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 int firstMaybeSetBit = scan(valueStamp.upMask() & mask); 60 min = firstMaybeSetBit; 61 max = lastMaybeSetBit; 62 } else { 63 int firstMaybeSetBit = scan(valueStamp.upMask() & mask); 64 min = firstMaybeSetBit; 65 max = firstAlwaysSetBit; 66 } 67 return updateStamp(StampFactory.forInteger(Kind.Int, min, max)); 68 } 69 70 @Override 71 public ValueNode canonical(CanonicalizerTool tool, ValueNode forValue) { 72 if (forValue.isConstant()) { 73 JavaConstant c = forValue.asJavaConstant(); 74 if (c.asLong() != 0) { 75 return ConstantNode.forInt(forValue.getKind() == Kind.Int ? scan(c.asInt()) : scan(c.asLong())); 76 } 77 } 78 return this; 79 } 80 81 /** 82 * Utility method with defined return value for 0. 83 * 84 * @param v 85 * @return number of trailing zeros or -1 if {@code v} == 0. 86 */ 87 public static int scan(long v) { 88 if (v == 0) { 89 return -1; 90 } 91 return Long.numberOfTrailingZeros(v); 92 } 93 94 /** 95 * Utility method with defined return value for 0. 96 * 97 * @param v 98 * @return number of trailing zeros or -1 if {@code v} == 0. 99 */ 100 public static int scan(int v) { 101 return scan(0xffffffffL & v); 102 } 103 104 /** 105 * Raw intrinsic for bsf instruction. 106 * 107 * @param v 108 * @return number of trailing zeros or an undefined value if {@code v} == 0. 109 */ 110 @NodeIntrinsic 111 public static native int unsafeScan(long v); 112 113 /** 114 * Raw intrinsic for bsf instruction. 115 * 116 * @param v 117 * @return number of trailing zeros or an undefined value if {@code v} == 0. 118 */ 119 @NodeIntrinsic 120 public static native int unsafeScan(int v); 121 122 @Override 123 public void generate(NodeLIRBuilderTool gen) { 124 Value result = gen.getLIRGeneratorTool().emitBitScanForward(gen.operand(getValue())); 125 gen.setResult(this, result); 126 } 127 }