/*
 * Copyright (C) 2013-2018 Apple Inc. All rights reserved.
 * Copyright (C) 2014 Yusuke Suzuki <utatane.tea@gmail.com>
 *
 * 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. AND ITS CONTRIBUTORS ``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 ITS 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 "SelectorCompiler.h"

#if ENABLE(CSS_SELECTOR_JIT)

#include "CSSSelector.h"
#include "CSSSelectorList.h"
#include "DOMJITHelpers.h"
#include "Element.h"
#include "ElementData.h"
#include "ElementRareData.h"
#include "FunctionCall.h"
#include "HTMLDocument.h"
#include "HTMLNames.h"
#include "HTMLParserIdioms.h"
#include "InspectorInstrumentation.h"
#include "NodeRenderStyle.h"
#include "QualifiedName.h"
#include "RegisterAllocator.h"
#include "RenderElement.h"
#include "RenderStyle.h"
#include "SVGElement.h"
#include "SelectorCheckerTestFunctions.h"
#include "StackAllocator.h"
#include "StyleRelations.h"
#include "StyledElement.h"
#include <JavaScriptCore/GPRInfo.h>
#include <JavaScriptCore/LinkBuffer.h>
#include <JavaScriptCore/MacroAssembler.h>
#include <JavaScriptCore/VM.h>
#include <limits>
#include <wtf/Deque.h>
#include <wtf/HashMap.h>
#include <wtf/HashSet.h>
#include <wtf/Vector.h>
#include <wtf/text/CString.h>

namespace WebCore {
namespace SelectorCompiler {

#define CSS_SELECTOR_JIT_DEBUGGING 0

enum class BacktrackingAction {
    NoBacktracking,
    JumpToDescendantEntryPoint,
    JumpToIndirectAdjacentEntryPoint,
    JumpToDescendantTreeWalkerEntryPoint,
    JumpToIndirectAdjacentTreeWalkerEntryPoint,
    JumpToDescendantTail,
    JumpToDirectAdjacentTail
};

struct BacktrackingFlag {
    enum {
        DescendantEntryPoint = 1,
        IndirectAdjacentEntryPoint = 1 << 1,
        SaveDescendantBacktrackingStart = 1 << 2,
        SaveAdjacentBacktrackingStart = 1 << 3,
        DirectAdjacentTail = 1 << 4,
        DescendantTail = 1 << 5,
        InChainWithDescendantTail = 1 << 6,
        InChainWithAdjacentTail = 1 << 7
    };
};

enum class FragmentRelation {
    Rightmost,
    Descendant,
    Child,
    DirectAdjacent,
    IndirectAdjacent
};

enum class FunctionType {
    SimpleSelectorChecker,
    SelectorCheckerWithCheckingContext,
    CannotMatchAnything,
    CannotCompile
};

enum class FragmentPositionInRootFragments {
    Rightmost,
    AdjacentToRightmost,
    Other
};

enum class VisitedMode {
    None,
    Visited
};

enum class AttributeCaseSensitivity {
    CaseSensitive,
    // Some values are matched case-insensitively for HTML elements.
    // That is a legacy behavior decided by HTMLDocument::isCaseSensitiveAttribute().
    HTMLLegacyCaseInsensitive,
    CaseInsensitive
};

static AttributeCaseSensitivity attributeSelectorCaseSensitivity(const CSSSelector& selector)
{
    ASSERT(selector.isAttributeSelector());

    // This is by convention, the case is irrelevant for Set.
    if (selector.match() == CSSSelector::Set)
        return AttributeCaseSensitivity::CaseSensitive;

    if (selector.attributeValueMatchingIsCaseInsensitive())
        return AttributeCaseSensitivity::CaseInsensitive;
    if (HTMLDocument::isCaseSensitiveAttribute(selector.attribute()))
        return AttributeCaseSensitivity::CaseSensitive;
    return AttributeCaseSensitivity::HTMLLegacyCaseInsensitive;
}

class AttributeMatchingInfo {
public:
    explicit AttributeMatchingInfo(const CSSSelector& selector)
        : m_selector(&selector)
        , m_attributeCaseSensitivity(attributeSelectorCaseSensitivity(selector))
    {
        ASSERT(!(m_attributeCaseSensitivity == AttributeCaseSensitivity::CaseInsensitive && !selector.attributeValueMatchingIsCaseInsensitive()));
        ASSERT(!(selector.match() == CSSSelector::Set && m_attributeCaseSensitivity != AttributeCaseSensitivity::CaseSensitive));
    }

    AttributeCaseSensitivity attributeCaseSensitivity() const { return m_attributeCaseSensitivity; }
    const CSSSelector& selector() const { return *m_selector; }

private:
    const CSSSelector* m_selector;
    AttributeCaseSensitivity m_attributeCaseSensitivity;
};

static const unsigned invalidHeight = std::numeric_limits<unsigned>::max();
static const unsigned invalidWidth = std::numeric_limits<unsigned>::max();

struct SelectorFragment;
class SelectorFragmentList;

class SelectorList : public Vector<SelectorFragmentList> {
public:
    unsigned registerRequirements = std::numeric_limits<unsigned>::max();
    unsigned stackRequirements = std::numeric_limits<unsigned>::max();
    bool clobberElementAddressRegister = true;
};

struct NthChildOfSelectorInfo {
    int a;
    int b;
    SelectorList selectorList;
};

struct SelectorFragment {
    FragmentRelation relationToLeftFragment;
    FragmentRelation relationToRightFragment;
    FragmentPositionInRootFragments positionInRootFragments;
    bool isRightmostOrAdjacent { false };

    BacktrackingAction traversalBacktrackingAction = BacktrackingAction::NoBacktracking;
    BacktrackingAction matchingTagNameBacktrackingAction = BacktrackingAction::NoBacktracking;
    BacktrackingAction matchingPostTagNameBacktrackingAction = BacktrackingAction::NoBacktracking;
    unsigned char backtrackingFlags = 0;
    unsigned tagNameMatchedBacktrackingStartHeightFromDescendant = invalidHeight;
    unsigned tagNameNotMatchedBacktrackingStartHeightFromDescendant = invalidHeight;
    unsigned heightFromDescendant = 0;
    unsigned tagNameMatchedBacktrackingStartWidthFromIndirectAdjacent = invalidWidth;
    unsigned tagNameNotMatchedBacktrackingStartWidthFromIndirectAdjacent = invalidWidth;
    unsigned widthFromIndirectAdjacent = 0;

    FunctionType appendUnoptimizedPseudoClassWithContext(bool (*matcher)(const SelectorChecker::CheckingContext&));

    // FIXME: the large stack allocation caused by the inline capacity causes memory inefficiency. We should dump
    // the min/max/average of the vectors and pick better inline capacity.
    const CSSSelector* tagNameSelector = nullptr;
    const AtomicString* id = nullptr;
    Vector<const Vector<AtomicString>*> languageArgumentsList;
    Vector<const AtomicStringImpl*, 8> classNames;
    HashSet<unsigned> pseudoClasses;
    Vector<JSC::FunctionPtr<CSSOperationPtrTag>, 4> unoptimizedPseudoClasses;
    Vector<JSC::FunctionPtr<CSSOperationPtrTag>, 4> unoptimizedPseudoClassesWithContext;
    Vector<AttributeMatchingInfo, 4> attributes;
    Vector<std::pair<int, int>, 2> nthChildFilters;
    Vector<NthChildOfSelectorInfo> nthChildOfFilters;
    Vector<std::pair<int, int>, 2> nthLastChildFilters;
    Vector<NthChildOfSelectorInfo> nthLastChildOfFilters;
    SelectorList notFilters;
    Vector<SelectorList> matchesFilters;
    Vector<Vector<SelectorFragment>> anyFilters;
    const CSSSelector* pseudoElementSelector = nullptr;

    // For quirks mode, follow this: http://quirks.spec.whatwg.org/#the-:active-and-:hover-quirk
    // In quirks mode, a compound selector 'selector' that matches the following conditions must not match elements that would not also match the ':any-link' selector.
    //
    //    selector uses the ':active' or ':hover' pseudo-classes.
    //    selector does not use a type selector.
    //    selector does not use an attribute selector.
    //    selector does not use an ID selector.
    //    selector does not use a class selector.
    //    selector does not use a pseudo-class selector other than ':active' and ':hover'.
    //    selector does not use a pseudo-element selector.
    //    selector is not part of an argument to a functional pseudo-class or pseudo-element.
    bool onlyMatchesLinksInQuirksMode = true;
};

class SelectorFragmentList : public Vector<SelectorFragment, 4> {
public:
    unsigned registerRequirements = std::numeric_limits<unsigned>::max();
    unsigned stackRequirements = std::numeric_limits<unsigned>::max();
    unsigned staticSpecificity = 0;
    bool clobberElementAddressRegister = true;
};

struct TagNamePattern {
    const CSSSelector* tagNameSelector = nullptr;
    bool inverted = false;
};

typedef JSC::MacroAssembler Assembler;
typedef Vector<TagNamePattern, 32> TagNameList;

struct BacktrackingLevel {
    Assembler::Label descendantEntryPoint;
    Assembler::Label indirectAdjacentEntryPoint;
    Assembler::Label descendantTreeWalkerBacktrackingPoint;
    Assembler::Label indirectAdjacentTreeWalkerBacktrackingPoint;

    StackAllocator::StackReference descendantBacktrackingStart;
    Assembler::JumpList descendantBacktrackingFailureCases;
    StackAllocator::StackReference adjacentBacktrackingStart;
    Assembler::JumpList adjacentBacktrackingFailureCases;
};

class SelectorCodeGenerator {
public:
    SelectorCodeGenerator(const CSSSelector*, SelectorContext);
    SelectorCompilationStatus compile(JSC::MacroAssemblerCodeRef<CSSSelectorPtrTag>&);

private:
    static const Assembler::RegisterID returnRegister;
    static const Assembler::RegisterID elementAddressRegister;
    static const Assembler::RegisterID checkingContextRegister;
    static const Assembler::RegisterID callFrameRegister;

    void generateSelectorChecker();
    void generateSelectorCheckerExcludingPseudoElements(Assembler::JumpList& failureCases, const SelectorFragmentList&);
    void generateElementMatchesSelectorList(Assembler::JumpList& failureCases, Assembler::RegisterID elementToMatch, const SelectorList&);

    // Element relations tree walker.
    void generateRightmostTreeWalker(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateWalkToParentNode(Assembler::RegisterID targetRegister);
    void generateWalkToParentElement(Assembler::JumpList& failureCases, Assembler::RegisterID targetRegister);
    void generateWalkToParentElementOrShadowRoot(Assembler::JumpList& failureCases, Assembler::RegisterID targetRegister);
    void generateParentElementTreeWalker(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateAncestorTreeWalker(Assembler::JumpList& failureCases, const SelectorFragment&);

    void generateWalkToNextAdjacentElement(Assembler::JumpList& failureCases, Assembler::RegisterID);
    void generateWalkToPreviousAdjacentElement(Assembler::JumpList& failureCases, Assembler::RegisterID);
    void generateWalkToPreviousAdjacent(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateDirectAdjacentTreeWalker(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateIndirectAdjacentTreeWalker(Assembler::JumpList& failureCases, const SelectorFragment&);

    void linkFailures(Assembler::JumpList& globalFailureCases, BacktrackingAction, Assembler::JumpList& localFailureCases);
    void generateAdjacentBacktrackingTail();
    void generateDescendantBacktrackingTail();
    void generateBacktrackingTailsIfNeeded(Assembler::JumpList& failureCases, const SelectorFragment&);

    // Element properties matchers.
    void generateElementMatching(Assembler::JumpList& matchingTagNameFailureCases, Assembler::JumpList& matchingPostTagNameFailureCases, const SelectorFragment&);
    void generateElementDataMatching(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementLinkMatching(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementFunctionCallTest(Assembler::JumpList& failureCases, JSC::FunctionPtr<CSSOperationPtrTag>);
    void generateContextFunctionCallTest(Assembler::JumpList& failureCases, JSC::FunctionPtr<CSSOperationPtrTag>);
    void generateElementIsActive(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementIsEmpty(Assembler::JumpList& failureCases);
    void generateElementIsFirstChild(Assembler::JumpList& failureCases);
    void generateElementIsHovered(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementIsInLanguage(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementIsInLanguage(Assembler::JumpList& failureCases, const Vector<AtomicString>*);
    void generateElementIsLastChild(Assembler::JumpList& failureCases);
    void generateElementIsOnlyChild(Assembler::JumpList& failureCases);
    void generateElementHasPlaceholderShown(Assembler::JumpList& failureCases);
    void generateSynchronizeStyleAttribute(Assembler::RegisterID elementDataArraySizeAndFlags);
    void generateSynchronizeAllAnimatedSVGAttribute(Assembler::RegisterID elementDataArraySizeAndFlags);
    void generateElementAttributesMatching(Assembler::JumpList& failureCases, const LocalRegister& elementDataAddress, const SelectorFragment&);
    void generateElementAttributeMatching(Assembler::JumpList& failureCases, Assembler::RegisterID currentAttributeAddress, Assembler::RegisterID decIndexRegister, const AttributeMatchingInfo& attributeInfo);
    void generateElementAttributeValueMatching(Assembler::JumpList& failureCases, Assembler::RegisterID currentAttributeAddress, const AttributeMatchingInfo& attributeInfo);
    void generateElementAttributeValueExactMatching(Assembler::JumpList& failureCases, Assembler::RegisterID currentAttributeAddress, const AtomicString& expectedValue, AttributeCaseSensitivity valueCaseSensitivity);
    void generateElementAttributeFunctionCallValueMatching(Assembler::JumpList& failureCases, Assembler::RegisterID currentAttributeAddress, const AtomicString& expectedValue, AttributeCaseSensitivity valueCaseSensitivity, JSC::FunctionPtr<CSSOperationPtrTag> caseSensitiveTest, JSC::FunctionPtr<CSSOperationPtrTag> caseInsensitiveTest);
    void generateElementHasTagName(Assembler::JumpList& failureCases, const CSSSelector& tagMatchingSelector);
    void generateElementHasId(Assembler::JumpList& failureCases, const LocalRegister& elementDataAddress, const AtomicString& idToMatch);
    void generateElementHasClasses(Assembler::JumpList& failureCases, const LocalRegister& elementDataAddress, const Vector<const AtomicStringImpl*, 8>& classNames);
    void generateElementIsLink(Assembler::JumpList& failureCases);
    void generateElementIsNthChild(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementIsNthChildOf(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementIsNthLastChild(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementIsNthLastChildOf(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementMatchesNotPseudoClass(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementMatchesAnyPseudoClass(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementMatchesMatchesPseudoClass(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementHasPseudoElement(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateElementIsRoot(Assembler::JumpList& failureCases);
    void generateElementIsScopeRoot(Assembler::JumpList& failureCases);
    void generateElementIsTarget(Assembler::JumpList& failureCases);
    void generateElementHasFocusWithin(Assembler::JumpList& failureCases);

    // Helpers.
    void generateAddStyleRelationIfResolvingStyle(Assembler::RegisterID element, Style::Relation::Type, Optional<Assembler::RegisterID> value = { });
    void generateAddStyleRelation(Assembler::RegisterID checkingContext, Assembler::RegisterID element, Style::Relation::Type, Optional<Assembler::RegisterID> value = { });
    Assembler::Jump branchOnResolvingModeWithCheckingContext(Assembler::RelationalCondition, SelectorChecker::Mode, Assembler::RegisterID checkingContext);
    Assembler::Jump branchOnResolvingMode(Assembler::RelationalCondition, SelectorChecker::Mode, Assembler::RegisterID checkingContext);
    void generateElementIsFirstLink(Assembler::JumpList& failureCases, Assembler::RegisterID element);
    void generateStoreLastVisitedElement(Assembler::RegisterID element);
    void generateMarkPseudoStyleForPseudoElement(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateNthFilterTest(Assembler::JumpList& failureCases, Assembler::RegisterID counter, int a, int b);
    void generateRequestedPseudoElementEqualsToSelectorPseudoElement(Assembler::JumpList& failureCases, const SelectorFragment&, Assembler::RegisterID checkingContext);
    void generateSpecialFailureInQuirksModeForActiveAndHoverIfNeeded(Assembler::JumpList& failureCases, const SelectorFragment&);
    Assembler::JumpList jumpIfNoPreviousAdjacentElement();
    Assembler::JumpList jumpIfNoNextAdjacentElement();
    Assembler::Jump jumpIfNotResolvingStyle(Assembler::RegisterID checkingContextRegister);
    void loadCheckingContext(Assembler::RegisterID checkingContext);
    Assembler::Jump modulo(JSC::MacroAssembler::ResultCondition, Assembler::RegisterID inputDividend, int divisor);
    void moduloIsZero(Assembler::JumpList& failureCases, Assembler::RegisterID inputDividend, int divisor);

    void generateNthChildParentCheckAndRelationUpdate(Assembler::JumpList& failureCases, const SelectorFragment&);
    void generateNthLastChildParentCheckAndRelationUpdate(Assembler::JumpList& failureCases, const SelectorFragment&);

    void pushMacroAssemblerRegisters();
    void popMacroAssemblerRegisters(StackAllocator&);
    bool generatePrologue();
    void generateEpilogue(StackAllocator&);
    StackAllocator::StackReferenceVector m_macroAssemblerRegistersStackReferences;
    StackAllocator::StackReferenceVector m_prologueStackReferences;

    Assembler m_assembler;
    RegisterAllocator m_registerAllocator;
    StackAllocator m_stackAllocator;
    Vector<std::pair<Assembler::Call, JSC::FunctionPtr<CSSOperationPtrTag>>, 32> m_functionCalls;

    SelectorContext m_selectorContext;
    FunctionType m_functionType;
    SelectorFragmentList m_selectorFragments;
    VisitedMode m_visitedMode;

    StackAllocator::StackReference m_checkingContextStackReference;

    bool m_descendantBacktrackingStartInUse;
    Assembler::RegisterID m_descendantBacktrackingStart;
    StackAllocator::StackReferenceVector m_backtrackingStack;
    Deque<BacktrackingLevel, 32> m_backtrackingLevels;
    StackAllocator::StackReference m_lastVisitedElement;
    StackAllocator::StackReference m_startElement;

#if CSS_SELECTOR_JIT_DEBUGGING
    const CSSSelector* m_originalSelector;
#endif
};

const Assembler::RegisterID SelectorCodeGenerator::returnRegister = JSC::GPRInfo::returnValueGPR;
const Assembler::RegisterID SelectorCodeGenerator::elementAddressRegister = JSC::GPRInfo::argumentGPR0;
const Assembler::RegisterID SelectorCodeGenerator::checkingContextRegister = JSC::GPRInfo::argumentGPR1;
const Assembler::RegisterID SelectorCodeGenerator::callFrameRegister = JSC::GPRInfo::callFrameRegister;

enum class FragmentsLevel {
    Root = 0,
    InFunctionalPseudoType = 1
};

enum class PseudoElementMatchingBehavior { CanMatch, NeverMatch };

static FunctionType constructFragments(const CSSSelector* rootSelector, SelectorContext, SelectorFragmentList& selectorFragments, FragmentsLevel, FragmentPositionInRootFragments, bool visitedMatchEnabled, VisitedMode&, PseudoElementMatchingBehavior);

static void computeBacktrackingInformation(SelectorFragmentList& selectorFragments, unsigned level = 0);

SelectorCompilationStatus compileSelector(const CSSSelector* lastSelector, SelectorContext selectorContext, JSC::MacroAssemblerCodeRef<CSSSelectorPtrTag>& codeRef)
{
    if (!JSC::VM::canUseJIT())
        return SelectorCompilationStatus::CannotCompile;
    SelectorCodeGenerator codeGenerator(lastSelector, selectorContext);
    return codeGenerator.compile(codeRef);
}

static inline FragmentRelation fragmentRelationForSelectorRelation(CSSSelector::RelationType relation)
{
    switch (relation) {
    case CSSSelector::DescendantSpace:
        return FragmentRelation::Descendant;
    case CSSSelector::Child:
        return FragmentRelation::Child;
    case CSSSelector::DirectAdjacent:
        return FragmentRelation::DirectAdjacent;
    case CSSSelector::IndirectAdjacent:
        return FragmentRelation::IndirectAdjacent;
    case CSSSelector::Subselector:
    case CSSSelector::ShadowDescendant:
        ASSERT_NOT_REACHED();
    }
    ASSERT_NOT_REACHED();
    return FragmentRelation::Descendant;
}

static inline FunctionType mostRestrictiveFunctionType(FunctionType a, FunctionType b)
{
    return std::max(a, b);
}

static inline bool fragmentMatchesTheRightmostElement(const SelectorFragment& fragment)
{
    return fragment.relationToRightFragment == FragmentRelation::Rightmost && fragment.positionInRootFragments == FragmentPositionInRootFragments::Rightmost;
}

static inline bool fragmentMatchesRightmostOrAdjacentElement(const SelectorFragment& fragment)
{
    return fragment.isRightmostOrAdjacent && fragment.positionInRootFragments != FragmentPositionInRootFragments::Other;
}

FunctionType SelectorFragment::appendUnoptimizedPseudoClassWithContext(bool (*matcher)(const SelectorChecker::CheckingContext&))
{
    unoptimizedPseudoClassesWithContext.append(JSC::FunctionPtr<CSSOperationPtrTag>(matcher));
    return FunctionType::SelectorCheckerWithCheckingContext;
}

static inline FunctionType addScrollbarPseudoClassType(const CSSSelector&, SelectorFragment&)
{
    // FIXME: scrollbar pseudoclass interaction with :not doesn't behave correctly.
    // Compile them when they are fixed and tested.
    // https://bugs.webkit.org/show_bug.cgi?id=146221
    return FunctionType::CannotCompile;
}

// Handle the forward :nth-child() and backward :nth-last-child().
static FunctionType addNthChildType(const CSSSelector& selector, SelectorContext selectorContext, FragmentPositionInRootFragments positionInRootFragments, CSSSelector::PseudoClassType firstMatchAlternative, bool visitedMatchEnabled, Vector<std::pair<int, int>, 2>& simpleCases, Vector<NthChildOfSelectorInfo>& filteredCases, HashSet<unsigned>& pseudoClasses, unsigned& internalSpecificity)
{
    int a = selector.nthA();
    int b = selector.nthB();

    // The element count is always positive.
    if (a <= 0 && b < 1)
        return FunctionType::CannotMatchAnything;

    if (const CSSSelectorList* selectorList = selector.selectorList()) {
        NthChildOfSelectorInfo nthChildOfSelectorInfo;
        nthChildOfSelectorInfo.a = a;
        nthChildOfSelectorInfo.b = b;

        FunctionType globalFunctionType = FunctionType::SimpleSelectorChecker;
        if (selectorContext != SelectorContext::QuerySelector)
            globalFunctionType = FunctionType::SelectorCheckerWithCheckingContext;

        unsigned firstFragmentListSpecificity = 0;
        bool firstFragmentListSpecificitySet = false;

        SelectorFragmentList* selectorFragments = nullptr;
        for (const CSSSelector* subselector = selectorList->first(); subselector; subselector = CSSSelectorList::next(subselector)) {
            if (!selectorFragments) {
                nthChildOfSelectorInfo.selectorList.append(SelectorFragmentList());
                selectorFragments = &nthChildOfSelectorInfo.selectorList.last();
            }

            VisitedMode ignoreVisitedMode = VisitedMode::None;
            FunctionType functionType = constructFragments(subselector, selectorContext, *selectorFragments, FragmentsLevel::InFunctionalPseudoType, positionInRootFragments, visitedMatchEnabled, ignoreVisitedMode, PseudoElementMatchingBehavior::NeverMatch);
            ASSERT_WITH_MESSAGE(ignoreVisitedMode == VisitedMode::None, ":visited is disabled in the functional pseudo classes");
            switch (functionType) {
            case FunctionType::SimpleSelectorChecker:
            case FunctionType::SelectorCheckerWithCheckingContext:
                break;
            case FunctionType::CannotMatchAnything:
                continue;
            case FunctionType::CannotCompile:
                return FunctionType::CannotCompile;
            }

            if (firstFragmentListSpecificitySet) {
                // The CSS JIT does not handle dynamic specificity yet.
                if (selectorContext == SelectorContext::RuleCollector && selectorFragments->staticSpecificity != firstFragmentListSpecificity)
                    return FunctionType::CannotCompile;
            } else {
                firstFragmentListSpecificitySet = true;
                firstFragmentListSpecificity = selectorFragments->staticSpecificity;
            }

            globalFunctionType = mostRestrictiveFunctionType(globalFunctionType, functionType);
            selectorFragments = nullptr;
        }

