/*
 * Copyright (C) 2012-2015 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#include "config.h"
#include "DFGConstantFoldingPhase.h"

#if ENABLE(DFG_JIT)

#include "DFGAbstractInterpreterInlines.h"
#include "DFGArgumentsUtilities.h"
#include "DFGBasicBlockInlines.h"
#include "DFGGraph.h"
#include "DFGInPlaceAbstractState.h"
#include "DFGInferredTypeCheck.h"
#include "DFGInsertionSet.h"
#include "DFGPhase.h"
#include "GetByIdStatus.h"
#include "JSCInlines.h"
#include "PutByIdStatus.h"

namespace JSC { namespace DFG {

class ConstantFoldingPhase : public Phase {
public:
    ConstantFoldingPhase(Graph& graph)
        : Phase(graph, "constant folding")
        , m_state(graph)
        , m_interpreter(graph, m_state)
        , m_insertionSet(graph)
    {
    }
    
    bool run()
    {
        bool changed = false;

        for (BasicBlock* block : m_graph.blocksInNaturalOrder()) {
            if (block->cfaFoundConstants)
                changed |= foldConstants(block);
        }
        
        if (changed && m_graph.m_form == SSA) {
            // It's now possible that we have Upsilons pointed at JSConstants. Fix that.
            for (BasicBlock* block : m_graph.blocksInNaturalOrder())
                fixUpsilons(block);
        }

        if (m_graph.m_form == SSA) {
            // It's now possible to simplify basic blocks by placing an Unreachable terminator right
            // after anything that invalidates AI.
            bool didClipBlock = false;
            Vector<Node*> nodesToDelete;
            for (BasicBlock* block : m_graph.blocksInNaturalOrder()) {
                m_state.beginBasicBlock(block);
                for (unsigned nodeIndex = 0; nodeIndex < block->size(); ++nodeIndex) {
                    if (block->at(nodeIndex)->isTerminal()) {
                        // It's possible that we have something after the terminal. It could be a
                        // no-op Check node, for example. We don't want the logic below to turn that
                        // node into Unreachable, since then we'd have two terminators.
                        break;
                    }
                    if (!m_state.isValid()) {
                        NodeOrigin origin = block->at(nodeIndex)->origin;
                        for (unsigned killIndex = nodeIndex; killIndex < block->size(); ++killIndex)
                            nodesToDelete.append(block->at(killIndex));
                        block->resize(nodeIndex);
                        block->appendNode(m_graph, SpecNone, Unreachable, origin);
                        didClipBlock = true;
                        break;
                    }
                    m_interpreter.execute(nodeIndex);
                }
                m_state.reset();
            }

            if (didClipBlock) {
                changed = true;

                m_graph.invalidateNodeLiveness();

                for (Node* node : nodesToDelete)
                    m_graph.deleteNode(node);

                m_graph.invalidateCFG();
                m_graph.resetReachability();
                m_graph.killUnreachableBlocks();
            }
        }
         
        return changed;
    }

private:
    bool foldConstants(BasicBlock* block)
    {
        bool changed = false;
        m_state.beginBasicBlock(block);
        for (unsigned indexInBlock = 0; indexInBlock < block->size(); ++indexInBlock) {
            if (!m_state.isValid())
                break;
            
            Node* node = block->at(indexInBlock);

            bool alreadyHandled = false;
            bool eliminated = false;
                    
            switch (node->op()) {
            case BooleanToNumber: {
                if (node->child1().useKind() == UntypedUse
                    && !m_interpreter.needsTypeCheck(node->child1(), SpecBoolean))
                    node->child1().setUseKind(BooleanUse);
                break;
            }

            case CompareEq: {
                // FIXME: We should add back the broken folding phase here for comparisions where we prove at least one side has type SpecOther.
                // See: https://bugs.webkit.org/show_bug.cgi?id=174844
                break;
            }

            case CompareStrictEq: {
                if (node->isBinaryUseKind(UntypedUse)) {
                    JSValue child1Constant = m_state.forNode(node->child1().node()).value();
                    JSValue child2Constant = m_state.forNode(node->child2().node()).value();

