MATCH: Add patterns from phiopt's minmax_replacement

[official-gcc.git] / libgo / go / regexp / onepass.go

// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package regexp

import (
        "regexp/syntax"
        "sort"
        "strings"
        "unicode"
        "unicode/utf8"
)

// "One-pass" regexp execution.
// Some regexps can be analyzed to determine that they never need
// backtracking: they are guaranteed to run in one pass over the string
// without bothering to save all the usual NFA state.
// Detect those and execute them more quickly.

// A onePassProg is a compiled one-pass regular expression program.
// It is the same as syntax.Prog except for the use of onePassInst.
type onePassProg struct {
        Inst   []onePassInst
        Start  int // index of start instruction
        NumCap int // number of InstCapture insts in re
}

// A onePassInst is a single instruction in a one-pass regular expression program.
// It is the same as syntax.Inst except for the new 'Next' field.
type onePassInst struct {
        syntax.Inst
        Next []uint32
}

// OnePassPrefix returns a literal string that all matches for the
// regexp must start with. Complete is true if the prefix
// is the entire match. Pc is the index of the last rune instruction
// in the string. The OnePassPrefix skips over the mandatory
// EmptyBeginText
func onePassPrefix(p *syntax.Prog) (prefix string, complete bool, pc uint32) {
        i := &p.Inst[p.Start]
        if i.Op != syntax.InstEmptyWidth || (syntax.EmptyOp(i.Arg))&syntax.EmptyBeginText == 0 {
                return "", i.Op == syntax.InstMatch, uint32(p.Start)
        }
        pc = i.Out
        i = &p.Inst[pc]
        for i.Op == syntax.InstNop {
                pc = i.Out
                i = &p.Inst[pc]
        }
        // Avoid allocation of buffer if prefix is empty.
        if iop(i) != syntax.InstRune || len(i.Rune) != 1 {
                return "", i.Op == syntax.InstMatch, uint32(p.Start)
        }

        // Have prefix; gather characters.
        var buf strings.Builder
        for iop(i) == syntax.InstRune && len(i.Rune) == 1 && syntax.Flags(i.Arg)&syntax.FoldCase == 0 && i.Rune[0] != utf8.RuneError {
                buf.WriteRune(i.Rune[0])
                pc, i = i.Out, &p.Inst[i.Out]
        }
        if i.Op == syntax.InstEmptyWidth &&
                syntax.EmptyOp(i.Arg)&syntax.EmptyEndText != 0 &&
                p.Inst[i.Out].Op == syntax.InstMatch {
                complete = true
        }
        return buf.String(), complete, pc
}

// OnePassNext selects the next actionable state of the prog, based on the input character.
// It should only be called when i.Op == InstAlt or InstAltMatch, and from the one-pass machine.
// One of the alternates may ultimately lead without input to end of line. If the instruction
// is InstAltMatch the path to the InstMatch is in i.Out, the normal node in i.Next.
func onePassNext(i *onePassInst, r rune) uint32 {
        next := i.MatchRunePos(r)
        if next >= 0 {
                return i.Next[next]
        }
        if i.Op == syntax.InstAltMatch {
                return i.Out
        }
        return 0
}

func iop(i *syntax.Inst) syntax.InstOp {
        op := i.Op
        switch op {
        case syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
                op = syntax.InstRune
        }
        return op
}

// Sparse Array implementation is used as a queueOnePass.
type queueOnePass struct {
        sparse          []uint32
        dense           []uint32
        size, nextIndex uint32
}

func (q *queueOnePass) empty() bool {
        return q.nextIndex >= q.size
}

func (q *queueOnePass) next() (n uint32) {
        n = q.dense[q.nextIndex]
        q.nextIndex++
        return
}

func (q *queueOnePass) clear() {
        q.size = 0
        q.nextIndex = 0
}

func (q *queueOnePass) contains(u uint32) bool {
        if u >= uint32(len(q.sparse)) {
                return false
        }
        return q.sparse[u] < q.size && q.dense[q.sparse[u]] == u
}

func (q *queueOnePass) insert(u uint32) {
        if !q.contains(u) {
                q.insertNew(u)
        }
}

func (q *queueOnePass) insertNew(u uint32) {
        if u >= uint32(len(q.sparse)) {
                return
        }
        q.sparse[u] = q.size
        q.dense[q.size] = u
        q.size++
}

func newQueue(size int) (q *queueOnePass) {
        return &queueOnePass{
                sparse: make([]uint32, size),
                dense:  make([]uint32, size),
        }
}

