 */ 99 public static int scan(int v) { 100 return scan(0xffffffffL & v); 101 } 102 103 /** 104 * Raw intrinsic for bsf instruction. 105 * 106 * @param v 107 * @return number of trailing zeros or an undefined value if {@code v} == 0. 108 */ 109 @NodeIntrinsic 110 public static native int unsafeScan(long v); 111 112 /** 113 * Raw intrinsic for bsf instruction. 114 * 115 * @param v 116 * @return number of trailing zeros or an undefined value if {@code v} == 0. 117 */ 118 @NodeIntrinsic 119 public static native int unsafeScan(int v); 120 121 @Override 122 public void generate(NodeLIRBuilderTool gen) { 123 Value result = gen.getLIRGeneratorTool().emitBitScanForward(gen.operand(getValue())); 124 gen.setResult(this, result); 125 } 126 }