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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package org.graalvm.compiler.loop.phases;

import static org.graalvm.compiler.core.common.GraalOptions.MaximumDesiredSize;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import jdk.internal.vm.compiler.collections.EconomicMap;
import org.graalvm.compiler.core.common.RetryableBailoutException;
import org.graalvm.compiler.core.common.calc.CanonicalCondition;
import org.graalvm.compiler.debug.DebugContext;
import org.graalvm.compiler.graph.Graph.Mark;
import org.graalvm.compiler.graph.Graph.NodeEventScope;
import org.graalvm.compiler.graph.Node;
import org.graalvm.compiler.graph.Position;
import org.graalvm.compiler.graph.spi.Simplifiable;
import org.graalvm.compiler.graph.spi.SimplifierTool;
import org.graalvm.compiler.loop.CountedLoopInfo;
import org.graalvm.compiler.loop.DefaultLoopPolicies;
import org.graalvm.compiler.loop.InductionVariable.Direction;
import org.graalvm.compiler.loop.LoopEx;
import org.graalvm.compiler.loop.LoopFragmentInside;
import org.graalvm.compiler.loop.LoopFragmentWhole;
import org.graalvm.compiler.nodeinfo.InputType;
import org.graalvm.compiler.nodes.AbstractBeginNode;
import org.graalvm.compiler.nodes.AbstractEndNode;
import org.graalvm.compiler.nodes.AbstractMergeNode;
import org.graalvm.compiler.nodes.BeginNode;
import org.graalvm.compiler.nodes.ControlSplitNode;
import org.graalvm.compiler.nodes.EndNode;
import org.graalvm.compiler.nodes.FixedGuardNode;
import org.graalvm.compiler.nodes.FixedNode;
import org.graalvm.compiler.nodes.FixedWithNextNode;
import org.graalvm.compiler.nodes.IfNode;
import org.graalvm.compiler.nodes.LogicNode;
import org.graalvm.compiler.nodes.LoopBeginNode;
import org.graalvm.compiler.nodes.NodeView;
import org.graalvm.compiler.nodes.PhiNode;
import org.graalvm.compiler.nodes.SafepointNode;
import org.graalvm.compiler.nodes.StructuredGraph;
import org.graalvm.compiler.nodes.ValueNode;
import org.graalvm.compiler.nodes.calc.AddNode;
import org.graalvm.compiler.nodes.calc.CompareNode;
import org.graalvm.compiler.nodes.calc.ConditionalNode;
import org.graalvm.compiler.nodes.extended.OpaqueNode;
import org.graalvm.compiler.nodes.extended.SwitchNode;
import org.graalvm.compiler.nodes.spi.CoreProviders;
import org.graalvm.compiler.nodes.util.GraphUtil;
import org.graalvm.compiler.nodes.util.IntegerHelper;
import org.graalvm.compiler.phases.common.CanonicalizerPhase;
import org.graalvm.compiler.phases.common.util.EconomicSetNodeEventListener;

public abstract class LoopTransformations {

    private LoopTransformations() {
        // does not need to be instantiated
    }

    public static void peel(LoopEx loop) {
        loop.detectCounted();
        loop.inside().duplicate().insertBefore(loop);
        if (loop.isCounted()) {
            // For counted loops we assume that we have an effect on the loop frequency.
            loop.loopBegin().setLoopFrequency(Math.max(1.0, loop.loopBegin().loopFrequency() - 1));
        }
        loop.loopBegin().incrementPeelings();
    }

