From 93238623e2c8dfa23c2d0845613349ff8df7fbb7 Mon Sep 17 00:00:00 2001 From: Michael Matloob Date: Sun, 28 Dec 2014 00:17:01 -0800 Subject: [PATCH] regexp: port RE2's bitstate backtracker to the regexp package This is a port of RE2's bitstate backtracker, which triggers under the same conditions that the RE2 backtracker triggers. However I wasn't sure how to port over some of the optimizations in the RE2 backtracker, and there is a ~2% penalty on benchmarks that don't trigger the backtracker. benchmark old ns/op new ns/op delta BenchmarkLiteral 312 189 -39.42% BenchmarkNotLiteral 4435 3001 -32.33% BenchmarkMatchClass 5758 4378 -23.97% BenchmarkMatchClass_InRange 5385 4084 -24.16% BenchmarkReplaceAll 5291 3505 -33.76% BenchmarkAnchoredLiteralShortNonMatch 190 200 +5.26% BenchmarkAnchoredLiteralLongNonMatch 189 194 +2.65% BenchmarkAnchoredShortMatch 479 304 -36.53% BenchmarkAnchoredLongMatch 478 499 +4.39% BenchmarkOnePassShortA 791 798 +0.88% BenchmarkNotOnePassShortA 3202 1571 -50.94% BenchmarkOnePassShortB 614 633 +3.09% BenchmarkNotOnePassShortB 2685 881 -67.19% BenchmarkOnePassLongPrefix 152 154 +1.32% BenchmarkOnePassLongNotPrefix 505 533 +5.54% BenchmarkMatchEasy0_32 139 171 +23.02% BenchmarkMatchEasy0_1K 653 1797 +175.19% BenchmarkMatchEasy0_32K 12032 13346 +10.92% BenchmarkMatchEasy0_1M 462882 461272 -0.35% BenchmarkMatchEasy0_32M 15015339 15365238 +2.33% BenchmarkMatchEasy1_32 122 168 +37.70% BenchmarkMatchEasy1_1K 3339 2612 -21.77% BenchmarkMatchEasy1_32K 72330 71721 -0.84% BenchmarkMatchEasy1_1M 2545410 2652284 +4.20% BenchmarkMatchEasy1_32M 80072063 82609750 +3.17% BenchmarkMatchMedium_32 2359 1980 -16.07% BenchmarkMatchMedium_1K 75939 58593 -22.84% BenchmarkMatchMedium_32K 2450907 2501106 +2.05% BenchmarkMatchMedium_1M 78707697 80174418 +1.86% BenchmarkMatchMedium_32M 2535146010 2570896441 +1.41% BenchmarkMatchHard_32 4297 2960 -31.11% BenchmarkMatchHard_1K 133592 88997 -33.38% BenchmarkMatchHard_32K 4240445 4336907 +2.27% BenchmarkMatchHard_1M 136187006 139350238 +2.32% BenchmarkMatchHard_32M 4350855890 4478537306 +2.93% benchmark old MB/s new MB/s speedup BenchmarkMatchEasy0_32 228.74 186.11 0.81x BenchmarkMatchEasy0_1K 1565.91 569.64 0.36x BenchmarkMatchEasy0_32K 2723.31 2455.10 0.90x BenchmarkMatchEasy0_1M 2265.32 2273.22 1.00x BenchmarkMatchEasy0_32M 2234.68 2183.79 0.98x BenchmarkMatchEasy1_32 261.08 190.22 0.73x BenchmarkMatchEasy1_1K 306.59 391.91 1.28x BenchmarkMatchEasy1_32K 453.03 456.88 1.01x BenchmarkMatchEasy1_1M 411.95 395.35 0.96x BenchmarkMatchEasy1_32M 419.05 406.18 0.97x BenchmarkMatchMedium_32 13.56 16.16 1.19x BenchmarkMatchMedium_1K 13.48 17.48 1.30x BenchmarkMatchMedium_32K 13.37 13.10 0.98x BenchmarkMatchMedium_1M 13.32 13.08 0.98x BenchmarkMatchMedium_32M 13.24 13.05 0.99x BenchmarkMatchHard_32 7.45 10.81 1.45x BenchmarkMatchHard_1K 7.67 11.51 1.50x BenchmarkMatchHard_32K 7.73 7.56 0.98x BenchmarkMatchHard_1M 7.70 7.52 0.98x BenchmarkMatchHard_32M 7.71 7.49 0.97x Fixes #4154 Change-Id: Iff7fb9507f0872b320d08afc08679751ed1b28bc Reviewed-on: https://go-review.googlesource.com/2153 Reviewed-by: Russ Cox --- src/regexp/backtrack.go | 351 ++++++++++++++++++++++++++++++++++++++++ src/regexp/exec.go | 30 +++- 2 files changed, 374 insertions(+), 7 deletions(-) create mode 100644 src/regexp/backtrack.go diff --git a/src/regexp/backtrack.go b/src/regexp/backtrack.go new file mode 100644 index 00000000000..824014ba2ab --- /dev/null +++ b/src/regexp/backtrack.go @@ -0,0 +1,351 @@ +// Copyright 2015 