                    // FIXME: Revisit this condition when introducing BigInt to JSC.
                    auto isNonStringOrBigIntCellConstant = [] (JSValue value) {
                        return value && value.isCell() && !value.isString() && !value.isBigInt();
                    };

                    if (isNonStringOrBigIntCellConstant(child1Constant)) {
                        node->convertToCompareEqPtr(m_graph.freezeStrong(child1Constant.asCell()), node->child2());
                        changed = true;
                    } else if (isNonStringOrBigIntCellConstant(child2Constant)) {
                        node->convertToCompareEqPtr(m_graph.freezeStrong(child2Constant.asCell()), node->child1());
                        changed = true;
                    }
                }
                break;
            }

            case CheckStructureOrEmpty: {
                const AbstractValue& value = m_state.forNode(node->child1());
                if (value.m_type & SpecEmpty)
                    break;
                node->convertCheckStructureOrEmptyToCheckStructure();
                changed = true;
                FALLTHROUGH;
            }
            case CheckStructure:
            case ArrayifyToStructure: {
                AbstractValue& value = m_state.forNode(node->child1());
                RegisteredStructureSet set;
                if (node->op() == ArrayifyToStructure)
                    set = node->structure();
                else {
                    set = node->structureSet();
                    if ((SpecCellCheck & SpecEmpty) && node->child1().useKind() == CellUse && m_state.forNode(node->child1()).m_type & SpecEmpty) {
                        m_insertionSet.insertNode(
                            indexInBlock, SpecNone, AssertNotEmpty, node->origin, Edge(node->child1().node(), UntypedUse));
                    }
                }
                if (value.m_structure.isSubsetOf(set)) {
                    m_interpreter.execute(indexInBlock); // Catch the fact that we may filter on cell.
                    node->remove(m_graph);
                    eliminated = true;
                    break;
                }
                break;
            }

            case CheckSubClass: {
                JSValue constant = m_state.forNode(node->child1()).value();
                if (constant) {
                    if (constant.isCell() && constant.asCell()->inherits(m_graph.m_vm, node->classInfo())) {
                        m_interpreter.execute(indexInBlock);
                        node->remove(m_graph);
                        eliminated = true;
                        break;
                    }
                }

                AbstractValue& value = m_state.forNode(node->child1());

                if (value.m_structure.isSubClassOf(node->classInfo())) {
                    m_interpreter.execute(indexInBlock);
                    node->remove(m_graph);
                    eliminated = true;
                    break;
                }
                break;
            }
                
            case GetIndexedPropertyStorage: {
                JSArrayBufferView* view = m_graph.tryGetFoldableView(
                    m_state.forNode(node->child1()).m_value, node->arrayMode());
                if (!view)
                    break;
                
                if (view->mode() == FastTypedArray) {
                    // FIXME: It would be awesome to be able to fold the property storage for
                    // these GC-allocated typed arrays. For now it doesn't matter because the
                    // most common use-cases for constant typed arrays involve large arrays with
                    // aliased buffer views.
                    // https://bugs.webkit.org/show_bug.cgi?id=125425
                    break;
                }
                
                m_interpreter.execute(indexInBlock);
                eliminated = true;
                
                m_insertionSet.insertCheck(indexInBlock, node->origin, node->children);
                node->convertToConstantStoragePointer(view->vector());
                break;
            }
                
            case CheckStructureImmediate: {
                AbstractValue& value = m_state.forNode(node->child1());
                const RegisteredStructureSet& set = node->structureSet();
                
                if (value.value()) {
                    if (Structure* structure = jsDynamicCast<Structure*>(m_graph.m_vm, value.value())) {
                        if (set.contains(m_graph.registerStructure(structure))) {
                            m_interpreter.execute(indexInBlock);
                            node->remove(m_graph);
                            eliminated = true;
                            break;
                        }
                    }
                }
                
                if (PhiChildren* phiChildren = m_interpreter.phiChildren()) {
                    bool allGood = true;
                    phiChildren->forAllTransitiveIncomingValues(
                        node,
                        [&] (Node* incoming) {
                            if (Structure* structure = incoming->dynamicCastConstant<Structure*>(m_graph.m_vm)) {
                                if (set.contains(m_graph.registerStructure(structure)))
                                    return;
                            }
                            allGood = false;
                        });
                    if (allGood) {
                        m_interpreter.execute(indexInBlock);
                        node->remove(m_graph);
                        eliminated = true;
                        break;
                    }
                }
                break;
            }
                
            case CheckArray:
            case Arrayify: {
                if (!node->arrayMode().alreadyChecked(m_graph, node, m_state.forNode(node->child1())))
                    break;
                node->remove(m_graph);
                eliminated = true;
                break;
            }
                
            case PutStructure: {
                if (m_state.forNode(node->child1()).m_structure.onlyStructure() != node->transition()->next)
                    break;
                
                node->remove(m_graph);
                eliminated = true;
                break;
            }
                
            case CheckCell: {
                if (m_state.forNode(node->child1()).value() != node->cellOperand()->value())
                    break;
                node->remove(m_graph);
                eliminated = true;
                break;
            }

            case AssertNotEmpty:
            case CheckNotEmpty: {
                if (m_state.forNode(node->child1()).m_type & SpecEmpty)
                    break;
                node->remove(m_graph);
                eliminated = true;
                break;
            }

            case CheckStringIdent: {
                UniquedStringImpl* uid = node->uidOperand();
                const UniquedStringImpl* constantUid = nullptr;

