1 /*
   2  * Copyright (c) 2011, 2018, 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 
  24 
  25 package org.graalvm.compiler.nodes.calc;
  26 
  27 import org.graalvm.compiler.core.common.type.ArithmeticOpTable;
  28 import org.graalvm.compiler.core.common.type.ArithmeticOpTable.ShiftOp.Shr;
  29 import org.graalvm.compiler.core.common.type.IntegerStamp;
  30 import org.graalvm.compiler.core.common.type.Stamp;
  31 import org.graalvm.compiler.graph.NodeClass;
  32 import org.graalvm.compiler.graph.spi.CanonicalizerTool;
  33 import org.graalvm.compiler.lir.gen.ArithmeticLIRGeneratorTool;
  34 import org.graalvm.compiler.nodeinfo.NodeInfo;
  35 import org.graalvm.compiler.nodes.ConstantNode;
  36 import org.graalvm.compiler.nodes.NodeView;
  37 import org.graalvm.compiler.nodes.ValueNode;
  38 import org.graalvm.compiler.nodes.spi.NodeLIRBuilderTool;
  39 
  40 import jdk.vm.ci.code.CodeUtil;
  41 
  42 @NodeInfo(shortName = ">>")
  43 public final class RightShiftNode extends ShiftNode<Shr> {
  44 
  45     public static final NodeClass<RightShiftNode> TYPE = NodeClass.create(RightShiftNode.class);
  46 
  47     public RightShiftNode(ValueNode x, ValueNode y) {
  48         super(TYPE, ArithmeticOpTable::getShr, x, y);
  49     }
  50 
  51     public static ValueNode create(ValueNode x, int y, NodeView view) {
  52         if (y == 0) {
  53             return x;
  54         }
  55         return create(x, ConstantNode.forInt(y), view);
  56     }
  57 
  58     public static ValueNode create(ValueNode x, ValueNode y, NodeView view) {
  59         ArithmeticOpTable.ShiftOp<Shr> op = ArithmeticOpTable.forStamp(x.stamp(view)).getShr();
  60         Stamp stamp = op.foldStamp(x.stamp(view), (IntegerStamp) y.stamp(view));
  61         ValueNode value = ShiftNode.canonical(op, stamp, x, y, view);
  62         if (value != null) {
  63             return value;
  64         }
  65 
  66         return canonical(null, op, stamp, x, y, view);
  67     }
  68 
  69     @Override
  70     public ValueNode canonical(CanonicalizerTool tool, ValueNode forX, ValueNode forY) {
  71         NodeView view = NodeView.from(tool);
  72         ValueNode ret = super.canonical(tool, forX, forY);
  73         if (ret != this) {
  74             return ret;
  75         }
  76 
  77         return canonical(this, getArithmeticOp(), stamp(view), forX, forY, view);
  78     }
  79 
  80     private static ValueNode canonical(RightShiftNode rightShiftNode, ArithmeticOpTable.ShiftOp<Shr> op, Stamp stamp, ValueNode forX, ValueNode forY, NodeView view) {
  81         RightShiftNode self = rightShiftNode;
  82         if (forX.stamp(view) instanceof IntegerStamp && ((IntegerStamp) forX.stamp(view)).isPositive()) {
  83             return new UnsignedRightShiftNode(forX, forY);
  84         }
  85 
  86         if (forY.isConstant()) {
  87             int amount = forY.asJavaConstant().asInt();
  88             int originalAmout = amount;
  89             int mask = op.getShiftAmountMask(stamp);
  90             amount &= mask;
  91             if (amount == 0) {
  92                 return forX;
  93             }
  94             if (forX instanceof ShiftNode) {
  95                 ShiftNode<?> other = (ShiftNode<?>) forX;
  96                 if (other.getY().isConstant()) {
  97                     int otherAmount = other.getY().asJavaConstant().asInt() & mask;
  98                     if (other instanceof RightShiftNode) {
  99                         int total = amount + otherAmount;
 100                         if (total != (total & mask)) {
 101                             assert other.getX().stamp(view) instanceof IntegerStamp;
 102                             IntegerStamp istamp = (IntegerStamp) other.getX().stamp(view);
 103 
 104                             if (istamp.isPositive()) {
 105                                 return ConstantNode.forIntegerKind(stamp.getStackKind(), 0);
 106                             }
 107                             if (istamp.isStrictlyNegative()) {
 108                                 return ConstantNode.forIntegerKind(stamp.getStackKind(), -1L);
 109                             }
 110 
 111                             /*
 112                              * if we cannot replace both shifts with a constant, replace them by a
 113                              * full shift for this kind
 114                              */
 115                             assert total >= mask;
 116                             return new RightShiftNode(other.getX(), ConstantNode.forInt(mask));
 117                         }
 118                         return new RightShiftNode(other.getX(), ConstantNode.forInt(total));
 119                     }
 120                 }
 121             }
 122             if (originalAmout != amount) {
 123                 return new RightShiftNode(forX, ConstantNode.forInt(amount));
 124             }
 125         }
 126         if (self == null) {
 127             self = new RightShiftNode(forX, forY);
 128         }
 129         return self;
 130     }
 131 
 132     @Override
 133     public void generate(NodeLIRBuilderTool nodeValueMap, ArithmeticLIRGeneratorTool gen) {
 134         nodeValueMap.setResult(this, gen.emitShr(nodeValueMap.operand(getX()), nodeValueMap.operand(getY())));
 135     }
 136 
 137     @Override
 138     public boolean isNarrowable(int resultBits) {
 139         if (super.isNarrowable(resultBits)) {
 140             /*
 141              * For signed right shifts, the narrow can be done before the shift if the cut off bits
 142              * are all equal to the sign bit of the input. That's equivalent to the condition that
 143              * the input is in the signed range of the narrow type.
 144              */
 145             IntegerStamp inputStamp = (IntegerStamp) getX().stamp(NodeView.DEFAULT);
 146             return CodeUtil.minValue(resultBits) <= inputStamp.lowerBound() && inputStamp.upperBound() <= CodeUtil.maxValue(resultBits);
 147         } else {
 148             return false;
 149         }
 150     }
 151 }