source: webkit/trunk/JavaScriptCore/yarr/RegexJIT.cpp@ 44514

/*
 * Copyright (C) 2009 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#include "config.h"
#include "RegexJIT.h"

#include "ASCIICType.h"
#include "JSGlobalData.h"
#include "MacroAssembler.h"
#include "RegexCompiler.h"

#include "pcre.h" // temporary, remove when fallback is removed.

#if ENABLE(YARR_JIT)

using namespace WTF;

namespace JSC { namespace Yarr {


class RegexGenerator : private MacroAssembler {
    friend void jitCompileRegex(JSGlobalData* globalData, RegexCodeBlock& jitObject, const UString& pattern, unsigned& numSubpatterns, const char*& error, bool ignoreCase, bool multiline);

#if PLATFORM(ARM_V7)
    static const RegisterID input = ARM::r0;
    static const RegisterID index = ARM::r1;
    static const RegisterID length = ARM::r2;

    static const RegisterID output = ARM::r4;
    static const RegisterID regT0 = ARM::r5;
    static const RegisterID regT1 = ARM::r6;

    static const RegisterID returnRegister = ARM::r0;
#endif
#if PLATFORM(X86)
    static const RegisterID input = X86::eax;
    static const RegisterID index = X86::edx;
    static const RegisterID length = X86::ecx;
    static const RegisterID output = X86::edi;

    static const RegisterID regT0 = X86::ebx;
    static const RegisterID regT1 = X86::esi;

    static const RegisterID returnRegister = X86::eax;
#endif
#if PLATFORM(X86_64)
    static const RegisterID input = X86::edi;
    static const RegisterID index = X86::esi;
    static const RegisterID length = X86::edx;
    static const RegisterID output = X86::ecx;

    static const RegisterID regT0 = X86::eax;
    static const RegisterID regT1 = X86::ebx;

    static const RegisterID returnRegister = X86::eax;
#endif

    void optimizeAlternative(PatternAlternative* alternative)
    {
        if (!alternative->m_terms.size())
            return;

        for (unsigned i = 0; i < alternative->m_terms.size() - 1; ++i) {
            PatternTerm& term = alternative->m_terms[i];
            PatternTerm& nextTerm = alternative->m_terms[i + 1];

            if ((term.type == PatternTerm::TypeCharacterClass)
                && (term.quantityType == QuantifierFixedCount)
                && (nextTerm.type == PatternTerm::TypePatternCharacter)
                && (nextTerm.quantityType == QuantifierFixedCount)) {
                PatternTerm termCopy = term;
                alternative->m_terms[i] = nextTerm;
                alternative->m_terms[i + 1] = termCopy;
            }
        }
    }

    void matchCharacterClassRange(RegisterID character, JumpList& failures, JumpList& matchDest, const CharacterRange* ranges, unsigned count, unsigned* matchIndex, const UChar* matches, unsigned matchCount)
    {
        do {
            // pick which range we're going to generate
            int which = count >> 1;
            char lo = ranges[which].begin;
            char hi = ranges[which].end;
            
            // check if there are any ranges or matches below lo.  If not, just jl to failure -
            // if there is anything else to check, check that first, if it falls through jmp to failure.
            if ((*matchIndex < matchCount) && (matches[*matchIndex] < lo)) {
                Jump loOrAbove = branch32(GreaterThanOrEqual, character, Imm32((unsigned short)lo));
                
                // generate code for all ranges before this one
                if (which)
                    matchCharacterClassRange(character, failures, matchDest, ranges, which, matchIndex, matches, matchCount);
                
                while ((*matchIndex < matchCount) && (matches[*matchIndex] < lo)) {
                    matchDest.append(branch32(Equal, character, Imm32((unsigned short)matches[*matchIndex])));
                    ++*matchIndex;
                }
                failures.append(jump());

                loOrAbove.link(this);
            } else if (which) {
                Jump loOrAbove = branch32(GreaterThanOrEqual, character, Imm32((unsigned short)lo));

                matchCharacterClassRange(character, failures, matchDest, ranges, which, matchIndex, matches, matchCount);
                failures.append(jump());

                loOrAbove.link(this);
            } else
                failures.append(branch32(LessThan, character, Imm32((unsigned short)lo)));

            while ((*matchIndex < matchCount) && (matches[*matchIndex] <= hi))
                ++*matchIndex;

            matchDest.append(branch32(LessThanOrEqual, character, Imm32((unsigned short)hi)));
            // fall through to here, the value is above hi.

            // shuffle along & loop around if there are any more matches to handle.
            unsigned next = which + 1;
            ranges += next;
            count -= next;
        } while (count);
    }

    void matchCharacterClass(RegisterID character, JumpList& matchDest, const CharacterClass* charClass)
    {
        Jump unicodeFail;
        if (charClass->m_matchesUnicode.size() || charClass->m_rangesUnicode.size()) {
            Jump isAscii = branch32(LessThanOrEqual, character, Imm32(0x7f));
        
            if (charClass->m_matchesUnicode.size()) {
                for (unsigned i = 0; i < charClass->m_matchesUnicode.size(); ++i) {
                    UChar ch = charClass->m_matchesUnicode[i];
                    matchDest.append(branch32(Equal, character, Imm32(ch)));
                }
            }
            
            if (charClass->m_rangesUnicode.size()) {
                for (unsigned i = 0; i < charClass->m_rangesUnicode.size(); ++i) {
                    UChar lo = charClass->m_rangesUnicode[i].begin;
                    UChar hi = charClass->m_rangesUnicode[i].end;
                    
                    Jump below = branch32(LessThan, character, Imm32(lo));
                    matchDest.append(branch32(LessThanOrEqual, character, Imm32(hi)));
                    below.link(this);
                }
            }

            unicodeFail = jump();
            isAscii.link(this);
        }

        if (charClass->m_ranges.size()) {
            unsigned matchIndex = 0;
            JumpList failures; 
            matchCharacterClassRange(character, failures, matchDest, charClass->m_ranges.begin(), charClass->m_ranges.size(), &matchIndex, charClass->m_matches.begin(), charClass->m_matches.size());
            while (matchIndex < charClass->m_matches.size())
                matchDest.append(branch32(Equal, character, Imm32((unsigned short)charClass->m_matches[matchIndex++])));

            failures.link(this);
        } else if (charClass->m_matches.size()) {
            // optimization: gather 'a','A' etc back together, can mask & test once.
            Vector<char> matchesAZaz;

            for (unsigned i = 0; i < charClass->m_matches.size(); ++i) {
                char ch = charClass->m_matches[i];
                if (m_pattern.m_ignoreCase) {
                    if (isASCIILower(ch)) {
                        matchesAZaz.append(ch);
                        continue;
                    }
                    if (isASCIIUpper(ch))
                        continue;
                }
                matchDest.append(branch32(Equal, character, Imm32((unsigned short)ch)));
            }

            if (unsigned countAZaz = matchesAZaz.size()) {
                or32(Imm32(32), character);
                for (unsigned i = 0; i < countAZaz; ++i)
                    matchDest.append(branch32(Equal, character, Imm32(matchesAZaz[i])));
            }
        }

        if (charClass->m_matchesUnicode.size() || charClass->m_rangesUnicode.size())
            unicodeFail.link(this);
    }