// mergeRuneSets merges two non-intersecting runesets, and returns the merged result,
// and a NextIp array. The idea is that if a rune matches the OnePassRunes at index
// i, NextIp[i/2] is the target. If the input sets intersect, an empty runeset and a
// NextIp array with the single element mergeFailed is returned.
// The code assumes that both inputs contain ordered and non-intersecting rune pairs.
const mergeFailed = uint32(0xffffffff)

var (
        noRune = []rune{}
        noNext = []uint32{mergeFailed}
)

func mergeRuneSets(leftRunes, rightRunes *[]rune, leftPC, rightPC uint32) ([]rune, []uint32) {
        leftLen := len(*leftRunes)
        rightLen := len(*rightRunes)
        if leftLen&0x1 != 0 || rightLen&0x1 != 0 {
                panic("mergeRuneSets odd length []rune")
        }
        var (
                lx, rx int
        )
        merged := make([]rune, 0)
        next := make([]uint32, 0)
        ok := true
        defer func() {
                if !ok {
                        merged = nil
                        next = nil
                }
        }()

        ix := -1
        extend := func(newLow *int, newArray *[]rune, pc uint32) bool {
                if ix > 0 && (*newArray)[*newLow] <= merged[ix] {
                        return false
                }
                merged = append(merged, (*newArray)[*newLow], (*newArray)[*newLow+1])
                *newLow += 2
                ix += 2
                next = append(next, pc)
                return true
        }

        for lx < leftLen || rx < rightLen {
                switch {
                case rx >= rightLen:
                        ok = extend(&lx, leftRunes, leftPC)
                case lx >= leftLen:
                        ok = extend(&rx, rightRunes, rightPC)
                case (*rightRunes)[rx] < (*leftRunes)[lx]:
                        ok = extend(&rx, rightRunes, rightPC)
                default:
                        ok = extend(&lx, leftRunes, leftPC)
                }
                if !ok {
                        return noRune, noNext
                }
        }
        return merged, next
}

// cleanupOnePass drops working memory, and restores certain shortcut instructions.
func cleanupOnePass(prog *onePassProg, original *syntax.Prog) {
        for ix, instOriginal := range original.Inst {
                switch instOriginal.Op {
                case syntax.InstAlt, syntax.InstAltMatch, syntax.InstRune:
                case syntax.InstCapture, syntax.InstEmptyWidth, syntax.InstNop, syntax.InstMatch, syntax.InstFail:
                        prog.Inst[ix].Next = nil
                case syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
                        prog.Inst[ix].Next = nil
                        prog.Inst[ix] = onePassInst{Inst: instOriginal}
                }
        }
}

// onePassCopy creates a copy of the original Prog, as we'll be modifying it
func onePassCopy(prog *syntax.Prog) *onePassProg {
        p := &onePassProg{
                Start:  prog.Start,
                NumCap: prog.NumCap,
                Inst:   make([]onePassInst, len(prog.Inst)),
        }
        for i, inst := range prog.Inst {
                p.Inst[i] = onePassInst{Inst: inst}
        }

        // rewrites one or more common Prog constructs that enable some otherwise
        // non-onepass Progs to be onepass. A:BD (for example) means an InstAlt at
        // ip A, that points to ips B & C.
        // A:BC + B:DA => A:BC + B:CD
        // A:BC + B:DC => A:DC + B:DC
        for pc := range p.Inst {
                switch p.Inst[pc].Op {
                default:
                        continue
                case syntax.InstAlt, syntax.InstAltMatch:
                        // A:Bx + B:Ay
                        p_A_Other := &p.Inst[pc].Out
                        p_A_Alt := &p.Inst[pc].Arg
                        // make sure a target is another Alt
                        instAlt := p.Inst[*p_A_Alt]
                        if !(instAlt.Op == syntax.InstAlt || instAlt.Op == syntax.InstAltMatch) {
                                p_A_Alt, p_A_Other = p_A_Other, p_A_Alt
                                instAlt = p.Inst[*p_A_Alt]
                                if !(instAlt.Op == syntax.InstAlt || instAlt.Op == syntax.InstAltMatch) {
                                        continue
                                }
                        }
                        instOther := p.Inst[*p_A_Other]
                        // Analyzing both legs pointing to Alts is for another day
                        if instOther.Op == syntax.InstAlt || instOther.Op == syntax.InstAltMatch {
                                // too complicated
                                continue
                        }
                        // simple empty transition loop
                        // A:BC + B:DA => A:BC + B:DC
                        p_B_Alt := &p.Inst[*p_A_Alt].Out
                        p_B_Other := &p.Inst[*p_A_Alt].Arg
                        patch := false
                        if instAlt.Out == uint32(pc) {
                                patch = true
                        } else if instAlt.Arg == uint32(pc) {
                                patch = true
                                p_B_Alt, p_B_Other = p_B_Other, p_B_Alt
                        }
                        if patch {
                                *p_B_Alt = *p_A_Other
                        }