                JSValue childConstant = m_state.forNode(node->child1()).value();
                if (childConstant) {
                    if (childConstant.isString()) {
                        if (const auto* impl = asString(childConstant)->tryGetValueImpl()) {
                            // Edge filtering requires that a value here should be StringIdent.
                            // However, a constant value propagated in DFG is not filtered.
                            // So here, we check the propagated value is actually an atomic string.
                            // And if it's not, we just ignore.
                            if (impl->isAtomic())
                                constantUid = static_cast<const UniquedStringImpl*>(impl);
                        }
                    }
                }

                if (constantUid == uid) {
                    node->remove(m_graph);
                    eliminated = true;
                }
                break;
            }

            case CheckInBounds: {
                JSValue left = m_state.forNode(node->child1()).value();
                JSValue right = m_state.forNode(node->child2()).value();
                if (left && right && left.isInt32() && right.isInt32()
                    && static_cast<uint32_t>(left.asInt32()) < static_cast<uint32_t>(right.asInt32())) {
                    node->remove(m_graph);
                    eliminated = true;
                    break;
                }
                
                break;
            }
                
            case GetMyArgumentByVal:
            case GetMyArgumentByValOutOfBounds: {
                JSValue indexValue = m_state.forNode(node->child2()).value();
                if (!indexValue || !indexValue.isUInt32())
                    break;

                Checked<unsigned, RecordOverflow> checkedIndex = indexValue.asUInt32();
                checkedIndex += node->numberOfArgumentsToSkip();
                if (checkedIndex.hasOverflowed())
                    break;
                
                unsigned index = checkedIndex.unsafeGet();
                Node* arguments = node->child1().node();
                InlineCallFrame* inlineCallFrame = arguments->origin.semantic.inlineCallFrame;
                
                // Don't try to do anything if the index is known to be outside our static bounds. Note
                // that our static bounds are usually strictly larger than the dynamic bounds. The
                // exception is something like this, assuming foo() is not inlined:
                //
                // function foo() { return arguments[5]; }
                //
                // Here the static bound on number of arguments is 0, and we're accessing index 5. We
                // will not strength-reduce this to GetStack because GetStack is otherwise assumed by the
                // compiler to access those variables that are statically accounted for; for example if
                // we emitted a GetStack on arg6 we would have out-of-bounds access crashes anywhere that
                // uses an Operands<> map. There is not much cost to continuing to use a
                // GetMyArgumentByVal in such statically-out-of-bounds accesses; we just lose CFA unless
                // GCSE removes the access entirely.
                if (inlineCallFrame) {
                    if (index >= inlineCallFrame->argumentCountIncludingThis - 1)
                        break;
                } else {
                    if (index >= m_state.variables().numberOfArguments() - 1)
                        break;
                }
                
                m_interpreter.execute(indexInBlock); // Push CFA over this node after we get the state before.
                
                StackAccessData* data;
                if (inlineCallFrame) {
                    data = m_graph.m_stackAccessData.add(
                        VirtualRegister(
                            inlineCallFrame->stackOffset +
                            CallFrame::argumentOffset(index)),
                        FlushedJSValue);
                } else {
                    data = m_graph.m_stackAccessData.add(
                        virtualRegisterForArgument(index + 1), FlushedJSValue);
                }
                
                if (inlineCallFrame && !inlineCallFrame->isVarargs() && index < inlineCallFrame->argumentCountIncludingThis - 1) {
                    node->convertToGetStack(data);
                    eliminated = true;
                    break;
                }
                
                if (node->op() == GetMyArgumentByValOutOfBounds)
                    break;
                
                Node* length = emitCodeToGetArgumentsArrayLength(
                    m_insertionSet, arguments, indexInBlock, node->origin);
                m_insertionSet.insertNode(
                    indexInBlock, SpecNone, CheckInBounds, node->origin,
                    node->child2(), Edge(length, Int32Use));
                node->convertToGetStack(data);
                eliminated = true;
                break;
            }
                
            case MultiGetByOffset: {
                Edge baseEdge = node->child1();
                Node* base = baseEdge.node();
                MultiGetByOffsetData& data = node->multiGetByOffsetData();

                // First prune the variants, then check if the MultiGetByOffset can be
                // strength-reduced to a GetByOffset.
                