    // Jumps if input not available; will have (incorrectly) incremented already!
    Jump jumpIfNoAvailableInput(unsigned countToCheck)
    {
        add32(Imm32(countToCheck), index);
        return branch32(Above, index, length);
    }

    Jump jumpIfAvailableInput(unsigned countToCheck)
    {
        add32(Imm32(countToCheck), index);
        return branch32(BelowOrEqual, index, length);
    }

    Jump checkInput()
    {
        return branch32(BelowOrEqual, index, length);
    }

    Jump atEndOfInput()
    {
        return branch32(Equal, index, length);
    }

    Jump notAtEndOfInput()
    {
        return branch32(NotEqual, index, length);
    }

    Jump jumpIfCharEquals(UChar ch, int inputPosition)
    {
        return branch16(Equal, BaseIndex(input, index, TimesTwo, inputPosition * sizeof(UChar)), Imm32(ch));
    }

    Jump jumpIfCharNotEquals(UChar ch, int inputPosition)
    {
        return branch16(NotEqual, BaseIndex(input, index, TimesTwo, inputPosition * sizeof(UChar)), Imm32(ch));
    }

    void readCharacter(int inputPosition, RegisterID reg)
    {
        load16(BaseIndex(input, index, TimesTwo, inputPosition * sizeof(UChar)), reg);
    }

    void storeToFrame(RegisterID reg, unsigned frameLocation)
    {
        poke(reg, frameLocation);
    }

    void storeToFrame(Imm32 imm, unsigned frameLocation)
    {
        poke(imm, frameLocation);
    }

    DataLabelPtr storeToFrameWithPatch(unsigned frameLocation)
    {
        return storePtrWithPatch(ImmPtr(0), Address(stackPointerRegister, frameLocation * sizeof(void*)));
    }

    void loadFromFrame(unsigned frameLocation, RegisterID reg)
    {
        peek(reg, frameLocation);
    }

    void loadFromFrameAndJump(unsigned frameLocation)
    {
        jump(Address(stackPointerRegister, frameLocation * sizeof(void*)));
    }

    struct AlternativeBacktrackRecord {
        DataLabelPtr dataLabel;
        Label backtrackLocation;

        AlternativeBacktrackRecord(DataLabelPtr dataLabel, Label backtrackLocation)
            : dataLabel(dataLabel)
            , backtrackLocation(backtrackLocation)
        {
        }
    };

    struct TermGenerationState {
        TermGenerationState(PatternDisjunction* disjunction, unsigned checkedTotal)
            : disjunction(disjunction)
            , checkedTotal(checkedTotal)
        {
        }

        void resetAlternative()
        {
            isBackTrackGenerated = false;
            alt = 0;
        }
        bool alternativeValid()
        {
            return alt < disjunction->m_alternatives.size();
        }
        void nextAlternative()
        {
            ++alt;
        }
        PatternAlternative* alternative()
        {
            return disjunction->m_alternatives[alt];
        }

        void resetTerm()
        {
            ASSERT(alternativeValid());
            t = 0;
        }
        bool termValid()
        {
            ASSERT(alternativeValid());
            return t < alternative()->m_terms.size();
        }
        void nextTerm()
        {
            ASSERT(alternativeValid());
            ++t;
        }
        PatternTerm& term()
        {
            ASSERT(alternativeValid());
            return alternative()->m_terms[t];
        }

        PatternTerm& lookaheadTerm()
        {
            ASSERT(alternativeValid());
            ASSERT((t + 1) < alternative()->m_terms.size());
            return alternative()->m_terms[t + 1];
        }
        bool isSinglePatternCharacterLookaheadTerm()
        {
            ASSERT(alternativeValid());
            return ((t + 1) < alternative()->m_terms.size())
                && (lookaheadTerm().type == PatternTerm::TypePatternCharacter)
                && (lookaheadTerm().quantityType == QuantifierFixedCount)
                && (lookaheadTerm().quantityCount == 1);
        }

        int inputOffset()
        {
            return term().inputPosition - checkedTotal;
        }

        void jumpToBacktrack(Jump jump, MacroAssembler* masm)
        {
            if (isBackTrackGenerated)
                jump.linkTo(backtrackLabel, masm);
            else
                backTrackJumps.append(jump);
        }
        void jumpToBacktrack(JumpList& jumps, MacroAssembler* masm)
        {
            if (isBackTrackGenerated)
                jumps.linkTo(backtrackLabel, masm);
            else
                backTrackJumps.append(jumps);
        }
        bool plantJumpToBacktrackIfExists(MacroAssembler* masm)
        {
            if (isBackTrackGenerated) {
                masm->jump(backtrackLabel);
                return true;
            }
            return false;
        }
        void addBacktrackJump(Jump jump)
        {
            backTrackJumps.append(jump);
        }
        void setBacktrackGenerated(Label label)
        {
            isBackTrackGenerated = true;
            backtrackLabel = label;
        }
        void linkAlternativeBacktracks(MacroAssembler* masm)
        {
            isBackTrackGenerated = false;
            backTrackJumps.link(masm);
        }
        void linkAlternativeBacktracksTo(Label label, MacroAssembler* masm)
        {
            isBackTrackGenerated = false;
            backTrackJumps.linkTo(label, masm);
        }
        void propagateBacktrackingFrom(TermGenerationState& nestedParenthesesState, MacroAssembler* masm)
        {
            jumpToBacktrack(nestedParenthesesState.backTrackJumps, masm);
            if (nestedParenthesesState.isBackTrackGenerated)
                setBacktrackGenerated(nestedParenthesesState.backtrackLabel);
        }

        PatternDisjunction* disjunction;
        int checkedTotal;
    private:
        unsigned alt;
        unsigned t;
        JumpList backTrackJumps;
        Label backtrackLabel;
        bool isBackTrackGenerated;
    };

    void generateAssertionBOL(TermGenerationState& state)
    {
        PatternTerm& term = state.term();

        if (m_pattern.m_multiline) {
            const RegisterID character = regT0;