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. + +// backtrack is a regular expression search with submatch +// tracking for small regular expressions and texts. It allocates +// a bit vector with (length of input) * (length of prog) bits, +// to make sure it never explores the same (character position, instruction) +// state multiple times. This limits the search to run in time linear in +// the length of the test. +// +// backtrack is a fast replacement for the NFA code on small +// regexps when onepass cannot be used. + +package regexp + +import "regexp/syntax" + +// A job is an entry on the backtracker's job stack. It holds +// the instruction pc and the position in the input. +type job struct { + pc uint32 + arg int + pos int +} + +const ( + visitedBits = 32 + maxBacktrackProg = 500 // len(prog.Inst) <= max + maxBacktrackVector = 256 * 1024 // bit vector size <= max (bits) +) + +// bitState holds state for the backtracker. +type bitState struct { + prog *syntax.Prog + + end int + cap []int + reqcap bool // whether any captures are requested + input input + jobs []job + visited []uint32 +} + +var notBacktrack *bitState = nil + +// maxBitStateLen returns the maximum length of a string to search with +// the backtracker using prog. +func maxBitStateLen(prog *syntax.Prog) int { + return maxBacktrackVector / len(prog.Inst) +} + +// newBitState returns a new bitState for the given prog, +// or notBacktrack if the size of the prog exceeds the maximum size that +// the backtracker will be run for. +func newBitState(prog *syntax.Prog) *bitState { + if len(prog.Inst) > maxBacktrackProg { + return notBacktrack + } + return &bitState{ + prog: prog, + } +} + +// reset resets the state of the backtracker. +// end is the end position in the input. ncap and reqcap are the number +// of the machine's capture registers and the number of user-requested +// captures respectively. +func (b *bitState) reset(end int, ncap int, reqcap int) { + b.end = end + b.reqcap = reqcap > 0 + + if cap(b.jobs) == 0 { + b.jobs = make([]job, 0, 256) + } else { + b.jobs = b.jobs[:0] + } + + visitedSize := (len(b.prog.Inst)*(end+1) + visitedBits - 1) / visitedBits + if cap(b.visited) < visitedSize { + b.visited = make([]uint32, visitedSize, maxBacktrackVector/visitedBits) + } else { + b.visited = b.visited[:visitedSize] + for i := range b.visited { + b.visited[i] = 0 + } + } + + if len(b.cap) < ncap { + b.cap = make([]int, ncap) + } + for i := range b.cap { + b.cap[i] = -1 + } +} + +// shouldVisit reports whether the combination of (pc, pos) has not +// been visited yet. +func (b *bitState) shouldVisit(pc uint32, pos int) bool { + n := uint(int(pc)*(b.end+1) + pos) + if b.visited[n/visitedBits]&(1<<(n&(visitedBits-1))) != 0 { + return false + } + b.visited[n/visitedBits] |= 1 << (n & (visitedBits - 1)) + return true +} + +// push pushes (pc, pos, arg) onto the job stack if it should be +// visited. +func (b *bitState) push(pc uint32, pos int, arg int) { + if b.prog.Inst[pc].Op == syntax.InstFail { + return + } + + // Only check shouldVisit when arg == 0. + // When arg > 0, we are continuing a previous visit. + if arg == 0 && !b.shouldVisit(pc, pos) { + return + } + + b.jobs = append(b.jobs, job{pc: pc, arg: arg, pos: pos}) +} + +// tryBacktrack runs a backtracking search starting at pos. +func (m *machine) tryBacktrack(b *bitState, i input, pc uint32, pos int) bool { + longest := m.re.longest + m.matched = false + + b.push(pc, pos, 0) + for len(b.jobs) > 0 { + l := len(b.jobs) - 1 + // Pop job off