                AbstractValue baseValue = m_state.forNode(base);
                
                m_interpreter.execute(indexInBlock); // Push CFA over this node after we get the state before.
                alreadyHandled = true; // Don't allow the default constant folder to do things to this.
                
                for (unsigned i = 0; i < data.cases.size(); ++i) {
                    MultiGetByOffsetCase& getCase = data.cases[i];
                    getCase.set().filter(baseValue);
                    if (getCase.set().isEmpty()) {
                        data.cases[i--] = data.cases.last();
                        data.cases.removeLast();
                        changed = true;
                    }
                }
                
                if (data.cases.size() != 1)
                    break;
                
                emitGetByOffset(indexInBlock, node, baseValue, data.cases[0], data.identifierNumber);
                changed = true;
                break;
            }
                
            case MultiPutByOffset: {
                Edge baseEdge = node->child1();
                Node* base = baseEdge.node();
                MultiPutByOffsetData& data = node->multiPutByOffsetData();
                
                AbstractValue baseValue = m_state.forNode(base);

                m_interpreter.execute(indexInBlock); // Push CFA over this node after we get the state before.
                alreadyHandled = true; // Don't allow the default constant folder to do things to this.
                

                for (unsigned i = 0; i < data.variants.size(); ++i) {
                    PutByIdVariant& variant = data.variants[i];
                    variant.oldStructure().genericFilter([&] (Structure* structure) -> bool {
                        return baseValue.contains(m_graph.registerStructure(structure));
                    });
                    
                    if (variant.oldStructure().isEmpty()) {
                        data.variants[i--] = data.variants.last();
                        data.variants.removeLast();
                        changed = true;
                        continue;
                    }
                    
                    if (variant.kind() == PutByIdVariant::Transition
                        && variant.oldStructure().onlyStructure() == variant.newStructure()) {
                        variant = PutByIdVariant::replace(
                            variant.oldStructure(),
                            variant.offset(),
                            variant.requiredType());
                        changed = true;
                    }
                }

                if (data.variants.size() != 1)
                    break;
                
                emitPutByOffset(
                    indexInBlock, node, baseValue, data.variants[0], data.identifierNumber);
                changed = true;
                break;
            }
        
            case GetByIdDirect:
            case GetByIdDirectFlush:
            case GetById:
            case GetByIdFlush: {
                Edge childEdge = node->child1();
                Node* child = childEdge.node();
                unsigned identifierNumber = node->identifierNumber();
                
                AbstractValue baseValue = m_state.forNode(child);

                m_interpreter.execute(indexInBlock); // Push CFA over this node after we get the state before.
                alreadyHandled = true; // Don't allow the default constant folder to do things to this.

                if (!baseValue.m_structure.isFinite()
                    || (node->child1().useKind() == UntypedUse || (baseValue.m_type & ~SpecCell)))
                    break;
                
                GetByIdStatus status = GetByIdStatus::computeFor(
                    baseValue.m_structure.toStructureSet(), m_graph.identifiers()[identifierNumber]);
                if (!status.isSimple())
                    break;
                
                for (unsigned i = status.numVariants(); i--;) {
                    if (!status[i].conditionSet().isEmpty()) {
                        // FIXME: We could handle prototype cases.
                        // https://bugs.webkit.org/show_bug.cgi?id=110386
                        break;
                    }
                }
                
                if (status.numVariants() == 1) {
                    emitGetByOffset(indexInBlock, node, baseValue, status[0], identifierNumber);
                    changed = true;
                    break;
                }
                
                if (!isFTL(m_graph.m_plan.mode))
                    break;
                
                MultiGetByOffsetData* data = m_graph.m_multiGetByOffsetData.add();
                for (const GetByIdVariant& variant : status.variants()) {
                    data->cases.append(
                        MultiGetByOffsetCase(
                            *m_graph.addStructureSet(variant.structureSet()),
                            GetByOffsetMethod::load(variant.offset())));
                }
                data->identifierNumber = identifierNumber;
                node->convertToMultiGetByOffset(data);
                changed = true;
                break;
            }
                
            case PutById:
            case PutByIdDirect:
            case PutByIdFlush: {
                NodeOrigin origin = node->origin;
                Edge childEdge = node->child1();
                Node* child = childEdge.node();
                unsigned identifierNumber = node->identifierNumber();
                
                ASSERT(childEdge.useKind() == CellUse);
                