        // If there is still a SelectorFragmentList open, the last Fragment(s) cannot match anything,
        // we have one FragmentList too many in our selector list.
        if (selectorFragments)
            nthChildOfSelectorInfo.selectorList.removeLast();

        if (nthChildOfSelectorInfo.selectorList.isEmpty())
            return FunctionType::CannotMatchAnything;

        internalSpecificity = firstFragmentListSpecificity;
        filteredCases.append(nthChildOfSelectorInfo);
        return globalFunctionType;
    }

    if (b == 1 && a <= 0)
        pseudoClasses.add(firstMatchAlternative);
    else
        simpleCases.append(std::pair<int, int>(a, b));
    if (selectorContext == SelectorContext::QuerySelector)
        return FunctionType::SimpleSelectorChecker;
    return FunctionType::SelectorCheckerWithCheckingContext;
}

static inline FunctionType addPseudoClassType(const CSSSelector& selector, SelectorFragment& fragment, unsigned& internalSpecificity, SelectorContext selectorContext, FragmentsLevel fragmentLevel, FragmentPositionInRootFragments positionInRootFragments, bool visitedMatchEnabled, VisitedMode& visitedMode, PseudoElementMatchingBehavior pseudoElementMatchingBehavior)
{
    CSSSelector::PseudoClassType type = selector.pseudoClassType();
    switch (type) {
    // Unoptimized pseudo selector. They are just function call to a simple testing function.
    case CSSSelector::PseudoClassAutofill:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(isAutofilled));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassAutofillStrongPassword:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(isAutofilledStrongPassword));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassChecked:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(isChecked));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassDefault:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesDefaultPseudoClass));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassDisabled:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesDisabledPseudoClass));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassEnabled:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesEnabledPseudoClass));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassDefined:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(isDefinedElement));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassFocus:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(SelectorChecker::matchesFocusPseudoClass));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassFullPageMedia:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(isMediaDocument));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassInRange:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(isInRange));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassIndeterminate:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesIndeterminatePseudoClass));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassInvalid:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(isInvalid));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassOptional:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(isOptionalFormControl));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassOutOfRange:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(isOutOfRange));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassReadOnly:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesReadOnlyPseudoClass));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassReadWrite:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesReadWritePseudoClass));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassRequired:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(isRequiredFormControl));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassValid:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(isValid));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassWindowInactive:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(isWindowInactive));
        return FunctionType::SimpleSelectorChecker;

#if ENABLE(FULLSCREEN_API)
    case CSSSelector::PseudoClassFullScreen:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesFullScreenPseudoClass));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassFullScreenDocument:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesFullScreenDocumentPseudoClass));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassFullScreenAncestor:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesFullScreenAncestorPseudoClass));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassAnimatingFullScreenTransition:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesFullScreenAnimatingFullScreenTransitionPseudoClass));
        return FunctionType::SimpleSelectorChecker;

    case CSSSelector::PseudoClassFullScreenControlsHidden:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesFullScreenControlsHiddenPseudoClass));
        return FunctionType::SimpleSelectorChecker;
#endif
#if ENABLE(VIDEO_TRACK)
    case CSSSelector::PseudoClassFuture:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesFutureCuePseudoClass));
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassPast:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(matchesPastCuePseudoClass));
        return FunctionType::SimpleSelectorChecker;
#endif

#if ENABLE(ATTACHMENT_ELEMENT)
    case CSSSelector::PseudoClassHasAttachment:
        fragment.unoptimizedPseudoClasses.append(JSC::FunctionPtr<CSSOperationPtrTag>(hasAttachment));
        return FunctionType::SimpleSelectorChecker;
#endif

    // These pseudo-classes only have meaning with scrollbars.
    case CSSSelector::PseudoClassHorizontal:
    case CSSSelector::PseudoClassVertical:
    case CSSSelector::PseudoClassDecrement:
    case CSSSelector::PseudoClassIncrement:
    case CSSSelector::PseudoClassStart:
    case CSSSelector::PseudoClassEnd:
    case CSSSelector::PseudoClassDoubleButton:
    case CSSSelector::PseudoClassSingleButton:
    case CSSSelector::PseudoClassNoButton:
    case CSSSelector::PseudoClassCornerPresent:
        return FunctionType::CannotMatchAnything;

    // FIXME: Compile these pseudoclasses, too!
    case CSSSelector::PseudoClassFirstOfType:
    case CSSSelector::PseudoClassLastOfType:
    case CSSSelector::PseudoClassOnlyOfType:
    case CSSSelector::PseudoClassNthOfType:
    case CSSSelector::PseudoClassNthLastOfType:
    case CSSSelector::PseudoClassDrag:
#if ENABLE(CSS_SELECTORS_LEVEL4)
    case CSSSelector::PseudoClassDir:
    case CSSSelector::PseudoClassRole:
#endif
        return FunctionType::CannotCompile;

    // Optimized pseudo selectors.
    case CSSSelector::PseudoClassAnyLink:
    case CSSSelector::PseudoClassLink:
    case CSSSelector::PseudoClassRoot:
    case CSSSelector::PseudoClassTarget:
        fragment.pseudoClasses.add(type);
        return FunctionType::SimpleSelectorChecker;
    case CSSSelector::PseudoClassAnyLinkDeprecated:
        fragment.pseudoClasses.add(CSSSelector::PseudoClassAnyLink);
        return FunctionType::SimpleSelectorChecker;

    case CSSSelector::PseudoClassVisited:
        // Determine this :visited cannot match anything statically.
        if (!visitedMatchEnabled)
            return FunctionType::CannotMatchAnything;

        // Inside functional pseudo class except for :not, :visited never matches.
        // And in the case inside :not, returning CannotMatchAnything indicates that :not(:visited) can match over anything.
        if (fragmentLevel == FragmentsLevel::InFunctionalPseudoType)
            return FunctionType::CannotMatchAnything;

        fragment.pseudoClasses.add(type);
        visitedMode = VisitedMode::Visited;
        return FunctionType::SimpleSelectorChecker;

    case CSSSelector::PseudoClassScope:
        if (selectorContext != SelectorContext::QuerySelector) {
            fragment.pseudoClasses.add(CSSSelector::PseudoClassRoot);
            return FunctionType::SimpleSelectorChecker;
        }
        fragment.pseudoClasses.add(CSSSelector::PseudoClassScope);
        return FunctionType::SelectorCheckerWithCheckingContext;

    case CSSSelector::PseudoClassActive:
    case CSSSelector::PseudoClassEmpty:
    case CSSSelector::PseudoClassFirstChild:
    case CSSSelector::PseudoClassHover:
    case CSSSelector::PseudoClassLastChild:
    case CSSSelector::PseudoClassOnlyChild:
    case CSSSelector::PseudoClassPlaceholderShown:
    case CSSSelector::PseudoClassFocusWithin:
        fragment.pseudoClasses.add(type);
        if (selectorContext == SelectorContext::QuerySelector)
            return FunctionType::SimpleSelectorChecker;
        return FunctionType::SelectorCheckerWithCheckingContext;

    case CSSSelector::PseudoClassNthChild:
        return addNthChildType(selector, selectorContext, positionInRootFragments, CSSSelector::PseudoClassFirstChild, visitedMatchEnabled, fragment.nthChildFilters, fragment.nthChildOfFilters, fragment.pseudoClasses, internalSpecificity);

    case CSSSelector::PseudoClassNthLastChild:
        return addNthChildType(selector, selectorContext, positionInRootFragments, CSSSelector::PseudoClassLastChild, visitedMatchEnabled, fragment.nthLastChildFilters, fragment.nthLastChildOfFilters, fragment.pseudoClasses, internalSpecificity);

    case CSSSelector::PseudoClassNot:
        {
            const CSSSelectorList* selectorList = selector.selectorList();

            ASSERT_WITH_MESSAGE(selectorList, "The CSS Parser should never produce valid :not() CSSSelector with an empty selectorList.");
            if (!selectorList)
                return FunctionType::CannotMatchAnything;

            FunctionType functionType = FunctionType::SimpleSelectorChecker;
            SelectorFragmentList* selectorFragments = nullptr;
            for (const CSSSelector* subselector = selectorList->first(); subselector; subselector = CSSSelectorList::next(subselector)) {
                if (!selectorFragments) {
                    fragment.notFilters.append(SelectorFragmentList());
                    selectorFragments = &fragment.notFilters.last();
                }

                VisitedMode ignoreVisitedMode = VisitedMode::None;
                FunctionType localFunctionType = constructFragments(subselector, selectorContext, *selectorFragments, FragmentsLevel::InFunctionalPseudoType, positionInRootFragments, visitedMatchEnabled, ignoreVisitedMode, PseudoElementMatchingBehavior::NeverMatch);
                ASSERT_WITH_MESSAGE(ignoreVisitedMode == VisitedMode::None, ":visited is disabled in the functional pseudo classes");

                // Since this is not pseudo class filter, CannotMatchAnything implies this filter always passes.
                if (localFunctionType == FunctionType::CannotMatchAnything)
                    continue;

                if (localFunctionType == FunctionType::CannotCompile)
                    return FunctionType::CannotCompile;

                functionType = mostRestrictiveFunctionType(functionType, localFunctionType);
                selectorFragments = nullptr;
            }

            // If there is still a SelectorFragmentList open, the last Fragment(s) cannot match anything,
            // we have one FragmentList too many in our selector list.
            if (selectorFragments)
                fragment.notFilters.removeLast();

            return functionType;
        }

    case CSSSelector::PseudoClassAny:
        {
            Vector<SelectorFragment, 32> anyFragments;
            FunctionType functionType = FunctionType::SimpleSelectorChecker;
            for (const CSSSelector* rootSelector = selector.selectorList()->first(); rootSelector; rootSelector = CSSSelectorList::next(rootSelector)) {
                SelectorFragmentList fragmentList;
                VisitedMode ignoreVisitedMode = VisitedMode::None;
                FunctionType subFunctionType = constructFragments(rootSelector, selectorContext, fragmentList, FragmentsLevel::InFunctionalPseudoType, positionInRootFragments, visitedMatchEnabled, ignoreVisitedMode, PseudoElementMatchingBehavior::NeverMatch);
                ASSERT_WITH_MESSAGE(ignoreVisitedMode == VisitedMode::None, ":visited is disabled in the functional pseudo classes");

                // Since this fragment always unmatch against the element, don't insert it to anyFragments.
                if (subFunctionType == FunctionType::CannotMatchAnything)
                    continue;

                if (subFunctionType == FunctionType::CannotCompile)
                    return FunctionType::CannotCompile;

                // :any() may not contain complex selectors which have combinators.
                ASSERT(fragmentList.size() == 1);
                if (fragmentList.size() != 1)
                    return FunctionType::CannotCompile;

                const SelectorFragment& subFragment = fragmentList.first();
                anyFragments.append(subFragment);
                functionType = mostRestrictiveFunctionType(functionType, subFunctionType);
            }

            // Since all fragments in :any() cannot match anything, this :any() filter cannot match anything.
            if (anyFragments.isEmpty())
                return FunctionType::CannotMatchAnything;

            ASSERT(!anyFragments.isEmpty());
            fragment.anyFilters.append(anyFragments);

            return functionType;
        }

    case CSSSelector::PseudoClassLang:
        {
            const Vector<AtomicString>* selectorLangArgumentList = selector.langArgumentList();
            ASSERT(selectorLangArgumentList && !selectorLangArgumentList->isEmpty());
            fragment.languageArgumentsList.append(selectorLangArgumentList);
            return FunctionType::SimpleSelectorChecker;
        }

    case CSSSelector::PseudoClassMatches:
        {
            SelectorList matchesList;
            const CSSSelectorList* selectorList = selector.selectorList();
            FunctionType functionType = FunctionType::SimpleSelectorChecker;
            unsigned firstFragmentListSpecificity = 0;
            bool firstFragmentListSpecificitySet = false;
            SelectorFragmentList* selectorFragments = nullptr;
            for (const CSSSelector* subselector = selectorList->first(); subselector; subselector = CSSSelectorList::next(subselector)) {
                if (!selectorFragments) {
                    matchesList.append(SelectorFragmentList());
                    selectorFragments = &matchesList.last();
                }

                VisitedMode ignoreVisitedMode = VisitedMode::None;
                FunctionType localFunctionType = constructFragments(subselector, selectorContext, *selectorFragments, FragmentsLevel::InFunctionalPseudoType, positionInRootFragments, visitedMatchEnabled, ignoreVisitedMode, pseudoElementMatchingBehavior);
                ASSERT_WITH_MESSAGE(ignoreVisitedMode == VisitedMode::None, ":visited is disabled in the functional pseudo classes");

                // Since this fragment never matches against the element, don't insert it to matchesList.
                if (localFunctionType == FunctionType::CannotMatchAnything)
                    continue;

                if (localFunctionType == FunctionType::CannotCompile)
                    return FunctionType::CannotCompile;

                // FIXME: Currently pseudo elements inside :matches are supported in non-JIT code.
                if (selectorFragments->first().pseudoElementSelector)
                    return FunctionType::CannotCompile;

                if (firstFragmentListSpecificitySet) {
                    // The CSS JIT does not handle dynamic specificity yet.
                    if (selectorContext == SelectorContext::RuleCollector && selectorFragments->staticSpecificity != firstFragmentListSpecificity)
                        return FunctionType::CannotCompile;
                } else {
                    firstFragmentListSpecificitySet = true;
                    firstFragmentListSpecificity = selectorFragments->staticSpecificity;
                }

                functionType = mostRestrictiveFunctionType(functionType, localFunctionType);
                selectorFragments = nullptr;
            }

            // If there is still a SelectorFragmentList open, the last Fragment(s) cannot match anything,
            // we have one FragmentList too many in our selector list.
            if (selectorFragments)
                matchesList.removeLast();

            // Since all selector list in :matches() cannot match anything, the whole :matches() filter cannot match anything.
            if (matchesList.isEmpty())
                return FunctionType::CannotMatchAnything;

            internalSpecificity = firstFragmentListSpecificity;

            fragment.matchesFilters.append(matchesList);

            return functionType;
        }
    case CSSSelector::PseudoClassHost:
        return FunctionType::CannotCompile;
    case CSSSelector::PseudoClassUnknown:
        ASSERT_NOT_REACHED();
        return FunctionType::CannotMatchAnything;
    }

    ASSERT_NOT_REACHED();
    return FunctionType::CannotCompile;
}

inline SelectorCodeGenerator::SelectorCodeGenerator(const CSSSelector* rootSelector, SelectorContext selectorContext)
    : m_stackAllocator(m_assembler)
    , m_selectorContext(selectorContext)
    , m_functionType(FunctionType::SimpleSelectorChecker)
    , m_visitedMode(VisitedMode::None)
    , m_descendantBacktrackingStartInUse(false)
#if CSS_SELECTOR_JIT_DEBUGGING
    , m_originalSelector(rootSelector)
#endif
{
#if CSS_SELECTOR_JIT_DEBUGGING
    dataLogF("Compiling \"%s\"\n", m_originalSelector->selectorText().utf8().data());
#endif

    // In QuerySelector context, :visited always has no effect due to security issues.
    bool visitedMatchEnabled = selectorContext != SelectorContext::QuerySelector;

    m_functionType = constructFragments(rootSelector, m_selectorContext, m_selectorFragments, FragmentsLevel::Root, FragmentPositionInRootFragments::Rightmost, visitedMatchEnabled, m_visitedMode, PseudoElementMatchingBehavior::CanMatch);
    if (m_functionType != FunctionType::CannotCompile && m_functionType != FunctionType::CannotMatchAnything)
        computeBacktrackingInformation(m_selectorFragments);
}

static bool pseudoClassOnlyMatchesLinksInQuirksMode(const CSSSelector& selector)
{
    CSSSelector::PseudoClassType pseudoClassType = selector.pseudoClassType();
    return pseudoClassType == CSSSelector::PseudoClassHover || pseudoClassType == CSSSelector::PseudoClassActive;
}

static bool isScrollbarPseudoElement(CSSSelector::PseudoElementType type)
{
    return type >= CSSSelector::PseudoElementScrollbar && type <= CSSSelector::PseudoElementScrollbarTrackPiece;
}

static FunctionType constructFragmentsInternal(const CSSSelector* rootSelector, SelectorContext selectorContext, SelectorFragmentList& selectorFragments, FragmentsLevel fragmentLevel, FragmentPositionInRootFragments positionInRootFragments, bool visitedMatchEnabled, VisitedMode& visitedMode, PseudoElementMatchingBehavior pseudoElementMatchingBehavior)
{
    FragmentRelation relationToPreviousFragment = FragmentRelation::Rightmost;
    bool isRightmostOrAdjacent = positionInRootFragments != FragmentPositionInRootFragments::Other;
    FunctionType functionType = FunctionType::SimpleSelectorChecker;
    SelectorFragment* fragment = nullptr;
    unsigned specificity = 0;
    for (const CSSSelector* selector = rootSelector; selector; selector = selector->tagHistory()) {
        if (!fragment) {
            selectorFragments.append(SelectorFragment());
            fragment = &selectorFragments.last();
        }

        specificity = CSSSelector::addSpecificities(specificity, selector->simpleSelectorSpecificity());

        // A selector is invalid if something follows a pseudo-element.
        // We make an exception for scrollbar pseudo elements and allow a set of pseudo classes (but nothing else)
        // to follow the pseudo elements.
        if (fragment->pseudoElementSelector && !isScrollbarPseudoElement(fragment->pseudoElementSelector->pseudoElementType()))
            return FunctionType::CannotMatchAnything;

        switch (selector->match()) {
        case CSSSelector::Tag:
            ASSERT(!fragment->tagNameSelector);
            fragment->tagNameSelector = selector;
            if (fragment->tagNameSelector->tagQName() != anyQName())
                fragment->onlyMatchesLinksInQuirksMode = false;
            break;
        case CSSSelector::Id: {
            const AtomicString& id = selector->value();
            if (fragment->id) {
                if (id != *fragment->id)
                    return FunctionType::CannotMatchAnything;
            } else
                fragment->id = &(selector->value());
            fragment->onlyMatchesLinksInQuirksMode = false;
            break;
        }
        case CSSSelector::Class:
            fragment->classNames.append(selector->value().impl());
            fragment->onlyMatchesLinksInQuirksMode = false;
            break;
        case CSSSelector::PseudoClass: {
            FragmentPositionInRootFragments subPosition = positionInRootFragments;
            if (relationToPreviousFragment != FragmentRelation::Rightmost)
                subPosition = isRightmostOrAdjacent ? FragmentPositionInRootFragments::AdjacentToRightmost : FragmentPositionInRootFragments::Other;
            if (fragment->pseudoElementSelector && isScrollbarPseudoElement(fragment->pseudoElementSelector->pseudoElementType()))
                functionType = mostRestrictiveFunctionType(functionType, addScrollbarPseudoClassType(*selector, *fragment));
            else {
                unsigned internalSpecificity = 0;
                functionType = mostRestrictiveFunctionType(functionType, addPseudoClassType(*selector, *fragment, internalSpecificity, selectorContext, fragmentLevel, subPosition, visitedMatchEnabled, visitedMode, pseudoElementMatchingBehavior));
                specificity = CSSSelector::addSpecificities(specificity, internalSpecificity);
            }
            if (!pseudoClassOnlyMatchesLinksInQuirksMode(*selector))
                fragment->onlyMatchesLinksInQuirksMode = false;
            if (functionType == FunctionType::CannotCompile || functionType == FunctionType::CannotMatchAnything)
                return functionType;
            break;
        }
        case CSSSelector::PseudoElement: {
            fragment->onlyMatchesLinksInQuirksMode = false;

            // In the QuerySelector context, PseudoElement selectors always fail.
            if (selectorContext == SelectorContext::QuerySelector)
                return FunctionType::CannotMatchAnything;

            switch (selector->pseudoElementType()) {
            case CSSSelector::PseudoElementAfter:
            case CSSSelector::PseudoElementBefore:
            case CSSSelector::PseudoElementFirstLetter:
            case CSSSelector::PseudoElementFirstLine:
            case CSSSelector::PseudoElementScrollbar:
            case CSSSelector::PseudoElementScrollbarButton:
            case CSSSelector::PseudoElementScrollbarCorner:
            case CSSSelector::PseudoElementScrollbarThumb:
            case CSSSelector::PseudoElementScrollbarTrack:
            case CSSSelector::PseudoElementScrollbarTrackPiece:
                ASSERT(!fragment->pseudoElementSelector);
                fragment->pseudoElementSelector = selector;
                break;
            case CSSSelector::PseudoElementUnknown:
                ASSERT_NOT_REACHED();
                return FunctionType::CannotMatchAnything;
            // FIXME: Support PseudoId::Resizer, PseudoId::Selection etc.
            default:
                // This branch includes custom pseudo elements.
                return FunctionType::CannotCompile;
            }

            if (pseudoElementMatchingBehavior == PseudoElementMatchingBehavior::NeverMatch)
                return FunctionType::CannotMatchAnything;

            functionType = FunctionType::SelectorCheckerWithCheckingContext;
            break;
        }
        case CSSSelector::List:
            if (selector->value().find(isHTMLSpace<UChar>) != notFound)
                return FunctionType::CannotMatchAnything;
            FALLTHROUGH;
        case CSSSelector::Begin:
        case CSSSelector::End:
        case CSSSelector::Contain:
            if (selector->value().isEmpty())
                return FunctionType::CannotMatchAnything;
            FALLTHROUGH;
        case CSSSelector::Exact:
        case CSSSelector::Hyphen:
            fragment->onlyMatchesLinksInQuirksMode = false;
            fragment->attributes.append(AttributeMatchingInfo(*selector));
            break;

        case CSSSelector::Set:
            fragment->onlyMatchesLinksInQuirksMode = false;
            fragment->attributes.append(AttributeMatchingInfo(*selector));
            break;
        case CSSSelector::PagePseudoClass:
            fragment->onlyMatchesLinksInQuirksMode = false;
            // Pseudo page class are only relevant for style resolution, they are ignored for matching.
            break;
        case CSSSelector::Unknown:
            ASSERT_NOT_REACHED();
            return FunctionType::CannotMatchAnything;
        }

        auto relation = selector->relation();
        if (relation == CSSSelector::Subselector)
            continue;

        if (relation == CSSSelector::ShadowDescendant && !selector->isLastInTagHistory())
            return FunctionType::CannotCompile;

        if (relation == CSSSelector::DirectAdjacent || relation == CSSSelector::IndirectAdjacent) {
            FunctionType relationFunctionType = FunctionType::SelectorCheckerWithCheckingContext;
            if (selectorContext == SelectorContext::QuerySelector)
                relationFunctionType = FunctionType::SimpleSelectorChecker;
            functionType = mostRestrictiveFunctionType(functionType, relationFunctionType);

            // When the relation is adjacent, disable :visited match.
            visitedMatchEnabled = false;
        }

        // Virtual pseudo element is only effective in the rightmost fragment.
        pseudoElementMatchingBehavior = PseudoElementMatchingBehavior::NeverMatch;

        fragment->relationToLeftFragment = fragmentRelationForSelectorRelation(relation);
        fragment->relationToRightFragment = relationToPreviousFragment;
        fragment->positionInRootFragments = positionInRootFragments;
        fragment->isRightmostOrAdjacent = isRightmostOrAdjacent;
        relationToPreviousFragment = fragment->relationToLeftFragment;
        if (relationToPreviousFragment != FragmentRelation::Rightmost && relationToPreviousFragment != FragmentRelation::DirectAdjacent && relationToPreviousFragment != FragmentRelation::IndirectAdjacent)
            isRightmostOrAdjacent = false;

        if (fragmentLevel != FragmentsLevel::Root)
            fragment->onlyMatchesLinksInQuirksMode = false;

        fragment = nullptr;
    }

    ASSERT(!fragment);

    selectorFragments.staticSpecificity = specificity;

    return functionType;
}

static FunctionType constructFragments(const CSSSelector* rootSelector, SelectorContext selectorContext, SelectorFragmentList& selectorFragments, FragmentsLevel fragmentLevel, FragmentPositionInRootFragments positionInRootFragments, bool visitedMatchEnabled, VisitedMode& visitedMode, PseudoElementMatchingBehavior pseudoElementMatchingBehavior)
{
    ASSERT(selectorFragments.isEmpty());

    FunctionType functionType = constructFragmentsInternal(rootSelector, selectorContext, selectorFragments, fragmentLevel, positionInRootFragments, visitedMatchEnabled, visitedMode, pseudoElementMatchingBehavior);
    if (functionType != FunctionType::SimpleSelectorChecker && functionType != FunctionType::SelectorCheckerWithCheckingContext)
        selectorFragments.clear();
    return functionType;
}

static inline bool attributeNameTestingRequiresNamespaceRegister(const CSSSelector& attributeSelector)
{
    return attributeSelector.attribute().prefix() != starAtom() && !attributeSelector.attribute().namespaceURI().isNull();
}

static inline bool attributeValueTestingRequiresExtraRegister(const AttributeMatchingInfo& attributeInfo)
{
    switch (attributeInfo.attributeCaseSensitivity()) {
    case AttributeCaseSensitivity::CaseSensitive:
        return false;
    case AttributeCaseSensitivity::HTMLLegacyCaseInsensitive:
        return true;
    case AttributeCaseSensitivity::CaseInsensitive:
        return attributeInfo.selector().match() == CSSSelector::Exact;
    }
    return true;
}