                        // empty transition to common target
                        // A:BC + B:DC => A:DC + B:DC
                        if *p_A_Other == *p_B_Alt {
                                *p_A_Alt = *p_B_Other
                        }
                }
        }
        return p
}

// runeSlice exists to permit sorting the case-folded rune sets.
type runeSlice []rune

func (p runeSlice) Len() int           { return len(p) }
func (p runeSlice) Less(i, j int) bool { return p[i] < p[j] }
func (p runeSlice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }

var anyRuneNotNL = []rune{0, '\n' - 1, '\n' + 1, unicode.MaxRune}
var anyRune = []rune{0, unicode.MaxRune}

// makeOnePass creates a onepass Prog, if possible. It is possible if at any alt,
// the match engine can always tell which branch to take. The routine may modify
// p if it is turned into a onepass Prog. If it isn't possible for this to be a
// onepass Prog, the Prog nil is returned. makeOnePass is recursive
// to the size of the Prog.
func makeOnePass(p *onePassProg) *onePassProg {
        // If the machine is very long, it's not worth the time to check if we can use one pass.
        if len(p.Inst) >= 1000 {
                return nil
        }

        var (
                instQueue    = newQueue(len(p.Inst))
                visitQueue   = newQueue(len(p.Inst))
                check        func(uint32, []bool) bool
                onePassRunes = make([][]rune, len(p.Inst))
        )

        // check that paths from Alt instructions are unambiguous, and rebuild the new
        // program as a onepass program
        check = func(pc uint32, m []bool) (ok bool) {
                ok = true
                inst := &p.Inst[pc]
                if visitQueue.contains(pc) {
                        return
                }
                visitQueue.insert(pc)
                switch inst.Op {
                case syntax.InstAlt, syntax.InstAltMatch:
                        ok = check(inst.Out, m) && check(inst.Arg, m)
                        // check no-input paths to InstMatch
                        matchOut := m[inst.Out]
                        matchArg := m[inst.Arg]
                        if matchOut && matchArg {
                                ok = false
                                break
                        }
                        // Match on empty goes in inst.Out
                        if matchArg {
                                inst.Out, inst.Arg = inst.Arg, inst.Out
                                matchOut, matchArg = matchArg, matchOut
                        }
                        if matchOut {
                                m[pc] = true
                                inst.Op = syntax.InstAltMatch
                        }