            JumpList matchDest;
            if (!term.inputPosition)
                matchDest.append(branch32(Equal, index, Imm32(state.checkedTotal)));

            readCharacter(state.inputOffset() - 1, character);
            matchCharacterClass(character, matchDest, m_pattern.newlineCharacterClass());
            state.jumpToBacktrack(jump(), this);

            matchDest.link(this);
        } else {
            // Erk, really should poison out these alternatives early. :-/
            if (term.inputPosition)
                state.jumpToBacktrack(jump(), this);
            else
                state.jumpToBacktrack(branch32(NotEqual, index, Imm32(state.checkedTotal)), this);
        }
    }

    void generateAssertionEOL(TermGenerationState& state)
    {
        PatternTerm& term = state.term();

        if (m_pattern.m_multiline) {
            const RegisterID character = regT0;

            JumpList matchDest;
            if (term.inputPosition == state.checkedTotal)
                matchDest.append(atEndOfInput());

            readCharacter(state.inputOffset(), character);
            matchCharacterClass(character, matchDest, m_pattern.newlineCharacterClass());
            state.jumpToBacktrack(jump(), this);

            matchDest.link(this);
        } else {
            if (term.inputPosition == state.checkedTotal)
                state.jumpToBacktrack(notAtEndOfInput(), this);
            // Erk, really should poison out these alternatives early. :-/
            else
                state.jumpToBacktrack(jump(), this);
        }
    }

    // Also falls though on nextIsNotWordChar.
    void matchAssertionWordchar(TermGenerationState& state, JumpList& nextIsWordChar, JumpList& nextIsNotWordChar)
    {
        const RegisterID character = regT0;
        PatternTerm& term = state.term();

        if (term.inputPosition == state.checkedTotal)
            nextIsNotWordChar.append(atEndOfInput());

        readCharacter(state.inputOffset(), character);
        matchCharacterClass(character, nextIsWordChar, m_pattern.wordcharCharacterClass());
    }

    void generateAssertionWordBoundary(TermGenerationState& state)
    {
        const RegisterID character = regT0;
        PatternTerm& term = state.term();

        Jump atBegin;
        JumpList matchDest;
        if (!term.inputPosition)
            atBegin = branch32(Equal, index, Imm32(state.checkedTotal));
        readCharacter(state.inputOffset() - 1, character);
        matchCharacterClass(character, matchDest, m_pattern.wordcharCharacterClass());
        if (!term.inputPosition)
            atBegin.link(this);

        // We fall through to here if the last character was not a wordchar.
        JumpList nonWordCharThenWordChar;
        JumpList nonWordCharThenNonWordChar;
        if (term.invertOrCapture) {
            matchAssertionWordchar(state, nonWordCharThenNonWordChar, nonWordCharThenWordChar);
            nonWordCharThenWordChar.append(jump());
        } else {
            matchAssertionWordchar(state, nonWordCharThenWordChar, nonWordCharThenNonWordChar);
            nonWordCharThenNonWordChar.append(jump());
        }
        state.jumpToBacktrack(nonWordCharThenNonWordChar, this);

        // We jump here if the last character was a wordchar.
        matchDest.link(this);
        JumpList wordCharThenWordChar;
        JumpList wordCharThenNonWordChar;
        if (term.invertOrCapture) {
            matchAssertionWordchar(state, wordCharThenNonWordChar, wordCharThenWordChar);
            wordCharThenWordChar.append(jump());
        } else {
            matchAssertionWordchar(state, wordCharThenWordChar, wordCharThenNonWordChar);
            // This can fall-though!
        }

        state.jumpToBacktrack(wordCharThenWordChar, this);
        
        nonWordCharThenWordChar.link(this);
        wordCharThenNonWordChar.link(this);
    }

    void generatePatternCharacterSingle(TermGenerationState& state)
    {
        const RegisterID character = regT0;
        UChar ch = state.term().patternCharacter;

        if (m_pattern.m_ignoreCase && isASCIIAlpha(ch)) {
            readCharacter(state.inputOffset(), character);
            or32(Imm32(32), character);
            state.jumpToBacktrack(branch32(NotEqual, character, Imm32(Unicode::toLower(ch))), this);
        } else {
            ASSERT(!m_pattern.m_ignoreCase || (Unicode::toLower(ch) == Unicode::toUpper(ch)));
            state.jumpToBacktrack(jumpIfCharNotEquals(ch, state.inputOffset()), this);
        }
    }

    void generatePatternCharacterPair(TermGenerationState& state)
    {
        const RegisterID character = regT0;
        UChar ch1 = state.term().patternCharacter;
        UChar ch2 = state.lookaheadTerm().patternCharacter;

        int mask = 0;
        int chPair = ch1 | (ch2 << 16);
        
        if (m_pattern.m_ignoreCase) {
            if (isASCIIAlpha(ch1))
                mask |= 32;
            if (isASCIIAlpha(ch2))
                mask |= 32 << 16;
        }

        if (mask) {
            load32(BaseIndex(input, index, TimesTwo, state.inputOffset() * sizeof(UChar)), character);
            or32(Imm32(mask), character);
            state.jumpToBacktrack(branch32(NotEqual, character, Imm32(chPair | mask)), this);
        } else
            state.jumpToBacktrack(branch32(NotEqual, BaseIndex(input, index, TimesTwo, state.inputOffset() * sizeof(UChar)), Imm32(chPair)), this);
    }

    void generatePatternCharacterFixed(TermGenerationState& state)
    {
        const RegisterID character = regT0;
        const RegisterID countRegister = regT1;
        PatternTerm& term = state.term();
        UChar ch = term.patternCharacter;

        move(index, countRegister);
        sub32(Imm32(term.quantityCount), countRegister);

        Label loop(this);
        if (m_pattern.m_ignoreCase && isASCIIAlpha(ch)) {
            load16(BaseIndex(input, countRegister, TimesTwo, (state.inputOffset() + term.quantityCount) * sizeof(UChar)), character);
            or32(Imm32(32), character);
            state.jumpToBacktrack(branch32(NotEqual, character, Imm32(Unicode::toLower(ch))), this);
        } else {
            ASSERT(!m_pattern.m_ignoreCase || (Unicode::toLower(ch) == Unicode::toUpper(ch)));
            state.jumpToBacktrack(branch16(NotEqual, BaseIndex(input, countRegister, TimesTwo, (state.inputOffset() + term.quantityCount) * sizeof(UChar)), Imm32(ch)), this);
        }
        add32(Imm32(1), countRegister);
        branch32(NotEqual, countRegister, index).linkTo(loop, this);
    }

    void generatePatternCharacterGreedy(TermGenerationState& state)
    {
        const RegisterID character = regT0;
        const RegisterID countRegister = regT1;
        PatternTerm& term = state.term();
        UChar ch = term.patternCharacter;
    
        move(Imm32(0), countRegister);