// Element + ElementData + a pointer to values + an index on that pointer + the value we expect;
static const unsigned minimumRequiredRegisterCount = 5;
// Element + ElementData + scratchRegister + attributeArrayPointer + expectedLocalName + (qualifiedNameImpl && expectedValue).
static const unsigned minimumRequiredRegisterCountForAttributeFilter = 6;
// On x86, we always need 6 registers: Element + SiblingCounter + SiblingCounterCopy + divisor + dividend + remainder.
// On other architectures, we need 6 registers for style resolution:
//     Element + elementCounter + previousSibling + checkingContext + lastRelation + nextSiblingElement.
static const unsigned minimumRequiredRegisterCountForNthChildFilter = 6;

static unsigned minimumRegisterRequirements(const SelectorFragment& selectorFragment)
{
    unsigned minimum = minimumRequiredRegisterCount;
    const auto& attributes = selectorFragment.attributes;

    // Attributes cause some register pressure.
    unsigned attributeCount = attributes.size();
    for (unsigned attributeIndex = 0; attributeIndex < attributeCount; ++attributeIndex) {
        unsigned attributeMinimum = minimumRequiredRegisterCountForAttributeFilter;

        if (attributeIndex + 1 < attributeCount)
            attributeMinimum += 2; // For the local copy of the counter and attributeArrayPointer.

        const AttributeMatchingInfo& attributeInfo = attributes[attributeIndex];
        const CSSSelector& attributeSelector = attributeInfo.selector();
        if (attributeNameTestingRequiresNamespaceRegister(attributeSelector)
            || attributeValueTestingRequiresExtraRegister(attributeInfo))
            attributeMinimum += 1;

        minimum = std::max(minimum, attributeMinimum);
    }

    if (!selectorFragment.nthChildFilters.isEmpty() || !selectorFragment.nthChildOfFilters.isEmpty() || !selectorFragment.nthLastChildFilters.isEmpty() || !selectorFragment.nthLastChildOfFilters.isEmpty())
        minimum = std::max(minimum, minimumRequiredRegisterCountForNthChildFilter);

    // :any pseudo class filters cause some register pressure.
    for (const auto& subFragments : selectorFragment.anyFilters) {
        for (const SelectorFragment& subFragment : subFragments) {
            unsigned anyFilterMinimum = minimumRegisterRequirements(subFragment);
            minimum = std::max(minimum, anyFilterMinimum);
        }
    }

    return minimum;
}

bool hasAnyCombinators(const Vector<SelectorFragmentList>& selectorList);
template <size_t inlineCapacity>
bool hasAnyCombinators(const Vector<SelectorFragment, inlineCapacity>& selectorFragmentList);

bool hasAnyCombinators(const Vector<SelectorFragmentList>& selectorList)
{
    for (const SelectorFragmentList& selectorFragmentList : selectorList) {
        if (hasAnyCombinators(selectorFragmentList))
            return true;
    }
    return false;
}

template <size_t inlineCapacity>
bool hasAnyCombinators(const Vector<SelectorFragment, inlineCapacity>& selectorFragmentList)
{
    if (selectorFragmentList.isEmpty())
        return false;
    if (selectorFragmentList.size() != 1)
        return true;
    if (hasAnyCombinators(selectorFragmentList.first().notFilters))
        return true;
    for (const SelectorList& matchesList : selectorFragmentList.first().matchesFilters) {
        if (hasAnyCombinators(matchesList))
            return true;
    }
    for (const NthChildOfSelectorInfo& nthChildOfSelectorInfo : selectorFragmentList.first().nthChildOfFilters) {
        if (hasAnyCombinators(nthChildOfSelectorInfo.selectorList))
            return true;
    }
    for (const NthChildOfSelectorInfo& nthLastChildOfSelectorInfo : selectorFragmentList.first().nthLastChildOfFilters) {
        if (hasAnyCombinators(nthLastChildOfSelectorInfo.selectorList))
            return true;
    }
    return false;
}

// The CSS JIT has only been validated with a strict minimum of 6 allocated registers.
const unsigned minimumRegisterRequirement = 6;

void computeBacktrackingMemoryRequirements(SelectorFragmentList& selectorFragments, bool backtrackingRegisterReserved = false);

static void computeBacktrackingMemoryRequirements(SelectorList& selectorList, unsigned& totalRegisterRequirements, unsigned& totalStackRequirements, bool backtrackingRegisterReservedForFragment = false)
{
    unsigned selectorListRegisterRequirements = 0;
    unsigned selectorListStackRequirements = 0;
    bool clobberElementAddressRegister = false;

    for (SelectorFragmentList& selectorFragmentList : selectorList) {
        computeBacktrackingMemoryRequirements(selectorFragmentList, backtrackingRegisterReservedForFragment);

        selectorListRegisterRequirements = std::max(selectorListRegisterRequirements, selectorFragmentList.registerRequirements);
        selectorListStackRequirements = std::max(selectorListStackRequirements, selectorFragmentList.stackRequirements);
        clobberElementAddressRegister = clobberElementAddressRegister || selectorFragmentList.clobberElementAddressRegister;
    }

    totalRegisterRequirements = std::max(totalRegisterRequirements, selectorListRegisterRequirements);
    totalStackRequirements = std::max(totalStackRequirements, selectorListStackRequirements);

    selectorList.registerRequirements = std::max(selectorListRegisterRequirements, minimumRegisterRequirement);
    selectorList.stackRequirements = selectorListStackRequirements;
    selectorList.clobberElementAddressRegister = clobberElementAddressRegister;
}

void computeBacktrackingMemoryRequirements(SelectorFragmentList& selectorFragments, bool backtrackingRegisterReserved)
{
    selectorFragments.registerRequirements = minimumRegisterRequirement;
    selectorFragments.stackRequirements = 0;
    selectorFragments.clobberElementAddressRegister = hasAnyCombinators(selectorFragments);

    for (SelectorFragment& selectorFragment : selectorFragments) {
        unsigned fragmentRegisterRequirements = minimumRegisterRequirements(selectorFragment);
        unsigned fragmentStackRequirements = 0;

        bool backtrackingRegisterReservedForFragment = backtrackingRegisterReserved || selectorFragment.backtrackingFlags & BacktrackingFlag::InChainWithDescendantTail;

        computeBacktrackingMemoryRequirements(selectorFragment.notFilters, fragmentRegisterRequirements, fragmentStackRequirements, backtrackingRegisterReservedForFragment);

        for (SelectorList& matchesList : selectorFragment.matchesFilters)
            computeBacktrackingMemoryRequirements(matchesList, fragmentRegisterRequirements, fragmentStackRequirements, backtrackingRegisterReservedForFragment);

        for (NthChildOfSelectorInfo& nthChildOfSelectorInfo : selectorFragment.nthChildOfFilters)
            computeBacktrackingMemoryRequirements(nthChildOfSelectorInfo.selectorList, fragmentRegisterRequirements, fragmentStackRequirements, backtrackingRegisterReservedForFragment);

        for (NthChildOfSelectorInfo& nthLastChildOfSelectorInfo : selectorFragment.nthLastChildOfFilters)
            computeBacktrackingMemoryRequirements(nthLastChildOfSelectorInfo.selectorList, fragmentRegisterRequirements, fragmentStackRequirements, backtrackingRegisterReservedForFragment);

        if (selectorFragment.backtrackingFlags & BacktrackingFlag::InChainWithDescendantTail) {
            if (!backtrackingRegisterReserved)
                ++fragmentRegisterRequirements;
            else
                ++fragmentStackRequirements;
        }
        if (selectorFragment.backtrackingFlags & BacktrackingFlag::InChainWithAdjacentTail)
            ++fragmentStackRequirements;

        selectorFragments.registerRequirements = std::max(selectorFragments.registerRequirements, fragmentRegisterRequirements);
        selectorFragments.stackRequirements = std::max(selectorFragments.stackRequirements, fragmentStackRequirements);
    }
}

inline SelectorCompilationStatus SelectorCodeGenerator::compile(JSC::MacroAssemblerCodeRef<CSSSelectorPtrTag>& codeRef)
{
    switch (m_functionType) {
    case FunctionType::SimpleSelectorChecker:
    case FunctionType::SelectorCheckerWithCheckingContext:
        generateSelectorChecker();
        break;
    case FunctionType::CannotMatchAnything:
        m_assembler.tagReturnAddress();
        m_assembler.move(Assembler::TrustedImm32(0), returnRegister);
        m_assembler.ret();
        break;
    case FunctionType::CannotCompile:
        return SelectorCompilationStatus::CannotCompile;
    }

    JSC::LinkBuffer linkBuffer(m_assembler, CSS_CODE_ID, JSC::JITCompilationCanFail);
    if (!linkBuffer.isValid()) {
        // This could be SelectorCompilationStatus::NotCompiled but that would cause us to re-enter
        // the CSS JIT every time we evaluate that selector.
        // If we failed to allocate the buffer, we have bigger problems than CSS performance, it is fine
        // to be slower.
        return SelectorCompilationStatus::CannotCompile;
    }

    for (unsigned i = 0; i < m_functionCalls.size(); i++)
        linkBuffer.link(m_functionCalls[i].first, m_functionCalls[i].second);

#if CSS_SELECTOR_JIT_DEBUGGING
    codeRef = linkBuffer.finalizeCodeWithDisassembly(CSSSelectorPtrTag, "CSS Selector JIT for \"%s\"", m_originalSelector->selectorText().utf8().data());
#else
    codeRef = FINALIZE_CODE(linkBuffer, CSSSelectorPtrTag, "CSS Selector JIT");
#endif

    if (m_functionType == FunctionType::SimpleSelectorChecker || m_functionType == FunctionType::CannotMatchAnything)
        return SelectorCompilationStatus::SimpleSelectorChecker;
    return SelectorCompilationStatus::SelectorCheckerWithCheckingContext;
}


static inline void updateChainStates(const SelectorFragment& fragment, bool& hasDescendantRelationOnTheRight, unsigned& ancestorPositionSinceDescendantRelation, bool& hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain, unsigned& adjacentPositionSinceIndirectAdjacentTreeWalk)
{
    switch (fragment.relationToRightFragment) {
    case FragmentRelation::Rightmost:
        break;
    case FragmentRelation::Descendant:
        hasDescendantRelationOnTheRight = true;
        ancestorPositionSinceDescendantRelation = 0;
        hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain = false;
        break;
    case FragmentRelation::Child:
        if (hasDescendantRelationOnTheRight)
            ++ancestorPositionSinceDescendantRelation;
        hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain = false;
        break;
    case FragmentRelation::DirectAdjacent:
        if (hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain)
            ++adjacentPositionSinceIndirectAdjacentTreeWalk;
        break;
    case FragmentRelation::IndirectAdjacent:
        hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain = true;
        adjacentPositionSinceIndirectAdjacentTreeWalk = 0;
        break;
    }
}

static inline bool isFirstAncestor(unsigned ancestorPositionSinceDescendantRelation)
{
    return ancestorPositionSinceDescendantRelation == 1;
}

static inline bool isFirstAdjacent(unsigned adjacentPositionSinceIndirectAdjacentTreeWalk)
{
    return adjacentPositionSinceIndirectAdjacentTreeWalk == 1;
}

static inline BacktrackingAction solveDescendantBacktrackingActionForChild(const SelectorFragment& fragment, unsigned backtrackingStartHeightFromDescendant)
{
    // If height is invalid (e.g. There's no tag name).
    if (backtrackingStartHeightFromDescendant == invalidHeight)
        return BacktrackingAction::NoBacktracking;

    // Start backtracking from the current element.
    if (backtrackingStartHeightFromDescendant == fragment.heightFromDescendant)
        return BacktrackingAction::JumpToDescendantEntryPoint;

    // Start backtracking from the parent of current element.
    if (backtrackingStartHeightFromDescendant == (fragment.heightFromDescendant + 1))
        return BacktrackingAction::JumpToDescendantTreeWalkerEntryPoint;

    return BacktrackingAction::JumpToDescendantTail;
}

static inline BacktrackingAction solveAdjacentBacktrackingActionForDirectAdjacent(const SelectorFragment& fragment, unsigned backtrackingStartWidthFromIndirectAdjacent)
{
    // If width is invalid (e.g. There's no tag name).
    if (backtrackingStartWidthFromIndirectAdjacent == invalidWidth)
        return BacktrackingAction::NoBacktracking;

    // Start backtracking from the current element.
    if (backtrackingStartWidthFromIndirectAdjacent == fragment.widthFromIndirectAdjacent)
        return BacktrackingAction::JumpToIndirectAdjacentEntryPoint;

    // Start backtracking from the previous adjacent of current element.
    if (backtrackingStartWidthFromIndirectAdjacent == (fragment.widthFromIndirectAdjacent + 1))
        return BacktrackingAction::JumpToIndirectAdjacentTreeWalkerEntryPoint;

    return BacktrackingAction::JumpToDirectAdjacentTail;
}

static inline BacktrackingAction solveAdjacentTraversalBacktrackingAction(const SelectorFragment& fragment, bool hasDescendantRelationOnTheRight)
{
    if (!hasDescendantRelationOnTheRight)
        return BacktrackingAction::NoBacktracking;

    if (fragment.tagNameMatchedBacktrackingStartHeightFromDescendant == (fragment.heightFromDescendant + 1))
        return BacktrackingAction::JumpToDescendantTreeWalkerEntryPoint;

    return BacktrackingAction::JumpToDescendantTail;
}

static inline void solveBacktrackingAction(SelectorFragment& fragment, bool hasDescendantRelationOnTheRight, bool hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain)
{
    switch (fragment.relationToRightFragment) {
    case FragmentRelation::Rightmost:
    case FragmentRelation::Descendant:
        break;
    case FragmentRelation::Child:
        // Failure to match the element should resume matching at the nearest ancestor/descendant entry point.
        if (hasDescendantRelationOnTheRight) {
            fragment.matchingTagNameBacktrackingAction = solveDescendantBacktrackingActionForChild(fragment, fragment.tagNameNotMatchedBacktrackingStartHeightFromDescendant);
            fragment.matchingPostTagNameBacktrackingAction = solveDescendantBacktrackingActionForChild(fragment, fragment.tagNameMatchedBacktrackingStartHeightFromDescendant);
        }
        break;
    case FragmentRelation::DirectAdjacent:
        // Failure on traversal implies no other sibling traversal can match. Matching should resume at the
        // nearest ancestor/descendant traversal.
        fragment.traversalBacktrackingAction = solveAdjacentTraversalBacktrackingAction(fragment, hasDescendantRelationOnTheRight);

        // If the rightmost relation is a indirect adjacent, matching sould resume from there.
        // Otherwise, we resume from the latest ancestor/descendant if any.
        if (hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain) {
            fragment.matchingTagNameBacktrackingAction = solveAdjacentBacktrackingActionForDirectAdjacent(fragment, fragment.tagNameNotMatchedBacktrackingStartWidthFromIndirectAdjacent);
            fragment.matchingPostTagNameBacktrackingAction = solveAdjacentBacktrackingActionForDirectAdjacent(fragment, fragment.tagNameMatchedBacktrackingStartWidthFromIndirectAdjacent);
        } else if (hasDescendantRelationOnTheRight) {
            // Since we resume from the latest ancestor/descendant, the action is the same as the traversal action.
            fragment.matchingTagNameBacktrackingAction = fragment.traversalBacktrackingAction;
            fragment.matchingPostTagNameBacktrackingAction = fragment.traversalBacktrackingAction;
        }
        break;
    case FragmentRelation::IndirectAdjacent:
        // Failure on traversal implies no other sibling matching will succeed. Matching can resume
        // from the latest ancestor/descendant.
        fragment.traversalBacktrackingAction = solveAdjacentTraversalBacktrackingAction(fragment, hasDescendantRelationOnTheRight);
        break;
    }
}

enum class TagNameEquality {
    StrictlyNotEqual,
    MaybeEqual,
    StrictlyEqual
};

static inline TagNameEquality equalTagNames(const CSSSelector* lhs, const CSSSelector* rhs)
{
    if (!lhs || !rhs)
        return TagNameEquality::MaybeEqual;

    const QualifiedName& lhsQualifiedName = lhs->tagQName();
    if (lhsQualifiedName == anyQName())
        return TagNameEquality::MaybeEqual;

    const QualifiedName& rhsQualifiedName = rhs->tagQName();
    if (rhsQualifiedName == anyQName())
        return TagNameEquality::MaybeEqual;

    const AtomicString& lhsLocalName = lhsQualifiedName.localName();
    const AtomicString& rhsLocalName = rhsQualifiedName.localName();
    if (lhsLocalName != starAtom() && rhsLocalName != starAtom()) {
        const AtomicString& lhsLowercaseLocalName = lhs->tagLowercaseLocalName();
        const AtomicString& rhsLowercaseLocalName = rhs->tagLowercaseLocalName();

        if (lhsLowercaseLocalName != rhsLowercaseLocalName)
            return TagNameEquality::StrictlyNotEqual;

        if (lhsLocalName == lhsLowercaseLocalName && rhsLocalName == rhsLowercaseLocalName)
            return TagNameEquality::StrictlyEqual;
        return TagNameEquality::MaybeEqual;
    }

    const AtomicString& lhsNamespaceURI = lhsQualifiedName.namespaceURI();
    const AtomicString& rhsNamespaceURI = rhsQualifiedName.namespaceURI();
    if (lhsNamespaceURI != starAtom() && rhsNamespaceURI != starAtom()) {
        if (lhsNamespaceURI != rhsNamespaceURI)
            return TagNameEquality::StrictlyNotEqual;
        return TagNameEquality::StrictlyEqual;
    }

    return TagNameEquality::MaybeEqual;
}

static inline bool equalTagNamePatterns(const TagNamePattern& lhs, const TagNamePattern& rhs)
{
    TagNameEquality result = equalTagNames(lhs.tagNameSelector, rhs.tagNameSelector);
    if (result == TagNameEquality::MaybeEqual)
        return true;

    // If both rhs & lhs have actual localName (or NamespaceURI),
    // TagNameEquality result becomes StrictlyEqual or StrictlyNotEqual Since inverted lhs never matches on rhs.
    bool equal = result == TagNameEquality::StrictlyEqual;
    if (lhs.inverted)
        return !equal;
    return equal;
}

// Find the largest matching prefix from already known tagNames.
// And by using this, compute an appropriate height of backtracking start element from the closest base element in the chain.
static inline unsigned computeBacktrackingStartOffsetInChain(const TagNameList& tagNames, unsigned maxPrefixSize)
{
    RELEASE_ASSERT(!tagNames.isEmpty());
    RELEASE_ASSERT(maxPrefixSize < tagNames.size());

    for (unsigned largestPrefixSize = maxPrefixSize; largestPrefixSize > 0; --largestPrefixSize) {
        unsigned offsetToLargestPrefix = tagNames.size() - largestPrefixSize;
        bool matched = true;
        // Since TagNamePatterns are pushed to a tagNames, check tagNames with reverse order.
        for (unsigned i = 0; i < largestPrefixSize; ++i) {
            unsigned lastIndex = tagNames.size() - 1;
            unsigned currentIndex = lastIndex - i;
            if (!equalTagNamePatterns(tagNames[currentIndex], tagNames[currentIndex - offsetToLargestPrefix])) {
                matched = false;
                break;
            }
        }
        if (matched)
            return offsetToLargestPrefix;
    }
    return tagNames.size();
}

static inline void computeBacktrackingHeightFromDescendant(SelectorFragment& fragment, TagNameList& tagNamesForChildChain, bool hasDescendantRelationOnTheRight, const SelectorFragment*& previousChildFragmentInChildChain)
{
    if (!hasDescendantRelationOnTheRight)
        return;

    if (fragment.relationToRightFragment == FragmentRelation::Descendant) {
        tagNamesForChildChain.clear();

        TagNamePattern pattern;
        pattern.tagNameSelector = fragment.tagNameSelector;
        tagNamesForChildChain.append(pattern);
        fragment.heightFromDescendant = 0;
        previousChildFragmentInChildChain = nullptr;
    } else if (fragment.relationToRightFragment == FragmentRelation::Child) {
        TagNamePattern pattern;
        pattern.tagNameSelector = fragment.tagNameSelector;
        tagNamesForChildChain.append(pattern);

        unsigned maxPrefixSize = tagNamesForChildChain.size() - 1;
        if (previousChildFragmentInChildChain) {
            RELEASE_ASSERT(tagNamesForChildChain.size() >= previousChildFragmentInChildChain->tagNameMatchedBacktrackingStartHeightFromDescendant);
            maxPrefixSize = tagNamesForChildChain.size() - previousChildFragmentInChildChain->tagNameMatchedBacktrackingStartHeightFromDescendant;
        }

        if (pattern.tagNameSelector) {
            // Compute height from descendant in the case that tagName is not matched.
            tagNamesForChildChain.last().inverted = true;
            fragment.tagNameNotMatchedBacktrackingStartHeightFromDescendant = computeBacktrackingStartOffsetInChain(tagNamesForChildChain, maxPrefixSize);
        }

        // Compute height from descendant in the case that tagName is matched.
        tagNamesForChildChain.last().inverted = false;
        fragment.tagNameMatchedBacktrackingStartHeightFromDescendant = computeBacktrackingStartOffsetInChain(tagNamesForChildChain, maxPrefixSize);
        fragment.heightFromDescendant = tagNamesForChildChain.size() - 1;
        previousChildFragmentInChildChain = &fragment;
    } else {
        if (previousChildFragmentInChildChain) {
            fragment.tagNameNotMatchedBacktrackingStartHeightFromDescendant = previousChildFragmentInChildChain->tagNameNotMatchedBacktrackingStartHeightFromDescendant;
            fragment.tagNameMatchedBacktrackingStartHeightFromDescendant = previousChildFragmentInChildChain->tagNameMatchedBacktrackingStartHeightFromDescendant;
            fragment.heightFromDescendant = previousChildFragmentInChildChain->heightFromDescendant;
        } else {
            fragment.tagNameNotMatchedBacktrackingStartHeightFromDescendant = tagNamesForChildChain.size();
            fragment.tagNameMatchedBacktrackingStartHeightFromDescendant = tagNamesForChildChain.size();
            fragment.heightFromDescendant = 0;
        }
    }
}

static inline void computeBacktrackingWidthFromIndirectAdjacent(SelectorFragment& fragment, TagNameList& tagNamesForDirectAdjacentChain, bool hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain, const SelectorFragment*& previousDirectAdjacentFragmentInDirectAdjacentChain)
{
    if (!hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain)
        return;

    if (fragment.relationToRightFragment == FragmentRelation::IndirectAdjacent) {
        tagNamesForDirectAdjacentChain.clear();

        TagNamePattern pattern;
        pattern.tagNameSelector = fragment.tagNameSelector;
        tagNamesForDirectAdjacentChain.append(pattern);
        fragment.widthFromIndirectAdjacent = 0;
        previousDirectAdjacentFragmentInDirectAdjacentChain = nullptr;
    } else if (fragment.relationToRightFragment == FragmentRelation::DirectAdjacent) {
        TagNamePattern pattern;
        pattern.tagNameSelector = fragment.tagNameSelector;
        tagNamesForDirectAdjacentChain.append(pattern);

        unsigned maxPrefixSize = tagNamesForDirectAdjacentChain.size() - 1;
        if (previousDirectAdjacentFragmentInDirectAdjacentChain) {
            RELEASE_ASSERT(tagNamesForDirectAdjacentChain.size() >= previousDirectAdjacentFragmentInDirectAdjacentChain->tagNameMatchedBacktrackingStartWidthFromIndirectAdjacent);
            maxPrefixSize = tagNamesForDirectAdjacentChain.size() - previousDirectAdjacentFragmentInDirectAdjacentChain->tagNameMatchedBacktrackingStartWidthFromIndirectAdjacent;
        }

        if (pattern.tagNameSelector) {
            // Compute height from descendant in the case that tagName is not matched.
            tagNamesForDirectAdjacentChain.last().inverted = true;
            fragment.tagNameNotMatchedBacktrackingStartWidthFromIndirectAdjacent = computeBacktrackingStartOffsetInChain(tagNamesForDirectAdjacentChain, maxPrefixSize);
        }

        // Compute height from descendant in the case that tagName is matched.
        tagNamesForDirectAdjacentChain.last().inverted = false;
        fragment.tagNameMatchedBacktrackingStartWidthFromIndirectAdjacent = computeBacktrackingStartOffsetInChain(tagNamesForDirectAdjacentChain, maxPrefixSize);
        fragment.widthFromIndirectAdjacent = tagNamesForDirectAdjacentChain.size() - 1;
        previousDirectAdjacentFragmentInDirectAdjacentChain = &fragment;
    }
}

static bool requiresAdjacentTail(const SelectorFragment& fragment)
{
    ASSERT(fragment.traversalBacktrackingAction != BacktrackingAction::JumpToDirectAdjacentTail);
    return fragment.matchingTagNameBacktrackingAction == BacktrackingAction::JumpToDirectAdjacentTail || fragment.matchingPostTagNameBacktrackingAction == BacktrackingAction::JumpToDirectAdjacentTail;
}

static bool requiresDescendantTail(const SelectorFragment& fragment)
{
    return fragment.matchingTagNameBacktrackingAction == BacktrackingAction::JumpToDescendantTail || fragment.matchingPostTagNameBacktrackingAction == BacktrackingAction::JumpToDescendantTail || fragment.traversalBacktrackingAction == BacktrackingAction::JumpToDescendantTail;
}

void computeBacktrackingInformation(SelectorFragmentList& selectorFragments, unsigned level)
{
    bool hasDescendantRelationOnTheRight = false;
    unsigned ancestorPositionSinceDescendantRelation = 0;
    bool hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain = false;
    unsigned adjacentPositionSinceIndirectAdjacentTreeWalk = 0;

    bool needsAdjacentTail = false;
    bool needsDescendantTail = false;
    unsigned saveDescendantBacktrackingStartFragmentIndex = std::numeric_limits<unsigned>::max();
    unsigned saveIndirectAdjacentBacktrackingStartFragmentIndex = std::numeric_limits<unsigned>::max();