                        // build a dispatch operator from the two legs of the alt.
                        onePassRunes[pc], inst.Next = mergeRuneSets(
                                &onePassRunes[inst.Out], &onePassRunes[inst.Arg], inst.Out, inst.Arg)
                        if len(inst.Next) > 0 && inst.Next[0] == mergeFailed {
                                ok = false
                                break
                        }
                case syntax.InstCapture, syntax.InstNop:
                        ok = check(inst.Out, m)
                        m[pc] = m[inst.Out]
                        // pass matching runes back through these no-ops.
                        onePassRunes[pc] = append([]rune{}, onePassRunes[inst.Out]...)
                        inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
                        for i := range inst.Next {
                                inst.Next[i] = inst.Out
                        }
                case syntax.InstEmptyWidth:
                        ok = check(inst.Out, m)
                        m[pc] = m[inst.Out]
                        onePassRunes[pc] = append([]rune{}, onePassRunes[inst.Out]...)
                        inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
                        for i := range inst.Next {
                                inst.Next[i] = inst.Out
                        }
                case syntax.InstMatch, syntax.InstFail:
                        m[pc] = inst.Op == syntax.InstMatch
                case syntax.InstRune:
                        m[pc] = false
                        if len(inst.Next) > 0 {
                                break
                        }
                        instQueue.insert(inst.Out)
                        if len(inst.Rune) == 0 {
                                onePassRunes[pc] = []rune{}
                                inst.Next = []uint32{inst.Out}
                                break
                        }
                        runes := make([]rune, 0)
                        if len(inst.Rune) == 1 && syntax.Flags(inst.Arg)&syntax.FoldCase != 0 {
                                r0 := inst.Rune[0]
                                runes = append(runes, r0, r0)
                                for r1 := unicode.SimpleFold(r0); r1 != r0; r1 = unicode.SimpleFold(r1) {
                                        runes = append(runes, r1, r1)
                                }
                                sort.Sort(runeSlice(runes))
                        } else {
                                runes = append(runes, inst.Rune...)
                        }
                        onePassRunes[pc] = runes
                        inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
                        for i := range inst.Next {
                                inst.Next[i] = inst.Out
                        }
                        inst.Op = syntax.InstRune
                case syntax.InstRune1:
                        m[pc] = false
                        if len(inst.Next) > 0 {
                                break
                        }
                        instQueue.insert(inst.Out)
                        runes := []rune{}
                        // expand case-folded runes
                        if syntax.Flags(inst.Arg)&syntax.FoldCase != 0 {
                                r0 := inst.Rune[0]
                                runes = append(runes, r0, r0)
                                for r1 := unicode.SimpleFold(r0); r1 != r0; r1 = unicode.SimpleFold(r1) {
                                        runes = append(runes, r1, r1)
                                }
                                sort.Sort(runeSlice(runes))
                        } else {
                                runes = append(runes, inst.Rune[0], inst.Rune[0])
                        }
                        onePassRunes[pc] = runes
                        inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
                        for i := range inst.Next {
                                inst.Next[i] = inst.Out
                        }
                        inst.Op = syntax.InstRune
                case syntax.InstRuneAny:
                        m[pc] = false
                        if len(inst.Next) > 0 {
                                break
                        }
                        instQueue.insert(inst.Out)
                        onePassRunes[pc] = append([]rune{}, anyRune...)
                        inst.Next = []uint32{inst.Out}
                case syntax.InstRuneAnyNotNL:
                        m[pc] = false
                        if len(inst.Next) > 0 {
                                break
                        }
                        instQueue.insert(inst.Out)
                        onePassRunes[pc] = append([]rune{}, anyRuneNotNL...)
                        inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
                        for i := range inst.Next {
                                inst.Next[i] = inst.Out
                        }
                }
                return
        }

        instQueue.clear()
        instQueue.insert(uint32(p.Start))
        m := make([]bool, len(p.Inst))
        for !instQueue.empty() {
                visitQueue.clear()
                pc := instQueue.next()
                if !check(pc, m) {
                        p = nil
                        break
                }
        }
        if p != nil {
                for i := range p.Inst {
                        p.Inst[i].Rune = onePassRunes[i]
                }
        }
        return p
}

// compileOnePass returns a new *syntax.Prog suitable for onePass execution if the original Prog
// can be recharacterized as a one-pass regexp program, or syntax.nil if the
// Prog cannot be converted. For a one pass prog, the fundamental condition that must
// be true is: at any InstAlt, there must be no ambiguity about what branch to  take.
func compileOnePass(prog *syntax.Prog) (p *onePassProg) {
        if prog.Start == 0 {
                return nil
        }
        // onepass regexp is anchored
        if prog.Inst[prog.Start].Op != syntax.InstEmptyWidth ||
                syntax.EmptyOp(prog.Inst[prog.Start].Arg)&syntax.EmptyBeginText != syntax.EmptyBeginText {
                return nil
        }
        // every instruction leading to InstMatch must be EmptyEndText
        for _, inst := range prog.Inst {
                opOut := prog.Inst[inst.Out].Op
                switch inst.Op {
                default:
                        if opOut == syntax.InstMatch {
                                return nil
                        }
                case syntax.InstAlt, syntax.InstAltMatch:
                        if opOut == syntax.InstMatch || prog.Inst[inst.Arg].Op == syntax.InstMatch {
                                return nil
                        }
                case syntax.InstEmptyWidth:
                        if opOut == syntax.InstMatch {
                                if syntax.EmptyOp(inst.Arg)&syntax.EmptyEndText == syntax.EmptyEndText {
                                        continue
                                }
                                return nil
                        }
                }
        }
        // Creates a slightly optimized copy of the original Prog
        // that cleans up some Prog idioms that block valid onepass programs
        p = onePassCopy(prog)

        // checkAmbiguity on InstAlts, build onepass Prog if possible
        p = makeOnePass(p)

        if p != nil {
                cleanupOnePass(p, prog)
        }
        return p
}