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package org.graalvm.compiler.replacements.nodes;

import static org.graalvm.compiler.nodeinfo.NodeCycles.CYCLES_2;
import static org.graalvm.compiler.nodeinfo.NodeSize.SIZE_1;

import org.graalvm.compiler.core.common.type.IntegerStamp;
import org.graalvm.compiler.core.common.type.PrimitiveStamp;
import org.graalvm.compiler.core.common.type.Stamp;
import org.graalvm.compiler.core.common.type.StampFactory;
import org.graalvm.compiler.graph.NodeClass;
import org.graalvm.compiler.graph.spi.CanonicalizerTool;
import org.graalvm.compiler.lir.gen.ArithmeticLIRGeneratorTool;
import org.graalvm.compiler.nodeinfo.NodeInfo;
import org.graalvm.compiler.nodes.ConstantNode;
import org.graalvm.compiler.nodes.NodeView;
import org.graalvm.compiler.nodes.ValueNode;
import org.graalvm.compiler.nodes.calc.UnaryNode;
import org.graalvm.compiler.nodes.spi.ArithmeticLIRLowerable;
import org.graalvm.compiler.nodes.spi.NodeLIRBuilderTool;

import jdk.vm.ci.code.CodeUtil;
import jdk.vm.ci.meta.JavaConstant;
import jdk.vm.ci.meta.JavaKind;

Determines the index of the most significant "1" bit. Note that the result is undefined if the input is zero.
/** * Determines the index of the most significant "1" bit. Note that the result is undefined if the * input is zero. */
@NodeInfo(cycles = CYCLES_2, size = SIZE_1) public final class BitScanReverseNode extends UnaryNode implements ArithmeticLIRLowerable { public static final NodeClass<BitScanReverseNode> TYPE = NodeClass.create(BitScanReverseNode.class); public BitScanReverseNode(ValueNode value) { super(TYPE, StampFactory.forInteger(JavaKind.Int, 0, ((PrimitiveStamp) value.stamp(NodeView.DEFAULT)).getBits()), value); assert value.getStackKind() == JavaKind.Int || value.getStackKind() == JavaKind.Long; } @Override public Stamp foldStamp(Stamp newStamp) { assert newStamp.isCompatible(getValue().stamp(NodeView.DEFAULT)); IntegerStamp valueStamp = (IntegerStamp) newStamp; int min; int max; long mask = CodeUtil.mask(valueStamp.getBits()); int lastAlwaysSetBit = scan(valueStamp.downMask() & mask); if (lastAlwaysSetBit == -1) { int firstMaybeSetBit = BitScanForwardNode.scan(valueStamp.upMask() & mask); min = firstMaybeSetBit; } else { min = lastAlwaysSetBit; } int lastMaybeSetBit = scan(valueStamp.upMask() & mask); max = lastMaybeSetBit; return StampFactory.forInteger(JavaKind.Int, min, max); } @Override public ValueNode canonical(CanonicalizerTool tool, ValueNode forValue) { if (forValue.isConstant()) { JavaConstant c = forValue.asJavaConstant(); if (c.asLong() != 0) { return ConstantNode.forInt(forValue.getStackKind() == JavaKind.Int ? scan(c.asInt()) : scan(c.asLong())); } } return this; }
Utility method with defined return value for 0.
Params:
  • v –
Returns:index of first set bit or -1 if v == 0.
/** * Utility method with defined return value for 0. * * @param v * @return index of first set bit or -1 if {@code v} == 0. */
public static int scan(long v) { return 63 - Long.numberOfLeadingZeros(v); }
Utility method with defined return value for 0.
Params:
  • v –
Returns:index of first set bit or -1 if v == 0.
/** * Utility method with defined return value for 0. * * @param v * @return index of first set bit or -1 if {@code v} == 0. */
public static int scan(int v) { return 31 - Integer.numberOfLeadingZeros(v); }
Raw intrinsic for bsr instruction.
Params:
  • v –
Returns:index of first set bit or an undefined value if v == 0.
/** * Raw intrinsic for bsr instruction. * * @param v * @return index of first set bit or an undefined value if {@code v} == 0. */
@NodeIntrinsic public static native int unsafeScan(int v);
Raw intrinsic for bsr instruction.
Params:
  • v –
Returns:index of first set bit or an undefined value if v == 0.
/** * Raw intrinsic for bsr instruction. * * @param v * @return index of first set bit or an undefined value if {@code v} == 0. */
@NodeIntrinsic public static native int unsafeScan(long v); @Override public void generate(NodeLIRBuilderTool builder, ArithmeticLIRGeneratorTool gen) { builder.setResult(this, gen.emitBitScanReverse(builder.operand(getValue()))); } }