        JumpList failures;
        Label loop(this);
        failures.append(atEndOfInput());
        if (m_pattern.m_ignoreCase && isASCIIAlpha(ch)) {
            readCharacter(state.inputOffset(), character);
            or32(Imm32(32), character);
            failures.append(branch32(NotEqual, character, Imm32(Unicode::toLower(ch))));
        } else {
            ASSERT(!m_pattern.m_ignoreCase || (Unicode::toLower(ch) == Unicode::toUpper(ch)));
            failures.append(jumpIfCharNotEquals(ch, state.inputOffset()));
        }
        add32(Imm32(1), countRegister);
        add32(Imm32(1), index);
        branch32(NotEqual, countRegister, Imm32(term.quantityCount)).linkTo(loop, this);
        failures.append(jump());

        Label backtrackBegin(this);
        loadFromFrame(term.frameLocation, countRegister);
        state.jumpToBacktrack(branchTest32(Zero, countRegister), this);
        sub32(Imm32(1), countRegister);
        sub32(Imm32(1), index);

        failures.link(this);

        storeToFrame(countRegister, term.frameLocation);

        state.setBacktrackGenerated(backtrackBegin);
    }

    void generatePatternCharacterNonGreedy(TermGenerationState& state)
    {
        const RegisterID character = regT0;
        const RegisterID countRegister = regT1;
        PatternTerm& term = state.term();
        UChar ch = term.patternCharacter;
    
        move(Imm32(0), countRegister);

        Jump firstTimeDoNothing = jump();

        Label hardFail(this);
        sub32(countRegister, index);
        state.jumpToBacktrack(jump(), this);

        Label backtrackBegin(this);
        loadFromFrame(term.frameLocation, countRegister);

        atEndOfInput().linkTo(hardFail, this);
        branch32(Equal, countRegister, Imm32(term.quantityCount), hardFail);
        if (m_pattern.m_ignoreCase && isASCIIAlpha(ch)) {
            readCharacter(state.inputOffset(), character);
            or32(Imm32(32), character);
            branch32(NotEqual, character, Imm32(Unicode::toLower(ch))).linkTo(hardFail, this);
        } else {
            ASSERT(!m_pattern.m_ignoreCase || (Unicode::toLower(ch) == Unicode::toUpper(ch)));
            jumpIfCharNotEquals(ch, state.inputOffset()).linkTo(hardFail, this);
        }

        add32(Imm32(1), countRegister);
        add32(Imm32(1), index);

        firstTimeDoNothing.link(this);
        storeToFrame(countRegister, term.frameLocation);

        state.setBacktrackGenerated(backtrackBegin);
    }

    void generateCharacterClassSingle(TermGenerationState& state)
    {
        const RegisterID character = regT0;
        PatternTerm& term = state.term();

        JumpList matchDest;
        readCharacter(state.inputOffset(), character);
        matchCharacterClass(character, matchDest, term.characterClass);

        if (term.invertOrCapture)
            state.jumpToBacktrack(matchDest, this);
        else {
            state.jumpToBacktrack(jump(), this);
            matchDest.link(this);
        }
    }

    void generateCharacterClassFixed(TermGenerationState& state)
    {
        const RegisterID character = regT0;
        const RegisterID countRegister = regT1;
        PatternTerm& term = state.term();

        move(index, countRegister);
        sub32(Imm32(term.quantityCount), countRegister);

        Label loop(this);
        JumpList matchDest;
        load16(BaseIndex(input, countRegister, TimesTwo, (state.inputOffset() + term.quantityCount) * sizeof(UChar)), character);
        matchCharacterClass(character, matchDest, term.characterClass);

        if (term.invertOrCapture)
            state.jumpToBacktrack(matchDest, this);
        else {
            state.jumpToBacktrack(jump(), this);
            matchDest.link(this);
        }

        add32(Imm32(1), countRegister);
        branch32(NotEqual, countRegister, index).linkTo(loop, this);
    }

    void generateCharacterClassGreedy(TermGenerationState& state)
    {
        const RegisterID character = regT0;
        const RegisterID countRegister = regT1;
        PatternTerm& term = state.term();
    
        move(Imm32(0), countRegister);

        JumpList failures;
        Label loop(this);
        failures.append(atEndOfInput());

        if (term.invertOrCapture) {
            readCharacter(state.inputOffset(), character);
            matchCharacterClass(character, failures, term.characterClass);
        } else {
            JumpList matchDest;
            readCharacter(state.inputOffset(), character);
            matchCharacterClass(character, matchDest, term.characterClass);
            failures.append(jump());
            matchDest.link(this);
        }

        add32(Imm32(1), countRegister);
        add32(Imm32(1), index);
        branch32(NotEqual, countRegister, Imm32(term.quantityCount)).linkTo(loop, this);
        failures.append(jump());

        Label backtrackBegin(this);
        loadFromFrame(term.frameLocation, countRegister);
        state.jumpToBacktrack(branchTest32(Zero, countRegister), this);
        sub32(Imm32(1), countRegister);
        sub32(Imm32(1), index);

        failures.link(this);

        storeToFrame(countRegister, term.frameLocation);

        state.setBacktrackGenerated(backtrackBegin);
    }

    void generateCharacterClassNonGreedy(TermGenerationState& state)
    {
        const RegisterID character = regT0;
        const RegisterID countRegister = regT1;
        PatternTerm& term = state.term();
    
        move(Imm32(0), countRegister);

        Jump firstTimeDoNothing = jump();

        Label hardFail(this);
        sub32(countRegister, index);
        state.jumpToBacktrack(jump(), this);

        Label backtrackBegin(this);
        loadFromFrame(term.frameLocation, countRegister);

        atEndOfInput().linkTo(hardFail, this);
        branch32(Equal, countRegister, Imm32(term.quantityCount), hardFail);