    TagNameList tagNamesForChildChain;
    TagNameList tagNamesForDirectAdjacentChain;
    const SelectorFragment* previousChildFragmentInChildChain = nullptr;
    const SelectorFragment* previousDirectAdjacentFragmentInDirectAdjacentChain = nullptr;

    for (unsigned i = 0; i < selectorFragments.size(); ++i) {
        SelectorFragment& fragment = selectorFragments[i];

        updateChainStates(fragment, hasDescendantRelationOnTheRight, ancestorPositionSinceDescendantRelation, hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain, adjacentPositionSinceIndirectAdjacentTreeWalk);

        computeBacktrackingHeightFromDescendant(fragment, tagNamesForChildChain, hasDescendantRelationOnTheRight, previousChildFragmentInChildChain);

        computeBacktrackingWidthFromIndirectAdjacent(fragment, tagNamesForDirectAdjacentChain, hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain, previousDirectAdjacentFragmentInDirectAdjacentChain);

#if CSS_SELECTOR_JIT_DEBUGGING
        dataLogF("%*sComputing fragment[%d] backtracking height %u. NotMatched %u / Matched %u | width %u. NotMatched %u / Matched %u\n", level * 4, "", i, fragment.heightFromDescendant, fragment.tagNameNotMatchedBacktrackingStartHeightFromDescendant, fragment.tagNameMatchedBacktrackingStartHeightFromDescendant, fragment.widthFromIndirectAdjacent, fragment.tagNameNotMatchedBacktrackingStartWidthFromIndirectAdjacent, fragment.tagNameMatchedBacktrackingStartWidthFromIndirectAdjacent);
#endif

        solveBacktrackingAction(fragment, hasDescendantRelationOnTheRight, hasIndirectAdjacentRelationOnTheRightOfDirectAdjacentChain);

        needsAdjacentTail |= requiresAdjacentTail(fragment);
        needsDescendantTail |= requiresDescendantTail(fragment);

        // Add code generation flags.
        if (fragment.relationToLeftFragment != FragmentRelation::Descendant && fragment.relationToRightFragment == FragmentRelation::Descendant)
            fragment.backtrackingFlags |= BacktrackingFlag::DescendantEntryPoint;
        if (fragment.relationToLeftFragment == FragmentRelation::DirectAdjacent && fragment.relationToRightFragment == FragmentRelation::IndirectAdjacent)
            fragment.backtrackingFlags |= BacktrackingFlag::IndirectAdjacentEntryPoint;
        if (fragment.relationToLeftFragment != FragmentRelation::Descendant && fragment.relationToRightFragment == FragmentRelation::Child && isFirstAncestor(ancestorPositionSinceDescendantRelation)) {
            ASSERT(saveDescendantBacktrackingStartFragmentIndex == std::numeric_limits<unsigned>::max());
            saveDescendantBacktrackingStartFragmentIndex = i;
        }
        if (fragment.relationToLeftFragment == FragmentRelation::DirectAdjacent && fragment.relationToRightFragment == FragmentRelation::DirectAdjacent && isFirstAdjacent(adjacentPositionSinceIndirectAdjacentTreeWalk)) {
            ASSERT(saveIndirectAdjacentBacktrackingStartFragmentIndex == std::numeric_limits<unsigned>::max());
            saveIndirectAdjacentBacktrackingStartFragmentIndex = i;
        }
        if (fragment.relationToLeftFragment != FragmentRelation::DirectAdjacent) {
            if (needsAdjacentTail) {
                ASSERT(fragment.relationToRightFragment == FragmentRelation::DirectAdjacent);
                ASSERT(saveIndirectAdjacentBacktrackingStartFragmentIndex != std::numeric_limits<unsigned>::max());
                fragment.backtrackingFlags |= BacktrackingFlag::DirectAdjacentTail;
                selectorFragments[saveIndirectAdjacentBacktrackingStartFragmentIndex].backtrackingFlags |= BacktrackingFlag::SaveAdjacentBacktrackingStart;
                needsAdjacentTail = false;
                for (unsigned j = saveIndirectAdjacentBacktrackingStartFragmentIndex; j <= i; ++j)
                    selectorFragments[j].backtrackingFlags |= BacktrackingFlag::InChainWithAdjacentTail;
            }
            saveIndirectAdjacentBacktrackingStartFragmentIndex = std::numeric_limits<unsigned>::max();
        }
        if (fragment.relationToLeftFragment == FragmentRelation::Descendant) {
            if (needsDescendantTail) {
                ASSERT(saveDescendantBacktrackingStartFragmentIndex != std::numeric_limits<unsigned>::max());
                fragment.backtrackingFlags |= BacktrackingFlag::DescendantTail;
                selectorFragments[saveDescendantBacktrackingStartFragmentIndex].backtrackingFlags |= BacktrackingFlag::SaveDescendantBacktrackingStart;
                needsDescendantTail = false;
                for (unsigned j = saveDescendantBacktrackingStartFragmentIndex; j <= i; ++j)
                    selectorFragments[j].backtrackingFlags |= BacktrackingFlag::InChainWithDescendantTail;
            }
            saveDescendantBacktrackingStartFragmentIndex = std::numeric_limits<unsigned>::max();
        }
    }

    for (SelectorFragment& fragment : selectorFragments) {
        if (!fragment.notFilters.isEmpty()) {
#if CSS_SELECTOR_JIT_DEBUGGING
            dataLogF("%*s  Subselectors for :not():\n", level * 4, "");
#endif

            for (SelectorFragmentList& selectorList : fragment.notFilters)
                computeBacktrackingInformation(selectorList, level + 1);
        }

        if (!fragment.matchesFilters.isEmpty()) {
            for (SelectorList& matchesList : fragment.matchesFilters) {
#if CSS_SELECTOR_JIT_DEBUGGING
                dataLogF("%*s  Subselectors for :matches():\n", level * 4, "");
#endif

                for (SelectorFragmentList& selectorList : matchesList)
                    computeBacktrackingInformation(selectorList, level + 1);
            }
        }

        for (NthChildOfSelectorInfo& nthChildOfSelectorInfo : fragment.nthChildOfFilters) {
#if CSS_SELECTOR_JIT_DEBUGGING
            dataLogF("%*s  Subselectors for %dn+%d:\n", level * 4, "", nthChildOfSelectorInfo.a, nthChildOfSelectorInfo.b);
#endif

            for (SelectorFragmentList& selectorList : nthChildOfSelectorInfo.selectorList)
                computeBacktrackingInformation(selectorList, level + 1);
        }

        for (NthChildOfSelectorInfo& nthLastChildOfSelectorInfo : fragment.nthLastChildOfFilters) {
#if CSS_SELECTOR_JIT_DEBUGGING
            dataLogF("%*s  Subselectors for %dn+%d:\n", level * 4, "", nthLastChildOfSelectorInfo.a, nthLastChildOfSelectorInfo.b);
#endif

            for (SelectorFragmentList& selectorList : nthLastChildOfSelectorInfo.selectorList)
                computeBacktrackingInformation(selectorList, level + 1);
        }
    }
}

inline void SelectorCodeGenerator::pushMacroAssemblerRegisters()
{
#if CPU(ARM_THUMB2)
    // r6 is tempRegister in RegisterAllocator.h and addressTempRegister in MacroAssemblerARMv7.h and must be preserved by the callee.
    Vector<JSC::MacroAssembler::RegisterID, 1> macroAssemblerRegisters({ JSC::ARMRegisters::r6 });
    m_macroAssemblerRegistersStackReferences = m_stackAllocator.push(macroAssemblerRegisters);
#endif
}

inline void SelectorCodeGenerator::popMacroAssemblerRegisters(StackAllocator& stackAllocator)
{
#if CPU(ARM_THUMB2)
    Vector<JSC::MacroAssembler::RegisterID, 1> macroAssemblerRegisters({ JSC::ARMRegisters::r6 });
    stackAllocator.pop(m_macroAssemblerRegistersStackReferences, macroAssemblerRegisters);
#else
    UNUSED_PARAM(stackAllocator);
#endif
}

inline bool SelectorCodeGenerator::generatePrologue()
{
#if CPU(ARM64)
    Vector<JSC::MacroAssembler::RegisterID, 2> prologueRegisters;
    prologueRegisters.append(JSC::ARM64Registers::lr);
    prologueRegisters.append(JSC::ARM64Registers::fp);
    m_prologueStackReferences = m_stackAllocator.push(prologueRegisters);
    return true;
#elif CPU(ARM_THUMB2)
    Vector<JSC::MacroAssembler::RegisterID, 1> prologueRegisters;
    prologueRegisters.append(JSC::ARMRegisters::lr);
    m_prologueStackReferences = m_stackAllocator.push(prologueRegisters);
    return true;
#elif CPU(X86_64) && CSS_SELECTOR_JIT_DEBUGGING
    Vector<JSC::MacroAssembler::RegisterID, 1> prologueRegister;
    prologueRegister.append(callFrameRegister);
    m_prologueStackReferences = m_stackAllocator.push(prologueRegister);
    return true;
#endif
    return false;
}

inline void SelectorCodeGenerator::generateEpilogue(StackAllocator& stackAllocator)
{
#if CPU(ARM64)
    Vector<JSC::MacroAssembler::RegisterID, 2> prologueRegisters({ JSC::ARM64Registers::lr, JSC::ARM64Registers::fp });
    stackAllocator.pop(m_prologueStackReferences, prologueRegisters);
#elif CPU(ARM_THUMB2)
    Vector<JSC::MacroAssembler::RegisterID, 1> prologueRegister({ JSC::ARMRegisters::lr });
    stackAllocator.pop(m_prologueStackReferences, prologueRegister);
#elif CPU(X86_64) && CSS_SELECTOR_JIT_DEBUGGING
    Vector<JSC::MacroAssembler::RegisterID, 1> prologueRegister({ callFrameRegister });
    stackAllocator.pop(m_prologueStackReferences, prologueRegister);
#else
    UNUSED_PARAM(stackAllocator);
#endif
}

static bool isAdjacentRelation(FragmentRelation relation)
{
    return relation == FragmentRelation::DirectAdjacent || relation == FragmentRelation::IndirectAdjacent;
}

static bool shouldMarkStyleIsAffectedByPreviousSibling(const SelectorFragment& fragment)
{
    return isAdjacentRelation(fragment.relationToLeftFragment) && !isAdjacentRelation(fragment.relationToRightFragment);
}

void SelectorCodeGenerator::generateSelectorChecker()
{
    m_assembler.tagReturnAddress();
    pushMacroAssemblerRegisters();
    StackAllocator earlyFailureStack = m_stackAllocator;

    Assembler::JumpList failureOnFunctionEntry;
    // Test selector's pseudo element equals to requested PseudoId.
    if (m_selectorContext != SelectorContext::QuerySelector && m_functionType == FunctionType::SelectorCheckerWithCheckingContext) {
        ASSERT_WITH_MESSAGE(fragmentMatchesTheRightmostElement(m_selectorFragments.first()), "Matching pseudo elements only make sense for the rightmost fragment.");
        generateRequestedPseudoElementEqualsToSelectorPseudoElement(failureOnFunctionEntry, m_selectorFragments.first(), checkingContextRegister);
    }

    if (m_selectorContext == SelectorContext::RuleCollector) {
        unsigned specificity = m_selectorFragments.staticSpecificity;
        if (m_functionType == FunctionType::SelectorCheckerWithCheckingContext)
            m_assembler.store32(Assembler::TrustedImm32(specificity), JSC::GPRInfo::argumentGPR2);
        else
            m_assembler.store32(Assembler::TrustedImm32(specificity), JSC::GPRInfo::argumentGPR1);
    }

    computeBacktrackingMemoryRequirements(m_selectorFragments);
    unsigned availableRegisterCount = m_registerAllocator.reserveCallerSavedRegisters(m_selectorFragments.registerRequirements);

#if CSS_SELECTOR_JIT_DEBUGGING
    dataLogF("Compiling with minimum required register count %u, minimum stack space %u\n", m_selectorFragments.registerRequirements, m_selectorFragments.stackRequirements);
#endif

    // We do not want unbounded stack allocation for backtracking. Going down 8 enry points would already be incredibly inefficient.
    unsigned maximumBacktrackingAllocations = 8;
    if (m_selectorFragments.stackRequirements > maximumBacktrackingAllocations) {
        m_assembler.move(Assembler::TrustedImm32(0), returnRegister);
        popMacroAssemblerRegisters(m_stackAllocator);
        m_assembler.ret();
        return;
    }

    bool needsEpilogue = generatePrologue();

    StackAllocator::StackReferenceVector calleeSavedRegisterStackReferences;
    bool reservedCalleeSavedRegisters = false;
    ASSERT(m_selectorFragments.registerRequirements <= maximumRegisterCount);
    if (availableRegisterCount < m_selectorFragments.registerRequirements) {
        reservedCalleeSavedRegisters = true;
        calleeSavedRegisterStackReferences = m_stackAllocator.push(m_registerAllocator.reserveCalleeSavedRegisters(m_selectorFragments.registerRequirements - availableRegisterCount));
    }

    m_registerAllocator.allocateRegister(elementAddressRegister);

    StackAllocator::StackReference temporaryStackBase = m_stackAllocator.stackTop();

    if (m_functionType == FunctionType::SelectorCheckerWithCheckingContext)
        m_checkingContextStackReference = m_stackAllocator.push(checkingContextRegister);

    unsigned stackRequirementCount = m_selectorFragments.stackRequirements;
    if (m_visitedMode == VisitedMode::Visited)
        stackRequirementCount += 2;

    StackAllocator::StackReferenceVector temporaryStack;
    if (stackRequirementCount)
        temporaryStack = m_stackAllocator.allocateUninitialized(stackRequirementCount);

    if (m_visitedMode == VisitedMode::Visited) {
        m_lastVisitedElement = temporaryStack.takeLast();
        m_startElement = temporaryStack.takeLast();
        m_assembler.storePtr(elementAddressRegister, m_stackAllocator.addressOf(m_startElement));
        m_assembler.storePtr(Assembler::TrustedImmPtr(nullptr), m_stackAllocator.addressOf(m_lastVisitedElement));
    }

    m_backtrackingStack = temporaryStack;

    Assembler::JumpList failureCases;
    generateSelectorCheckerExcludingPseudoElements(failureCases, m_selectorFragments);

    if (m_selectorContext != SelectorContext::QuerySelector && m_functionType == FunctionType::SelectorCheckerWithCheckingContext) {
        ASSERT(!m_selectorFragments.isEmpty());
        generateMarkPseudoStyleForPseudoElement(failureCases, m_selectorFragments.first());
    }

    if (m_visitedMode == VisitedMode::Visited) {
        LocalRegister lastVisitedElement(m_registerAllocator);
        m_assembler.loadPtr(m_stackAllocator.addressOf(m_lastVisitedElement), lastVisitedElement);
        Assembler::Jump noLastVisitedElement = m_assembler.branchTestPtr(Assembler::Zero, lastVisitedElement);
        generateElementIsFirstLink(failureCases, lastVisitedElement);
        noLastVisitedElement.link(&m_assembler);
    }

    m_registerAllocator.deallocateRegister(elementAddressRegister);

    if (m_functionType == FunctionType::SimpleSelectorChecker) {
        if (temporaryStackBase == m_stackAllocator.stackTop() && !reservedCalleeSavedRegisters && !needsEpilogue) {
            StackAllocator successStack = m_stackAllocator;
            StackAllocator failureStack = m_stackAllocator;

            ASSERT(!m_selectorFragments.stackRequirements);
            // Success.
            m_assembler.move(Assembler::TrustedImm32(1), returnRegister);
            popMacroAssemblerRegisters(successStack);
            m_assembler.ret();

            // Failure.
            ASSERT_WITH_MESSAGE(failureOnFunctionEntry.empty(), "Early failure on function entry is used for pseudo element. When early failure is used, function type is SelectorCheckerWithCheckingContext.");
            if (!failureCases.empty()) {
                failureCases.link(&m_assembler);
                m_assembler.move(Assembler::TrustedImm32(0), returnRegister);
                popMacroAssemblerRegisters(failureStack);
                m_assembler.ret();
            } else
                failureStack = successStack;

            m_stackAllocator.merge(WTFMove(successStack), WTFMove(failureStack));
            return;
        }
    }

    // Success.
    m_assembler.move(Assembler::TrustedImm32(1), returnRegister);

    // Failure.
    if (!failureCases.empty()) {
        Assembler::Jump skipFailureCase = m_assembler.jump();
        failureCases.link(&m_assembler);
        m_assembler.move(Assembler::TrustedImm32(0), returnRegister);
        skipFailureCase.link(&m_assembler);
    }

    if (temporaryStackBase != m_stackAllocator.stackTop())
        m_stackAllocator.popAndDiscardUpTo(temporaryStackBase);
    if (reservedCalleeSavedRegisters)
        m_stackAllocator.pop(calleeSavedRegisterStackReferences, m_registerAllocator.restoreCalleeSavedRegisters());

    StackAllocator successStack = m_stackAllocator;
    if (needsEpilogue)
        generateEpilogue(successStack);
    popMacroAssemblerRegisters(successStack);
    m_assembler.ret();

    // Early failure on function entry case.
    if (!failureOnFunctionEntry.empty()) {
        failureOnFunctionEntry.link(&m_assembler);
        m_assembler.move(Assembler::TrustedImm32(0), returnRegister);
        popMacroAssemblerRegisters(earlyFailureStack);
        m_assembler.ret();
    } else
        earlyFailureStack = successStack;
    m_stackAllocator.merge(WTFMove(successStack), WTFMove(earlyFailureStack));
}

void SelectorCodeGenerator::generateSelectorCheckerExcludingPseudoElements(Assembler::JumpList& failureCases, const SelectorFragmentList& selectorFragmentList)
{
    m_backtrackingLevels.append(BacktrackingLevel());

    for (const SelectorFragment& fragment : selectorFragmentList) {
        switch (fragment.relationToRightFragment) {
        case FragmentRelation::Rightmost:
            generateRightmostTreeWalker(failureCases, fragment);
            break;
        case FragmentRelation::Descendant:
            generateAncestorTreeWalker(failureCases, fragment);
            break;
        case FragmentRelation::Child:
            generateParentElementTreeWalker(failureCases, fragment);
            break;
        case FragmentRelation::DirectAdjacent:
            generateDirectAdjacentTreeWalker(failureCases, fragment);
            break;
        case FragmentRelation::IndirectAdjacent:
            generateIndirectAdjacentTreeWalker(failureCases, fragment);
            break;
        }
        if (shouldMarkStyleIsAffectedByPreviousSibling(fragment)) {
            if (fragmentMatchesTheRightmostElement(fragment))
                generateAddStyleRelationIfResolvingStyle(elementAddressRegister, Style::Relation::AffectedByPreviousSibling);
            else
                generateAddStyleRelationIfResolvingStyle(elementAddressRegister, Style::Relation::DescendantsAffectedByPreviousSibling);
        }
        generateBacktrackingTailsIfNeeded(failureCases, fragment);
    }

    ASSERT(!m_backtrackingLevels.last().descendantBacktrackingStart.isValid());
    ASSERT(!m_backtrackingLevels.last().adjacentBacktrackingStart.isValid());
    m_backtrackingLevels.takeLast();
}

void SelectorCodeGenerator::generateElementMatchesSelectorList(Assembler::JumpList& failingCases, Assembler::RegisterID elementToMatch, const SelectorList& selectorList)
{
    ASSERT(!selectorList.isEmpty());

    RegisterVector registersToSave;

    // The contract is that existing registers are preserved. Two special cases are elementToMatch and elementAddressRegister
    // because they are used by the matcher itself.
    // To simplify things for now, we just always preserve them on the stack.
    unsigned elementToTestIndex = std::numeric_limits<unsigned>::max();
    bool isElementToMatchOnStack = false;
    if (selectorList.clobberElementAddressRegister) {
        if (elementToMatch != elementAddressRegister) {
            registersToSave.append(elementAddressRegister);
            registersToSave.append(elementToMatch);
            elementToTestIndex = 1;
            isElementToMatchOnStack = true;
        } else {
            registersToSave.append(elementAddressRegister);
            elementToTestIndex = 0;
        }
    } else if (elementToMatch != elementAddressRegister)
        registersToSave.append(elementAddressRegister);

    // Next, we need to free as many registers as needed by the nested selector list.
    unsigned availableRegisterCount = m_registerAllocator.availableRegisterCount();

    // Do not count elementAddressRegister, it will remain allocated.
    ++availableRegisterCount;

    if (isElementToMatchOnStack)
        ++availableRegisterCount;

    if (selectorList.registerRequirements > availableRegisterCount) {
        unsigned registerToPushCount = selectorList.registerRequirements - availableRegisterCount;
        for (Assembler::RegisterID registerId : m_registerAllocator.allocatedRegisters()) {
            if (registerId == elementAddressRegister)
                continue; // Handled separately above.
            if (isElementToMatchOnStack && registerId == elementToMatch)
                continue; // Do not push the element twice to the stack!

            registersToSave.append(registerId);

            --registerToPushCount;
            if (!registerToPushCount)
                break;
        }
    }

    StackAllocator::StackReferenceVector allocatedRegistersOnStack = m_stackAllocator.push(registersToSave);
    for (Assembler::RegisterID registerID : registersToSave) {
        if (registerID != elementAddressRegister)
            m_registerAllocator.deallocateRegister(registerID);
    }


    if (elementToMatch != elementAddressRegister)
        m_assembler.move(elementToMatch, elementAddressRegister);

    Assembler::JumpList localFailureCases;
    if (selectorList.size() == 1) {
        const SelectorFragmentList& nestedSelectorFragmentList = selectorList.first();
        generateSelectorCheckerExcludingPseudoElements(localFailureCases, nestedSelectorFragmentList);
    } else {
        Assembler::JumpList matchFragmentList;

        unsigned selectorListSize = selectorList.size();
        unsigned selectorListLastIndex = selectorListSize - 1;
        for (unsigned i = 0; i < selectorList.size(); ++i) {
            const SelectorFragmentList& nestedSelectorFragmentList = selectorList[i];
            Assembler::JumpList localSelectorFailureCases;
            generateSelectorCheckerExcludingPseudoElements(localSelectorFailureCases, nestedSelectorFragmentList);
            if (i != selectorListLastIndex) {
                matchFragmentList.append(m_assembler.jump());
                localSelectorFailureCases.link(&m_assembler);

                if (nestedSelectorFragmentList.clobberElementAddressRegister) {
                    RELEASE_ASSERT(elementToTestIndex != std::numeric_limits<unsigned>::max());
                    m_assembler.loadPtr(m_stackAllocator.addressOf(allocatedRegistersOnStack[elementToTestIndex]), elementAddressRegister);
                }
            } else
                localFailureCases.append(localSelectorFailureCases);
        }
        matchFragmentList.link(&m_assembler);
    }

    // Finally, restore all the registers in the state they were before this selector checker.
    for (Assembler::RegisterID registerID : registersToSave) {
        if (registerID != elementAddressRegister)
            m_registerAllocator.allocateRegister(registerID);
    }

    if (allocatedRegistersOnStack.isEmpty()) {
        failingCases.append(localFailureCases);
        return;
    }

    if (localFailureCases.empty())
        m_stackAllocator.pop(allocatedRegistersOnStack, registersToSave);
    else {
        StackAllocator successStack = m_stackAllocator;
        StackAllocator failureStack = m_stackAllocator;

        successStack.pop(allocatedRegistersOnStack, registersToSave);

