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             int firstMaybeSetBit = BitScanForwardNode.scan(valueStamp.upMask() & mask);
  59             min = firstMaybeSetBit;
  60         } else {
  61             min = lastAlwaysSetBit;
  62         }
  63         int lastMaybeSetBit = scan(valueStamp.upMask() & mask);
  64         max = lastMaybeSetBit;
  65         return updateStamp(StampFactory.forInteger(Kind.Int, min, max));
  66     }
  67 
  68     @Override
  69     public ValueNode canonical(CanonicalizerTool tool, ValueNode forValue) {
  70         if (forValue.isConstant()) {
  71             JavaConstant c = forValue.asJavaConstant();
  72             if (c.asLong() != 0) {
  73                 return ConstantNode.forInt(forValue.getKind() == Kind.Int ? scan(c.asInt()) : scan(c.asLong()));
  74             }
  75         }
  76         return this;
  77     }
  78 
  79     /**
  80      * Utility method with defined return value for 0.
  81      *
  82      * @param v
  83      * @return index of first set bit or -1 if {@code v} == 0.
  84      */
  85     public static int scan(long v) {
  86         return 63 - Long.numberOfLeadingZeros(v);
  87     }
  88 
  89     /**
  90      * Utility method with defined return value for 0.
  91      *
  92      * @param v
  93      * @return index of first set bit or -1 if {@code v} == 0.
  94      */
  95     public static int scan(int v) {
  96         return 31 - Integer.numberOfLeadingZeros(v);
  97     }
  98 
  99     /**
 100      * Raw intrinsic for bsr instruction.
 101      *
 102      * @param v
 103      * @return index of first set bit or an undefined value if {@code v} == 0.
 104      */
 105     @NodeIntrinsic
 106     public static native int unsafeScan(int v);
 107 
 108     /**
 109      * Raw intrinsic for bsr instruction.
 110      *
 111      * @param v
 112      * @return index of first set bit or an undefined value if {@code v} == 0.
 113      */
 114     @NodeIntrinsic
 115     public static native int unsafeScan(long v);
 116 
 117     @Override
 118     public void generate(NodeLIRBuilderTool gen) {
 119         Value result = gen.getLIRGeneratorTool().emitBitScanReverse(gen.operand(getValue()));
 120         gen.setResult(this, result);
 121     }
 122 
 123 }