        JumpList matchDest;
        readCharacter(state.inputOffset(), character);
        matchCharacterClass(character, matchDest, term.characterClass);

        if (term.invertOrCapture)
            matchDest.linkTo(hardFail, this);
        else {
            jump(hardFail);
            matchDest.link(this);
        }

        add32(Imm32(1), countRegister);
        add32(Imm32(1), index);

        firstTimeDoNothing.link(this);
        storeToFrame(countRegister, term.frameLocation);

        state.setBacktrackGenerated(backtrackBegin);
    }

    void generateParenthesesDisjunction(PatternTerm& parenthesesTerm, TermGenerationState& state, unsigned alternativeFrameLocation)
    {
        ASSERT((parenthesesTerm.type == PatternTerm::TypeParenthesesSubpattern) || (parenthesesTerm.type == PatternTerm::TypeParentheticalAssertion));
        ASSERT(parenthesesTerm.quantityCount == 1);
    
        PatternDisjunction* disjunction = parenthesesTerm.parentheses.disjunction;
        unsigned preCheckedCount = ((parenthesesTerm.quantityType == QuantifierFixedCount) && (parenthesesTerm.type != PatternTerm::TypeParentheticalAssertion)) ? disjunction->m_minimumSize : 0;

        if (disjunction->m_alternatives.size() == 1) {
            state.resetAlternative();
            ASSERT(state.alternativeValid());
            PatternAlternative* alternative = state.alternative();
            optimizeAlternative(alternative);

            int countToCheck = alternative->m_minimumSize - preCheckedCount;
            if (countToCheck) {
                ASSERT((parenthesesTerm.type == PatternTerm::TypeParentheticalAssertion) || (parenthesesTerm.quantityType != QuantifierFixedCount));

                // FIXME: This is quite horrible.  The call to 'plantJumpToBacktrackIfExists'
                // will be forced to always trampoline into here, just to decrement the index.
                // Ick. 
                Jump skip = jump();

                Label backtrackBegin(this);
                sub32(Imm32(countToCheck), index);
                state.addBacktrackJump(jump());
                
                skip.link(this);

                state.setBacktrackGenerated(backtrackBegin);

                state.jumpToBacktrack(jumpIfNoAvailableInput(countToCheck), this);
                state.checkedTotal += countToCheck;
            }

            for (state.resetTerm(); state.termValid(); state.nextTerm())
                generateTerm(state);

            state.checkedTotal -= countToCheck;
        } else {
            JumpList successes;

            for (state.resetAlternative(); state.alternativeValid(); state.nextAlternative()) {

                PatternAlternative* alternative = state.alternative();
                optimizeAlternative(alternative);

                ASSERT(alternative->m_minimumSize >= preCheckedCount);
                int countToCheck = alternative->m_minimumSize - preCheckedCount;
                if (countToCheck) {
                    state.addBacktrackJump(jumpIfNoAvailableInput(countToCheck));
                    state.checkedTotal += countToCheck;
                }

                for (state.resetTerm(); state.termValid(); state.nextTerm())
                    generateTerm(state);

                // Matched an alternative.
                DataLabelPtr dataLabel = storeToFrameWithPatch(alternativeFrameLocation);
                successes.append(jump());

                // Alternative did not match.
                Label backtrackLocation(this);
                
                // Can we backtrack the alternative? - if so, do so.  If not, just fall through to the next one.
                state.plantJumpToBacktrackIfExists(this);
                
                state.linkAlternativeBacktracks(this);

                if (countToCheck) {
                    sub32(Imm32(countToCheck), index);
                    state.checkedTotal -= countToCheck;
                }

                m_backtrackRecords.append(AlternativeBacktrackRecord(dataLabel, backtrackLocation));
            }
            // We fall through to here when the last alternative fails.
            // Add a backtrack out of here for the parenthese handling code to link up.
            state.addBacktrackJump(jump());

            // Generate a trampoline for the parens code to backtrack to, to retry the
            // next alternative.
            state.setBacktrackGenerated(label());
            loadFromFrameAndJump(alternativeFrameLocation);

            // FIXME: both of the above hooks are a little inefficient, in that you
            // may end up trampolining here, just to trampoline back out to the
            // parentheses code, or vice versa.  We can probably eliminate a jump
            // by restructuring, but coding this way for now for simplicity during
            // development.

            successes.link(this);
        }
    }

    void generateParenthesesSingle(TermGenerationState& state)
    {
        const RegisterID indexTemporary = regT0;
        PatternTerm& term = state.term();
        PatternDisjunction* disjunction = term.parentheses.disjunction;
        ASSERT(term.quantityCount == 1);

        unsigned preCheckedCount = ((term.quantityCount == 1) && (term.quantityType == QuantifierFixedCount)) ? disjunction->m_minimumSize : 0;

        unsigned parenthesesFrameLocation = term.frameLocation;
        unsigned alternativeFrameLocation = parenthesesFrameLocation;
        if (term.quantityType != QuantifierFixedCount)
            alternativeFrameLocation += RegexStackSpaceForBackTrackInfoParenthesesOnce;

        // optimized case - no capture & no quantifier can be handled in a light-weight manner.
        if (!term.invertOrCapture && (term.quantityType == QuantifierFixedCount)) {
            TermGenerationState parenthesesState(disjunction, state.checkedTotal);
            generateParenthesesDisjunction(state.term(), parenthesesState, alternativeFrameLocation);
            // this expects that any backtracks back out of the parentheses will be in the
            // parenthesesState's backTrackJumps vector, and that if they need backtracking
            // they will have set an entry point on the parenthesesState's backtrackLabel.
            state.propagateBacktrackingFrom(parenthesesState, this);
        } else {
            Jump nonGreedySkipParentheses;
            Label nonGreedyTryParentheses;
            if (term.quantityType == QuantifierGreedy)
                storeToFrame(Imm32(1), parenthesesFrameLocation);
            else if (term.quantityType == QuantifierNonGreedy) {
                storeToFrame(Imm32(0), parenthesesFrameLocation);
                nonGreedySkipParentheses = jump();
                nonGreedyTryParentheses = label();
                storeToFrame(Imm32(1), parenthesesFrameLocation);
            }

            // store the match start index
            if (term.invertOrCapture) {
                int inputOffset = state.inputOffset() - preCheckedCount;
                if (inputOffset) {
                    move(index, indexTemporary);
                    add32(Imm32(inputOffset), indexTemporary);
                    store32(indexTemporary, Address(output, (term.parentheses.subpatternId << 1) * sizeof(int)));
                } else
                    store32(index, Address(output, (term.parentheses.subpatternId << 1) * sizeof(int)));
            }

            // generate the body of the parentheses
            TermGenerationState parenthesesState(disjunction, state.checkedTotal);
            generateParenthesesDisjunction(state.term(), parenthesesState, alternativeFrameLocation);