    @SuppressWarnings("try")
    public static void fullUnroll(LoopEx loop, CoreProviders context, CanonicalizerPhase canonicalizer) {
        // assert loop.isCounted(); //TODO (gd) strengthen : counted with known trip count
        LoopBeginNode loopBegin = loop.loopBegin();
        StructuredGraph graph = loopBegin.graph();
        int initialNodeCount = graph.getNodeCount();
        SimplifierTool defaultSimplifier = GraphUtil.getDefaultSimplifier(context, canonicalizer.getCanonicalizeReads(), graph.getAssumptions(), graph.getOptions());
        /*
         * IMPORTANT: Canonicalizations inside the body of the remaining loop can introduce new
         * control flow that is not automatically picked up by the control flow graph computation of
         * the original LoopEx data structure, thus we disable simplification and manually simplify
         * conditions in the peeled iteration to simplify the exit path.
         */
        CanonicalizerPhase c = canonicalizer.copyWithoutSimplification();
        EconomicSetNodeEventListener l = new EconomicSetNodeEventListener();
        int peelings = 0;
        try (NodeEventScope ev = graph.trackNodeEvents(l)) {
            while (!loopBegin.isDeleted()) {
                Mark newNodes = graph.getMark();
                /*
                 * Mark is not enough for the canonicalization of the floating nodes in the unrolled
                 * code since pre-existing constants are not new nodes. Therefore, we canonicalize
                 * (without simplification) all floating nodes changed during peeling but only
                 * simplify new (in the peeled iteration) ones.
                 */
                EconomicSetNodeEventListener peeledListener = new EconomicSetNodeEventListener();
                try (NodeEventScope peeledScope = graph.trackNodeEvents(peeledListener)) {
                    LoopTransformations.peel(loop);
                }
                graph.getDebug().dump(DebugContext.VERY_DETAILED_LEVEL, graph, "After peeling loop %s", loop);
                c.applyIncremental(graph, context, peeledListener.getNodes());
                loop.invalidateFragments();
                for (Node n : graph.getNewNodes(newNodes)) {
                    if (n.isAlive() && (n instanceof IfNode || n instanceof SwitchNode || n instanceof FixedGuardNode || n instanceof BeginNode)) {
                        Simplifiable s = (Simplifiable) n;
                        s.simplify(defaultSimplifier);
                        graph.getDebug().dump(DebugContext.VERY_DETAILED_LEVEL, graph, "After simplifying if %s", s);
                    }
                }
                if (graph.getNodeCount() > initialNodeCount + MaximumDesiredSize.getValue(graph.getOptions()) * 2 ||
                                peelings > DefaultLoopPolicies.Options.FullUnrollMaxIterations.getValue(graph.getOptions())) {
                    throw new RetryableBailoutException("FullUnroll : Graph seems to grow out of proportion");
                }
                peelings++;
            }
        }
        // Canonicalize with the original canonicalizer to capture all simplifications
        canonicalizer.applyIncremental(graph, context, l.getNodes());
    }

    public static void unswitch(LoopEx loop, List<ControlSplitNode> controlSplitNodeSet) {
        ControlSplitNode firstNode = controlSplitNodeSet.iterator().next();
        LoopFragmentWhole originalLoop = loop.whole();
        StructuredGraph graph = firstNode.graph();

        loop.loopBegin().incrementUnswitches();

        // create new control split out of loop
        ControlSplitNode newControlSplit = (ControlSplitNode) firstNode.copyWithInputs();
        originalLoop.entryPoint().replaceAtPredecessor(newControlSplit);

        /*
         * The code below assumes that all of the control split nodes have the same successor
         * structure, which should have been enforced by findUnswitchable.
         */
        Iterator<Position> successors = firstNode.successorPositions().iterator();
        assert successors.hasNext();
        // original loop is used as first successor
        Position firstPosition = successors.next();
        AbstractBeginNode originalLoopBegin = BeginNode.begin(originalLoop.entryPoint());
        firstPosition.set(newControlSplit, originalLoopBegin);
        originalLoopBegin.setNodeSourcePosition(firstPosition.get(firstNode).getNodeSourcePosition());

        while (successors.hasNext()) {
            Position position = successors.next();
            // create a new loop duplicate and connect it.
            LoopFragmentWhole duplicateLoop = originalLoop.duplicate();
            AbstractBeginNode newBegin = BeginNode.begin(duplicateLoop.entryPoint());
            newBegin.setNodeSourcePosition(position.get(firstNode).getNodeSourcePosition());
            position.set(newControlSplit, newBegin);

            // For each cloned ControlSplitNode, simplify the proper path
            for (ControlSplitNode controlSplitNode : controlSplitNodeSet) {
                ControlSplitNode duplicatedControlSplit = duplicateLoop.getDuplicatedNode(controlSplitNode);
                if (duplicatedControlSplit.isAlive()) {
                    AbstractBeginNode survivingSuccessor = (AbstractBeginNode) position.get(duplicatedControlSplit);
                    survivingSuccessor.replaceAtUsages(newBegin, InputType.Guard);
                    graph.removeSplitPropagate(duplicatedControlSplit, survivingSuccessor);
                }
            }
        }
        // original loop is simplified last to avoid deleting controlSplitNode too early
        for (ControlSplitNode controlSplitNode : controlSplitNodeSet) {
            if (controlSplitNode.isAlive()) {
                AbstractBeginNode survivingSuccessor = (AbstractBeginNode) firstPosition.get(controlSplitNode);
                survivingSuccessor.replaceAtUsages(originalLoopBegin, InputType.Guard);
                graph.removeSplitPropagate(controlSplitNode, survivingSuccessor);
            }
        }