        Assembler::Jump skipFailureCase = m_assembler.jump();
        localFailureCases.link(&m_assembler);
        failureStack.pop(allocatedRegistersOnStack, registersToSave);
        failingCases.append(m_assembler.jump());

        skipFailureCase.link(&m_assembler);

        m_stackAllocator.merge(WTFMove(successStack), WTFMove(failureStack));
    }
}

void SelectorCodeGenerator::generateRightmostTreeWalker(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    generateElementMatching(failureCases, failureCases, fragment);
}

void SelectorCodeGenerator::generateWalkToParentNode(Assembler::RegisterID targetRegister)
{
    m_assembler.loadPtr(Assembler::Address(elementAddressRegister, Node::parentNodeMemoryOffset()), targetRegister);
}

void SelectorCodeGenerator::generateWalkToParentElement(Assembler::JumpList& failureCases, Assembler::RegisterID targetRegister)
{
    //    ContainerNode* parent = parentNode()
    //    if (!parent || !parent->isElementNode())
    //         failure
    generateWalkToParentNode(targetRegister);
    failureCases.append(m_assembler.branchTestPtr(Assembler::Zero, targetRegister));
    failureCases.append(DOMJIT::branchTestIsElementFlagOnNode(m_assembler, Assembler::Zero, targetRegister));
}

void SelectorCodeGenerator::generateWalkToParentElementOrShadowRoot(Assembler::JumpList& failureCases, Assembler::RegisterID targetRegister)
{
    //    ContainerNode* parent = parentNode()
    //    if (!parent || !(parent->isElementNode() || parent->isShadowRoot()))
    //         failure
    generateWalkToParentNode(targetRegister);
    failureCases.append(m_assembler.branchTestPtr(Assembler::Zero, targetRegister));
    failureCases.append(DOMJIT::branchTestIsElementOrShadowRootFlagOnNode(m_assembler, Assembler::Zero, targetRegister));
}

void SelectorCodeGenerator::generateParentElementTreeWalker(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    Assembler::JumpList traversalFailureCases;
    generateWalkToParentElement(traversalFailureCases, elementAddressRegister);
    linkFailures(failureCases, fragment.traversalBacktrackingAction, traversalFailureCases);

    Assembler::JumpList matchingTagNameFailureCases;
    Assembler::JumpList matchingPostTagNameFailureCases;
    generateElementMatching(matchingTagNameFailureCases, matchingPostTagNameFailureCases, fragment);
    linkFailures(failureCases, fragment.matchingTagNameBacktrackingAction, matchingTagNameFailureCases);
    linkFailures(failureCases, fragment.matchingPostTagNameBacktrackingAction, matchingPostTagNameFailureCases);

    if (fragment.backtrackingFlags & BacktrackingFlag::SaveDescendantBacktrackingStart) {
        if (!m_descendantBacktrackingStartInUse) {
            m_descendantBacktrackingStart = m_registerAllocator.allocateRegister();
            m_assembler.move(elementAddressRegister, m_descendantBacktrackingStart);
            m_descendantBacktrackingStartInUse = true;
        } else {
            BacktrackingLevel& currentBacktrackingLevel = m_backtrackingLevels.last();
            ASSERT(!currentBacktrackingLevel.descendantBacktrackingStart.isValid());
            currentBacktrackingLevel.descendantBacktrackingStart = m_backtrackingStack.takeLast();

            m_assembler.storePtr(elementAddressRegister, m_stackAllocator.addressOf(currentBacktrackingLevel.descendantBacktrackingStart));
        }
    }
}

void SelectorCodeGenerator::generateAncestorTreeWalker(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    // Loop over the ancestors until one of them matches the fragment.
    Assembler::Label loopStart(m_assembler.label());

    if (fragment.backtrackingFlags & BacktrackingFlag::DescendantEntryPoint)
        m_backtrackingLevels.last().descendantTreeWalkerBacktrackingPoint = m_assembler.label();

    generateWalkToParentElement(failureCases, elementAddressRegister);

    if (fragment.backtrackingFlags & BacktrackingFlag::DescendantEntryPoint)
        m_backtrackingLevels.last().descendantEntryPoint = m_assembler.label();

    Assembler::JumpList matchingFailureCases;
    generateElementMatching(matchingFailureCases, matchingFailureCases, fragment);
    matchingFailureCases.linkTo(loopStart, &m_assembler);
}

inline void SelectorCodeGenerator::generateWalkToNextAdjacentElement(Assembler::JumpList& failureCases, Assembler::RegisterID workRegister)
{
    Assembler::Label loopStart = m_assembler.label();
    m_assembler.loadPtr(Assembler::Address(workRegister, Node::nextSiblingMemoryOffset()), workRegister);
    failureCases.append(m_assembler.branchTestPtr(Assembler::Zero, workRegister));
    DOMJIT::branchTestIsElementFlagOnNode(m_assembler, Assembler::Zero, workRegister).linkTo(loopStart, &m_assembler);
}

inline void SelectorCodeGenerator::generateWalkToPreviousAdjacentElement(Assembler::JumpList& failureCases, Assembler::RegisterID workRegister)
{
    Assembler::Label loopStart = m_assembler.label();
    m_assembler.loadPtr(Assembler::Address(workRegister, Node::previousSiblingMemoryOffset()), workRegister);
    failureCases.append(m_assembler.branchTestPtr(Assembler::Zero, workRegister));
    DOMJIT::branchTestIsElementFlagOnNode(m_assembler, Assembler::Zero, workRegister).linkTo(loopStart, &m_assembler);
}

void SelectorCodeGenerator::generateWalkToPreviousAdjacent(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    //    do {
    //        previousSibling = previousSibling->previousSibling();
    //        if (!previousSibling)
    //            failure!
    //    while (!previousSibling->isElement());
    Assembler::RegisterID previousSibling;
    bool useTailOnTraversalFailure = fragment.traversalBacktrackingAction >= BacktrackingAction::JumpToDescendantTail;
    if (!useTailOnTraversalFailure) {
        // If the current fragment is not dependant on a previously saved elementAddressRegister, a fast recover
        // from a failure would resume with elementAddressRegister.
        // When walking to the previous sibling, the failure can be that previousSibling is null. We cannot backtrack
        // with a null elementAddressRegister so we do the traversal on a copy.
        previousSibling = m_registerAllocator.allocateRegister();
        m_assembler.move(elementAddressRegister, previousSibling);
    } else
        previousSibling = elementAddressRegister;

    Assembler::JumpList traversalFailureCases;
    generateWalkToPreviousAdjacentElement(traversalFailureCases, previousSibling);
    linkFailures(failureCases, fragment.traversalBacktrackingAction, traversalFailureCases);

    // On success, move previousSibling over to elementAddressRegister if we could not work on elementAddressRegister directly.
    if (!useTailOnTraversalFailure) {
        m_assembler.move(previousSibling, elementAddressRegister);
        m_registerAllocator.deallocateRegister(previousSibling);
    }
}

void SelectorCodeGenerator::generateDirectAdjacentTreeWalker(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    generateWalkToPreviousAdjacent(failureCases, fragment);
    generateAddStyleRelationIfResolvingStyle(elementAddressRegister, Style::Relation::AffectsNextSibling);

    Assembler::JumpList matchingTagNameFailureCases;
    Assembler::JumpList matchingPostTagNameFailureCases;
    generateElementMatching(matchingTagNameFailureCases, matchingPostTagNameFailureCases, fragment);
    linkFailures(failureCases, fragment.matchingTagNameBacktrackingAction, matchingTagNameFailureCases);
    linkFailures(failureCases, fragment.matchingPostTagNameBacktrackingAction, matchingPostTagNameFailureCases);

    if (fragment.backtrackingFlags & BacktrackingFlag::SaveAdjacentBacktrackingStart) {
        BacktrackingLevel& currentBacktrackingLevel = m_backtrackingLevels.last();
        ASSERT(!currentBacktrackingLevel.adjacentBacktrackingStart.isValid());
        currentBacktrackingLevel.adjacentBacktrackingStart = m_backtrackingStack.takeLast();

        m_assembler.storePtr(elementAddressRegister, m_stackAllocator.addressOf(currentBacktrackingLevel.adjacentBacktrackingStart));
    }
}

void SelectorCodeGenerator::generateIndirectAdjacentTreeWalker(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    Assembler::Label loopStart(m_assembler.label());

    if (fragment.backtrackingFlags & BacktrackingFlag::IndirectAdjacentEntryPoint)
        m_backtrackingLevels.last().indirectAdjacentTreeWalkerBacktrackingPoint = m_assembler.label();

    generateWalkToPreviousAdjacent(failureCases, fragment);
    generateAddStyleRelationIfResolvingStyle(elementAddressRegister, Style::Relation::AffectsNextSibling);

    if (fragment.backtrackingFlags & BacktrackingFlag::IndirectAdjacentEntryPoint)
        m_backtrackingLevels.last().indirectAdjacentEntryPoint = m_assembler.label();

    Assembler::JumpList localFailureCases;
    generateElementMatching(localFailureCases, localFailureCases, fragment);
    localFailureCases.linkTo(loopStart, &m_assembler);
}

void SelectorCodeGenerator::generateAddStyleRelationIfResolvingStyle(Assembler::RegisterID element, Style::Relation::Type relationType, Optional<Assembler::RegisterID> value)
{
    if (m_selectorContext == SelectorContext::QuerySelector)
        return;

    LocalRegister checkingContext(m_registerAllocator);
    Assembler::Jump notResolvingStyle = jumpIfNotResolvingStyle(checkingContext);

    generateAddStyleRelation(checkingContext, element, relationType, value);

    notResolvingStyle.link(&m_assembler);
}

static void addStyleRelationFunction(SelectorChecker::CheckingContext* checkingContext, const Element* element)
{
    checkingContext->styleRelations.append({ *element, Style::Relation::AffectedByActive, 1 });
}

void SelectorCodeGenerator::generateAddStyleRelation(Assembler::RegisterID checkingContext, Assembler::RegisterID element, Style::Relation::Type relationType, Optional<Assembler::RegisterID> value)
{
    ASSERT(m_selectorContext != SelectorContext::QuerySelector);

    Assembler::Address vectorAddress(checkingContext, OBJECT_OFFSETOF(SelectorChecker::CheckingContext, styleRelations));
    auto dataAddress = vectorAddress.withOffset(Style::Relations::dataMemoryOffset());
    auto sizeAddress = vectorAddress.withOffset(Style::Relations::sizeMemoryOffset());

    auto getLastRelationPointer = [&] (Assembler::RegisterID sizeAndTarget) {
        m_assembler.sub32(Assembler::TrustedImm32(1), sizeAndTarget);
#if CPU(ADDRESS64)
        static_assert(sizeof(Style::Relation) == 16, "");
        static_assert(1 << 4 == 16, "");
        m_assembler.lshiftPtr(Assembler::TrustedImm32(4), sizeAndTarget);
#else
        m_assembler.mul32(Assembler::TrustedImm32(sizeof(Style::Relation)), sizeAndTarget, sizeAndTarget);
#endif
        m_assembler.addPtr(dataAddress, sizeAndTarget);
    };

    // For AffectsNextSibling we just increment the count if the previous added relation was in the same sibling chain.
    Assembler::JumpList mergeSuccess;
    if (relationType == Style::Relation::AffectsNextSibling) {
        Assembler::JumpList mergeFailure;

        LocalRegister lastRelation(m_registerAllocator);
        m_assembler.load32(sizeAddress, lastRelation);

        // if (!checkingContext.styleRelations.isEmpty())
        mergeFailure.append(m_assembler.branchTest32(Assembler::Zero, lastRelation));

        // Style::Relation& lastRelation = checkingContext.styleRelations.last();
        getLastRelationPointer(lastRelation);

        // if (lastRelation.type == Style::Relation::AffectsNextSibling)
        Assembler::Address typeAddress(lastRelation, OBJECT_OFFSETOF(Style::Relation, type));
        mergeFailure.append(m_assembler.branch32(Assembler::NotEqual, typeAddress, Assembler::TrustedImm32(Style::Relation::AffectsNextSibling)));

        Assembler::Address elementAddress(lastRelation, OBJECT_OFFSETOF(Style::Relation, element));
        {
            // if (element.nextSiblingElement() == lastRelation.element)
            LocalRegister nextSiblingElement(m_registerAllocator);
            m_assembler.move(element, nextSiblingElement);
            generateWalkToNextAdjacentElement(mergeFailure, nextSiblingElement);
            mergeFailure.append(m_assembler.branchPtr(Assembler::NotEqual, nextSiblingElement, elementAddress));
        }

        // ++lastRelation.value;
        Assembler::Address valueAddress(lastRelation, OBJECT_OFFSETOF(Style::Relation, value));
        m_assembler.add32(Assembler::TrustedImm32(1), valueAddress);

        // lastRelation.element = &element;
        m_assembler.storePtr(element, elementAddress);

        mergeSuccess.append(m_assembler.jump());
        mergeFailure.link(&m_assembler);
    }

    // FIXME: Append to vector without a function call at least when there is sufficient capacity.
    FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
    functionCall.setFunctionAddress(addStyleRelationFunction);
    functionCall.setTwoArguments(checkingContext, element);
    functionCall.call();

    LocalRegister relationPointer(m_registerAllocator);
    m_assembler.load32(sizeAddress, relationPointer);
    getLastRelationPointer(relationPointer);

    Assembler::Address typeAddress(relationPointer, OBJECT_OFFSETOF(Style::Relation, type));
    m_assembler.store32(Assembler::TrustedImm32(relationType), typeAddress);

    if (value) {
        Assembler::Address valueAddress(relationPointer, OBJECT_OFFSETOF(Style::Relation, value));
        m_assembler.store32(*value, valueAddress);
    }

    mergeSuccess.link(&m_assembler);
}

Assembler::JumpList SelectorCodeGenerator::jumpIfNoPreviousAdjacentElement()
{
    Assembler::JumpList successCase;
    LocalRegister previousSibling(m_registerAllocator);
    m_assembler.move(elementAddressRegister, previousSibling);
    generateWalkToPreviousAdjacentElement(successCase, previousSibling);
    return successCase;
}

Assembler::JumpList SelectorCodeGenerator::jumpIfNoNextAdjacentElement()
{
    Assembler::JumpList successCase;
    LocalRegister nextSibling(m_registerAllocator);
    m_assembler.move(elementAddressRegister, nextSibling);
    generateWalkToNextAdjacentElement(successCase, nextSibling);
    return successCase;
}


void SelectorCodeGenerator::loadCheckingContext(Assembler::RegisterID checkingContext)
{
    // Get the checking context.
    RELEASE_ASSERT(m_functionType == FunctionType::SelectorCheckerWithCheckingContext);
    m_assembler.loadPtr(m_stackAllocator.addressOf(m_checkingContextStackReference), checkingContext);
}

Assembler::Jump SelectorCodeGenerator::branchOnResolvingModeWithCheckingContext(Assembler::RelationalCondition condition, SelectorChecker::Mode mode, Assembler::RegisterID checkingContext)
{
    // Depend on the specified resolving mode and our current mode, branch.
    static_assert(sizeof(SelectorChecker::Mode) == 1, "We generate a byte load/test for the SelectorChecker::Mode.");
    return m_assembler.branch8(condition, Assembler::Address(checkingContext, OBJECT_OFFSETOF(SelectorChecker::CheckingContext, resolvingMode)), Assembler::TrustedImm32(static_cast<std::underlying_type<SelectorChecker::Mode>::type>(mode)));

}

Assembler::Jump SelectorCodeGenerator::branchOnResolvingMode(Assembler::RelationalCondition condition, SelectorChecker::Mode mode, Assembler::RegisterID checkingContext)
{
    loadCheckingContext(checkingContext);
    return branchOnResolvingModeWithCheckingContext(condition, mode, checkingContext);
}

Assembler::Jump SelectorCodeGenerator::jumpIfNotResolvingStyle(Assembler::RegisterID checkingContext)
{
    return branchOnResolvingMode(Assembler::NotEqual, SelectorChecker::Mode::ResolvingStyle, checkingContext);
}

void SelectorCodeGenerator::generateSpecialFailureInQuirksModeForActiveAndHoverIfNeeded(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    if (fragment.onlyMatchesLinksInQuirksMode) {
        // If the element is a link, it can always match :hover or :active.
        Assembler::Jump isLink = m_assembler.branchTest32(Assembler::NonZero, Assembler::Address(elementAddressRegister, Node::nodeFlagsMemoryOffset()), Assembler::TrustedImm32(Node::flagIsLink()));

        // Only quirks mode restrict :hover and :active.
        static_assert(sizeof(DocumentCompatibilityMode) == 1, "We generate a byte load/test for the compatibility mode.");
        LocalRegister documentAddress(m_registerAllocator);
        DOMJIT::loadDocument(m_assembler, elementAddressRegister, documentAddress);
        failureCases.append(m_assembler.branchTest8(Assembler::NonZero, Assembler::Address(documentAddress, Document::compatibilityModeMemoryOffset()), Assembler::TrustedImm32(static_cast<std::underlying_type<DocumentCompatibilityMode>::type>(DocumentCompatibilityMode::QuirksMode))));

        isLink.link(&m_assembler);
    }
}

#if CPU(ARM_THUMB2) && !CPU(APPLE_ARMV7S)
// FIXME: This could be implemented in assembly to avoid a function call, and we know the divisor at jit-compile time.
static int moduloHelper(int dividend, int divisor)
{
    return dividend % divisor;
}
#endif

// The value in inputDividend is destroyed by the modulo operation.
Assembler::Jump SelectorCodeGenerator::modulo(Assembler::ResultCondition condition, Assembler::RegisterID inputDividend, int divisor)
{
    RELEASE_ASSERT(divisor);
#if CPU(ARM64) || CPU(APPLE_ARMV7S)
    LocalRegister divisorRegister(m_registerAllocator);
    m_assembler.move(Assembler::TrustedImm32(divisor), divisorRegister);

    LocalRegister resultRegister(m_registerAllocator);
    m_assembler.m_assembler.sdiv<32>(resultRegister, inputDividend, divisorRegister);
    m_assembler.mul32(divisorRegister, resultRegister);
    return m_assembler.branchSub32(condition, inputDividend, resultRegister, resultRegister);
#elif CPU(ARM_THUMB2) && !CPU(APPLE_ARMV7S)
    LocalRegisterWithPreference divisorRegister(m_registerAllocator, JSC::GPRInfo::argumentGPR1);
    m_assembler.move(Assembler::TrustedImm32(divisor), divisorRegister);
    FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
    functionCall.setFunctionAddress(moduloHelper);
    functionCall.setTwoArguments(inputDividend, divisorRegister);
    return functionCall.callAndBranchOnBooleanReturnValue(condition);
#elif CPU(X86_64)
    // idiv takes RAX + an arbitrary register, and return RAX + RDX. Most of this code is about doing
    // an efficient allocation of those registers. If a register is already in use and is not the inputDividend,
    // we first try to copy it to a temporary register, it that is not possible we fall back to the stack.
    enum class RegisterAllocationType {
        External,
        AllocatedLocally,
        CopiedToTemporary,
        PushedToStack
    };

    // 1) Get RAX and RDX.
    // If they are already used, push them to the stack.
    Assembler::RegisterID dividend = JSC::X86Registers::eax;
    RegisterAllocationType dividendAllocation = RegisterAllocationType::External;
    StackAllocator::StackReference temporaryDividendStackReference;
    Assembler::RegisterID temporaryDividendCopy = JSC::InvalidGPRReg;
    if (inputDividend != dividend) {
        bool registerIsInUse = m_registerAllocator.allocatedRegisters().contains(dividend);
        if (registerIsInUse) {
            if (m_registerAllocator.availableRegisterCount() > 1) {
                temporaryDividendCopy = m_registerAllocator.allocateRegister();
                m_assembler.move(dividend, temporaryDividendCopy);
                dividendAllocation = RegisterAllocationType::CopiedToTemporary;
            } else {
                temporaryDividendStackReference = m_stackAllocator.push(dividend);
                dividendAllocation = RegisterAllocationType::PushedToStack;
            }
        } else {
            m_registerAllocator.allocateRegister(dividend);
            dividendAllocation = RegisterAllocationType::AllocatedLocally;
        }
        m_assembler.move(inputDividend, dividend);
    }

    Assembler::RegisterID remainder = JSC::X86Registers::edx;
    RegisterAllocationType remainderAllocation = RegisterAllocationType::External;
    StackAllocator::StackReference temporaryRemainderStackReference;
    Assembler::RegisterID temporaryRemainderCopy = JSC::InvalidGPRReg;
    if (inputDividend != remainder) {
        bool registerIsInUse = m_registerAllocator.allocatedRegisters().contains(remainder);
        if (registerIsInUse) {
            if (m_registerAllocator.availableRegisterCount() > 1) {
                temporaryRemainderCopy = m_registerAllocator.allocateRegister();
                m_assembler.move(remainder, temporaryRemainderCopy);
                remainderAllocation = RegisterAllocationType::CopiedToTemporary;
            } else {
                temporaryRemainderStackReference = m_stackAllocator.push(remainder);
                remainderAllocation = RegisterAllocationType::PushedToStack;
            }
        } else {
            m_registerAllocator.allocateRegister(remainder);
            remainderAllocation = RegisterAllocationType::AllocatedLocally;
        }
    }

    // If the input register is used by idiv, save its value to restore it after the operation.
    Assembler::RegisterID inputDividendCopy;
    StackAllocator::StackReference pushedInputDividendStackReference;
    RegisterAllocationType savedInputDividendAllocationType = RegisterAllocationType::External;
    if (inputDividend == dividend || inputDividend == remainder) {
        if (m_registerAllocator.availableRegisterCount() > 1) {
            inputDividendCopy = m_registerAllocator.allocateRegister();
            m_assembler.move(inputDividend, inputDividendCopy);
            savedInputDividendAllocationType = RegisterAllocationType::CopiedToTemporary;
        } else {
            pushedInputDividendStackReference = m_stackAllocator.push(inputDividend);
            savedInputDividendAllocationType = RegisterAllocationType::PushedToStack;
        }
    }

    m_assembler.m_assembler.cdq();

    // 2) Perform the division with idiv.
    {
        LocalRegister divisorRegister(m_registerAllocator);
        m_assembler.move(Assembler::TrustedImm64(divisor), divisorRegister);
        m_assembler.m_assembler.idivl_r(divisorRegister);
        m_assembler.test32(remainder);
    }

    // 3) Return RAX and RDX.
    if (remainderAllocation == RegisterAllocationType::AllocatedLocally)
        m_registerAllocator.deallocateRegister(remainder);
    else if (remainderAllocation == RegisterAllocationType::CopiedToTemporary) {
        m_assembler.move(temporaryRemainderCopy, remainder);
        m_registerAllocator.deallocateRegister(temporaryRemainderCopy);
    } else if (remainderAllocation == RegisterAllocationType::PushedToStack)
        m_stackAllocator.pop(temporaryRemainderStackReference, remainder);

    if (dividendAllocation == RegisterAllocationType::AllocatedLocally)
        m_registerAllocator.deallocateRegister(dividend);
    else if (dividendAllocation == RegisterAllocationType::CopiedToTemporary) {
        m_assembler.move(temporaryDividendCopy, dividend);
        m_registerAllocator.deallocateRegister(temporaryDividendCopy);
    } else if (dividendAllocation == RegisterAllocationType::PushedToStack)
        m_stackAllocator.pop(temporaryDividendStackReference, dividend);

    if (savedInputDividendAllocationType != RegisterAllocationType::External) {
        if (savedInputDividendAllocationType == RegisterAllocationType::CopiedToTemporary) {
            m_assembler.move(inputDividendCopy, inputDividend);
            m_registerAllocator.deallocateRegister(inputDividendCopy);
        } else if (savedInputDividendAllocationType == RegisterAllocationType::PushedToStack)
            m_stackAllocator.pop(pushedInputDividendStackReference, inputDividend);
    }

    // 4) Branch on the test.
    return m_assembler.branch(condition);
#else
#error Modulo is not implemented for this architecture.
#endif
}

void SelectorCodeGenerator::moduloIsZero(Assembler::JumpList& failureCases, Assembler::RegisterID inputDividend, int divisor)
{
    if (divisor == 1 || divisor == -1)
        return;
    if (divisor == 2 || divisor == -2) {
        failureCases.append(m_assembler.branchTest32(Assembler::NonZero, inputDividend, Assembler::TrustedImm32(1)));
        return;
    }

    failureCases.append(modulo(Assembler::NonZero, inputDividend, divisor));
}

void SelectorCodeGenerator::linkFailures(Assembler::JumpList& globalFailureCases, BacktrackingAction backtrackingAction, Assembler::JumpList& localFailureCases)
{
    switch (backtrackingAction) {
    case BacktrackingAction::NoBacktracking:
        globalFailureCases.append(localFailureCases);
        break;
    case BacktrackingAction::JumpToDescendantEntryPoint:
        localFailureCases.linkTo(m_backtrackingLevels.last().descendantEntryPoint, &m_assembler);
        break;
    case BacktrackingAction::JumpToDescendantTreeWalkerEntryPoint:
        localFailureCases.linkTo(m_backtrackingLevels.last().descendantTreeWalkerBacktrackingPoint, &m_assembler);
        break;
    case BacktrackingAction::JumpToDescendantTail:
        m_backtrackingLevels.last().descendantBacktrackingFailureCases.append(localFailureCases);
        break;
    case BacktrackingAction::JumpToIndirectAdjacentEntryPoint:
        localFailureCases.linkTo(m_backtrackingLevels.last().indirectAdjacentEntryPoint, &m_assembler);
        break;
    case BacktrackingAction::JumpToIndirectAdjacentTreeWalkerEntryPoint:
        localFailureCases.linkTo(m_backtrackingLevels.last().indirectAdjacentTreeWalkerBacktrackingPoint, &m_assembler);
        break;
    case BacktrackingAction::JumpToDirectAdjacentTail:
        m_backtrackingLevels.last().adjacentBacktrackingFailureCases.append(localFailureCases);
        break;
    }
}

void SelectorCodeGenerator::generateAdjacentBacktrackingTail()
{
    // Recovering tail.
    m_backtrackingLevels.last().adjacentBacktrackingFailureCases.link(&m_assembler);
    m_backtrackingLevels.last().adjacentBacktrackingFailureCases.clear();