            // store the match end index
            if (term.invertOrCapture) {
                int inputOffset = state.inputOffset();
                if (inputOffset) {
                    move(index, indexTemporary);
                    add32(Imm32(state.inputOffset()), indexTemporary);
                    store32(indexTemporary, Address(output, ((term.parentheses.subpatternId << 1) + 1) * sizeof(int)));
                } else
                    store32(index, Address(output, ((term.parentheses.subpatternId << 1) + 1) * sizeof(int)));
            }
            Jump success = jump();

            // A failure AFTER the parens jumps here
            Label backtrackFromAfterParens(this);

            if (term.quantityType == QuantifierGreedy) {
                // If this is zero we have now tested with both with and without the parens.
                loadFromFrame(parenthesesFrameLocation, indexTemporary);
                state.jumpToBacktrack(branchTest32(Zero, indexTemporary), this);
            } else if (term.quantityType == QuantifierNonGreedy) {
                // If this is zero we have now tested with both with and without the parens.
                loadFromFrame(parenthesesFrameLocation, indexTemporary);
                branchTest32(Zero, indexTemporary).linkTo(nonGreedyTryParentheses, this);
            }

            parenthesesState.plantJumpToBacktrackIfExists(this);
            // A failure WITHIN the parens jumps here
            parenthesesState.linkAlternativeBacktracks(this);
            if (term.invertOrCapture) {
                store32(Imm32(-1), Address(output, (term.parentheses.subpatternId << 1) * sizeof(int)));
                store32(Imm32(-1), Address(output, ((term.parentheses.subpatternId << 1) + 1) * sizeof(int)));
            }

            if (term.quantityType == QuantifierGreedy)
                storeToFrame(Imm32(0), parenthesesFrameLocation);
            else
                state.jumpToBacktrack(jump(), this);

            state.setBacktrackGenerated(backtrackFromAfterParens);
            if (term.quantityType == QuantifierNonGreedy)
                nonGreedySkipParentheses.link(this);
            success.link(this);
        }
    }

    void generateParentheticalAssertion(TermGenerationState& state)
    {
        PatternTerm& term = state.term();
        PatternDisjunction* disjunction = term.parentheses.disjunction;
        ASSERT(term.quantityCount == 1);
        ASSERT(term.quantityType == QuantifierFixedCount);

        unsigned parenthesesFrameLocation = term.frameLocation;
        unsigned alternativeFrameLocation = parenthesesFrameLocation + RegexStackSpaceForBackTrackInfoParentheticalAssertion;

        int countCheckedAfterAssertion = state.checkedTotal - term.inputPosition;

        if (term.invertOrCapture) {
            // Inverted case
            storeToFrame(index, parenthesesFrameLocation);

            state.checkedTotal -= countCheckedAfterAssertion;
            if (countCheckedAfterAssertion)
                sub32(Imm32(countCheckedAfterAssertion), index);

            TermGenerationState parenthesesState(disjunction, state.checkedTotal);
            generateParenthesesDisjunction(state.term(), parenthesesState, alternativeFrameLocation);
            // Success! - which means - Fail!
            loadFromFrame(parenthesesFrameLocation, index);
            state.jumpToBacktrack(jump(), this);

            // And fail means success.
            parenthesesState.linkAlternativeBacktracks(this);
            loadFromFrame(parenthesesFrameLocation, index);

            state.checkedTotal += countCheckedAfterAssertion;
        } else {
            // Normal case
            storeToFrame(index, parenthesesFrameLocation);

            state.checkedTotal -= countCheckedAfterAssertion;
            if (countCheckedAfterAssertion)
                sub32(Imm32(countCheckedAfterAssertion), index);

            TermGenerationState parenthesesState(disjunction, state.checkedTotal);
            generateParenthesesDisjunction(state.term(), parenthesesState, alternativeFrameLocation);
            // Success! - which means - Success!
            loadFromFrame(parenthesesFrameLocation, index);
            Jump success = jump();

            parenthesesState.linkAlternativeBacktracks(this);
            loadFromFrame(parenthesesFrameLocation, index);
            state.jumpToBacktrack(jump(), this);

            success.link(this);

            state.checkedTotal += countCheckedAfterAssertion;
        }
    }

    void generateTerm(TermGenerationState& state)
    {
        PatternTerm& term = state.term();

        switch (term.type) {
        case PatternTerm::TypeAssertionBOL:
            generateAssertionBOL(state);
            break;
        
        case PatternTerm::TypeAssertionEOL:
            generateAssertionEOL(state);
            break;
        
        case PatternTerm::TypeAssertionWordBoundary:
            generateAssertionWordBoundary(state);
            break;
        
        case PatternTerm::TypePatternCharacter:
            switch (term.quantityType) {
            case QuantifierFixedCount:
                if (term.quantityCount == 1) {
                    if (state.isSinglePatternCharacterLookaheadTerm() && (state.lookaheadTerm().inputPosition == (term.inputPosition + 1))) {
                        generatePatternCharacterPair(state);
                        state.nextTerm();
                    } else
                        generatePatternCharacterSingle(state);
                } else
                    generatePatternCharacterFixed(state);
                break;
            case QuantifierGreedy:
                generatePatternCharacterGreedy(state);
                break;
            case QuantifierNonGreedy:
                generatePatternCharacterNonGreedy(state);
                break;
            }
            break;

        case PatternTerm::TypeCharacterClass:
            switch (term.quantityType) {
            case QuantifierFixedCount:
                if (term.quantityCount == 1)
                    generateCharacterClassSingle(state);
                else
                    generateCharacterClassFixed(state);
                break;
            case QuantifierGreedy:
                generateCharacterClassGreedy(state);
                break;
            case QuantifierNonGreedy:
                generateCharacterClassNonGreedy(state);
                break;
            }
            break;

        case PatternTerm::TypeBackReference:
            m_generationFailed = true;
            break;

        case PatternTerm::TypeForwardReference:
            break;

        case PatternTerm::TypeParenthesesSubpattern:
            if ((term.quantityCount == 1) && !term.parentheses.isCopy)
                generateParenthesesSingle(state);
            else
                m_generationFailed = true;
            break;

        case PatternTerm::TypeParentheticalAssertion:
            generateParentheticalAssertion(state);
            break;
        }
    }

    void generateDisjunction(PatternDisjunction* disjunction)
    {
        TermGenerationState state(disjunction, 0);
        state.resetAlternative();

        // Plant a check to see if there is sufficient input available to run the first alternative.
        // Jumping back to the label 'firstAlternative' will get to this check, jumping to
        // 'firstAlternativeInputChecked' will jump directly to matching the alternative having
        // skipped this check.

