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 * Copyright (c) 2014, 2018, 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.

 *

 * 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.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package org.graalvm.compiler.phases.common;

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

import java.util.List;

import org.graalvm.compiler.debug.CounterKey;

import org.graalvm.compiler.debug.DebugContext;

import org.graalvm.compiler.graph.Node;

import org.graalvm.compiler.nodeinfo.InputType;

import org.graalvm.compiler.nodes.AbstractBeginNode;

import org.graalvm.compiler.nodes.AbstractDeoptimizeNode;

import org.graalvm.compiler.nodes.AbstractEndNode;

import org.graalvm.compiler.nodes.AbstractMergeNode;

import org.graalvm.compiler.nodes.BeginNode;

import org.graalvm.compiler.nodes.CompressionNode;

import org.graalvm.compiler.nodes.DeoptimizeNode;

import org.graalvm.compiler.nodes.DeoptimizingFixedWithNextNode;

import org.graalvm.compiler.nodes.DynamicDeoptimizeNode;

import org.graalvm.compiler.nodes.FixedNode;

import org.graalvm.compiler.nodes.IfNode;

import org.graalvm.compiler.nodes.LogicNode;

import org.graalvm.compiler.nodes.StructuredGraph;

import org.graalvm.compiler.nodes.ValueNode;

import org.graalvm.compiler.nodes.ValuePhiNode;

import org.graalvm.compiler.nodes.calc.IsNullNode;

import org.graalvm.compiler.nodes.extended.NullCheckNode;

import org.graalvm.compiler.nodes.memory.FixedAccessNode;

import org.graalvm.compiler.nodes.memory.address.AddressNode;

import org.graalvm.compiler.nodes.util.GraphUtil;

import org.graalvm.compiler.options.Option;

import org.graalvm.compiler.options.OptionKey;

import org.graalvm.compiler.options.OptionType;

import org.graalvm.compiler.phases.BasePhase;

import org.graalvm.compiler.phases.tiers.LowTierContext;

import jdk.vm.ci.meta.DeoptimizationReason;

import jdk.vm.ci.meta.MetaAccessProvider;

import jdk.vm.ci.meta.SpeculationLog;

import jdk.vm.ci.meta.SpeculationLog.Speculation;

public class UseTrappingNullChecksPhase extends BasePhase<LowTierContext> {

    private static final CounterKey counterTrappingNullCheck = DebugContext.counter("TrappingNullCheck");

    private static final CounterKey counterTrappingNullCheckExistingRead = DebugContext.counter("TrappingNullCheckExistingRead");

    private static final CounterKey counterTrappingNullCheckUnreached = DebugContext.counter("TrappingNullCheckUnreached");

    private static final CounterKey counterTrappingNullCheckDynamicDeoptimize = DebugContext.counter("TrappingNullCheckDynamicDeoptimize");

    public static class Options {

        // @formatter:off

        @Option(help = "Use traps for null checks instead of explicit null-checks", type = OptionType.Expert)

        public static final OptionKey<Boolean> UseTrappingNullChecks = new OptionKey<>(true);

        // @formatter:on

    }

    @Override

    protected void run(StructuredGraph graph, LowTierContext context) {

        if (!Options.UseTrappingNullChecks.getValue(graph.getOptions()) || context.getTarget().implicitNullCheckLimit <= 0) {

            return;

        }

        assert graph.getGuardsStage().areFrameStatesAtDeopts();

        long implicitNullCheckLimit = context.getTarget().implicitNullCheckLimit;

        for (DeoptimizeNode deopt : graph.getNodes(DeoptimizeNode.TYPE)) {

            tryUseTrappingNullCheck(deopt, deopt.predecessor(), deopt.getReason(), deopt.getSpeculation(), implicitNullCheckLimit);

        }

        for (DynamicDeoptimizeNode deopt : graph.getNodes(DynamicDeoptimizeNode.TYPE)) {

            tryUseTrappingNullCheck(context.getMetaAccess(), deopt, implicitNullCheckLimit);

        }

    }

    private static void tryUseTrappingNullCheck(MetaAccessProvider metaAccessProvider, DynamicDeoptimizeNode deopt, long implicitNullCheckLimit) {

        Node predecessor = deopt.predecessor();

        if (predecessor instanceof AbstractMergeNode) {

            AbstractMergeNode merge = (AbstractMergeNode) predecessor;

            // Process each predecessor at the merge, unpacking the reasons and speculations as

            // needed.