                AbstractValue baseValue = m_state.forNode(child);
                AbstractValue valueValue = m_state.forNode(node->child2());

                m_interpreter.execute(indexInBlock); // Push CFA over this node after we get the state before.
                alreadyHandled = true; // Don't allow the default constant folder to do things to this.

                if (!baseValue.m_structure.isFinite())
                    break;
                
                PutByIdStatus status = PutByIdStatus::computeFor(
                    m_graph.globalObjectFor(origin.semantic),
                    baseValue.m_structure.toStructureSet(),
                    m_graph.identifiers()[identifierNumber],
                    node->op() == PutByIdDirect);
                
                if (!status.isSimple())
                    break;

                ASSERT(status.numVariants());
                
                if (status.numVariants() > 1 && !isFTL(m_graph.m_plan.mode))
                    break;
                
                changed = true;

                bool allGood = true;
                for (const PutByIdVariant& variant : status.variants()) {
                    if (!allGood)
                        break;
                    for (const ObjectPropertyCondition& condition : variant.conditionSet()) {
                        if (m_graph.watchCondition(condition))
                            continue;

                        Structure* structure = condition.object()->structure();
                        if (!condition.structureEnsuresValidity(structure)) {
                            allGood = false;
                            break;
                        }

                        m_insertionSet.insertNode(
                            indexInBlock, SpecNone, CheckStructure, node->origin,
                            OpInfo(m_graph.addStructureSet(structure)),
                            m_insertionSet.insertConstantForUse(
                                indexInBlock, node->origin, condition.object(), KnownCellUse));
                    }
                }

                if (!allGood)
                    break;
                
                if (status.numVariants() == 1) {
                    emitPutByOffset(indexInBlock, node, baseValue, status[0], identifierNumber);
                    break;
                }
                
                ASSERT(isFTL(m_graph.m_plan.mode));

                MultiPutByOffsetData* data = m_graph.m_multiPutByOffsetData.add();
                data->variants = status.variants();
                data->identifierNumber = identifierNumber;
                node->convertToMultiPutByOffset(data);
                break;
            }

            case ToPrimitive: {
                if (m_state.forNode(node->child1()).m_type & ~(SpecFullNumber | SpecBoolean | SpecString | SpecSymbol | SpecBigInt))
                    break;
                
                node->convertToIdentity();
                changed = true;
                break;
            }

            case ToThis: {
                ToThisResult result = isToThisAnIdentity(m_graph.m_vm, m_graph.executableFor(node->origin.semantic)->isStrictMode(), m_state.forNode(node->child1()));
                if (result == ToThisResult::Identity) {
                    node->convertToIdentity();
                    changed = true;
                    break;
                }
                if (result == ToThisResult::GlobalThis) {
                    node->convertToGetGlobalThis();
                    changed = true;
                    break;
                }
                break;
            }

            case CreateThis: {
                if (JSValue base = m_state.forNode(node->child1()).m_value) {
                    if (auto* function = jsDynamicCast<JSFunction*>(m_graph.m_vm, base)) {
                        if (FunctionRareData* rareData = function->rareData()) {
                            if (Structure* structure = rareData->objectAllocationStructure()) {
                                // FIXME: we should be able to allocate a poly proto object here:
                                // https://bugs.webkit.org/show_bug.cgi?id=177517
                                if (structure->hasMonoProto()) {
                                    m_graph.freeze(rareData);
                                    m_graph.watchpoints().addLazily(rareData->allocationProfileWatchpointSet());
                                    node->convertToNewObject(m_graph.registerStructure(structure));
                                    changed = true;
                                    break;
                                }
                            }
                        }
                    }
                }
                break;
            }

            case ToNumber: {
                if (m_state.forNode(node->child1()).m_type & ~SpecBytecodeNumber)
                    break;

                node->convertToIdentity();
                changed = true;
                break;
            }

            case NormalizeMapKey: {
                SpeculatedType typeMaybeNormalized = (SpecFullNumber & ~SpecInt32Only);
                if (m_state.forNode(node->child1()).m_type & typeMaybeNormalized)
                    break;

                node->convertToIdentity();
                changed = true;
                break;
            }

            case ParseInt: {
                AbstractValue& value = m_state.forNode(node->child1());
                if (!value.m_type || (value.m_type & ~SpecInt32Only))
                    break;

