1 /* 2 * Copyright (c) 2012, 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.replacements.nodes; 24 25 import static org.graalvm.compiler.nodeinfo.NodeCycles.CYCLES_3; 26 import static org.graalvm.compiler.nodeinfo.NodeSize.SIZE_1; 27 28 import org.graalvm.compiler.core.common.type.IntegerStamp; 29 import org.graalvm.compiler.core.common.type.PrimitiveStamp; 30 import org.graalvm.compiler.core.common.type.Stamp; 31 import org.graalvm.compiler.core.common.type.StampFactory; 32 import org.graalvm.compiler.graph.NodeClass; 33 import org.graalvm.compiler.graph.spi.CanonicalizerTool; 34 import org.graalvm.compiler.lir.gen.ArithmeticLIRGeneratorTool; 35 import org.graalvm.compiler.nodeinfo.NodeInfo; 36 import org.graalvm.compiler.nodes.ConstantNode; 37 import org.graalvm.compiler.nodes.ValueNode; 38 import org.graalvm.compiler.nodes.calc.UnaryNode; 39 import org.graalvm.compiler.nodes.spi.ArithmeticLIRLowerable; 40 import org.graalvm.compiler.nodes.spi.NodeLIRBuilderTool; 41 42 import jdk.vm.ci.code.CodeUtil; 43 import jdk.vm.ci.meta.JavaConstant; 44 import jdk.vm.ci.meta.JavaKind; 45 46 /** 47 * Determines the index of the least significant "1" bit. Note that the result is undefined if the 48 * input is zero. 49 */ 50 @NodeInfo(cycles = CYCLES_3, size = SIZE_1) 51 public final class BitScanForwardNode extends UnaryNode implements ArithmeticLIRLowerable { 52 53 public static final NodeClass<BitScanForwardNode> TYPE = NodeClass.create(BitScanForwardNode.class); 54 55 public BitScanForwardNode(ValueNode value) { 56 super(TYPE, StampFactory.forInteger(JavaKind.Int, 0, ((PrimitiveStamp) value.stamp()).getBits()), value); 57 assert value.getStackKind() == JavaKind.Int || value.getStackKind() == JavaKind.Long; 58 } 59 60 @Override 61 public Stamp foldStamp(Stamp newStamp) { 62 assert newStamp.isCompatible(getValue().stamp()); 63 IntegerStamp valueStamp = (IntegerStamp) newStamp; 64 int min; 65 int max; 66 long mask = CodeUtil.mask(valueStamp.getBits()); 67 int firstAlwaysSetBit = scan(valueStamp.downMask() & mask); 68 int firstMaybeSetBit = scan(valueStamp.upMask() & mask); 69 if (firstAlwaysSetBit == -1) { 70 int lastMaybeSetBit = BitScanReverseNode.scan(valueStamp.upMask() & mask); 71 min = firstMaybeSetBit; 72 max = lastMaybeSetBit; 73 } else { 74 min = firstMaybeSetBit; 75 max = firstAlwaysSetBit; 76 } 77 return StampFactory.forInteger(JavaKind.Int, min, max); 78 } 79 80 public static ValueNode tryFold(ValueNode value) { 81 if (value.isConstant()) { 82 JavaConstant c = value.asJavaConstant(); 83 if (c.asLong() != 0) { 84 return ConstantNode.forInt(value.getStackKind() == JavaKind.Int ? scan(c.asInt()) : scan(c.asLong())); 85 } 86 } 87 return null; 88 } 89 90 @Override 91 public ValueNode canonical(CanonicalizerTool tool, ValueNode forValue) { 92 ValueNode folded = tryFold(forValue); 93 return folded != null ? folded : this; 94 } 95 96 /** 97 * Utility method with defined return value for 0. 98 * 99 * @param v 100 * @return number of trailing zeros or -1 if {@code v} == 0. 101 */ 102 public static int scan(long v) { 103 if (v == 0) { 104 return -1; 105 } 106 return Long.numberOfTrailingZeros(v); 107 } 108 109 /** 110 * Utility method with defined return value for 0. 111 * 112 * @param v 113 * @return number of trailing zeros or -1 if {@code v} == 0. 114 */ 115 public static int scan(int v) { 116 return scan(0xffffffffL & v); 117 } 118 119 /** 120 * Raw intrinsic for bsf instruction. 121 * 122 * @param v 123 * @return number of trailing zeros or an undefined value if {@code v} == 0. 124 */ 125 @NodeIntrinsic 126 public static native int unsafeScan(long v); 127 128 /** 129 * Raw intrinsic for bsf instruction. 130 * 131 * @param v 132 * @return number of trailing zeros or an undefined value if {@code v} == 0. 133 */ 134 @NodeIntrinsic 135 public static native int unsafeScan(int v); 136 137 @Override 138 public void generate(NodeLIRBuilderTool builder, ArithmeticLIRGeneratorTool gen) { 139 builder.setResult(this, gen.emitBitScanForward(builder.operand(getValue()))); 140 } 141 }