        Label firstAlternative(this);

        // check availability for the next alternative
        int countCheckedForCurrentAlternative = 0;
        int countToCheckForFirstAlternative = 0;
        bool hasShorterAlternatives = false;
        JumpList notEnoughInputForPreviousAlternative;

        if (state.alternativeValid()) {
            PatternAlternative* alternative = state.alternative();
            countToCheckForFirstAlternative = alternative->m_minimumSize;
            state.checkedTotal += countToCheckForFirstAlternative;
            if (countToCheckForFirstAlternative)
                notEnoughInputForPreviousAlternative.append(jumpIfNoAvailableInput(countToCheckForFirstAlternative));
            countCheckedForCurrentAlternative = countToCheckForFirstAlternative;
        }

        Label firstAlternativeInputChecked(this);

        while (state.alternativeValid()) {
            // Track whether any alternatives are shorter than the first one.
            hasShorterAlternatives = hasShorterAlternatives || (countCheckedForCurrentAlternative < countToCheckForFirstAlternative);

            PatternAlternative* alternative = state.alternative();
            optimizeAlternative(alternative);

            for (state.resetTerm(); state.termValid(); state.nextTerm())
                generateTerm(state);

            // If we get here, the alternative matched.
            if (m_pattern.m_body->m_callFrameSize)
                addPtr(Imm32(m_pattern.m_body->m_callFrameSize * sizeof(void*)), stackPointerRegister);
            
            ASSERT(index != returnRegister);
            if (m_pattern.m_body->m_hasFixedSize) {
                move(index, returnRegister);
                if (alternative->m_minimumSize)
                    sub32(Imm32(alternative->m_minimumSize), returnRegister);
            } else
                pop(returnRegister);
            store32(index, Address(output, 4));
            store32(returnRegister, output);

            generateReturn();

            state.nextAlternative();

            // if there are any more alternatives, plant the check for input before looping.
            if (state.alternativeValid()) {
                PatternAlternative* nextAlternative = state.alternative();
                int countToCheckForNextAlternative = nextAlternative->m_minimumSize;

                if (countCheckedForCurrentAlternative > countToCheckForNextAlternative) { // CASE 1: current alternative was longer than the next one.
                    // If we get here, there the last input checked failed.
                    notEnoughInputForPreviousAlternative.link(this);

                    // Check if sufficent input available to run the next alternative 
                    notEnoughInputForPreviousAlternative.append(jumpIfNoAvailableInput(countToCheckForNextAlternative - countCheckedForCurrentAlternative));
                    // We are now in the correct state to enter the next alternative; this add is only required
                    // to mirror and revert operation of the sub32, just below.
                    add32(Imm32(countCheckedForCurrentAlternative - countToCheckForNextAlternative), index);

                    // If we get here, there the last input checked passed.
                    state.linkAlternativeBacktracks(this);
                    // No need to check if we can run the next alternative, since it is shorter -
                    // just update index.
                    sub32(Imm32(countCheckedForCurrentAlternative - countToCheckForNextAlternative), index);
                } else if (countCheckedForCurrentAlternative < countToCheckForNextAlternative) { // CASE 2: next alternative is longer than the current one.
                    // If we get here, there the last input checked failed.
                    // If there is insufficient input to run the current alternative, and the next alternative is longer,
                    // then there is definitely not enough input to run it - don't even check. Just adjust index, as if
                    // we had checked.
                    notEnoughInputForPreviousAlternative.link(this);
                    add32(Imm32(countToCheckForNextAlternative - countCheckedForCurrentAlternative), index);
                    notEnoughInputForPreviousAlternative.append(jump());

                    // The next alternative is longer than the current one; check the difference.
                    state.linkAlternativeBacktracks(this);
                    notEnoughInputForPreviousAlternative.append(jumpIfNoAvailableInput(countToCheckForNextAlternative - countCheckedForCurrentAlternative));
                } else { // CASE 3: Both alternatives are the same length.
                    ASSERT(countCheckedForCurrentAlternative == countToCheckForNextAlternative);

                    // If the next alterative is the same length as this one, then no need to check the input -
                    // if there was sufficent input to run the current alternative then there is sufficient
                    // input to run the next one; if not, there isn't.
                    state.linkAlternativeBacktracks(this);
                }

                state.checkedTotal -= countCheckedForCurrentAlternative;
                countCheckedForCurrentAlternative = countToCheckForNextAlternative;
                state.checkedTotal += countCheckedForCurrentAlternative;
            }
        }
        
        // If we get here, all Alternatives failed...

        state.checkedTotal -= countCheckedForCurrentAlternative;

        // How much more input need there be to be able to retry from the first alternative?
        // examples:
        //   /yarr_jit/ or /wrec|pcre/
        //     In these examples we need check for one more input before looping.
        //   /yarr_jit|pcre/
        //     In this case we need check for 5 more input to loop (+4 to allow for the first alterative
        //     being four longer than the last alternative checked, and another +1 to effectively move
        //     the start position along by one).
        //   /yarr|rules/ or /wrec|notsomuch/
        //     In these examples, provided that there was sufficient input to have just been matching for
        //     the second alternative we can loop without checking for available input (since the second
        //     alternative is longer than the first).  In the latter example we need to decrement index
        //     (by 4) so the start position is only progressed by 1 from the last iteration.
        int incrementForNextIter = (countToCheckForFirstAlternative - countCheckedForCurrentAlternative) + 1;

        // First, deal with the cases where there was sufficient input to try the last alternative.
        if (incrementForNextIter > 0) // We need to check for more input anyway, fall through to the checking below.
            state.linkAlternativeBacktracks(this);
        else if (m_pattern.m_body->m_hasFixedSize && !incrementForNextIter) // No need to update anything, link these backtracks straight to the to pof the loop!
            state.linkAlternativeBacktracksTo(firstAlternativeInputChecked, this);
        else { // no need to check the input, but we do have some bookkeeping to do first.
            state.linkAlternativeBacktracks(this);

            // Where necessary update our preserved start position.
            if (!m_pattern.m_body->m_hasFixedSize) {
                move(index, regT0);
                sub32(Imm32(countCheckedForCurrentAlternative - 1), regT0);
                poke(regT0, m_pattern.m_body->m_callFrameSize);
            }

