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The GraalVM compiler and the Graal-truffle optimizer.
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/*
 * Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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package jdk.graal.compiler.lir.ssa;

import java.util.ArrayList;

import jdk.graal.compiler.core.common.LIRKind;
import jdk.graal.compiler.core.common.cfg.BasicBlock;
import jdk.graal.compiler.debug.Assertions;
import jdk.graal.compiler.lir.LIR;
import jdk.graal.compiler.lir.LIRInstruction;
import jdk.graal.compiler.lir.StandardOp;
import jdk.graal.compiler.lir.StandardOp.JumpOp;
import jdk.vm.ci.meta.Value;

/**
 * Utilities for working with Static-Single-Assignment LIR form.
 *
 * Representation of PHIs
 *
 * There is no explicit PHI {@linkplain LIRInstruction}. Instead, they are implemented
 * as parallel copy that span across a control-flow edge.
 *
 * The variables introduced by PHIs of a specific {@linkplain BasicBlock merge block}
 * are {@linkplain StandardOp.LabelOp#setIncomingValues attached} to the
 * {@linkplain jdk.graal.compiler.lir.StandardOp.LabelOp} of the block. The outgoing values from the
 * predecessor are {@link StandardOp.JumpOp#getOutgoingValue input} to the
 * {@linkplain jdk.graal.compiler.lir.StandardOp.BlockEndOp} of the predecessor. Because there are
 * no critical edges we know that the {@link jdk.graal.compiler.lir.StandardOp.BlockEndOp} of the
 * predecessor has to be a {@link jdk.graal.compiler.lir.StandardOp.JumpOp}.
 *
 * Example:
 *
 *  * B0 -> B1
 *   ...
 *   v0|i = ...
 *   JUMP ~[v0|i, int[0|0x0]] destination: B0 -> B1
 * ________________________________________________
 *
 * B2 -> B1
 *   ...
 *   v1|i = ...
 *   v2|i = ...
 *   JUMP ~[v1|i, v2|i] destination: B2 -> B1
 * ________________________________________________
 *
 * B1 <- B0,B2
 *   [v3|i, v4|i] = LABEL
 *   ...
 * 
 */
public final class SSAUtil {

    public interface PhiValueVisitor {
        /**
         * @param phiIn the incoming value at the merge block
         * @param phiOut the outgoing value from the predecessor block
         */
        void visit(Value phiIn, Value phiOut);
    }

    /**
     * Visits each phi value pair of an edge, i.e. the outgoing value from the predecessor and the
     * incoming value to the merge block.
     */
    public static void forEachPhiValuePair(LIR lir, BasicBlock merge, BasicBlock pred, PhiValueVisitor visitor) {
        if (merge.getPredecessorCount() < 2) {
            return;
        }
        if (Assertions.assertionsEnabled()) {
            boolean found = false;
            for (int i = 0; i < merge.getPredecessorCount(); i++) {
                found = found || merge.getPredecessorAt(i) == pred;
            }
            assert found : String.format("%s not in predecessor list", pred);
        }
        assert pred.getSuccessorCount() == 1 : String.format("Merge predecessor block %s has more than one successor", pred);
        assert pred.getSuccessorAt(0) == merge : String.format("Predecessor block %s has wrong successor: %s, should be: %s", pred, pred.getSuccessorAt(0), merge);

        StandardOp.JumpOp jump = phiOut(lir, pred);
        StandardOp.LabelOp label = phiIn(lir, merge);

        assert label.getPhiSize() == jump.getPhiSize() : String.format("Phi In/Out size mismatch: in=%d vs. out=%d", label.getPhiSize(), jump.getPhiSize());

        for (int i = 0; i < label.getPhiSize(); i++) {
            visitor.visit(label.getIncomingValue(i), jump.getOutgoingValue(i));
        }
    }

    public static StandardOp.JumpOp phiOut(LIR lir, BasicBlock block) {
        assert block.getSuccessorCount() == 1 : Assertions.errorMessage(block);
        ArrayList instructions = lir.getLIRforBlock(block);
        int index = instructions.size() - 1;
        LIRInstruction op = instructions.get(index);
        return (StandardOp.JumpOp) op;
    }

    public static int phiOutIndex(LIR lir, BasicBlock block) {
        assert block.getSuccessorCount() == 1 : Assertions.errorMessage(block);
        ArrayList instructions = lir.getLIRforBlock(block);
        int index = instructions.size() - 1;
        assert instructions.get(index) instanceof JumpOp : instructions.get(index);
        return index;
    }

    public static StandardOp.LabelOp phiIn(LIR lir, BasicBlock block) {
        assert block.getPredecessorCount() > 1 : Assertions.errorMessageContext("block", block);
        StandardOp.LabelOp label = (StandardOp.LabelOp) lir.getLIRforBlock(block).get(0);
        return label;
    }

    public static void removePhiOut(LIR lir, BasicBlock block) {
        StandardOp.JumpOp jump = phiOut(lir, block);
        jump.clearOutgoingValues();
    }

    public static void removePhiIn(LIR lir, BasicBlock block) {
        StandardOp.LabelOp label = phiIn(lir, block);
        label.clearIncomingValues();
    }

    public static boolean verifySSAForm(LIR lir) {
        return new SSAVerifier(lir).verify();
    }

    public static void verifyPhi(LIR lir, BasicBlock merge) {
        assert merge.getPredecessorCount() > 1 : Assertions.errorMessageContext("merge", merge);
        for (int i = 0; i < merge.getPredecessorCount(); i++) {
            BasicBlock pred = merge.getPredecessorAt(i);
            forEachPhiValuePair(lir, merge, pred, (phiIn, phiOut) -> {
                assert phiIn.getValueKind().equals(phiOut.getValueKind()) ||
                                (phiIn.getPlatformKind().equals(phiOut.getPlatformKind()) && LIRKind.isUnknownReference(phiIn) && LIRKind.isValue(phiOut)) : Assertions.errorMessageContext(
                                                "phiIn",
                                                phiIn, "phiOut", phiOut);
            });
        }
    }

    public static int indexOfValue(StandardOp.LabelOp label, Value value) {
        for (int i = 0; i < label.getIncomingSize(); i++) {
            if (label.getIncomingValue(i).equals(value)) {
                return i;
            }
        }
        return -1;
    }
}