                JSValue radix;
                if (!node->child2())
                    radix = jsNumber(0);
                else
                    radix = m_state.forNode(node->child2()).m_value;

                if (!radix.isNumber())
                    break;

                if (radix.asNumber() == 0 || radix.asNumber() == 10) {
                    node->child2() = Edge();
                    node->convertToIdentity();
                    changed = true;
                }

                break;
            }

            case NumberToStringWithRadix: {
                JSValue radixValue = m_state.forNode(node->child2()).m_value;
                if (radixValue && radixValue.isInt32()) {
                    int32_t radix = radixValue.asInt32();
                    if (2 <= radix && radix <= 36) {
                        if (radix == 10) {
                            node->setOpAndDefaultFlags(ToString);
                            node->clearFlags(NodeMustGenerate);
                            node->child2() = Edge();
                        } else
                            node->convertToNumberToStringWithValidRadixConstant(radix);
                        changed = true;
                        break;
                    }
                }
                break;
            }

            case Check: {
                alreadyHandled = true;
                m_interpreter.execute(indexInBlock);
                for (unsigned i = 0; i < AdjacencyList::Size; ++i) {
                    Edge edge = node->children.child(i);
                    if (!edge)
                        break;
                    if (edge.isProved() || edge.willNotHaveCheck()) {
                        node->children.removeEdge(i--);
                        changed = true;
                    }
                }
                break;
            }

            case CheckVarargs: {
                alreadyHandled = true;
                m_interpreter.execute(indexInBlock);
                unsigned targetIndex = 0;
                for (unsigned i = 0; i < node->numChildren(); ++i) {
                    Edge& edge = m_graph.varArgChild(node, i);
                    if (!edge)
                        continue;
                    if (edge.isProved() || edge.willNotHaveCheck()) {
                        edge = Edge();
                        changed = true;
                        continue;
                    }
                    Edge& dst = m_graph.varArgChild(node, targetIndex++);
                    std::swap(dst, edge);
                }
                node->children.setNumChildren(targetIndex);
                break;
            }

            case MakeRope: {
                for (unsigned i = 0; i < AdjacencyList::Size; ++i) {
                    Edge& edge = node->children.child(i);
                    if (!edge)
                        break;
                    JSValue childConstant = m_state.forNode(edge).value();
                    if (!childConstant)
                        continue;
                    if (!childConstant.isString())
                        continue;
                    if (asString(childConstant)->length())
                        continue;

                    // Don't allow the MakeRope to have zero children.
                    if (!i && !node->child2())
                        break;

                    node->children.removeEdge(i--);
                    changed = true;
                }

                if (!node->child2()) {
                    ASSERT(!node->child3());
                    node->convertToIdentity();
                    changed = true;
                }
                break;
            }
                
            case PhantomNewObject:
            case PhantomNewFunction:
            case PhantomNewGeneratorFunction:
            case PhantomNewAsyncGeneratorFunction:
            case PhantomNewAsyncFunction:
            case PhantomCreateActivation:
            case PhantomDirectArguments:
            case PhantomClonedArguments:
            case PhantomCreateRest:
            case PhantomSpread:
            case PhantomNewArrayWithSpread:
            case PhantomNewArrayBuffer:
            case PhantomNewRegexp:
            case BottomValue:
                alreadyHandled = true;
                break;

            default:
                break;
            }
            
            if (eliminated) {
                changed = true;
                continue;
            }
                
            if (alreadyHandled)
                continue;
            
            m_interpreter.execute(indexInBlock);
            if (!m_state.isValid()) {
                // If we invalidated then we shouldn't attempt to constant-fold. Here's an
                // example:
                //
                //     c: JSConstant(4.2)
                //     x: ValueToInt32(Check:Int32:@const)
                //
                // It would be correct for an analysis to assume that execution cannot
                // proceed past @x. Therefore, constant-folding @x could be rather bad. But,
                // the CFA may report that it found a constant even though it also reported
                // that everything has been invalidated. This will only happen in a couple of
                // the constant folding cases; most of them are also separately defensive
                // about such things.
                break;
            }
            if (!node->shouldGenerate() || m_state.didClobber() || node->hasConstant())
                continue;
            
            // Interesting fact: this freezing that we do right here may turn an fragile value into
            // a weak value. See DFGValueStrength.h.
            FrozenValue* value = m_graph.freeze(m_state.forNode(node).value());
            if (!*value)
                continue;
            
            if (node->op() == GetLocal) {
                // Need to preserve bytecode liveness in ThreadedCPS form. This wouldn't be necessary
                // if it wasn't for https://bugs.webkit.org/show_bug.cgi?id=144086.
                m_insertionSet.insertNode(
                    indexInBlock, SpecNone, PhantomLocal, node->origin,
                    OpInfo(node->variableAccessData()));
                m_graph.dethread();
            } else
                m_insertionSet.insertCheck(m_graph, indexInBlock, node);
            m_graph.convertToConstant(node, value);
            
            changed = true;
        }
        m_state.reset();
        m_insertionSet.execute(block);
        
        return changed;
    }
    
    void emitGetByOffset(unsigned indexInBlock, Node* node, const AbstractValue& baseValue, const MultiGetByOffsetCase& getCase, unsigned identifierNumber)
    {
        // When we get to here we have already emitted all of the requisite checks for everything.
        // So, we just need to emit what the method object tells us to emit.
        