            ValueNode reason = deopt.getActionAndReason();

            ValuePhiNode reasonPhi = null;

            List<ValueNode> reasons = null;

            int expectedPhis = 0;

            if (reason instanceof ValuePhiNode) {

                reasonPhi = (ValuePhiNode) reason;

                if (reasonPhi.merge() != merge) {

                    return;

                }

                reasons = reasonPhi.values().snapshot();

                expectedPhis++;

            } else if (!reason.isConstant()) {

                return;

            }

            ValueNode speculation = deopt.getSpeculation();

            ValuePhiNode speculationPhi = null;

            List<ValueNode> speculations = null;

            if (speculation instanceof ValuePhiNode) {

                speculationPhi = (ValuePhiNode) speculation;

                if (speculationPhi.merge() != merge) {

                    return;

                }

                speculations = speculationPhi.values().snapshot();

                expectedPhis++;

            }

            if (merge.phis().count() != expectedPhis) {

                return;

            }

            int index = 0;

            for (AbstractEndNode end : merge.cfgPredecessors().snapshot()) {

                ValueNode thisReason = reasons != null ? reasons.get(index) : reason;

                if (!thisReason.isConstant() || !thisSpeculation.isConstant()) {

                    continue;

                }

                Speculation speculationConstant = metaAccessProvider.decodeSpeculation(thisSpeculation.asJavaConstant(), deopt.graph().getSpeculationLog());

                if (!speculationConstant.equals(SpeculationLog.NO_SPECULATION)) {

                    continue;

                }

                DeoptimizationReason deoptimizationReason = metaAccessProvider.decodeDeoptReason(thisReason.asJavaConstant());

                tryUseTrappingNullCheck(deopt, end.predecessor(), deoptimizationReason, SpeculationLog.NO_SPECULATION, implicitNullCheckLimit);

            }

        }

    }

    private static void tryUseTrappingNullCheck(AbstractDeoptimizeNode deopt, Node predecessor, DeoptimizationReason deoptimizationReason, Speculation speculation, long implicitNullCheckLimit) {

        if (deoptimizationReason != DeoptimizationReason.NullCheckException && deoptimizationReason != DeoptimizationReason.UnreachedCode) {

            return;

        }

        assert speculation != null;

        if (!speculation.equals(SpeculationLog.NO_SPECULATION)) {

            return;

        }

        if (predecessor instanceof AbstractMergeNode) {

            AbstractMergeNode merge = (AbstractMergeNode) predecessor;

            if (merge.phis().isEmpty()) {

                for (AbstractEndNode end : merge.cfgPredecessors().snapshot()) {

                    checkPredecessor(deopt, end.predecessor(), deoptimizationReason, implicitNullCheckLimit);

                }

            }

        } else if (predecessor instanceof AbstractBeginNode) {

            checkPredecessor(deopt, predecessor, deoptimizationReason, implicitNullCheckLimit);

        }

    }

    private static void checkPredecessor(AbstractDeoptimizeNode deopt, Node predecessor, DeoptimizationReason deoptimizationReason, long implicitNullCheckLimit) {

        Node current = predecessor;

        AbstractBeginNode branch = null;

        while (current instanceof AbstractBeginNode) {

            branch = (AbstractBeginNode) current;

            if (branch.anchored().isNotEmpty()) {

                // some input of the deopt framestate is anchored to this branch

                return;