            // Update index if necessary, and loop (without checking).
            if (incrementForNextIter)
                add32(Imm32(incrementForNextIter), index);
            jump().linkTo(firstAlternativeInputChecked, this);
        }

        notEnoughInputForPreviousAlternative.link(this);
        // Update our idea of the start position, if we're tracking this.
        if (!m_pattern.m_body->m_hasFixedSize) {
            if (countCheckedForCurrentAlternative - 1) {
                move(index, regT0);
                sub32(Imm32(countCheckedForCurrentAlternative - 1), regT0);
                poke(regT0, m_pattern.m_body->m_callFrameSize);
            } else
                poke(index, m_pattern.m_body->m_callFrameSize);
        }
        // Check if there is sufficent input to run the first alternative again.
        jumpIfAvailableInput(incrementForNextIter).linkTo(firstAlternativeInputChecked, this);
        // No - insufficent input to run the first alteranative, are there any other alternatives we
        // might need to check?  If so, the last check will have left the index incremented by
        // (countToCheckForFirstAlternative + 1), so we need test whether countToCheckForFirstAlternative
        // LESS input is available, to have the effect of just progressing the start position by 1
        // from the last iteration.  If this check passes we can just jump up to the check associated
        // with the first alternative in the loop.  This is a bit sad, since we'll end up trying the
        // first alternative again, and this check will fail (otherwise the check planted just above
        // here would have passed).  This is a bit sad, however it saves trying to do something more
        // complex here in compilation, and in the common case we should end up coallescing the checks.
        //
        // FIXME: a nice improvement here may be to stop trying to match sooner, based on the least
        // of the minimum-alterantive-lengths.  E.g. if I have two alternatives of length 200 and 150,
        // and a string of length 100, we'll end up looping index from 0 to 100, checking whether there
        // is sufficient input to run either alternative (constantly failing).  If there had been only
        // one alternative, or if the shorter alternative had come first, we would have terminated
        // immediately. :-/
        if (hasShorterAlternatives)
            jumpIfAvailableInput(-countToCheckForFirstAlternative).linkTo(firstAlternative, this);
        // index will now be a bit garbled (depending on whether 'hasShorterAlternatives' is true,
        // it has either been incremented by 1 or by (countToCheckForFirstAlternative + 1) ... 
        // but since we're about to return a failure this doesn't really matter!)

        unsigned frameSize = m_pattern.m_body->m_callFrameSize;
        if (!m_pattern.m_body->m_hasFixedSize)
            ++frameSize;
        if (frameSize)
            addPtr(Imm32(frameSize * sizeof(void*)), stackPointerRegister);

        move(Imm32(-1), returnRegister);

        generateReturn();
    }

    void generateEnter()
    {
#if PLATFORM(X86_64)
        push(X86::ebp);
        move(stackPointerRegister, X86::ebp);
#elif PLATFORM(X86)
        push(X86::ebp);
        move(stackPointerRegister, X86::ebp);
        // TODO: do we need spill registers to fill the output pointer if there are no sub captures?
        push(X86::ebx);
        push(X86::edi);
        push(X86::esi);
        // load output into edi (2 = saved ebp + return address).
    #if COMPILER(MSVC)
        loadPtr(Address(X86::ebp, 2 * sizeof(void*)), input);
        loadPtr(Address(X86::ebp, 3 * sizeof(void*)), index);
        loadPtr(Address(X86::ebp, 4 * sizeof(void*)), length);
        loadPtr(Address(X86::ebp, 5 * sizeof(void*)), output);
    #else
        loadPtr(Address(X86::ebp, 2 * sizeof(void*)), output);
    #endif
#elif PLATFORM(ARM_V7)
        push(ARM::r4);
        push(ARM::r5);
        push(ARM::r6);
        move(ARM::r3, output);
#endif
    }

    void generateReturn()
    {
#if PLATFORM(X86_64)
        pop(X86::ebp);
#elif PLATFORM(X86)
        pop(X86::esi);
        pop(X86::edi);
        pop(X86::ebx);
        pop(X86::ebp);
#elif PLATFORM(ARM_V7)
        pop(ARM::r6);
        pop(ARM::r5);
        pop(ARM::r4);
#endif
        ret();
    }

public:
    RegexGenerator(RegexPattern& pattern)
        : m_pattern(pattern)
        , m_generationFailed(false)
    {
    }

    void generate()
    {
        generateEnter();

        // TODO: do I really want this on the stack?
        if (!m_pattern.m_body->m_hasFixedSize)
            push(index);

        if (m_pattern.m_body->m_callFrameSize)
            subPtr(Imm32(m_pattern.m_body->m_callFrameSize * sizeof(void*)), stackPointerRegister);

        generateDisjunction(m_pattern.m_body);
    }

    void compile(JSGlobalData* globalData, RegexCodeBlock& jitObject)
    {
        generate();

        PatchBuffer patchBuffer(this, globalData->executableAllocator.poolForSize(size()));

        for (unsigned i = 0; i < m_backtrackRecords.size(); ++i)
            patchBuffer.patch(m_backtrackRecords[i].dataLabel, patchBuffer.locationOf(m_backtrackRecords[i].backtrackLocation));

        jitObject.set(patchBuffer.finalizeCode());
    }

    bool generationFailed()
    {
        return m_generationFailed;
    }

private:
    RegexPattern& m_pattern;
    Vector<AlternativeBacktrackRecord> m_backtrackRecords;
    bool m_generationFailed;
};

void jitCompileRegex(JSGlobalData* globalData, RegexCodeBlock& jitObject, const UString& patternString, unsigned& numSubpatterns, const char*& error, bool ignoreCase, bool multiline)
{
    RegexPattern pattern(ignoreCase, multiline);

    if ((error = compileRegex(patternString, pattern)))
        return;

    numSubpatterns = pattern.m_numSubpatterns;

    RegexGenerator generator(pattern);
    generator.compile(globalData, jitObject);

    if (generator.generationFailed()) {
        JSRegExpIgnoreCaseOption ignoreCaseOption = ignoreCase ? JSRegExpIgnoreCase : JSRegExpDoNotIgnoreCase;
        JSRegExpMultilineOption multilineOption = multiline ? JSRegExpMultiline : JSRegExpSingleLine;
        jitObject.setFallback(jsRegExpCompile(reinterpret_cast<const UChar*>(patternString.data()), patternString.size(), ignoreCaseOption, multilineOption, &numSubpatterns, &error));
    }
}

int executeRegex(RegexCodeBlock& jitObject, const UChar* input, unsigned start, unsigned length, int* output, int outputArraySize)
{
    if (JSRegExp* fallback = jitObject.getFallback())
        return (jsRegExpExecute(fallback, input, length, start, output, outputArraySize) < 0) ? -1 : output[0];

    return jitObject.execute(input, start, length, output);
}

}}

#endif