regexp: evaluate context flags lazily

There's no point in computing whether we're at the
beginning of the line if the NFA isn't going to ask.
Wait to compute that until asked.

Whatever minor slowdowns were introduced by
the conversion to pools that were not repaid by
other optimizations are taken care of by this one.

name                             old time/op    new time/op    delta
Find-12                             252ns ± 0%     260ns ± 0%   +3.34%  (p=0.000 n=10+8)
FindAllNoMatches-12                 136ns ± 4%     134ns ± 4%   -0.96%  (p=0.033 n=10+10)
FindString-12                       246ns ± 0%     250ns ± 0%   +1.46%  (p=0.000 n=8+10)
FindSubmatch-12                     332ns ± 1%     332ns ± 0%     ~     (p=0.101 n=9+10)
FindStringSubmatch-12               321ns ± 1%     322ns ± 1%     ~     (p=0.717 n=9+10)
Literal-12                         91.6ns ± 0%    92.3ns ± 0%   +0.74%  (p=0.000 n=9+9)
NotLiteral-12                      1.47µs ± 0%    1.47µs ± 0%   +0.38%  (p=0.000 n=9+8)
MatchClass-12                      2.15µs ± 0%    2.15µs ± 0%   +0.39%  (p=0.000 n=10+10)
MatchClass_InRange-12              2.09µs ± 0%    2.11µs ± 0%   +0.75%  (p=0.000 n=9+9)
ReplaceAll-12                      1.40µs ± 0%    1.40µs ± 0%     ~     (p=0.525 n=10+10)
AnchoredLiteralShortNonMatch-12    83.5ns ± 0%    81.6ns ± 0%   -2.28%  (p=0.000 n=9+10)
AnchoredLiteralLongNonMatch-12      101ns ± 0%      97ns ± 1%   -3.54%  (p=0.000 n=10+10)
AnchoredShortMatch-12               131ns ± 0%     128ns ± 0%   -2.29%  (p=0.000 n=10+9)
AnchoredLongMatch-12                268ns ± 1%     252ns ± 1%   -6.04%  (p=0.000 n=10+10)
OnePassShortA-12                    614ns ± 0%     587ns ± 1%   -4.33%  (p=0.000 n=6+10)
NotOnePassShortA-12                 552ns ± 0%     547ns ± 1%   -0.89%  (p=0.000 n=10+10)
OnePassShortB-12                    494ns ± 0%     455ns ± 0%   -7.96%  (p=0.000 n=9+9)
NotOnePassShortB-12                 411ns ± 0%     406ns ± 0%   -1.30%  (p=0.000 n=9+9)
OnePassLongPrefix-12                109ns ± 0%     108ns ± 1%     ~     (p=0.064 n=8+9)
OnePassLongNotPrefix-12             403ns ± 0%     349ns ± 0%  -13.30%  (p=0.000 n=9+8)
MatchParallelShared-12             38.9ns ± 1%    37.9ns ± 1%   -2.65%  (p=0.000 n=10+8)
MatchParallelCopied-12             39.2ns ± 1%    38.3ns ± 2%   -2.20%  (p=0.001 n=10+10)
QuoteMetaAll-12                    94.5ns ± 0%    94.7ns ± 0%   +0.18%  (p=0.043 n=10+9)
QuoteMetaNone-12                   52.7ns ± 0%    52.7ns ± 0%     ~     (all equal)
Match/Easy0/32-12                  72.2ns ± 0%    71.9ns ± 0%   -0.38%  (p=0.009 n=8+10)
Match/Easy0/1K-12                   296ns ± 1%     297ns ± 0%   +0.51%  (p=0.001 n=10+9)
Match/Easy0/32K-12                 4.57µs ± 3%    4.61µs ± 2%     ~     (p=0.280 n=10+10)
Match/Easy0/1M-12                   234µs ± 0%     234µs ± 0%     ~     (p=0.986 n=10+10)