        addBaseCheck(indexInBlock, node, baseValue, getCase.set());

        GetByOffsetMethod method = getCase.method();
        
        switch (method.kind()) {
        case GetByOffsetMethod::Invalid:
            RELEASE_ASSERT_NOT_REACHED();
            return;
            
        case GetByOffsetMethod::Constant:
            m_graph.convertToConstant(node, method.constant());
            return;
            
        case GetByOffsetMethod::Load:
            emitGetByOffset(indexInBlock, node, node->child1(), identifierNumber, method.offset());
            return;
            
        case GetByOffsetMethod::LoadFromPrototype: {
            Node* child = m_insertionSet.insertConstant(
                indexInBlock, node->origin, method.prototype());
            emitGetByOffset(
                indexInBlock, node, Edge(child, KnownCellUse), identifierNumber, method.offset());
            return;
        } }
        
        RELEASE_ASSERT_NOT_REACHED();
    }
    
    void emitGetByOffset(unsigned indexInBlock, Node* node, const AbstractValue& baseValue, const GetByIdVariant& variant, unsigned identifierNumber)
    {
        Edge childEdge = node->child1();

        addBaseCheck(indexInBlock, node, baseValue, variant.structureSet());
        
        // We aren't set up to handle prototype stuff.
        DFG_ASSERT(m_graph, node, variant.conditionSet().isEmpty());

        if (JSValue value = m_graph.tryGetConstantProperty(baseValue.m_value, *m_graph.addStructureSet(variant.structureSet()), variant.offset())) {
            m_graph.convertToConstant(node, m_graph.freeze(value));
            return;
        }
        
        emitGetByOffset(indexInBlock, node, childEdge, identifierNumber, variant.offset());
    }
    
    void emitGetByOffset(
        unsigned indexInBlock, Node* node, Edge childEdge, unsigned identifierNumber,
        PropertyOffset offset, const InferredType::Descriptor& inferredType = InferredType::Top)
    {
        childEdge.setUseKind(KnownCellUse);
        
        Edge propertyStorage;
        
        if (isInlineOffset(offset))
            propertyStorage = childEdge;
        else {
            propertyStorage = Edge(m_insertionSet.insertNode(
                indexInBlock, SpecNone, GetButterfly, node->origin, childEdge));
        }
        
        StorageAccessData& data = *m_graph.m_storageAccessData.add();
        data.offset = offset;
        data.identifierNumber = identifierNumber;
        data.inferredType = inferredType;
        
        node->convertToGetByOffset(data, propertyStorage, childEdge);
    }

    void emitPutByOffset(unsigned indexInBlock, Node* node, const AbstractValue& baseValue, const PutByIdVariant& variant, unsigned identifierNumber)
    {
        NodeOrigin origin = node->origin;
        Edge childEdge = node->child1();

        addBaseCheck(indexInBlock, node, baseValue, variant.oldStructure());
        insertInferredTypeCheck(
            m_insertionSet, indexInBlock, origin, node->child2().node(), variant.requiredType());

        node->child1().setUseKind(KnownCellUse);
        childEdge.setUseKind(KnownCellUse);

        Transition* transition = 0;
        if (variant.kind() == PutByIdVariant::Transition) {
            transition = m_graph.m_transitions.add(
                m_graph.registerStructure(variant.oldStructureForTransition()), m_graph.registerStructure(variant.newStructure()));
        }

        Edge propertyStorage;

        DFG_ASSERT(m_graph, node, origin.exitOK);
        bool canExit = true;
        bool didAllocateStorage = false;

        if (isInlineOffset(variant.offset()))
            propertyStorage = childEdge;
        else if (!variant.reallocatesStorage()) {
            propertyStorage = Edge(m_insertionSet.insertNode(
                indexInBlock, SpecNone, GetButterfly, origin, childEdge));
        } else if (!variant.oldStructureForTransition()->outOfLineCapacity()) {
            ASSERT(variant.newStructure()->outOfLineCapacity());
            ASSERT(!isInlineOffset(variant.offset()));
            Node* allocatePropertyStorage = m_insertionSet.insertNode(
                indexInBlock, SpecNone, AllocatePropertyStorage,
                origin, OpInfo(transition), childEdge);
            propertyStorage = Edge(allocatePropertyStorage);
            didAllocateStorage = true;
        } else {
            ASSERT(variant.oldStructureForTransition()->outOfLineCapacity());
            ASSERT(variant.newStructure()->outOfLineCapacity() > variant.oldStructureForTransition()->outOfLineCapacity());
            ASSERT(!isInlineOffset(variant.offset()));