        // TODO (gd) probabilities need some amount of fixup.. (probably also in other transforms)
    }

    public static void partialUnroll(LoopEx loop, EconomicMap<LoopBeginNode, OpaqueNode> opaqueUnrolledStrides) {
        assert loop.loopBegin().isMainLoop();
        loop.loopBegin().graph().getDebug().log("LoopPartialUnroll %s", loop);

        LoopFragmentInside newSegment = loop.inside().duplicate();
        newSegment.insertWithinAfter(loop, opaqueUnrolledStrides);

    }

    // This function splits candidate loops into pre, main and post loops,
    // dividing the iteration space to facilitate the majority of iterations
    // being executed in a main loop, which will have RCE implemented upon it.
    // The initial loop form is constrained to single entry/exit, but can have
    // flow. The translation looks like:
    //
    //  @formatter:off
    //
    //       (Simple Loop entry)                   (Pre Loop Entry)
    //                |                                  |
    //         (LoopBeginNode)                    (LoopBeginNode)
    //                |                                  |
    //       (Loop Control Test)<------   ==>  (Loop control Test)<------
    //         /               \       \         /               \       \
    //    (Loop Exit)      (Loop Body) |    (Loop Exit)      (Loop Body) |
    //        |                |       |        |                |       |
    // (continue code)     (Loop End)  |  if (M < length)*   (Loop End)  |
    //                         \       /       /      \           \      /
    //                          ----->        /       |            ----->
    //                                       /  if ( ... )*
    //                                      /     /       \
    //                                     /     /         \
    //                                    /     /           \
    //                                   |     /     (Main Loop Entry)
    //                                   |    |             |
    //                                   |    |      (LoopBeginNode)
    //                                   |    |             |
    //                                   |    |     (Loop Control Test)<------
    //                                   |    |      /               \        \
    //                                   |    |  (Loop Exit)      (Loop Body) |
    //                                    \   \      |                |       |
    //                                     \   \     |            (Loop End)  |
    //                                      \   \    |                \       /
    //                                       \   \   |                 ------>
    //                                        \   \  |
    //                                      (Main Loop Merge)*
    //                                               |
    //                                      (Post Loop Entry)
    //                                               |
    //                                        (LoopBeginNode)
    //                                               |
    //                                       (Loop Control Test)<-----
    //                                        /               \       \
    //                                    (Loop Exit)     (Loop Body) |
    //                                        |               |       |
    //                                 (continue code)    (Loop End)  |
    //                                                         \      /
    //                                                          ----->
    //
    // Key: "*" = optional.
    // @formatter:on
    //
    // The value "M" is the maximal value of the loop trip for the original
    // loop. The value of "length" is applicable to the number of arrays found
    // in the loop but is reduced if some or all of the arrays are known to be
    // the same length as "M". The maximum number of tests can be equal to the
    // number of arrays in the loop, where multiple instances of an array are
    // subsumed into a single test for that arrays length.
    //
    // If the optional main loop entry tests are absent, the Pre Loop exit
    // connects to the Main loops entry and there is no merge hanging off the
    // main loops exit to converge flow from said tests. All split use data
    // flow is mitigated through phi(s) in the main merge if present and
    // passed through the main and post loop phi(s) from the originating pre
    // loop with final phi(s) and data flow patched to the "continue code".
    // The pre loop is constrained to one iteration for now and will likely
    // be updated to produce vector alignment if applicable.

    public static LoopBeginNode insertPrePostLoops(LoopEx loop) {
        StructuredGraph graph = loop.loopBegin().graph();
        graph.getDebug().log("LoopTransformations.insertPrePostLoops %s", loop);
        LoopFragmentWhole preLoop = loop.whole();
        CountedLoopInfo preCounted = loop.counted();
        LoopBeginNode preLoopBegin = loop.loopBegin();
        AbstractBeginNode preLoopExitNode = preCounted.getCountedExit();

        assert preLoop.nodes().contains(preLoopBegin);
        assert preLoop.nodes().contains(preLoopExitNode);

        // Each duplication is inserted after the original, ergo create the post loop first
        LoopFragmentWhole mainLoop = preLoop.duplicate();
        LoopFragmentWhole postLoop = preLoop.duplicate();
        preLoopBegin.incrementSplits();
        preLoopBegin.incrementSplits();
        preLoopBegin.setPreLoop();
        graph.getDebug().dump(DebugContext.VERBOSE_LEVEL, graph, "After duplication");
        LoopBeginNode mainLoopBegin = mainLoop.getDuplicatedNode(preLoopBegin);
        mainLoopBegin.setMainLoop();
        LoopBeginNode postLoopBegin = postLoop.getDuplicatedNode(preLoopBegin);
        postLoopBegin.setPostLoop();