Match/Easy0/32M-12                 7.96ms ± 0%    7.98ms ± 0%   +0.22%  (p=0.010 n=10+9)
Match/Easy0i/32-12                 1.09µs ± 0%    1.10µs ± 0%   +0.23%  (p=0.000 n=8+9)
Match/Easy0i/1K-12                 31.7µs ± 0%    31.7µs ± 0%   +0.09%  (p=0.003 n=9+8)
Match/Easy0i/32K-12                1.61ms ± 0%    1.27ms ± 1%  -21.03%  (p=0.000 n=8+10)
Match/Easy0i/1M-12                 51.4ms ± 0%    40.4ms ± 0%  -21.29%  (p=0.000 n=8+8)
Match/Easy0i/32M-12                 1.65s ± 0%     1.30s ± 1%  -21.22%  (p=0.000 n=9+9)
Match/Easy1/32-12                  67.6ns ± 1%    67.2ns ± 0%     ~     (p=0.085 n=10+9)
Match/Easy1/1K-12                   873ns ± 2%     880ns ± 0%   +0.78%  (p=0.006 n=9+7)
Match/Easy1/32K-12                 39.7µs ± 1%    34.3µs ± 3%  -13.53%  (p=0.000 n=10+10)
Match/Easy1/1M-12                  1.41ms ± 1%    1.19ms ± 3%  -15.48%  (p=0.000 n=10+10)
Match/Easy1/32M-12                 44.9ms ± 1%    38.0ms ± 2%  -15.21%  (p=0.000 n=10+10)
Match/Medium/32-12                 1.04µs ± 0%    1.03µs ± 0%   -0.57%  (p=0.000 n=9+9)
Match/Medium/1K-12                 31.2µs ± 0%    31.4µs ± 1%   +0.61%  (p=0.000 n=8+10)
Match/Medium/32K-12                1.45ms ± 1%    1.20ms ± 0%  -17.70%  (p=0.000 n=10+8)
Match/Medium/1M-12                 46.4ms ± 0%    38.4ms ± 2%  -17.32%  (p=0.000 n=6+9)
Match/Medium/32M-12                 1.49s ± 1%     1.24s ± 1%  -16.81%  (p=0.000 n=10+10)
Match/Hard/32-12                   1.47µs ± 0%    1.47µs ± 0%   -0.31%  (p=0.000 n=9+10)
Match/Hard/1K-12                   44.5µs ± 1%    44.4µs ± 0%     ~     (p=0.075 n=10+10)
Match/Hard/32K-12                  2.09ms ± 0%    1.78ms ± 7%  -14.88%  (p=0.000 n=8+10)
Match/Hard/1M-12                   67.8ms ± 5%    56.9ms ± 7%  -16.05%  (p=0.000 n=10+10)
Match/Hard/32M-12                   2.17s ± 5%     1.84s ± 6%  -15.21%  (p=0.000 n=10+10)
Match/Hard1/32-12                  7.89µs ± 0%    7.94µs ± 0%   +0.61%  (p=0.000 n=9+9)
Match/Hard1/1K-12                   246µs ± 0%     245µs ± 0%   -0.30%  (p=0.010 n=9+10)
Match/Hard1/32K-12                 8.93ms ± 0%    8.17ms ± 0%   -8.44%  (p=0.000 n=9+8)
Match/Hard1/1M-12                   286ms ± 0%     269ms ± 9%   -5.66%  (p=0.028 n=9+10)
Match/Hard1/32M-12                  9.16s ± 0%     8.61s ± 8%   -5.98%  (p=0.028 n=9+10)
Match_onepass_regex/32-12           825ns ± 0%     712ns ± 0%  -13.75%  (p=0.000 n=8+8)
Match_onepass_regex/1K-12          28.7µs ± 1%    19.8µs ± 0%  -30.99%  (p=0.000 n=9+8)
Match_onepass_regex/32K-12          950µs ± 1%     628µs ± 0%  -33.83%  (p=0.000 n=9+8)
Match_onepass_regex/1M-12          30.4ms ± 0%    20.1ms ± 0%  -33.74%  (p=0.000 n=9+8)
Match_onepass_regex/32M-12          974ms ± 1%     646ms ± 0%  -33.73%  (p=0.000 n=9+8)
CompileOnepass-12                  4.60µs ± 0%    4.59µs ± 0%     ~     (p=0.063 n=8+9)
[Geo mean]                         23.1µs         21.3µs        -7.44%