the stack. + pc := b.jobs[l].pc + pos := b.jobs[l].pos + arg := b.jobs[l].arg + b.jobs = b.jobs[:l] + + // Optimization: rather than push and pop, + // code that is going to Push and continue + // the loop simply updates ip, p, and arg + // and jumps to CheckAndLoop. We have to + // do the ShouldVisit check that Push + // would have, but we avoid the stack + // manipulation. + goto Skip + CheckAndLoop: + if !b.shouldVisit(pc, pos) { + continue + } + Skip: + + inst := b.prog.Inst[pc] + + switch inst.Op { + default: + panic("bad inst") + case syntax.InstFail: + panic("unexpected InstFail") + case syntax.InstAlt: + // Cannot just + // b.push(inst.Out, pos, 0) + // b.push(inst.Arg, pos, 0) + // If during the processing of inst.Out, we encounter + // inst.Arg via another path, we want to process it then. + // Pushing it here will inhibit that. Instead, re-push + // inst with arg==1 as a reminder to push inst.Arg out + // later. + switch arg { + case 0: + b.push(pc, pos, 1) + pc = inst.Out + goto CheckAndLoop + case 1: + // Finished inst.Out; try inst.Arg. + arg = 0 + pc = inst.Arg + goto CheckAndLoop + } + panic("bad arg in InstAlt") + + case syntax.InstAltMatch: + // One opcode consumes runes; the other leads to match. + switch b.prog.Inst[inst.Out].Op { + case syntax.InstRune, syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL: + // inst.Arg is the match. + b.push(inst.Arg, pos, 0) + pc = inst.Arg + pos = b.end + goto CheckAndLoop + } + // inst.Out is the match - non-greedy + b.push(inst.Out, b.end, 0) + pc = inst.Out + goto CheckAndLoop + + case syntax.InstRune: + r, width := i.step(pos) + if !inst.MatchRune(r) { + continue + } + pos += width + pc = inst.Out + goto CheckAndLoop + + case syntax.InstRune1: + r, width := i.step(pos) + if r != inst.Rune[0] { + continue + } + pos += width + pc = inst.Out + goto CheckAndLoop + + case syntax.InstRuneAnyNotNL: + r, width := i.step(pos) + if r == '\n' || r == endOfText { + continue + } + pos += width + pc = inst.Out + goto CheckAndLoop + + case syntax.InstRuneAny: + r, width := i.step(pos) + if r == endOfText { + continue + } + pos += width + pc = inst.Out + goto CheckAndLoop + + case syntax.InstCapture: + switch arg { + case 0: + if 0 <= inst.Arg && inst.Arg < uint32(len(b.cap)) { + // Capture pos to register, but save old value. + b.push(pc, b.cap[inst.Arg], 1) // come back when we're done. + b.cap[inst.Arg] = pos + } + pc = inst.Out + goto CheckAndLoop + case 1: + // Finished inst.Out; restore the old value. + b.cap[inst.Arg] = pos + continue + + } + panic("bad arg in InstCapture") + continue + + case syntax.InstEmptyWidth: + if syntax.EmptyOp(inst.Arg)&^i.context(pos) != 0 { + continue + } + pc = inst.Out + goto CheckAndLoop + + case syntax.InstNop: + pc = inst.Out + goto CheckAndLoop + + case syntax.InstMatch: + // We found a match. If the caller doesn't care + // where the match is, no point going further. + if !b.reqcap { + m.matched = true + return m.matched + } + + // Record best match so far. + // Only need to check end point, because this entire + // call is only considering one start position. + b.cap[1] = pos + if !m.matched || (longest && pos > 0 && pos > m.matchcap[1]) { + copy(m.matchcap, b.cap) + } + m.matched = true + + // If going for first match, we're done. + if !longest { + return m.matched + } + + // If we used the entire text, no longer match is possible. + if pos == b.end { + return m.matched + } + + // Otherwise, continue on in hope of a longer match. + continue + } + panic("unreachable") + } + + return m.matched +} + +// backtrack runs a backtracking search of prog on the input starting at pos. +func (m *machine) backtrack(i input, pos int, end int, reqcap int) bool { + if !i.canCheckPrefix() { + panic("backtrack called for a RuneReader") + } + + startCond := m.re.cond + if startCond == ^syntax.EmptyOp(0) { // impossible + return false + } + if startCond&syntax.EmptyBeginText != 0 && pos != 0 { + // Anchored match, past beginning of text. + return false + } + + b := m.b + b.reset(end, len(m.matchcap), reqcap) + + for i := range m.matchcap { + m.matchcap[i] = -1 + } + + // Anchored search must start at the beginning of the input + if startCond&syntax.EmptyBeginText != 0 { + b.cap[0] = pos + return m.tryBacktrack(b, i, uint32(m.p.Start), pos) + } + + // Unanchored search, starting from each possible text position. + // Notice that we have to try the empty string at the end of + // the text, so the loop condition is pos <= end, not pos < end. + // This looks like it's quadratic in the size of the text, + // but we are not clearing visited between calls to TrySearch, + // so no work is duplicated and it ends up still being linear. + width := -1 + for ; pos <= end && width != 0; pos += width { + if len(m.re.prefix) > 0 { + // Match requires literal prefix; fast search for it. + advance := i.index(m.re, pos) + if advance < 0 { + return false + } + pos += advance + } + + b.cap[0] = pos + if m.tryBacktrack(b, i, uint32(m.p.Start), pos) { + // Match must be leftmost; done. + return true + } + _, width = i.step(pos) + } + return false +} diff --git a/src/regexp/exec.go b/src/regexp/exec.go index c4cb201f642..518272092ae 100644 --- a/src/regexp/exec.go +++ b/src/regexp/exec.go @@ -35,13 +35,15 @@ type thread struct { // A machine holds all the state during an NFA simulation for p. type machine struct { - re *Regexp // corresponding Regexp - p *syntax.Prog // compiled program - op *onePassProg // compiled onepass program, or notOnePass - q0, q1 queue // two queues for runq, nextq - pool []*thread // pool of available threads - matched bool // whether a match was found - matchcap []int // capture information for the match + re *Regexp // corresponding Regexp + p *syntax.Prog // compiled program + op *onePassProg // compiled onepass program, or notOnePass + maxBitStateLen int // max length of string to search with bitstate + b *bitState // state for backtracker, allocated lazily + q0, q1 queue // two queues for runq, nextq + pool []*thread // pool of available threads + matched bool // whether a match was found + matchcap []int // capture information for the match // cached inputs, to avoid allocation inputBytes inputBytes @@ -76,6 +78,9 @@ func progMachine(p *syntax.Prog, op *onePassProg) *machine { if ncap < 2 { ncap = 2 } + if op == notOnePass { + m.maxBitStateLen = maxBitStateLen(p) + } m.matchcap = make([]int, ncap) return m } @@ -422,18 +427,29 @@ var empty = make([]int, 0) func (re *Regexp) doExecute(r io.RuneReader, b []byte, s string, pos int, ncap int) []int { m := re.get() var i input + var size int if r != nil { i = m.newInputReader(r) } else if b != nil { i = m.newInputBytes(b) + size = len(b) } else { i = m.newInputString(s) + size = len(s) } if m.op != notOnePass { if !m.onepass(i, pos) { re.put(m) return nil } + } else if size < m.maxBitStateLen && r == nil { + if m.b == nil { + m.b = newBitState(m.p) + } + if !m.backtrack(i, pos, size, ncap) { + re.put(m) + return nil + } } else { m.init(ncap) if !m.match(i, pos) {