1 /*
   2  * Copyright (c) 2011, 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 
  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, ValueNode y, NodeView view) {
  52         ArithmeticOpTable.ShiftOp<Shr> op = ArithmeticOpTable.forStamp(x.stamp(view)).getShr();
  53         Stamp stamp = op.foldStamp(x.stamp(view), (IntegerStamp) y.stamp(view));
  54         ValueNode value = ShiftNode.canonical(op, stamp, x, y, view);
  55         if (value != null) {
  56             return value;
  57         }
  58 
  59         return canonical(null, op, stamp, x, y, view);
  60     }
  61 
  62     @Override
  63     public ValueNode canonical(CanonicalizerTool tool, ValueNode forX, ValueNode forY) {
  64         NodeView view = NodeView.from(tool);
  65         ValueNode ret = super.canonical(tool, forX, forY);
  66         if (ret != this) {
  67             return ret;
  68         }
  69 
  70         return canonical(this, getArithmeticOp(), stamp(view), forX, forY, view);
  71     }
  72 
  73     private static ValueNode canonical(RightShiftNode rightShiftNode, ArithmeticOpTable.ShiftOp<Shr> op, Stamp stamp, ValueNode forX, ValueNode forY, NodeView view) {
  74         RightShiftNode self = rightShiftNode;
  75         if (forX.stamp(view) instanceof IntegerStamp && ((IntegerStamp) forX.stamp(view)).isPositive()) {
  76             return new UnsignedRightShiftNode(forX, forY);
  77         }
  78 
  79         if (forY.isConstant()) {
  80             int amount = forY.asJavaConstant().asInt();
  81             int originalAmout = amount;
  82             int mask = op.getShiftAmountMask(stamp);
  83             amount &= mask;
  84             if (amount == 0) {
  85                 return forX;
  86             }
  87             if (forX instanceof ShiftNode) {
  88                 ShiftNode<?> other = (ShiftNode<?>) forX;
  89                 if (other.getY().isConstant()) {
  90                     int otherAmount = other.getY().asJavaConstant().asInt() & mask;
  91                     if (other instanceof RightShiftNode) {
  92                         int total = amount + otherAmount;
  93                         if (total != (total & mask)) {
  94                             assert other.getX().stamp(view) instanceof IntegerStamp;
  95                             IntegerStamp istamp = (IntegerStamp) other.getX().stamp(view);
  96 
  97                             if (istamp.isPositive()) {
  98                                 return ConstantNode.forIntegerKind(stamp.getStackKind(), 0);
  99                             }
 100                             if (istamp.isStrictlyNegative()) {
 101                                 return ConstantNode.forIntegerKind(stamp.getStackKind(), -1L);
 102                             }
 103 
 104                             /*
 105                              * if we cannot replace both shifts with a constant, replace them by a
 106                              * full shift for this kind
 107                              */
 108                             assert total >= mask;
 109                             return new RightShiftNode(other.getX(), ConstantNode.forInt(mask));
 110                         }
 111                         return new RightShiftNode(other.getX(), ConstantNode.forInt(total));
 112                     }
 113                 }
 114             }
 115             if (originalAmout != amount) {
 116                 return new RightShiftNode(forX, ConstantNode.forInt(amount));
 117             }
 118         }
 119         if (self == null) {
 120             self = new RightShiftNode(forX, forY);
 121         }
 122         return self;
 123     }
 124 
 125     @Override
 126     public void generate(NodeLIRBuilderTool nodeValueMap, ArithmeticLIRGeneratorTool gen) {
 127         nodeValueMap.setResult(this, gen.emitShr(nodeValueMap.operand(getX()), nodeValueMap.operand(getY())));
 128     }
 129 
 130     @Override
 131     public boolean isNarrowable(int resultBits) {
 132         if (super.isNarrowable(resultBits)) {
 133             /*
 134              * For signed right shifts, the narrow can be done before the shift if the cut off bits
 135              * are all equal to the sign bit of the input. That's equivalent to the condition that
 136              * the input is in the signed range of the narrow type.
 137              */
 138             IntegerStamp inputStamp = (IntegerStamp) getX().stamp(NodeView.DEFAULT);
 139             return CodeUtil.minValue(resultBits) <= inputStamp.lowerBound() && inputStamp.upperBound() <= CodeUtil.maxValue(resultBits);
 140         } else {
 141             return false;
 142         }
 143     }
 144 }