        AbstractBeginNode postLoopExitNode = postLoop.getDuplicatedNode(preLoopExitNode);
        EndNode postEndNode = getBlockEndAfterLoopExit(postLoopExitNode);
        AbstractMergeNode postMergeNode = postEndNode.merge();

        // Update the main loop phi initialization to carry from the pre loop
        for (PhiNode prePhiNode : preLoopBegin.phis()) {
            PhiNode mainPhiNode = mainLoop.getDuplicatedNode(prePhiNode);
            mainPhiNode.setValueAt(0, prePhiNode);
        }

        AbstractBeginNode mainLoopExitNode = mainLoop.getDuplicatedNode(preLoopExitNode);
        EndNode mainEndNode = getBlockEndAfterLoopExit(mainLoopExitNode);
        AbstractMergeNode mainMergeNode = mainEndNode.merge();
        AbstractEndNode postEntryNode = postLoopBegin.forwardEnd();

        // Exits have been merged, find the continuation below the merge
        FixedNode continuationNode = mainMergeNode.next();

        // In the case of no Bounds tests, we just flow right into the main loop
        AbstractBeginNode mainLandingNode = BeginNode.begin(postEntryNode);
        mainLoopExitNode.setNext(mainLandingNode);
        preLoopExitNode.setNext(mainLoopBegin.forwardEnd());

        // Add and update any phi edges as per merge usage as needed and update usages
        processPreLoopPhis(loop, mainLoop, postLoop);
        continuationNode.predecessor().clearSuccessors();
        postLoopExitNode.setNext(continuationNode);
        cleanupMerge(postMergeNode, postLoopExitNode);
        cleanupMerge(mainMergeNode, mainLandingNode);

        // Change the preLoop to execute one iteration for now
        updatePreLoopLimit(preCounted);
        preLoopBegin.setLoopFrequency(1.0);
        mainLoopBegin.setLoopFrequency(Math.max(1.0, mainLoopBegin.loopFrequency() - 2));
        postLoopBegin.setLoopFrequency(Math.max(1.0, postLoopBegin.loopFrequency() - 1));

        // The pre and post loops don't require safepoints at all
        for (SafepointNode safepoint : preLoop.nodes().filter(SafepointNode.class)) {
            graph.removeFixed(safepoint);
        }
        for (SafepointNode safepoint : postLoop.nodes().filter(SafepointNode.class)) {
            graph.removeFixed(safepoint);
        }
        graph.getDebug().dump(DebugContext.DETAILED_LEVEL, graph, "InsertPrePostLoops %s", loop);
        return mainLoopBegin;
    }

    
Cleanup the merge and remove the predecessors too.
/**
     * Cleanup the merge and remove the predecessors too.
     */
    private static void cleanupMerge(AbstractMergeNode mergeNode, AbstractBeginNode landingNode) {
        for (EndNode end : mergeNode.cfgPredecessors().snapshot()) {
            mergeNode.removeEnd(end);
            end.safeDelete();
        }
        mergeNode.prepareDelete(landingNode);
        mergeNode.safeDelete();
    }

    private static void processPreLoopPhis(LoopEx preLoop, LoopFragmentWhole mainLoop, LoopFragmentWhole postLoop) {
        // process phis for the post loop
        LoopBeginNode preLoopBegin = preLoop.loopBegin();
        for (PhiNode prePhiNode : preLoopBegin.phis()) {
            PhiNode postPhiNode = postLoop.getDuplicatedNode(prePhiNode);
            PhiNode mainPhiNode = mainLoop.getDuplicatedNode(prePhiNode);
            postPhiNode.setValueAt(0, mainPhiNode);

            // Build a work list to update the pre loop phis to the post loops phis
            for (Node usage : prePhiNode.usages().snapshot()) {
                if (usage == mainPhiNode) {
                    continue;
                }
                if (preLoop.isOutsideLoop(usage)) {
                    usage.replaceFirstInput(prePhiNode, postPhiNode);
                }
            }
        }
        for (Node node : preLoop.inside().nodes()) {
            for (Node externalUsage : node.usages().snapshot()) {
                if (preLoop.isOutsideLoop(externalUsage)) {
                    Node postUsage = postLoop.getDuplicatedNode(node);
                    assert postUsage != null;
                    externalUsage.replaceFirstInput(node, postUsage);
                }
            }
        }
    }