            Node* reallocatePropertyStorage = m_insertionSet.insertNode(
                indexInBlock, SpecNone, ReallocatePropertyStorage, origin,
                OpInfo(transition), childEdge,
                Edge(m_insertionSet.insertNode(
                    indexInBlock, SpecNone, GetButterfly, origin, childEdge)));
            propertyStorage = Edge(reallocatePropertyStorage);
            didAllocateStorage = true;
        }

        StorageAccessData& data = *m_graph.m_storageAccessData.add();
        data.offset = variant.offset();
        data.identifierNumber = identifierNumber;
        
        node->convertToPutByOffset(data, propertyStorage, childEdge);
        node->origin.exitOK = canExit;

        if (variant.kind() == PutByIdVariant::Transition) {
            if (didAllocateStorage) {
                m_insertionSet.insertNode(
                    indexInBlock + 1, SpecNone, NukeStructureAndSetButterfly,
                    origin.withInvalidExit(), childEdge, propertyStorage);
            }
            
            // FIXME: PutStructure goes last until we fix either
            // https://bugs.webkit.org/show_bug.cgi?id=142921 or
            // https://bugs.webkit.org/show_bug.cgi?id=142924.
            m_insertionSet.insertNode(
                indexInBlock + 1, SpecNone, PutStructure, origin.withInvalidExit(), OpInfo(transition),
                childEdge);
        }
    }
    
    void addBaseCheck(
        unsigned indexInBlock, Node* node, const AbstractValue& baseValue, const StructureSet& set)
    {
        addBaseCheck(indexInBlock, node, baseValue, *m_graph.addStructureSet(set));
    }

    void addBaseCheck(
        unsigned indexInBlock, Node* node, const AbstractValue& baseValue, const RegisteredStructureSet& set)
    {
        if (!baseValue.m_structure.isSubsetOf(set)) {
            // Arises when we prune MultiGetByOffset. We could have a
            // MultiGetByOffset with a single variant that checks for structure S,
            // and the input has structures S and T, for example.
            ASSERT(node->child1());
            m_insertionSet.insertNode(
                indexInBlock, SpecNone, CheckStructure, node->origin,
                OpInfo(m_graph.addStructureSet(set.toStructureSet())), node->child1());
            return;
        }
        
        if (baseValue.m_type & ~SpecCell)
            m_insertionSet.insertCheck(indexInBlock, node->origin, node->child1());
    }
    
    void addStructureTransitionCheck(NodeOrigin origin, unsigned indexInBlock, JSCell* cell, Structure* structure)
    {
        {
            StructureRegistrationResult result;
            m_graph.registerStructure(cell->structure(), result);
            if (result == StructureRegisteredAndWatched)
                return;
        }
        
        m_graph.registerStructure(structure);

        Node* weakConstant = m_insertionSet.insertNode(
            indexInBlock, speculationFromValue(cell), JSConstant, origin,
            OpInfo(m_graph.freeze(cell)));
        
        m_insertionSet.insertNode(
            indexInBlock, SpecNone, CheckStructure, origin,
            OpInfo(m_graph.addStructureSet(structure)), Edge(weakConstant, CellUse));
    }
    
    void fixUpsilons(BasicBlock* block)
    {
        for (unsigned nodeIndex = block->size(); nodeIndex--;) {
            Node* node = block->at(nodeIndex);
            if (node->op() != Upsilon)
                continue;
            switch (node->phi()->op()) {
            case Phi:
                break;
            case JSConstant:
            case DoubleConstant:
            case Int52Constant:
                node->remove(m_graph);
                break;
            default:
                DFG_CRASH(m_graph, node, "Bad Upsilon phi() pointer");
                break;
            }
        }
    }
    
    InPlaceAbstractState m_state;
    AbstractInterpreter<InPlaceAbstractState> m_interpreter;
    InsertionSet m_insertionSet;
};

bool performConstantFolding(Graph& graph)
{
    return runPhase<ConstantFoldingPhase>(graph);
}

} } // namespace JSC::DFG

#endif // ENABLE(DFG_JIT)