            }

            current = current.predecessor();

        }

        if (current instanceof IfNode) {

            IfNode ifNode = (IfNode) current;

            if (branch != ifNode.trueSuccessor()) {

                return;

            }

            LogicNode condition = ifNode.condition();

            if (condition instanceof IsNullNode) {

                replaceWithTrappingNullCheck(deopt, ifNode, condition, deoptimizationReason, implicitNullCheckLimit);

            }

        }

    }

    private static void replaceWithTrappingNullCheck(AbstractDeoptimizeNode deopt, IfNode ifNode, LogicNode condition, DeoptimizationReason deoptimizationReason, long implicitNullCheckLimit) {

        DebugContext debug = deopt.getDebug();

        counterTrappingNullCheck.increment(debug);

        if (deopt instanceof DynamicDeoptimizeNode) {

            counterTrappingNullCheckDynamicDeoptimize.increment(debug);

        }

        if (deoptimizationReason == DeoptimizationReason.UnreachedCode) {

            counterTrappingNullCheckUnreached.increment(debug);

        }

        IsNullNode isNullNode = (IsNullNode) condition;

        AbstractBeginNode nonTrappingContinuation = ifNode.falseSuccessor();

        AbstractBeginNode trappingContinuation = ifNode.trueSuccessor();

        DeoptimizingFixedWithNextNode trappingNullCheck = null;

        FixedNode nextNonTrapping = nonTrappingContinuation.next();

        ValueNode value = isNullNode.getValue();

        if (OptImplicitNullChecks.getValue(ifNode.graph().getOptions()) && implicitNullCheckLimit > 0) {

            if (nextNonTrapping instanceof FixedAccessNode) {

                FixedAccessNode fixedAccessNode = (FixedAccessNode) nextNonTrapping;

                if (fixedAccessNode.canNullCheck()) {

                    AddressNode address = fixedAccessNode.getAddress();

                    ValueNode base = address.getBase();

                    ValueNode index = address.getIndex();

                    // allow for architectures which cannot fold an

                    // intervening uncompress out of the address chain

                    if (base != null && base instanceof CompressionNode) {

                        base = ((CompressionNode) base).getValue();

                    }

                    if (index != null && index instanceof CompressionNode) {

                        index = ((CompressionNode) index).getValue();

                    }

                    if (((base == value && index == null) || (base == null && index == value)) && address.getMaxConstantDisplacement() < implicitNullCheckLimit) {

                        // Opportunity for implicit null check as part of an existing read found!

                        fixedAccessNode.setStateBefore(deopt.stateBefore());

                        fixedAccessNode.setNullCheck(true);

                        deopt.graph().removeSplit(ifNode, nonTrappingContinuation);

                        trappingNullCheck = fixedAccessNode;

                        counterTrappingNullCheckExistingRead.increment(debug);

                    }

                }

            }

        }

        if (trappingNullCheck == null) {

            // Need to add a null check node.

            trappingNullCheck = deopt.graph().add(new NullCheckNode(value));

            deopt.graph().replaceSplit(ifNode, trappingNullCheck, nonTrappingContinuation);

        }

        trappingNullCheck.setStateBefore(deopt.stateBefore());

        /*

         * We now have the pattern NullCheck/BeginNode/... It's possible some node is using the

         * BeginNode as a guard input, so replace guard users of the Begin with the NullCheck and

         * then remove the Begin from the graph.

         */

        nonTrappingContinuation.replaceAtUsages(InputType.Guard, trappingNullCheck);

        if (nonTrappingContinuation instanceof BeginNode) {

            GraphUtil.unlinkFixedNode(nonTrappingContinuation);

            nonTrappingContinuation.safeDelete();

        }

        GraphUtil.killCFG(trappingContinuation);

        GraphUtil.tryKillUnused(isNullNode);

    }

}