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 * 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.
 *
 * 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).
 *
 * You should have received a copy of the GNU General Public License version
 * 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 org.graalvm.compiler.core.common.cfg;

import static org.graalvm.compiler.core.common.cfg.AbstractBlockBase.BLOCK_ID_COMPARATOR;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public abstract class Loop<T extends AbstractBlockBase<T>> {

    private final Loop<T> parent;
    private final ArrayList<Loop<T>> children;

    private final int depth;
    private final int index;
    private final T header;
    private final ArrayList<T> blocks;
    private final ArrayList<T> exits;
    
Natural exits, ignoring LoopExitNodes.
See Also:
getNaturalExits()/**
     * Natural exits, ignoring LoopExitNodes.
     *
     * @see #getNaturalExits()
     */
    private final ArrayList<T> naturalExits;

    protected Loop(Loop<T> parent, int index, T header) {
        this.parent = parent;
        if (parent != null) {
            this.depth = parent.getDepth() + 1;
        } else {
            this.depth = 1;
        }
        this.index = index;
        this.header = header;
        this.blocks = new ArrayList<>();
        this.children = new ArrayList<>();
        this.exits = new ArrayList<>();
        this.naturalExits = new ArrayList<>();
    }

    public abstract long numBackedges();

    @Override
    public String toString() {
        return "loop " + index + " depth " + getDepth() + (parent != null ? " outer " + parent.index : "");
    }

    public Loop<T> getParent() {
        return parent;
    }

    public List<Loop<T>> getChildren() {
        return children;
    }

    public int getDepth() {
        return depth;
    }

    public int getIndex() {
        return index;
    }

    public T getHeader() {
        return header;
    }

    public List<T> getBlocks() {
        return blocks;
    }

    
Returns the loop exits. This might be a conservative set: before framestate assignment it matches the LoopExitNodes even if earlier blocks could be considered as exits. After framestate assignments, this is the same as getNaturalExits(). 

LoopExitNodes are inserted in the control-flow during parsing and are natural exits: they are
the earliest block at which we are guaranteed to have exited the loop. However, after some
transformations of the graph, the natural exit might go up but the LoopExitNodes are not
updated.


For example in:
for (int i = 0; i < N; i++) {
    if (c) {
        // Block 1
        if (dummy) {
            // ...
        } else {
            // ...
        }
        if (b) {
            continue;
        } else {
            // Block 2
            // LoopExitNode
            break;
        }
    }
}
 After parsing, the natural exits match the LoopExitNode: Block 2 is a natural exit and has a LoopExitNode. If the b condition gets canonicalized to false, the natural exit moves to Block 1 while the LoopExitNode remains in Block 2. In such a scenario, getLoopExits() will contain block 2 while getNaturalExits() will contain block 1. 
See Also:
getNaturalExits()/**
     * Returns the loop exits.
     *
     * This might be a conservative set: before framestate assignment it matches the LoopExitNodes
     * even if earlier blocks could be considered as exits. After framestate assignments, this is
     * the same as {@link #getNaturalExits()}.
     *
     * <p>
     * LoopExitNodes are inserted in the control-flow during parsing and are natural exits: they are
     * the earliest block at which we are guaranteed to have exited the loop. However, after some
     * transformations of the graph, the natural exit might go up but the LoopExitNodes are not
     * updated.
     * </p>
     *
     * <p>
     * For example in:
     *
     * <pre>
     * for (int i = 0; i < N; i++) {
     *     if (c) {
     *         // Block 1
     *         if (dummy) {
     *             // ...
     *         } else {
     *             // ...
     *         }
     *         if (b) {
     *             continue;
     *         } else {
     *             // Block 2
     *             // LoopExitNode
     *             break;
     *         }
     *     }
     * }
     * </pre>
     *
     * After parsing, the natural exits match the LoopExitNode: Block 2 is a natural exit and has a
     * LoopExitNode. If the {@code b} condition gets canonicalized to {@code false}, the natural
     * exit moves to Block 1 while the LoopExitNode remains in Block 2. In such a scenario,
     * {@code getLoopExits()} will contain block 2 while {@link #getNaturalExits()} will contain
     * block 1.
     *
     *
     * @see #getNaturalExits()
     */
    public List<T> getLoopExits() {
        return exits;
    }

    public boolean isLoopExit(T block) {
        assert isSorted(exits);
        return Collections.binarySearch(exits, block, BLOCK_ID_COMPARATOR) >= 0;
    }

    
Returns the natural exit points: these are the earliest block that are guaranteed to never
reach a back-edge.
This can not be used in the context of preserving or using loop-closed form.
See Also:
getLoopExits()/**
     * Returns the natural exit points: these are the earliest block that are guaranteed to never
     * reach a back-edge.
     *
     * This can not be used in the context of preserving or using loop-closed form.
     *
     * @see #getLoopExits()
     */
    public ArrayList<T> getNaturalExits() {
        return naturalExits;
    }

    public boolean isNaturalExit(T block) {
        assert isSorted(naturalExits);
        return Collections.binarySearch(naturalExits, block, BLOCK_ID_COMPARATOR) >= 0;
    }

    private static <T extends AbstractBlockBase<T>> boolean isSorted(List<T> list) {
        int lastId = Integer.MIN_VALUE;
        for (AbstractBlockBase<?> block : list) {
            if (block.getId() < lastId) {
                return false;
            }
            lastId = block.getId();
        }
        return true;
    }

    @Override
    public int hashCode() {
        return index + depth * 31;
    }

    @Override
    public boolean equals(Object obj) {
        return super.equals(obj);
    }
}