https://perf.golang.org/search?q=upload:20181004.4

Change-Id: I47cdd09f6dcde1d7c317080e9b4df42c7d0a8d24
Reviewed-on: https://go-review.googlesource.com/c/139782
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

3 files changed, 77 insertions, 21 deletions

diff --git a/src/regexp/backtrack.go b/src/regexp/backtrack.go
index 239abc3a57..9fb7d1e493 100644
--- a/src/regexp/backtrack.go
+++ b/src/regexp/backtrack.go
@@ -257,7 +257,8 @@ func (re *Regexp) tryBacktrack(b *bitState, i input, pc uint32, pos int) bool {
 			}
 
 		case syntax.InstEmptyWidth:
-			if syntax.EmptyOp(inst.Arg)&^i.context(pos) != 0 {
+			flag := i.context(pos)
+			if !flag.match(syntax.EmptyOp(inst.Arg)) {
 				continue
 			}
 			pc = inst.Out
diff --git a/src/regexp/exec.go b/src/regexp/exec.go
index e1870021f2..efe764e2dc 100644
--- a/src/regexp/exec.go
+++ b/src/regexp/exec.go
@@ -114,6 +114,61 @@ func (m *machine) alloc(i *syntax.Inst) *thread {
 	return t
 }
 
+// A lazyFlag is a lazily-evaluated syntax.EmptyOp,
+// for checking zero-width flags like ^ $ \A \z \B \b.
+// It records the pair of relevant runes and does not
+// determine the implied flags until absolutely necessary
+// (most of the time, that means never).
+type lazyFlag uint64
+
+func newLazyFlag(r1, r2 rune) lazyFlag {
+	return lazyFlag(uint64(r1)<<32 | uint64(uint32(r2)))
+}
+
+func (f lazyFlag) match(op syntax.EmptyOp) bool {
+	if op == 0 {
+		return true
+	}
+	r1 := rune(f >> 32)
+	if op&syntax.EmptyBeginLine != 0 {
+		if r1 != '\n' && r1 >= 0 {
+			return false
+		}
+		op &^= syntax.EmptyBeginLine
+	}
+	if op&syntax.EmptyBeginText != 0 {
+		if r1 >= 0 {
+			return false
+		}
+		op &^= syntax.EmptyBeginText
+	}
+	if op == 0 {
+		return true
+	}
+	r2 := rune(f)
+	if op&syntax.EmptyEndLine != 0 {
+		if r2 != '\n' && r2 >= 0 {
+			return false
+		}
+		op &^= syntax.EmptyEndLine
+	}
+	if op&syntax.EmptyEndText != 0 {
+		if r2 >= 0 {
+			return false
+		}
+		op &^= syntax.EmptyEndText
+	}
+	if op == 0 {
+		return true
+	}
+	if syntax.IsWordChar(r1) != syntax.IsWordChar(r2) {
+		op &^= syntax.EmptyWordBoundary
+	} else {
+		op &^= syntax.EmptyNoWordBoundary
+	}
+	return op == 0
+}
+
 // match runs the machine over the input starting at pos.
 // It reports whether a match was found.
 // If so, m.matchcap holds the submatch information.
@@ -133,9 +188,9 @@ func (m *machine) match(i input, pos int) bool {
 	if r != endOfText {
 		r1, width1 = i.step(pos + width)
 	}
-	var flag syntax.EmptyOp
+	var flag lazyFlag
 	if pos == 0 {
-		flag = syntax.EmptyOpContext(-1, r)
+		flag = newLazyFlag(-1, r)
 	} else {
 		flag = i.context(pos)
 	}
@@ -164,10 +219,10 @@ func (m *machine) match(i input, pos int) bool {
 			if len(m.matchcap) > 0 {
 				m.matchcap[0] = pos
 			}
-			m.add(runq, uint32(m.p.Start), pos, m.matchcap, flag, nil)
+			m.add(runq, uint32(m.p.Start), pos, m.matchcap, &flag, nil)
 		}
-		flag = syntax.EmptyOpContext(r, r1)
-		m.step(runq, nextq, pos, pos+width, r, flag)
+		flag = newLazyFlag(r, r1)
+		m.step(runq, nextq, pos, pos+width, r, &flag)
 		if width == 0 {
 			break
 		}
@@ -202,7 +257,7 @@ func (m *machine) clear(q *queue) {
 // The step processes the rune c (which may be endOfText),
 // which starts at position pos and ends at nextPos.