    
Find the end of the block following the LoopExit.
/**
     * Find the end of the block following the LoopExit.
     */
    private static EndNode getBlockEndAfterLoopExit(AbstractBeginNode exit) {
        FixedNode node = exit.next();
        // Find the last node after the exit blocks starts
        return getBlockEnd(node);
    }

    private static EndNode getBlockEnd(FixedNode node) {
        FixedNode curNode = node;
        while (curNode instanceof FixedWithNextNode) {
            curNode = ((FixedWithNextNode) curNode).next();
        }
        return (EndNode) curNode;
    }

    private static void updatePreLoopLimit(CountedLoopInfo preCounted) {
        // Update the pre loops limit test
        // Make new limit one iteration
        ValueNode newLimit = AddNode.add(preCounted.getStart(), preCounted.getCounter().strideNode(), NodeView.DEFAULT);
        // Fetch the variable we are not replacing and configure the one we are
        ValueNode ub = preCounted.getLimit();
        IntegerHelper helper = preCounted.getCounterIntegerHelper();
        LogicNode entryCheck;
        if (preCounted.getDirection() == Direction.Up) {
            entryCheck = helper.createCompareNode(newLimit, ub, NodeView.DEFAULT);
        } else {
            entryCheck = helper.createCompareNode(ub, newLimit, NodeView.DEFAULT);
        }
        newLimit = ConditionalNode.create(entryCheck, newLimit, ub, NodeView.DEFAULT);
        // Re-wire the condition with the new limit
        CompareNode compareNode = (CompareNode) preCounted.getLimitTest().condition();
        compareNode.replaceFirstInput(ub, compareNode.graph().addOrUniqueWithInputs(newLimit));
    }

    public static List<ControlSplitNode> findUnswitchable(LoopEx loop) {
        List<ControlSplitNode> controls = null;
        ValueNode invariantValue = null;
        for (IfNode ifNode : loop.whole().nodes().filter(IfNode.class)) {
            if (loop.isOutsideLoop(ifNode.condition())) {
                if (controls == null) {
                    invariantValue = ifNode.condition();
                    controls = new ArrayList<>();
                    controls.add(ifNode);
                } else if (ifNode.condition() == invariantValue) {
                    controls.add(ifNode);
                }
            }
        }
        if (controls == null) {
            SwitchNode firstSwitch = null;
            for (SwitchNode switchNode : loop.whole().nodes().filter(SwitchNode.class)) {
                if (switchNode.successors().count() > 1 && loop.isOutsideLoop(switchNode.value())) {
                    if (controls == null) {
                        firstSwitch = switchNode;
                        invariantValue = switchNode.value();
                        controls = new ArrayList<>();
                        controls.add(switchNode);
                    } else if (switchNode.value() == invariantValue) {
                        // Fortify: Suppress Null Dereference false positive
                        assert firstSwitch != null;

                        if (firstSwitch.structureEquals(switchNode)) {
                            // Only collect switches which test the same values in the same order
                            controls.add(switchNode);
                        }
                    }
                }
            }
        }
        return controls;
    }

    public static boolean isUnrollableLoop(LoopEx loop) {
        if (!loop.isCounted() || !loop.counted().getCounter().isConstantStride() || !loop.loop().getChildren().isEmpty()) {
            return false;
        }
        assert loop.counted().getDirection() != null;
        LoopBeginNode loopBegin = loop.loopBegin();
        LogicNode condition = loop.counted().getLimitTest().condition();
        if (!(condition instanceof CompareNode)) {
            return false;
        }
        if (((CompareNode) condition).condition() == CanonicalCondition.EQ) {
            condition.getDebug().log(DebugContext.VERBOSE_LEVEL, "isUnrollableLoop %s condition unsupported %s ", loopBegin, ((CompareNode) condition).condition());
            return false;
        }
        long stride = loop.counted().getCounter().constantStride();
        try {
            Math.addExact(stride, stride);
        } catch (ArithmeticException ae) {
            condition.getDebug().log(DebugContext.VERBOSE_LEVEL, "isUnrollableLoop %s doubling the stride overflows %d", loopBegin, stride);
            return false;
        }
        if (!loop.canDuplicateLoop()) {
            return false;
        }
        if (loopBegin.isMainLoop() || loopBegin.isSimpleLoop()) {
            // Flow-less loops to partial unroll for now. 3 blocks corresponds to an if that either
            // exits or continues the loop. There might be fixed and floating work within the loop
            // as well.
            if (loop.loop().getBlocks().size() < 3) {
                return true;
            }
            condition.getDebug().log(DebugContext.VERBOSE_LEVEL, "isUnrollableLoop %s too large to unroll %s ", loopBegin, loop.loop().getBlocks().size());
        }
        return false;
    }
}