    BacktrackingLevel& currentBacktrackingLevel = m_backtrackingLevels.last();
    m_assembler.loadPtr(m_stackAllocator.addressOf(currentBacktrackingLevel.adjacentBacktrackingStart), elementAddressRegister);
    m_backtrackingStack.append(currentBacktrackingLevel.adjacentBacktrackingStart);
    currentBacktrackingLevel.adjacentBacktrackingStart = StackAllocator::StackReference();

    m_assembler.jump(m_backtrackingLevels.last().indirectAdjacentEntryPoint);
}

void SelectorCodeGenerator::generateDescendantBacktrackingTail()
{
    m_backtrackingLevels.last().descendantBacktrackingFailureCases.link(&m_assembler);
    m_backtrackingLevels.last().descendantBacktrackingFailureCases.clear();

    BacktrackingLevel& currentBacktrackingLevel = m_backtrackingLevels.last();
    if (!currentBacktrackingLevel.descendantBacktrackingStart.isValid()) {
        m_assembler.move(m_descendantBacktrackingStart, elementAddressRegister);
        m_registerAllocator.deallocateRegister(m_descendantBacktrackingStart);
        m_descendantBacktrackingStartInUse = false;
    } else {
        m_assembler.loadPtr(m_stackAllocator.addressOf(currentBacktrackingLevel.descendantBacktrackingStart), elementAddressRegister);
        m_backtrackingStack.append(currentBacktrackingLevel.descendantBacktrackingStart);
        currentBacktrackingLevel.descendantBacktrackingStart = StackAllocator::StackReference();
    }

    m_assembler.jump(m_backtrackingLevels.last().descendantEntryPoint);
}

void SelectorCodeGenerator::generateBacktrackingTailsIfNeeded(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    if (fragment.backtrackingFlags & BacktrackingFlag::DirectAdjacentTail && fragment.backtrackingFlags & BacktrackingFlag::DescendantTail) {
        Assembler::Jump normalCase = m_assembler.jump();
        generateAdjacentBacktrackingTail();
        generateDescendantBacktrackingTail();
        normalCase.link(&m_assembler);
    } else if (fragment.backtrackingFlags & BacktrackingFlag::DirectAdjacentTail) {
        Assembler::Jump normalCase = m_assembler.jump();
        generateAdjacentBacktrackingTail();
        failureCases.append(m_assembler.jump());
        normalCase.link(&m_assembler);
    } else if (fragment.backtrackingFlags & BacktrackingFlag::DescendantTail) {
        Assembler::Jump normalCase = m_assembler.jump();
        generateDescendantBacktrackingTail();
        normalCase.link(&m_assembler);
    }
}

void SelectorCodeGenerator::generateElementMatching(Assembler::JumpList& matchingTagNameFailureCases, Assembler::JumpList& matchingPostTagNameFailureCases, const SelectorFragment& fragment)
{
    if (fragment.tagNameSelector)
        generateElementHasTagName(matchingTagNameFailureCases, *(fragment.tagNameSelector));

    generateElementLinkMatching(matchingPostTagNameFailureCases, fragment);

    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassRoot))
        generateElementIsRoot(matchingPostTagNameFailureCases);

    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassScope))
        generateElementIsScopeRoot(matchingPostTagNameFailureCases);

    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassTarget))
        generateElementIsTarget(matchingPostTagNameFailureCases);

    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassFocusWithin))
        generateElementHasFocusWithin(matchingPostTagNameFailureCases);

    for (unsigned i = 0; i < fragment.unoptimizedPseudoClasses.size(); ++i)
        generateElementFunctionCallTest(matchingPostTagNameFailureCases, fragment.unoptimizedPseudoClasses[i]);

    for (unsigned i = 0; i < fragment.unoptimizedPseudoClassesWithContext.size(); ++i)
        generateContextFunctionCallTest(matchingPostTagNameFailureCases, fragment.unoptimizedPseudoClassesWithContext[i]);

    generateElementDataMatching(matchingPostTagNameFailureCases, fragment);

    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassActive))
        generateElementIsActive(matchingPostTagNameFailureCases, fragment);
    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassEmpty))
        generateElementIsEmpty(matchingPostTagNameFailureCases);
    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassHover))
        generateElementIsHovered(matchingPostTagNameFailureCases, fragment);
    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassOnlyChild))
        generateElementIsOnlyChild(matchingPostTagNameFailureCases);
    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassPlaceholderShown))
        generateElementHasPlaceholderShown(matchingPostTagNameFailureCases);
    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassFirstChild))
        generateElementIsFirstChild(matchingPostTagNameFailureCases);
    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassLastChild))
        generateElementIsLastChild(matchingPostTagNameFailureCases);
    if (!fragment.nthChildFilters.isEmpty())
        generateElementIsNthChild(matchingPostTagNameFailureCases, fragment);
    if (!fragment.nthLastChildFilters.isEmpty())
        generateElementIsNthLastChild(matchingPostTagNameFailureCases, fragment);
    if (!fragment.notFilters.isEmpty())
        generateElementMatchesNotPseudoClass(matchingPostTagNameFailureCases, fragment);
    if (!fragment.anyFilters.isEmpty())
        generateElementMatchesAnyPseudoClass(matchingPostTagNameFailureCases, fragment);
    if (!fragment.matchesFilters.isEmpty())
        generateElementMatchesMatchesPseudoClass(matchingPostTagNameFailureCases, fragment);
    if (!fragment.languageArgumentsList.isEmpty())
        generateElementIsInLanguage(matchingPostTagNameFailureCases, fragment);
    if (!fragment.nthChildOfFilters.isEmpty())
        generateElementIsNthChildOf(matchingPostTagNameFailureCases, fragment);
    if (!fragment.nthLastChildOfFilters.isEmpty())
        generateElementIsNthLastChildOf(matchingPostTagNameFailureCases, fragment);
    if (fragment.pseudoElementSelector)
        generateElementHasPseudoElement(matchingPostTagNameFailureCases, fragment);

    // Reach here when the generateElementMatching matching succeeded.
    // Only when the matching succeeeded, the last visited element should be stored and checked at the end of the whole matching.
    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassVisited))
        generateStoreLastVisitedElement(elementAddressRegister);
}

void SelectorCodeGenerator::generateElementDataMatching(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    if (!fragment.id && fragment.classNames.isEmpty() && fragment.attributes.isEmpty())
        return;

    //  Generate:
    //     elementDataAddress = element->elementData();
    //     if (!elementDataAddress)
    //         failure!
    LocalRegister elementDataAddress(m_registerAllocator);
    m_assembler.loadPtr(Assembler::Address(elementAddressRegister, Element::elementDataMemoryOffset()), elementDataAddress);
    failureCases.append(m_assembler.branchTestPtr(Assembler::Zero, elementDataAddress));

    if (fragment.id)
        generateElementHasId(failureCases, elementDataAddress, *fragment.id);
    if (!fragment.classNames.isEmpty())
        generateElementHasClasses(failureCases, elementDataAddress, fragment.classNames);
    if (!fragment.attributes.isEmpty())
        generateElementAttributesMatching(failureCases, elementDataAddress, fragment);
}

void SelectorCodeGenerator::generateElementLinkMatching(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    if (fragment.pseudoClasses.contains(CSSSelector::PseudoClassLink)
        || fragment.pseudoClasses.contains(CSSSelector::PseudoClassAnyLink)
        || fragment.pseudoClasses.contains(CSSSelector::PseudoClassVisited))
        generateElementIsLink(failureCases);
}

static inline bool canMatchStyleAttribute(const SelectorFragment& fragment)
{
    for (unsigned i = 0; i < fragment.attributes.size(); ++i) {
        const CSSSelector& attributeSelector = fragment.attributes[i].selector();
        const QualifiedName& attributeName = attributeSelector.attribute();
        if (Attribute::nameMatchesFilter(HTMLNames::styleAttr, attributeName.prefix(), attributeName.localName(), attributeName.namespaceURI()))
            return true;

        const AtomicString& canonicalLocalName = attributeSelector.attributeCanonicalLocalName();
        if (attributeName.localName() != canonicalLocalName
            && Attribute::nameMatchesFilter(HTMLNames::styleAttr, attributeName.prefix(), attributeSelector.attributeCanonicalLocalName(), attributeName.namespaceURI())) {
            return true;
        }
    }
    return false;
}

void SelectorCodeGenerator::generateSynchronizeStyleAttribute(Assembler::RegisterID elementDataArraySizeAndFlags)
{
    // The style attribute is updated lazily based on the flag styleAttributeIsDirty.
    Assembler::Jump styleAttributeNotDirty = m_assembler.branchTest32(Assembler::Zero, elementDataArraySizeAndFlags, Assembler::TrustedImm32(ElementData::styleAttributeIsDirtyFlag()));

    FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
    functionCall.setFunctionAddress(StyledElement::synchronizeStyleAttributeInternal);
    Assembler::RegisterID elementAddress = elementAddressRegister;
    functionCall.setOneArgument(elementAddress);
    functionCall.call();

    styleAttributeNotDirty.link(&m_assembler);
}

static inline bool canMatchAnimatableSVGAttribute(const SelectorFragment& fragment)
{
    for (unsigned i = 0; i < fragment.attributes.size(); ++i) {
        const CSSSelector& attributeSelector = fragment.attributes[i].selector();
        const QualifiedName& selectorAttributeName = attributeSelector.attribute();

        const QualifiedName& candidateForLocalName = SVGElement::animatableAttributeForName(selectorAttributeName.localName());
        if (Attribute::nameMatchesFilter(candidateForLocalName, selectorAttributeName.prefix(), selectorAttributeName.localName(), selectorAttributeName.namespaceURI()))
            return true;

        const AtomicString& canonicalLocalName = attributeSelector.attributeCanonicalLocalName();
        if (selectorAttributeName.localName() != canonicalLocalName) {
            const QualifiedName& candidateForCanonicalLocalName = SVGElement::animatableAttributeForName(selectorAttributeName.localName());
            if (Attribute::nameMatchesFilter(candidateForCanonicalLocalName, selectorAttributeName.prefix(), selectorAttributeName.localName(), selectorAttributeName.namespaceURI()))
                return true;
        }
    }
    return false;
}

void SelectorCodeGenerator::generateSynchronizeAllAnimatedSVGAttribute(Assembler::RegisterID elementDataArraySizeAndFlags)
{
    // SVG attributes can be updated lazily depending on the flag AnimatedSVGAttributesAreDirty. We need to check
    // that first.
    Assembler::Jump animatedSVGAttributesNotDirty = m_assembler.branchTest32(Assembler::Zero, elementDataArraySizeAndFlags, Assembler::TrustedImm32(ElementData::animatedSVGAttributesAreDirtyFlag()));

    FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
    functionCall.setFunctionAddress(SVGElement::synchronizeAllAnimatedSVGAttribute);
    Assembler::RegisterID elementAddress = elementAddressRegister;
    functionCall.setOneArgument(elementAddress);
    functionCall.call();

    animatedSVGAttributesNotDirty.link(&m_assembler);
}

void SelectorCodeGenerator::generateElementAttributesMatching(Assembler::JumpList& failureCases, const LocalRegister& elementDataAddress, const SelectorFragment& fragment)
{
    LocalRegister scratchRegister(m_registerAllocator);
    Assembler::RegisterID elementDataArraySizeAndFlags = scratchRegister;
    Assembler::RegisterID attributeArrayLength = scratchRegister;

    m_assembler.load32(Assembler::Address(elementDataAddress, ElementData::arraySizeAndFlagsMemoryOffset()), elementDataArraySizeAndFlags);

    if (canMatchStyleAttribute(fragment))
        generateSynchronizeStyleAttribute(elementDataArraySizeAndFlags);

    if (canMatchAnimatableSVGAttribute(fragment))
        generateSynchronizeAllAnimatedSVGAttribute(elementDataArraySizeAndFlags);

    // Attributes can be stored either in a separate vector for UniqueElementData, or after the elementData itself
    // for ShareableElementData.
    LocalRegister attributeArrayPointer(m_registerAllocator);
    Assembler::Jump isShareableElementData  = m_assembler.branchTest32(Assembler::Zero, elementDataArraySizeAndFlags, Assembler::TrustedImm32(ElementData::isUniqueFlag()));
    {
        ptrdiff_t attributeVectorOffset = UniqueElementData::attributeVectorMemoryOffset();
        m_assembler.loadPtr(Assembler::Address(elementDataAddress, attributeVectorOffset + UniqueElementData::AttributeVector::dataMemoryOffset()), attributeArrayPointer);
        m_assembler.load32(Assembler::Address(elementDataAddress, attributeVectorOffset + UniqueElementData::AttributeVector::sizeMemoryOffset()), attributeArrayLength);
    }
    Assembler::Jump skipShareable = m_assembler.jump();

    {
        isShareableElementData.link(&m_assembler);
        m_assembler.urshift32(elementDataArraySizeAndFlags, Assembler::TrustedImm32(ElementData::arraySizeOffset()), attributeArrayLength);
        m_assembler.addPtr(Assembler::TrustedImm32(ShareableElementData::attributeArrayMemoryOffset()), elementDataAddress, attributeArrayPointer);
    }

    skipShareable.link(&m_assembler);

    // If there are no attributes, fail immediately.
    failureCases.append(m_assembler.branchTest32(Assembler::Zero, attributeArrayLength));

    unsigned attributeCount = fragment.attributes.size();
    for (unsigned i = 0; i < attributeCount; ++i) {
        Assembler::RegisterID decIndexRegister;
        Assembler::RegisterID currentAttributeAddress;

        bool isLastAttribute = i == (attributeCount - 1);
        if (!isLastAttribute) {
            // We need to make a copy to let the next iterations use the values.
            currentAttributeAddress = m_registerAllocator.allocateRegister();
            decIndexRegister = m_registerAllocator.allocateRegister();
            m_assembler.move(attributeArrayPointer, currentAttributeAddress);
            m_assembler.move(attributeArrayLength, decIndexRegister);
        } else {
            currentAttributeAddress = attributeArrayPointer;
            decIndexRegister = attributeArrayLength;
        }

        generateElementAttributeMatching(failureCases, currentAttributeAddress, decIndexRegister, fragment.attributes[i]);

        if (!isLastAttribute) {
            m_registerAllocator.deallocateRegister(decIndexRegister);
            m_registerAllocator.deallocateRegister(currentAttributeAddress);
        }
    }
}

void SelectorCodeGenerator::generateElementAttributeMatching(Assembler::JumpList& failureCases, Assembler::RegisterID currentAttributeAddress, Assembler::RegisterID decIndexRegister, const AttributeMatchingInfo& attributeInfo)
{
    // Get the localName used for comparison. HTML elements use a lowercase local name known in selectors as canonicalLocalName.
    LocalRegister localNameToMatch(m_registerAllocator);

    // In general, canonicalLocalName and localName are the same. When they differ, we have to check if the node is HTML to know
    // which one to use.
    const CSSSelector& attributeSelector = attributeInfo.selector();
    const AtomicStringImpl* canonicalLocalName = attributeSelector.attributeCanonicalLocalName().impl();
    const AtomicStringImpl* localName = attributeSelector.attribute().localName().impl();
    if (canonicalLocalName == localName)
        m_assembler.move(Assembler::TrustedImmPtr(canonicalLocalName), localNameToMatch);
    else {
        m_assembler.move(Assembler::TrustedImmPtr(canonicalLocalName), localNameToMatch);
        Assembler::Jump elementIsHTML = DOMJIT::branchTestIsHTMLFlagOnNode(m_assembler, Assembler::NonZero, elementAddressRegister);
        m_assembler.move(Assembler::TrustedImmPtr(localName), localNameToMatch);
        elementIsHTML.link(&m_assembler);
    }

    Assembler::JumpList successCases;
    Assembler::Label loopStart(m_assembler.label());

    {
        LocalRegister qualifiedNameImpl(m_registerAllocator);
        m_assembler.loadPtr(Assembler::Address(currentAttributeAddress, Attribute::nameMemoryOffset()), qualifiedNameImpl);

        bool shouldCheckNamespace = attributeSelector.attribute().prefix() != starAtom();
        if (shouldCheckNamespace) {
            Assembler::Jump nameDoesNotMatch = m_assembler.branchPtr(Assembler::NotEqual, Assembler::Address(qualifiedNameImpl, QualifiedName::QualifiedNameImpl::localNameMemoryOffset()), localNameToMatch);

            const AtomicStringImpl* namespaceURI = attributeSelector.attribute().namespaceURI().impl();
            if (namespaceURI) {
                LocalRegister namespaceToMatch(m_registerAllocator);
                m_assembler.move(Assembler::TrustedImmPtr(namespaceURI), namespaceToMatch);
                successCases.append(m_assembler.branchPtr(Assembler::Equal, Assembler::Address(qualifiedNameImpl, QualifiedName::QualifiedNameImpl::namespaceMemoryOffset()), namespaceToMatch));
            } else
                successCases.append(m_assembler.branchTestPtr(Assembler::Zero, Assembler::Address(qualifiedNameImpl, QualifiedName::QualifiedNameImpl::namespaceMemoryOffset())));
            nameDoesNotMatch.link(&m_assembler);
        } else
            successCases.append(m_assembler.branchPtr(Assembler::Equal, Assembler::Address(qualifiedNameImpl, QualifiedName::QualifiedNameImpl::localNameMemoryOffset()), localNameToMatch));
    }

    Assembler::Label loopReEntry(m_assembler.label());

    // If we reached the last element -> failure.
    failureCases.append(m_assembler.branchSub32(Assembler::Zero, Assembler::TrustedImm32(1), decIndexRegister));

    // Otherwise just loop over.
    m_assembler.addPtr(Assembler::TrustedImm32(sizeof(Attribute)), currentAttributeAddress);
    m_assembler.jump().linkTo(loopStart, &m_assembler);

    successCases.link(&m_assembler);

    if (attributeSelector.match() != CSSSelector::Set) {
        // We make the assumption that name matching fails in most cases and we keep value matching outside
        // of the loop. We re-enter the loop if needed.
        // FIXME: exact case sensitive value matching is so simple that it should be done in the loop.
        Assembler::JumpList localFailureCases;
        generateElementAttributeValueMatching(localFailureCases, currentAttributeAddress, attributeInfo);
        localFailureCases.linkTo(loopReEntry, &m_assembler);
    }
}

enum CaseSensitivity {
    CaseSensitive,
    CaseInsensitive
};

template<CaseSensitivity caseSensitivity>
static bool attributeValueBeginsWith(const Attribute* attribute, AtomicStringImpl* expectedString)
{
    ASSERT(expectedString);

    AtomicStringImpl& valueImpl = *attribute->value().impl();
    if (caseSensitivity == CaseSensitive)
        return valueImpl.startsWith(*expectedString);
    return valueImpl.startsWithIgnoringASCIICase(*expectedString);
}

template<CaseSensitivity caseSensitivity>
static bool attributeValueContains(const Attribute* attribute, AtomicStringImpl* expectedString)
{
    AtomicStringImpl& valueImpl = *attribute->value().impl();
    if (caseSensitivity == CaseSensitive)
        return valueImpl.find(expectedString) != notFound;
    return valueImpl.findIgnoringASCIICase(expectedString) != notFound;
}

template<CaseSensitivity caseSensitivity>
static bool attributeValueEndsWith(const Attribute* attribute, AtomicStringImpl* expectedString)
{
    ASSERT(expectedString);

    AtomicStringImpl& valueImpl = *attribute->value().impl();
    if (caseSensitivity == CaseSensitive)
        return valueImpl.endsWith(*expectedString);
    return valueImpl.endsWithIgnoringASCIICase(*expectedString);
}

template<CaseSensitivity caseSensitivity>
static bool attributeValueMatchHyphenRule(const Attribute* attribute, AtomicStringImpl* expectedString)
{
    ASSERT(expectedString);

    AtomicStringImpl& valueImpl = *attribute->value().impl();
    if (valueImpl.length() < expectedString->length())
        return false;

    bool valueStartsWithExpectedString;
    if (caseSensitivity == CaseSensitive)
        valueStartsWithExpectedString = valueImpl.startsWith(*expectedString);
    else
        valueStartsWithExpectedString = valueImpl.startsWithIgnoringASCIICase(*expectedString);

    if (!valueStartsWithExpectedString)
        return false;

    return valueImpl.length() == expectedString->length() || valueImpl[expectedString->length()] == '-';
}

template<CaseSensitivity caseSensitivity>
static bool attributeValueSpaceSeparetedListContains(const Attribute* attribute, AtomicStringImpl* expectedString)
{
    AtomicStringImpl& value = *attribute->value().impl();

    unsigned startSearchAt = 0;
    while (true) {
        size_t foundPos;
        if (caseSensitivity == CaseSensitive)
            foundPos = value.find(expectedString, startSearchAt);
        else
            foundPos = value.findIgnoringASCIICase(expectedString, startSearchAt);
        if (foundPos == notFound)
            return false;
        if (!foundPos || isHTMLSpace(value[foundPos - 1])) {
            unsigned endStr = foundPos + expectedString->length();
            if (endStr == value.length() || isHTMLSpace(value[endStr]))
                return true;
        }
        startSearchAt = foundPos + 1;
    }
    return false;
}

void SelectorCodeGenerator::generateElementAttributeValueMatching(Assembler::JumpList& failureCases, Assembler::RegisterID currentAttributeAddress, const AttributeMatchingInfo& attributeInfo)
{
    const CSSSelector& attributeSelector = attributeInfo.selector();
    const AtomicString& expectedValue = attributeSelector.value();
    ASSERT(!expectedValue.isNull());
    AttributeCaseSensitivity valueCaseSensitivity = attributeInfo.attributeCaseSensitivity();

    switch (attributeSelector.match()) {
    case CSSSelector::Begin:
        generateElementAttributeFunctionCallValueMatching(failureCases, currentAttributeAddress, expectedValue, valueCaseSensitivity, attributeValueBeginsWith<CaseSensitive>, attributeValueBeginsWith<CaseInsensitive>);
        break;
    case CSSSelector::Contain:
        generateElementAttributeFunctionCallValueMatching(failureCases, currentAttributeAddress, expectedValue, valueCaseSensitivity, attributeValueContains<CaseSensitive>, attributeValueContains<CaseInsensitive>);
        break;
    case CSSSelector::End:
        generateElementAttributeFunctionCallValueMatching(failureCases, currentAttributeAddress, expectedValue, valueCaseSensitivity, attributeValueEndsWith<CaseSensitive>, attributeValueEndsWith<CaseInsensitive>);
        break;
    case CSSSelector::Exact:
        generateElementAttributeValueExactMatching(failureCases, currentAttributeAddress, expectedValue, valueCaseSensitivity);
        break;
    case CSSSelector::Hyphen:
        generateElementAttributeFunctionCallValueMatching(failureCases, currentAttributeAddress, expectedValue, valueCaseSensitivity, attributeValueMatchHyphenRule<CaseSensitive>, attributeValueMatchHyphenRule<CaseInsensitive>);
        break;
    case CSSSelector::List:
        generateElementAttributeFunctionCallValueMatching(failureCases, currentAttributeAddress, expectedValue, valueCaseSensitivity, attributeValueSpaceSeparetedListContains<CaseSensitive>, attributeValueSpaceSeparetedListContains<CaseInsensitive>);
        break;
    default:
        ASSERT_NOT_REACHED();
    }
}

static inline Assembler::Jump testIsHTMLClassOnDocument(Assembler::ResultCondition condition, Assembler& assembler, Assembler::RegisterID documentAddress)
{
    return assembler.branchTest32(condition, Assembler::Address(documentAddress, Document::documentClassesMemoryOffset()), Assembler::TrustedImm32(Document::isHTMLDocumentClassFlag()));
}

void SelectorCodeGenerator::generateElementAttributeValueExactMatching(Assembler::JumpList& failureCases, Assembler::RegisterID currentAttributeAddress, const AtomicString& expectedValue, AttributeCaseSensitivity valueCaseSensitivity)
{
    LocalRegisterWithPreference expectedValueRegister(m_registerAllocator, JSC::GPRInfo::argumentGPR1);
    m_assembler.move(Assembler::TrustedImmPtr(expectedValue.impl()), expectedValueRegister);

    switch (valueCaseSensitivity) {
    case AttributeCaseSensitivity::CaseSensitive: {
        failureCases.append(m_assembler.branchPtr(Assembler::NotEqual, Assembler::Address(currentAttributeAddress, Attribute::valueMemoryOffset()), expectedValueRegister));
        break;
    }
    case AttributeCaseSensitivity::HTMLLegacyCaseInsensitive: {
        Assembler::Jump skipCaseInsensitiveComparison = m_assembler.branchPtr(Assembler::Equal, Assembler::Address(currentAttributeAddress, Attribute::valueMemoryOffset()), expectedValueRegister);

        // If the element is an HTML element, in a HTML dcoument (not including XHTML), value matching is case insensitive.
        // Taking the contrapositive, if we find the element is not HTML or is not in a HTML document, the condition above
        // sould be sufficient and we can fail early.
        failureCases.append(DOMJIT::branchTestIsHTMLFlagOnNode(m_assembler, Assembler::Zero, elementAddressRegister));

        {
            LocalRegister document(m_registerAllocator);
            DOMJIT::loadDocument(m_assembler, elementAddressRegister, document);
            failureCases.append(testIsHTMLClassOnDocument(Assembler::Zero, m_assembler, document));
        }

        LocalRegister valueStringImpl(m_registerAllocator);
        m_assembler.loadPtr(Assembler::Address(currentAttributeAddress, Attribute::valueMemoryOffset()), valueStringImpl);

        FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
        functionCall.setFunctionAddress(WTF::equalIgnoringASCIICaseNonNull);
        functionCall.setTwoArguments(valueStringImpl, expectedValueRegister);
        failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));

        skipCaseInsensitiveComparison.link(&m_assembler);
        break;
    }
    case AttributeCaseSensitivity::CaseInsensitive: {
        LocalRegister valueStringImpl(m_registerAllocator);
        m_assembler.loadPtr(Assembler::Address(currentAttributeAddress, Attribute::valueMemoryOffset()), valueStringImpl);

        Assembler::Jump skipCaseInsensitiveComparison = m_assembler.branchPtr(Assembler::Equal, valueStringImpl, expectedValueRegister);
        FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
        functionCall.setFunctionAddress(WTF::equalIgnoringASCIICaseNonNull);
        functionCall.setTwoArguments(valueStringImpl, expectedValueRegister);
        failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));
        skipCaseInsensitiveComparison.link(&m_assembler);
        break;
    }
    }
}

void SelectorCodeGenerator::generateElementAttributeFunctionCallValueMatching(Assembler::JumpList& failureCases, Assembler::RegisterID currentAttributeAddress, const AtomicString& expectedValue, AttributeCaseSensitivity valueCaseSensitivity, JSC::FunctionPtr<CSSOperationPtrTag> caseSensitiveTest, JSC::FunctionPtr<CSSOperationPtrTag> caseInsensitiveTest)
{
    LocalRegisterWithPreference expectedValueRegister(m_registerAllocator, JSC::GPRInfo::argumentGPR1);
    m_assembler.move(Assembler::TrustedImmPtr(expectedValue.impl()), expectedValueRegister);


    switch (valueCaseSensitivity) {
    case AttributeCaseSensitivity::CaseSensitive: {
        FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
        functionCall.setFunctionAddress(caseSensitiveTest);
        functionCall.setTwoArguments(currentAttributeAddress, expectedValueRegister);
        failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));
        break;
    }
    case AttributeCaseSensitivity::HTMLLegacyCaseInsensitive: {
        Assembler::JumpList shouldUseCaseSensitiveComparison;
        shouldUseCaseSensitiveComparison.append(DOMJIT::branchTestIsHTMLFlagOnNode(m_assembler, Assembler::Zero, elementAddressRegister));
        {
            LocalRegister scratchRegister(m_registerAllocator);
            // scratchRegister = pointer to treeScope.
            m_assembler.loadPtr(Assembler::Address(elementAddressRegister, Node::treeScopeMemoryOffset()), scratchRegister);
            // scratchRegister = pointer to document.
            m_assembler.loadPtr(Assembler::Address(scratchRegister, TreeScope::documentScopeMemoryOffset()), scratchRegister);
            shouldUseCaseSensitiveComparison.append(testIsHTMLClassOnDocument(Assembler::Zero, m_assembler, scratchRegister));
        }

        {
            FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
            functionCall.setFunctionAddress(caseInsensitiveTest);
            functionCall.setTwoArguments(currentAttributeAddress, expectedValueRegister);
            failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));
        }

        Assembler::Jump skipCaseSensitiveCase = m_assembler.jump();

        {
            shouldUseCaseSensitiveComparison.link(&m_assembler);
            FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
            functionCall.setFunctionAddress(caseSensitiveTest);
            functionCall.setTwoArguments(currentAttributeAddress, expectedValueRegister);
            failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));
        }

        skipCaseSensitiveCase.link(&m_assembler);
        break;
    }
    case AttributeCaseSensitivity::CaseInsensitive: {
        FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
        functionCall.setFunctionAddress(caseInsensitiveTest);
        functionCall.setTwoArguments(currentAttributeAddress, expectedValueRegister);
        failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));
        break;
    }
    }
}

void SelectorCodeGenerator::generateElementFunctionCallTest(Assembler::JumpList& failureCases, JSC::FunctionPtr<CSSOperationPtrTag> testFunction)
{
    Assembler::RegisterID elementAddress = elementAddressRegister;
    FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
    functionCall.setFunctionAddress(testFunction);
    functionCall.setOneArgument(elementAddress);
    failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));
}

void SelectorCodeGenerator::generateContextFunctionCallTest(Assembler::JumpList& failureCases, JSC::FunctionPtr<CSSOperationPtrTag> testFunction)
{
    Assembler::RegisterID checkingContext = m_registerAllocator.allocateRegister();
    loadCheckingContext(checkingContext);
    m_registerAllocator.deallocateRegister(checkingContext);

    FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
    functionCall.setFunctionAddress(testFunction);
    functionCall.setOneArgument(checkingContext);
    failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));
}

static bool elementIsActive(const Element* element)
{
    return element->active() || InspectorInstrumentation::forcePseudoState(*element, CSSSelector::PseudoClassActive);
}

void SelectorCodeGenerator::generateElementIsActive(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    generateSpecialFailureInQuirksModeForActiveAndHoverIfNeeded(failureCases, fragment);

    generateAddStyleRelationIfResolvingStyle(elementAddressRegister, Style::Relation::AffectedByActive);

    FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
    functionCall.setFunctionAddress(elementIsActive);
    functionCall.setOneArgument(elementAddressRegister);
    failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));
}

static void jumpIfElementIsNotEmpty(Assembler& assembler, RegisterAllocator& registerAllocator, Assembler::JumpList& notEmptyCases, Assembler::RegisterID element)
{
    LocalRegister currentChild(registerAllocator);
    assembler.loadPtr(Assembler::Address(element, ContainerNode::firstChildMemoryOffset()), currentChild);

    Assembler::Label loopStart(assembler.label());
    Assembler::Jump noMoreChildren = assembler.branchTestPtr(Assembler::Zero, currentChild);

    notEmptyCases.append(DOMJIT::branchTestIsElementFlagOnNode(assembler, Assembler::NonZero, currentChild));

    {
        Assembler::Jump skipTextNodeCheck = assembler.branchTest32(Assembler::Zero, Assembler::Address(currentChild, Node::nodeFlagsMemoryOffset()), Assembler::TrustedImm32(Node::flagIsText()));

        LocalRegister textStringImpl(registerAllocator);
        assembler.loadPtr(Assembler::Address(currentChild, CharacterData::dataMemoryOffset()), textStringImpl);
        notEmptyCases.append(assembler.branchTest32(Assembler::NonZero, Assembler::Address(textStringImpl, StringImpl::lengthMemoryOffset())));

        skipTextNodeCheck.link(&assembler);
    }

    assembler.loadPtr(Assembler::Address(currentChild, Node::nextSiblingMemoryOffset()), currentChild);
    assembler.jump().linkTo(loopStart, &assembler);

    noMoreChildren.link(&assembler);
}

void SelectorCodeGenerator::generateElementIsEmpty(Assembler::JumpList& failureCases)
{
    if (m_selectorContext == SelectorContext::QuerySelector) {
        jumpIfElementIsNotEmpty(m_assembler, m_registerAllocator, failureCases, elementAddressRegister);
        return;
    }

    LocalRegisterWithPreference isEmptyResults(m_registerAllocator, JSC::GPRInfo::argumentGPR1);
    m_assembler.move(Assembler::TrustedImm32(0), isEmptyResults);

    Assembler::JumpList notEmpty;
    jumpIfElementIsNotEmpty(m_assembler, m_registerAllocator, notEmpty, elementAddressRegister);
    m_assembler.move(Assembler::TrustedImm32(1), isEmptyResults);
    notEmpty.link(&m_assembler);

    generateAddStyleRelationIfResolvingStyle(elementAddressRegister, Style::Relation::AffectedByEmpty, Assembler::RegisterID(isEmptyResults));

    failureCases.append(m_assembler.branchTest32(Assembler::Zero, isEmptyResults));
}

void SelectorCodeGenerator::generateElementIsFirstChild(Assembler::JumpList& failureCases)
{
    if (m_selectorContext == SelectorContext::QuerySelector) {
        Assembler::JumpList successCase = jumpIfNoPreviousAdjacentElement();
        failureCases.append(m_assembler.jump());
        successCase.link(&m_assembler);
        LocalRegister parent(m_registerAllocator);
        generateWalkToParentElementOrShadowRoot(failureCases, parent);
        return;
    }

    // Zero in isFirstChildRegister is the success case. The register is set to non-zero if a sibling if found.
    LocalRegister isFirstChildRegister(m_registerAllocator);
    m_assembler.move(Assembler::TrustedImm32(0), isFirstChildRegister);

    {
        Assembler::JumpList successCase = jumpIfNoPreviousAdjacentElement();

        // If there was a sibling element, the element was not the first child -> failure case.
        m_assembler.move(Assembler::TrustedImm32(1), isFirstChildRegister);

        successCase.link(&m_assembler);
    }

    LocalRegister parentNode(m_registerAllocator);
    generateWalkToParentNode(parentNode);
    failureCases.append(m_assembler.branchTestPtr(Assembler::Zero, parentNode));
    Assembler::Jump notElement = DOMJIT::branchTestIsElementFlagOnNode(m_assembler, Assembler::Zero, parentNode);

    LocalRegister checkingContext(m_registerAllocator);
    Assembler::Jump notResolvingStyle = jumpIfNotResolvingStyle(checkingContext);

    generateAddStyleRelation(checkingContext, parentNode, Style::Relation::ChildrenAffectedByFirstChildRules);
    // The parent marking is unconditional. If the matching is not a success, we can now fail.
    // Otherwise we need to apply setFirstChildState() on the RenderStyle.
    Assembler::Label checkWithRelation(m_assembler.label());
    failureCases.append(m_assembler.branchTest32(Assembler::NonZero, isFirstChildRegister));
    generateAddStyleRelation(checkingContext, elementAddressRegister, Style::Relation::FirstChild);
    Assembler::Jump successCase = m_assembler.jump();

    notElement.link(&m_assembler);
    failureCases.append(DOMJIT::branchTestIsShadowRootFlagOnNode(m_assembler, Assembler::Zero, parentNode));
    jumpIfNotResolvingStyle(checkingContext).linkTo(checkWithRelation, &m_assembler);

    notResolvingStyle.link(&m_assembler);
    failureCases.append(m_assembler.branchTest32(Assembler::NonZero, isFirstChildRegister));

    successCase.link(&m_assembler);
}

static bool elementIsHovered(const Element* element)
{
    return element->hovered() || InspectorInstrumentation::forcePseudoState(*element, CSSSelector::PseudoClassHover);
}

void SelectorCodeGenerator::generateElementIsHovered(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    generateSpecialFailureInQuirksModeForActiveAndHoverIfNeeded(failureCases, fragment);

    generateAddStyleRelationIfResolvingStyle(elementAddressRegister, Style::Relation::AffectedByHover);

    Assembler::JumpList successCases;
    if (m_selectorContext != SelectorContext::QuerySelector && fragment.relationToRightFragment != FragmentRelation::Rightmost) {
        // :hover always matches when not in rightmost position when collecting rules for descendant style invalidation optimization.
        // Resolving style for a matching descendant will set parent childrenAffectedByHover bit even when the element is not currently hovered.
        // This bit has to be set for the event based :hover invalidation to work.
        // FIXME: We should just collect style relation bits and apply them as needed when computing style invalidation optimization.
        LocalRegister checkingContext(m_registerAllocator);
        successCases.append(branchOnResolvingMode(Assembler::Equal, SelectorChecker::Mode::CollectingRulesIgnoringVirtualPseudoElements, checkingContext));
    }

    FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
    functionCall.setFunctionAddress(elementIsHovered);
    functionCall.setOneArgument(elementAddressRegister);
    failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));

    successCases.link(&m_assembler);
}

void SelectorCodeGenerator::generateElementIsInLanguage(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    for (const Vector<AtomicString>* languageArguments : fragment.languageArgumentsList)
        generateElementIsInLanguage(failureCases, languageArguments);
}

void SelectorCodeGenerator::generateElementIsInLanguage(Assembler::JumpList& failureCases, const Vector<AtomicString>* languageArguments)
{
    LocalRegisterWithPreference langRangeRegister(m_registerAllocator, JSC::GPRInfo::argumentGPR1);
    m_assembler.move(Assembler::TrustedImmPtr(languageArguments), langRangeRegister);

    Assembler::RegisterID elementAddress = elementAddressRegister;
    FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
    functionCall.setFunctionAddress(matchesLangPseudoClass);
    functionCall.setTwoArguments(elementAddress, langRangeRegister);
    failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));
}

void SelectorCodeGenerator::generateElementIsLastChild(Assembler::JumpList& failureCases)
{
    if (m_selectorContext == SelectorContext::QuerySelector) {
        Assembler::JumpList successCase = jumpIfNoNextAdjacentElement();
        failureCases.append(m_assembler.jump());

        successCase.link(&m_assembler);
        LocalRegister parent(m_registerAllocator);
        generateWalkToParentElementOrShadowRoot(failureCases, parent);

        failureCases.append(m_assembler.branchTest32(Assembler::Zero, Assembler::Address(parent, Node::nodeFlagsMemoryOffset()), Assembler::TrustedImm32(Node::flagIsParsingChildrenFinished())));

        return;
    }

    LocalRegister parentNode(m_registerAllocator);
    generateWalkToParentNode(parentNode);
    failureCases.append(m_assembler.branchTestPtr(Assembler::Zero, parentNode));

    // Zero in isLastChildRegister is the success case. The register is set to non-zero if a sibling if found.
    LocalRegister isLastChildRegister(m_registerAllocator);
    m_assembler.move(Assembler::TrustedImm32(0), isLastChildRegister);

    {
        Assembler::Jump notFinishedParsingChildren = m_assembler.branchTest32(Assembler::Zero, Assembler::Address(parentNode, Node::nodeFlagsMemoryOffset()), Assembler::TrustedImm32(Node::flagIsParsingChildrenFinished()));

        Assembler::JumpList successCase = jumpIfNoNextAdjacentElement();

        notFinishedParsingChildren.link(&m_assembler);
        m_assembler.move(Assembler::TrustedImm32(1), isLastChildRegister);

        successCase.link(&m_assembler);
    }

    Assembler::Jump notElement = DOMJIT::branchTestIsElementFlagOnNode(m_assembler, Assembler::Zero, parentNode);

    LocalRegister checkingContext(m_registerAllocator);
    Assembler::Jump notResolvingStyle = jumpIfNotResolvingStyle(checkingContext);

    generateAddStyleRelation(checkingContext, parentNode, Style::Relation::ChildrenAffectedByLastChildRules);
    // The parent marking is unconditional. If the matching is not a success, we can now fail.
    // Otherwise we need to apply setLastChildState() on the RenderStyle.
    Assembler::Label checkWithRelation(m_assembler.label());
    failureCases.append(m_assembler.branchTest32(Assembler::NonZero, isLastChildRegister));
    generateAddStyleRelation(checkingContext, elementAddressRegister, Style::Relation::LastChild);
    Assembler::Jump successCase = m_assembler.jump();

    notElement.link(&m_assembler);
    failureCases.append(DOMJIT::branchTestIsShadowRootFlagOnNode(m_assembler, Assembler::Zero, parentNode));
    jumpIfNotResolvingStyle(checkingContext).linkTo(checkWithRelation, &m_assembler);

    notResolvingStyle.link(&m_assembler);
    failureCases.append(m_assembler.branchTest32(Assembler::NonZero, isLastChildRegister));

    successCase.link(&m_assembler);
}

void SelectorCodeGenerator::generateElementIsOnlyChild(Assembler::JumpList& failureCases)
{
    // Is Only child is pretty much a combination of isFirstChild + isLastChild. The main difference is that tree marking is combined.
    if (m_selectorContext == SelectorContext::QuerySelector) {
        Assembler::JumpList previousSuccessCase = jumpIfNoPreviousAdjacentElement();
        failureCases.append(m_assembler.jump());
        previousSuccessCase.link(&m_assembler);

        Assembler::JumpList nextSuccessCase = jumpIfNoNextAdjacentElement();
        failureCases.append(m_assembler.jump());
        nextSuccessCase.link(&m_assembler);

        LocalRegister parent(m_registerAllocator);
        generateWalkToParentElementOrShadowRoot(failureCases, parent);

        failureCases.append(m_assembler.branchTest32(Assembler::Zero, Assembler::Address(parent, Node::nodeFlagsMemoryOffset()), Assembler::TrustedImm32(Node::flagIsParsingChildrenFinished())));

        return;
    }

    LocalRegister parentNode(m_registerAllocator);
    generateWalkToParentNode(parentNode);
    failureCases.append(m_assembler.branchTestPtr(Assembler::Zero, parentNode));

    // Zero in isOnlyChildRegister is the success case. The register is set to non-zero if a sibling if found.
    LocalRegister isOnlyChildRegister(m_registerAllocator);
    m_assembler.move(Assembler::TrustedImm32(0), isOnlyChildRegister);

    {
        Assembler::JumpList localFailureCases;
        {
            Assembler::JumpList successCase = jumpIfNoPreviousAdjacentElement();
            localFailureCases.append(m_assembler.jump());
            successCase.link(&m_assembler);
        }
        localFailureCases.append(m_assembler.branchTest32(Assembler::Zero, Assembler::Address(parentNode, Node::nodeFlagsMemoryOffset()), Assembler::TrustedImm32(Node::flagIsParsingChildrenFinished())));
        Assembler::JumpList successCase = jumpIfNoNextAdjacentElement();

        localFailureCases.link(&m_assembler);
        m_assembler.move(Assembler::TrustedImm32(1), isOnlyChildRegister);

        successCase.link(&m_assembler);
    }

    Assembler::Jump notElement = DOMJIT::branchTestIsElementFlagOnNode(m_assembler, Assembler::Zero, parentNode);

    LocalRegister checkingContext(m_registerAllocator);
    Assembler::Jump notResolvingStyle = jumpIfNotResolvingStyle(checkingContext);

    generateAddStyleRelation(checkingContext, parentNode, Style::Relation::ChildrenAffectedByFirstChildRules);
    generateAddStyleRelation(checkingContext, parentNode, Style::Relation::ChildrenAffectedByLastChildRules);
    // The parent marking is unconditional. If the matching is not a success, we can now fail.
    // Otherwise we need to apply setLastChildState() on the RenderStyle.
    Assembler::Label checkWithRelation(m_assembler.label());
    failureCases.append(m_assembler.branchTest32(Assembler::NonZero, isOnlyChildRegister));
    generateAddStyleRelation(checkingContext, elementAddressRegister, Style::Relation::FirstChild);
    generateAddStyleRelation(checkingContext, elementAddressRegister, Style::Relation::LastChild);
    Assembler::Jump successCase = m_assembler.jump();

    notElement.link(&m_assembler);
    failureCases.append(DOMJIT::branchTestIsShadowRootFlagOnNode(m_assembler, Assembler::Zero, parentNode));
    jumpIfNotResolvingStyle(checkingContext).linkTo(checkWithRelation, &m_assembler);

    notResolvingStyle.link(&m_assembler);
    failureCases.append(m_assembler.branchTest32(Assembler::NonZero, isOnlyChildRegister));

    successCase.link(&m_assembler);
}

static bool makeContextStyleUniqueIfNecessaryAndTestIsPlaceholderShown(const Element* element, SelectorChecker::CheckingContext* checkingContext)
{
    if (is<HTMLTextFormControlElement>(*element) && element->isTextField()) {
        if (checkingContext->resolvingMode == SelectorChecker::Mode::ResolvingStyle)
            checkingContext->styleRelations.append({ *element, Style::Relation::Unique, 1 });
        return downcast<HTMLTextFormControlElement>(*element).isPlaceholderVisible();
    }
    return false;
}

static bool isPlaceholderShown(const Element* element)
{
    return is<HTMLTextFormControlElement>(*element) && downcast<HTMLTextFormControlElement>(*element).isPlaceholderVisible();
}

void SelectorCodeGenerator::generateElementHasPlaceholderShown(Assembler::JumpList& failureCases)
{
    if (m_selectorContext == SelectorContext::QuerySelector) {
        FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
        functionCall.setFunctionAddress(isPlaceholderShown);
        functionCall.setOneArgument(elementAddressRegister);
        failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));
        return;
    }

    Assembler::RegisterID checkingContext = m_registerAllocator.allocateRegisterWithPreference(JSC::GPRInfo::argumentGPR1);
    loadCheckingContext(checkingContext);
    m_registerAllocator.deallocateRegister(checkingContext);

    FunctionCall functionCall(m_assembler, m_registerAllocator, m_stackAllocator, m_functionCalls);
    functionCall.setFunctionAddress(makeContextStyleUniqueIfNecessaryAndTestIsPlaceholderShown);
    functionCall.setTwoArguments(elementAddressRegister, checkingContext);
    failureCases.append(functionCall.callAndBranchOnBooleanReturnValue(Assembler::Zero));
}

inline void SelectorCodeGenerator::generateElementHasTagName(Assembler::JumpList& failureCases, const CSSSelector& tagMatchingSelector)
{
    const QualifiedName& nameToMatch = tagMatchingSelector.tagQName();
    if (nameToMatch == anyQName())
        return;

    // Load the QualifiedNameImpl from the input.
    LocalRegister qualifiedNameImpl(m_registerAllocator);
    m_assembler.loadPtr(Assembler::Address(elementAddressRegister, Element::tagQNameMemoryOffset() + QualifiedName::implMemoryOffset()), qualifiedNameImpl);

    const AtomicString& selectorLocalName = nameToMatch.localName();
    if (selectorLocalName != starAtom()) {
        const AtomicString& lowercaseLocalName = tagMatchingSelector.tagLowercaseLocalName();

        if (selectorLocalName == lowercaseLocalName) {
            // Generate localName == element->localName().
            LocalRegister constantRegister(m_registerAllocator);
            m_assembler.move(Assembler::TrustedImmPtr(selectorLocalName.impl()), constantRegister);
            failureCases.append(m_assembler.branchPtr(Assembler::NotEqual, Assembler::Address(qualifiedNameImpl, QualifiedName::QualifiedNameImpl::localNameMemoryOffset()), constantRegister));
        } else {
            Assembler::JumpList caseSensitiveCases;
            caseSensitiveCases.append(DOMJIT::branchTestIsHTMLFlagOnNode(m_assembler, Assembler::Zero, elementAddressRegister));
            {
                LocalRegister document(m_registerAllocator);
                DOMJIT::loadDocument(m_assembler, elementAddressRegister, document);
                caseSensitiveCases.append(testIsHTMLClassOnDocument(Assembler::Zero, m_assembler, document));
            }

            LocalRegister constantRegister(m_registerAllocator);
            m_assembler.move(Assembler::TrustedImmPtr(lowercaseLocalName.impl()), constantRegister);
            Assembler::Jump skipCaseSensitiveCase = m_assembler.jump();

            caseSensitiveCases.link(&m_assembler);
            m_assembler.move(Assembler::TrustedImmPtr(selectorLocalName.impl()), constantRegister);
            skipCaseSensitiveCase.link(&m_assembler);

            failureCases.append(m_assembler.branchPtr(Assembler::NotEqual, Assembler::Address(qualifiedNameImpl, QualifiedName::QualifiedNameImpl::localNameMemoryOffset()), constantRegister));
        }
    }

    const AtomicString& selectorNamespaceURI = nameToMatch.namespaceURI();
    if (selectorNamespaceURI != starAtom()) {
        // Generate namespaceURI == element->namespaceURI().
        LocalRegister constantRegister(m_registerAllocator);
        m_assembler.move(Assembler::TrustedImmPtr(selectorNamespaceURI.impl()), constantRegister);
        failureCases.append(m_assembler.branchPtr(Assembler::NotEqual, Assembler::Address(qualifiedNameImpl, QualifiedName::QualifiedNameImpl::namespaceMemoryOffset()), constantRegister));
    }
}

void SelectorCodeGenerator::generateElementHasId(Assembler::JumpList& failureCases, const LocalRegister& elementDataAddress, const AtomicString& idToMatch)
{
    // Compare the pointers of the AtomicStringImpl from idForStyleResolution with the reference idToMatch.
    LocalRegister idToMatchRegister(m_registerAllocator);
    m_assembler.move(Assembler::TrustedImmPtr(idToMatch.impl()), idToMatchRegister);
    failureCases.append(m_assembler.branchPtr(Assembler::NotEqual, Assembler::Address(elementDataAddress, ElementData::idForStyleResolutionMemoryOffset()), idToMatchRegister));
}

void SelectorCodeGenerator::generateElementHasClasses(Assembler::JumpList& failureCases, const LocalRegister& elementDataAddress, const Vector<const AtomicStringImpl*, 8>& classNames)
{
    // Load m_classNames.
    LocalRegister spaceSplitStringData(m_registerAllocator);
    m_assembler.loadPtr(Assembler::Address(elementDataAddress, ElementData::classNamesMemoryOffset()), spaceSplitStringData);

    // If SpaceSplitString does not have a SpaceSplitStringData pointer, it is empty -> failure case.
    failureCases.append(m_assembler.branchTestPtr(Assembler::Zero, spaceSplitStringData));

    // We loop over the classes of SpaceSplitStringData for each class name we need to match.
    LocalRegister indexRegister(m_registerAllocator);
    for (unsigned i = 0; i < classNames.size(); ++i) {
        LocalRegister classNameToMatch(m_registerAllocator);
        m_assembler.move(Assembler::TrustedImmPtr(classNames[i]), classNameToMatch);
        m_assembler.move(Assembler::TrustedImm32(0), indexRegister);

        // Beginning of a loop over all the class name of element to find the one we are looking for.
        Assembler::Label loopStart(m_assembler.label());

        // If the pointers match, proceed to the next matcher.
        Assembler::Jump classFound = m_assembler.branchPtr(Assembler::Equal, Assembler::BaseIndex(spaceSplitStringData, indexRegister, Assembler::timesPtr(), SpaceSplitStringData::tokensMemoryOffset()), classNameToMatch);

        // Increment the index.
        m_assembler.add32(Assembler::TrustedImm32(1), indexRegister);

        // If we reached the last element -> failure.
        failureCases.append(m_assembler.branch32(Assembler::Equal, Assembler::Address(spaceSplitStringData, SpaceSplitStringData::sizeMemoryOffset()), indexRegister));
        // Otherwise just loop over.
        m_assembler.jump().linkTo(loopStart, &m_assembler);

        // Success case.
        classFound.link(&m_assembler);
    }
}

void SelectorCodeGenerator::generateElementIsLink(Assembler::JumpList& failureCases)
{
    failureCases.append(m_assembler.branchTest32(Assembler::Zero, Assembler::Address(elementAddressRegister, Node::nodeFlagsMemoryOffset()), Assembler::TrustedImm32(Node::flagIsLink())));
}

static bool nthFilterIsAlwaysSatisified(int a, int b)
{
    // Anything modulo 1 is zero. Unless b restricts the range, this does not filter anything out.
    if (a == 1 && (!b || (b == 1)))
        return true;
    return false;
}

void SelectorCodeGenerator::generateNthChildParentCheckAndRelationUpdate(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    LocalRegister parentNode(m_registerAllocator);
    generateWalkToParentNode(parentNode);
    failureCases.append(m_assembler.branchTestPtr(Assembler::Zero, parentNode));
    Assembler::Jump notElement = DOMJIT::branchTestIsElementFlagOnNode(m_assembler, Assembler::Zero, parentNode);

    auto relation = fragmentMatchesRightmostOrAdjacentElement(fragment)
        ? Style::Relation::ChildrenAffectedByForwardPositionalRules
        : Style::Relation::DescendantsAffectedByForwardPositionalRules;
    generateAddStyleRelationIfResolvingStyle(parentNode, relation);
    Assembler::Jump parentNodeCheckEnd = m_assembler.jump();

    notElement.link(&m_assembler);
    failureCases.append(DOMJIT::branchTestIsShadowRootFlagOnNode(m_assembler, Assembler::Zero, parentNode));

    parentNodeCheckEnd.link(&m_assembler);
}

void SelectorCodeGenerator::generateElementIsNthChild(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    generateNthChildParentCheckAndRelationUpdate(failureCases, fragment);

    Vector<std::pair<int, int>, 32> validSubsetFilters;
    validSubsetFilters.reserveInitialCapacity(fragment.nthChildFilters.size());
    for (const auto& slot : fragment.nthChildFilters) {
        if (nthFilterIsAlwaysSatisified(slot.first, slot.second))
            continue;
        validSubsetFilters.uncheckedAppend(slot);
    }
    if (validSubsetFilters.isEmpty())
        return;

    // Setup the counter at 1.
    LocalRegisterWithPreference elementCounter(m_registerAllocator, JSC::GPRInfo::argumentGPR1);
    m_assembler.move(Assembler::TrustedImm32(1), elementCounter);

    // Loop over the previous adjacent elements and increment the counter.
    {
        LocalRegister previousSibling(m_registerAllocator);
        m_assembler.move(elementAddressRegister, previousSibling);

        // Getting the child index is very efficient when it works. When there is no child index,
        // querying at every iteration is very inefficient. We solve this by only testing the child
        // index on the first direct adjacent.
        Assembler::JumpList noMoreSiblingsCases;

        Assembler::JumpList noCachedChildIndexCases;
        generateWalkToPreviousAdjacentElement(noMoreSiblingsCases, previousSibling);
        noCachedChildIndexCases.append(m_assembler.branchTest32(Assembler::Zero, Assembler::Address(previousSibling, Node::nodeFlagsMemoryOffset()), Assembler::TrustedImm32(Node::flagHasRareData())));
        {
            LocalRegister elementRareData(m_registerAllocator);
            m_assembler.loadPtr(Assembler::Address(previousSibling, Node::rareDataMemoryOffset()), elementRareData);
            LocalRegister cachedChildIndex(m_registerAllocator);
            m_assembler.load16(Assembler::Address(elementRareData, ElementRareData::childIndexMemoryOffset()), cachedChildIndex);
            noCachedChildIndexCases.append(m_assembler.branchTest32(Assembler::Zero, cachedChildIndex));
            m_assembler.add32(cachedChildIndex, elementCounter);
            noMoreSiblingsCases.append(m_assembler.jump());
        }
        noCachedChildIndexCases.link(&m_assembler);
        m_assembler.add32(Assembler::TrustedImm32(1), elementCounter);

        Assembler::Label loopStart = m_assembler.label();
        generateWalkToPreviousAdjacentElement(noMoreSiblingsCases, previousSibling);
        m_assembler.add32(Assembler::TrustedImm32(1), elementCounter);
        m_assembler.jump().linkTo(loopStart, &m_assembler);
        noMoreSiblingsCases.link(&m_assembler);
    }

    generateAddStyleRelationIfResolvingStyle(elementAddressRegister, Style::Relation::NthChildIndex, Assembler::RegisterID(elementCounter));

    for (const auto& slot : validSubsetFilters)
        generateNthFilterTest(failureCases, elementCounter, slot.first, slot.second);
}

void SelectorCodeGenerator::generateElementIsNthChildOf(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    generateNthChildParentCheckAndRelationUpdate(failureCases, fragment);

    // The initial element must match the selector list.
    for (const NthChildOfSelectorInfo& nthChildOfSelectorInfo : fragment.nthChildOfFilters)
        generateElementMatchesSelectorList(failureCases, elementAddressRegister, nthChildOfSelectorInfo.selectorList);

    Vector<const NthChildOfSelectorInfo*> validSubsetFilters;
    for (const NthChildOfSelectorInfo& nthChildOfSelectorInfo : fragment.nthChildOfFilters) {
        if (nthFilterIsAlwaysSatisified(nthChildOfSelectorInfo.a, nthChildOfSelectorInfo.b))
            continue;
        validSubsetFilters.append(&nthChildOfSelectorInfo);
    }
    if (validSubsetFilters.isEmpty())
        return;

    for (const NthChildOfSelectorInfo* nthChildOfSelectorInfo : validSubsetFilters) {
        // Setup the counter at 1.
        LocalRegisterWithPreference elementCounter(m_registerAllocator, JSC::GPRInfo::argumentGPR1);
        m_assembler.move(Assembler::TrustedImm32(1), elementCounter);

        // Loop over the previous adjacent elements and increment the counter.
        {
            LocalRegister previousSibling(m_registerAllocator);
            m_assembler.move(elementAddressRegister, previousSibling);

            Assembler::JumpList noMoreSiblingsCases;

            Assembler::Label loopStart = m_assembler.label();

            generateWalkToPreviousAdjacentElement(noMoreSiblingsCases, previousSibling);

            Assembler::JumpList localFailureCases;
            generateElementMatchesSelectorList(localFailureCases, previousSibling, nthChildOfSelectorInfo->selectorList);
            localFailureCases.linkTo(loopStart, &m_assembler);
            m_assembler.add32(Assembler::TrustedImm32(1), elementCounter);
            m_assembler.jump().linkTo(loopStart, &m_assembler);

            noMoreSiblingsCases.link(&m_assembler);
        }

        generateNthFilterTest(failureCases, elementCounter, nthChildOfSelectorInfo->a, nthChildOfSelectorInfo->b);
    }
}

void SelectorCodeGenerator::generateNthLastChildParentCheckAndRelationUpdate(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    LocalRegister parentNode(m_registerAllocator);
    generateWalkToParentNode(parentNode);
    failureCases.append(m_assembler.branchTestPtr(Assembler::Zero, parentNode));
    Assembler::Jump notElement = DOMJIT::branchTestIsElementFlagOnNode(m_assembler, Assembler::Zero, parentNode);

    auto relation = fragmentMatchesRightmostOrAdjacentElement(fragment)
        ? Style::Relation::ChildrenAffectedByBackwardPositionalRules
        : Style::Relation::DescendantsAffectedByBackwardPositionalRules;
    generateAddStyleRelationIfResolvingStyle(parentNode, relation);
    failureCases.append(m_assembler.branchTest32(Assembler::Zero, Assembler::Address(parentNode, Node::nodeFlagsMemoryOffset()),
        Assembler::TrustedImm32(Node::flagIsParsingChildrenFinished())));
    Assembler::Jump parentNodeCheckEnd = m_assembler.jump();

    notElement.link(&m_assembler);
    failureCases.append(DOMJIT::branchTestIsShadowRootFlagOnNode(m_assembler, Assembler::Zero, parentNode));

    parentNodeCheckEnd.link(&m_assembler);
}

void SelectorCodeGenerator::generateElementIsNthLastChild(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    generateNthLastChildParentCheckAndRelationUpdate(failureCases, fragment);

    Vector<std::pair<int, int>, 32> validSubsetFilters;
    validSubsetFilters.reserveInitialCapacity(fragment.nthLastChildFilters.size());
    for (const auto& slot : fragment.nthLastChildFilters) {
        if (nthFilterIsAlwaysSatisified(slot.first, slot.second))
            continue;
        validSubsetFilters.uncheckedAppend(slot);
    }
    if (validSubsetFilters.isEmpty())
        return;

    LocalRegister elementCounter(m_registerAllocator);
    { // Loop over the following sibling elements and increment the counter.
        LocalRegister nextSibling(m_registerAllocator);
        m_assembler.move(elementAddressRegister, nextSibling);
        // Setup the counter at 1.
        m_assembler.move(Assembler::TrustedImm32(1), elementCounter);

        Assembler::JumpList noMoreSiblingsCases;

        generateWalkToNextAdjacentElement(noMoreSiblingsCases, nextSibling);

        Assembler::Label loopStart = m_assembler.label();
        m_assembler.add32(Assembler::TrustedImm32(1), elementCounter);
        generateWalkToNextAdjacentElement(noMoreSiblingsCases, nextSibling);
        m_assembler.jump().linkTo(loopStart, &m_assembler);
        noMoreSiblingsCases.link(&m_assembler);
    }

    for (const auto& slot : validSubsetFilters)
        generateNthFilterTest(failureCases, elementCounter, slot.first, slot.second);
}

void SelectorCodeGenerator::generateElementIsNthLastChildOf(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    generateNthLastChildParentCheckAndRelationUpdate(failureCases, fragment);

    Vector<const NthChildOfSelectorInfo*> validSubsetFilters;
    validSubsetFilters.reserveInitialCapacity(fragment.nthLastChildOfFilters.size());

    // The initial element must match the selector list.
    for (const NthChildOfSelectorInfo& nthLastChildOfSelectorInfo : fragment.nthLastChildOfFilters)
        generateElementMatchesSelectorList(failureCases, elementAddressRegister, nthLastChildOfSelectorInfo.selectorList);
    
    for (const NthChildOfSelectorInfo& nthLastChildOfSelectorInfo : fragment.nthLastChildOfFilters) {
        if (nthFilterIsAlwaysSatisified(nthLastChildOfSelectorInfo.a, nthLastChildOfSelectorInfo.b))
            continue;
        validSubsetFilters.uncheckedAppend(&nthLastChildOfSelectorInfo);
    }
    if (validSubsetFilters.isEmpty())
        return;

    for (const NthChildOfSelectorInfo* nthLastChildOfSelectorInfo : validSubsetFilters) {
        // Setup the counter at 1.
        LocalRegisterWithPreference elementCounter(m_registerAllocator, JSC::GPRInfo::argumentGPR1);
        m_assembler.move(Assembler::TrustedImm32(1), elementCounter);

        // Loop over the following adjacent elements and increment the counter.
        {
            LocalRegister nextSibling(m_registerAllocator);
            m_assembler.move(elementAddressRegister, nextSibling);

            Assembler::JumpList noMoreSiblingsCases;

            Assembler::Label loopStart = m_assembler.label();

            generateWalkToNextAdjacentElement(noMoreSiblingsCases, nextSibling);

            Assembler::JumpList localFailureCases;
            generateElementMatchesSelectorList(localFailureCases, nextSibling, nthLastChildOfSelectorInfo->selectorList);
            localFailureCases.linkTo(loopStart, &m_assembler);
            m_assembler.add32(Assembler::TrustedImm32(1), elementCounter);
            m_assembler.jump().linkTo(loopStart, &m_assembler);

            noMoreSiblingsCases.link(&m_assembler);
        }

        generateNthFilterTest(failureCases, elementCounter, nthLastChildOfSelectorInfo->a, nthLastChildOfSelectorInfo->b);
    }
}

void SelectorCodeGenerator::generateElementMatchesNotPseudoClass(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    Assembler::JumpList localFailureCases;
    generateElementMatchesSelectorList(localFailureCases, elementAddressRegister, fragment.notFilters);
    // Since this is a not pseudo class filter, reaching here is a failure.
    failureCases.append(m_assembler.jump());
    localFailureCases.link(&m_assembler);
}

void SelectorCodeGenerator::generateElementMatchesAnyPseudoClass(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    for (const auto& subFragments : fragment.anyFilters) {
        RELEASE_ASSERT(!subFragments.isEmpty());

        // Don't handle the last fragment in this loop.
        Assembler::JumpList successCases;
        for (unsigned i = 0; i < subFragments.size() - 1; ++i) {
            Assembler::JumpList localFailureCases;
            generateElementMatching(localFailureCases, localFailureCases, subFragments[i]);
            successCases.append(m_assembler.jump());
            localFailureCases.link(&m_assembler);
        }

        // At the last fragment, optimize the failure jump to jump to the non-local failure directly.
        generateElementMatching(failureCases, failureCases, subFragments.last());
        successCases.link(&m_assembler);
    }
}

void SelectorCodeGenerator::generateElementMatchesMatchesPseudoClass(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    for (const SelectorList& matchesList : fragment.matchesFilters)
        generateElementMatchesSelectorList(failureCases, elementAddressRegister, matchesList);
}

void SelectorCodeGenerator::generateElementHasPseudoElement(Assembler::JumpList&, const SelectorFragment& fragment)
{
    ASSERT_UNUSED(fragment, fragment.pseudoElementSelector);
    ASSERT_WITH_MESSAGE(m_selectorContext != SelectorContext::QuerySelector, "When the fragment has pseudo element, the selector becomes CannotMatchAnything for QuerySelector and this test function is not called.");
    ASSERT_WITH_MESSAGE_UNUSED(fragment, fragmentMatchesTheRightmostElement(fragment), "Virtual pseudo elements handling is only effective in the rightmost fragment. If the current fragment is not rightmost fragment, CSS JIT compiler makes it CannotMatchAnything in fragment construction phase, so never reach here.");
}

void SelectorCodeGenerator::generateRequestedPseudoElementEqualsToSelectorPseudoElement(Assembler::JumpList& failureCases, const SelectorFragment& fragment, Assembler::RegisterID checkingContext)
{
    ASSERT(m_selectorContext != SelectorContext::QuerySelector);

    // Make sure that the requested pseudoId equals to the pseudo element of the rightmost fragment.
    // If the rightmost fragment doesn't have a pseudo element, the requested pseudoId need to be PseudoId::None to succeed the matching.
    // Otherwise, if the requested pseudoId is not PseudoId::None, the requested pseudoId need to equal to the pseudo element of the rightmost fragment.
    if (fragmentMatchesTheRightmostElement(fragment)) {
        if (!fragment.pseudoElementSelector)
            failureCases.append(m_assembler.branch8(Assembler::NotEqual, Assembler::Address(checkingContext, OBJECT_OFFSETOF(SelectorChecker::CheckingContext, pseudoId)), Assembler::TrustedImm32(static_cast<unsigned>(PseudoId::None))));
        else {
            Assembler::Jump skip = m_assembler.branch8(Assembler::Equal, Assembler::Address(checkingContext, OBJECT_OFFSETOF(SelectorChecker::CheckingContext, pseudoId)), Assembler::TrustedImm32(static_cast<unsigned>(PseudoId::None)));
            failureCases.append(m_assembler.branch8(Assembler::NotEqual, Assembler::Address(checkingContext, OBJECT_OFFSETOF(SelectorChecker::CheckingContext, pseudoId)), Assembler::TrustedImm32(static_cast<unsigned>(CSSSelector::pseudoId(fragment.pseudoElementSelector->pseudoElementType())))));
            skip.link(&m_assembler);
        }
    }
}

void SelectorCodeGenerator::generateElementIsRoot(Assembler::JumpList& failureCases)
{
    LocalRegister document(m_registerAllocator);
    DOMJIT::loadDocument(m_assembler, elementAddressRegister, document);
    failureCases.append(m_assembler.branchPtr(Assembler::NotEqual, Assembler::Address(document, Document::documentElementMemoryOffset()), elementAddressRegister));
}

void SelectorCodeGenerator::generateElementIsScopeRoot(Assembler::JumpList& failureCases)
{
    ASSERT(m_selectorContext == SelectorContext::QuerySelector);

    LocalRegister scope(m_registerAllocator);
    loadCheckingContext(scope);
    m_assembler.loadPtr(Assembler::Address(scope, OBJECT_OFFSETOF(SelectorChecker::CheckingContext, scope)), scope);

    Assembler::Jump scopeIsNotNull = m_assembler.branchTestPtr(Assembler::NonZero, scope);

    DOMJIT::loadDocument(m_assembler, elementAddressRegister, scope);
    DOMJIT::loadDocumentElement(m_assembler, scope, scope);

    scopeIsNotNull.link(&m_assembler);
    failureCases.append(m_assembler.branchPtr(Assembler::NotEqual, scope, elementAddressRegister));
}

void SelectorCodeGenerator::generateElementIsTarget(Assembler::JumpList& failureCases)
{
    LocalRegister document(m_registerAllocator);
    DOMJIT::loadDocument(m_assembler, elementAddressRegister, document);
    failureCases.append(m_assembler.branchPtr(Assembler::NotEqual, Assembler::Address(document, Document::cssTargetMemoryOffset()), elementAddressRegister));
}

void SelectorCodeGenerator::generateElementHasFocusWithin(Assembler::JumpList& failureCases)
{
    generateAddStyleRelationIfResolvingStyle(elementAddressRegister, Style::Relation::AffectedByFocusWithin);
    failureCases.append(m_assembler.branchTest32(Assembler::Zero, Assembler::Address(elementAddressRegister, Node::nodeFlagsMemoryOffset()), Assembler::TrustedImm32(Node::flagHasFocusWithin())));
}

void SelectorCodeGenerator::generateElementIsFirstLink(Assembler::JumpList& failureCases, Assembler::RegisterID element)
{
    LocalRegister currentElement(m_registerAllocator);
    m_assembler.loadPtr(m_stackAllocator.addressOf(m_startElement), currentElement);

    // Tree walking up to the provided element until link node is found.
    Assembler::Label loopStart(m_assembler.label());

    // The target element is always in the ancestors from the start element to the root node.
    // So the tree walking doesn't loop infinitely and it will be stopped with the following `currentElement == element` condition.
    Assembler::Jump reachedToElement = m_assembler.branchPtr(Assembler::Equal, currentElement, element);

    failureCases.append(m_assembler.branchTest32(Assembler::NonZero, Assembler::Address(currentElement, Node::nodeFlagsMemoryOffset()), Assembler::TrustedImm32(Node::flagIsLink())));

    // And these ancestors are guaranteed that they are element nodes.
    // So there's no need to check whether it is an element node and whether it is not a nullptr.
    m_assembler.loadPtr(Assembler::Address(currentElement, Node::parentNodeMemoryOffset()), currentElement);
    m_assembler.jump(loopStart);

    reachedToElement.link(&m_assembler);
}

void SelectorCodeGenerator::generateStoreLastVisitedElement(Assembler::RegisterID element)
{
    m_assembler.storePtr(element, m_stackAllocator.addressOf(m_lastVisitedElement));
}

void SelectorCodeGenerator::generateMarkPseudoStyleForPseudoElement(Assembler::JumpList& failureCases, const SelectorFragment& fragment)
{
    ASSERT(m_selectorContext != SelectorContext::QuerySelector);

    // When fragment doesn't have a pseudo element, there's no need to mark the pseudo element style.
    if (!fragment.pseudoElementSelector)
        return;

    LocalRegister checkingContext(m_registerAllocator);
    loadCheckingContext(checkingContext);

    Assembler::JumpList successCases;

    // When the requested pseudoId isn't PseudoId::None, there's no need to mark the pseudo element style.
    successCases.append(m_assembler.branch8(Assembler::NotEqual, Assembler::Address(checkingContext, OBJECT_OFFSETOF(SelectorChecker::CheckingContext, pseudoId)), Assembler::TrustedImm32(static_cast<unsigned>(PseudoId::None))));

    // When resolving mode is CollectingRulesIgnoringVirtualPseudoElements, there's no need to mark the pseudo element style.
    successCases.append(branchOnResolvingModeWithCheckingContext(Assembler::Equal, SelectorChecker::Mode::CollectingRulesIgnoringVirtualPseudoElements, checkingContext));

    // When resolving mode is ResolvingStyle, mark the pseudo style for pseudo element.
    PseudoId dynamicPseudo = CSSSelector::pseudoId(fragment.pseudoElementSelector->pseudoElementType());
    if (dynamicPseudo < PseudoId::FirstInternalPseudoId) {
        failureCases.append(branchOnResolvingModeWithCheckingContext(Assembler::NotEqual, SelectorChecker::Mode::ResolvingStyle, checkingContext));

        Assembler::Address pseudoIDSetAddress(checkingContext, OBJECT_OFFSETOF(SelectorChecker::CheckingContext, pseudoIDSet));
        auto pseudoIDSetDataAddress = pseudoIDSetAddress.withOffset(PseudoIdSet::dataMemoryOffset());
        PseudoIdSet value { dynamicPseudo };
        m_assembler.store32(Assembler::TrustedImm32(value.data()), pseudoIDSetDataAddress);
    }

    // We have a pseudoElementSelector, we are not in CollectingRulesIgnoringVirtualPseudoElements so
    // we must match that pseudo element. Since the context's pseudo selector is PseudoId::None, we fail matching
    // after the marking.
    failureCases.append(m_assembler.jump());

    successCases.link(&m_assembler);
}

void SelectorCodeGenerator::generateNthFilterTest(Assembler::JumpList& failureCases, Assembler::RegisterID counter, int a, int b)
{
    if (!a)
        failureCases.append(m_assembler.branch32(Assembler::NotEqual, Assembler::TrustedImm32(b), counter));
    else if (a > 0) {
        if (a == 2 && b == 1) {
            // This is the common case 2n+1 (or "odd"), we can test for odd values without doing the arithmetic.
            failureCases.append(m_assembler.branchTest32(Assembler::Zero, counter, Assembler::TrustedImm32(1)));
        } else {
            if (b) {
                LocalRegister counterCopy(m_registerAllocator);
                m_assembler.move(counter, counterCopy);
                failureCases.append(m_assembler.branchSub32(Assembler::Signed, Assembler::TrustedImm32(b), counterCopy));
                moduloIsZero(failureCases, counterCopy, a);
            } else
                moduloIsZero(failureCases, counter, a);
        }
    } else {
        LocalRegister bRegister(m_registerAllocator);
        m_assembler.move(Assembler::TrustedImm32(b), bRegister);

        failureCases.append(m_assembler.branchSub32(Assembler::Signed, counter, bRegister));
        moduloIsZero(failureCases, bRegister, a);
    }
}

}; // namespace SelectorCompiler.
}; // namespace WebCore.

#endif // ENABLE(CSS_SELECTOR_JIT)