 // nextCond gives the setting for the empty-width flags after c.
-func (m *machine) step(runq, nextq *queue, pos, nextPos int, c rune, nextCond syntax.EmptyOp) {
+func (m *machine) step(runq, nextq *queue, pos, nextPos int, c rune, nextCond *lazyFlag) {
 	longest := m.re.longest
 	for j := 0; j < len(runq.dense); j++ {
 		d := &runq.dense[j]
@@ -259,7 +314,7 @@ func (m *machine) step(runq, nextq *queue, pos, nextPos int, c rune, nextCond sy
 // It also recursively adds an entry for all instructions reachable from pc by following
 // empty-width conditions satisfied by cond.  pos gives the current position
 // in the input.
-func (m *machine) add(q *queue, pc uint32, pos int, cap []int, cond syntax.EmptyOp, t *thread) *thread {
+func (m *machine) add(q *queue, pc uint32, pos int, cap []int, cond *lazyFlag, t *thread) *thread {
 Again:
 	if pc == 0 {
 		return t
@@ -286,7 +341,7 @@ Again:
 		pc = i.Arg
 		goto Again
 	case syntax.InstEmptyWidth:
-		if syntax.EmptyOp(i.Arg)&^cond == 0 {
+		if cond.match(syntax.EmptyOp(i.Arg)) {
 			pc = i.Out
 			goto Again
 		}
@@ -365,16 +420,16 @@ func (re *Regexp) doOnePass(ir io.RuneReader, ib []byte, is string, pos, ncap in
 	if r != endOfText {
 		r1, width1 = i.step(pos + width)
 	}
-	var flag syntax.EmptyOp
+	var flag lazyFlag
 	if pos == 0 {
-		flag = syntax.EmptyOpContext(-1, r)
+		flag = newLazyFlag(-1, r)
 	} else {
 		flag = i.context(pos)
 	}
 	pc := re.onepass.Start
 	inst := re.onepass.Inst[pc]
 	// If there is a simple literal prefix, skip over it.
-	if pos == 0 && syntax.EmptyOp(inst.Arg)&^flag == 0 &&
+	if pos == 0 && flag.match(syntax.EmptyOp(inst.Arg)) &&
 		len(re.prefix) > 0 && i.canCheckPrefix() {
 		// Match requires literal prefix; fast search for it.
 		if !i.hasPrefix(re) {
@@ -422,7 +477,7 @@ func (re *Regexp) doOnePass(ir io.RuneReader, ib []byte, is string, pos, ncap in
 		case syntax.InstNop:
 			continue
 		case syntax.InstEmptyWidth:
-			if syntax.EmptyOp(inst.Arg)&^flag != 0 {
+			if !flag.match(syntax.EmptyOp(inst.Arg)) {
 				goto Return
 			}
 			continue
@@ -435,7 +490,7 @@ func (re *Regexp) doOnePass(ir io.RuneReader, ib []byte, is string, pos, ncap in
 		if width == 0 {
 			break
 		}
-		flag = syntax.EmptyOpContext(r, r1)
+		flag = newLazyFlag(r, r1)
 		pos += width
 		r, width = r1, width1
 		if r != endOfText {
diff --git a/src/regexp/regexp.go b/src/regexp/regexp.go
index 98146031c0..3586029555 100644
--- a/src/regexp/regexp.go
+++ b/src/regexp/regexp.go
@@ -311,7 +311,7 @@ type input interface {
 	canCheckPrefix() bool             // can we look ahead without losing info?
 	hasPrefix(re *Regexp) bool
 	index(re *Regexp, pos int) int
-	context(pos int) syntax.EmptyOp
+	context(pos int) lazyFlag
 }
 
 // inputString scans a string.
@@ -342,7 +342,7 @@ func (i *inputString) index(re *Regexp, pos int) int {
 	return strings.Index(i.str[pos:], re.prefix)
 }
 
-func (i *inputString) context(pos int) syntax.EmptyOp {
+func (i *inputString) context(pos int) lazyFlag {
 	r1, r2 := endOfText, endOfText
 	// 0 < pos && pos <= len(i.str)
 	if uint(pos-1) < uint(len(i.str)) {
@@ -358,7 +358,7 @@ func (i *inputString) context(pos int) syntax.EmptyOp {
 			r2, _ = utf8.DecodeRuneInString(i.str[pos:])
 		}
 	}
-	return syntax.EmptyOpContext(r1, r2)
+	return newLazyFlag(r1, r2)
 }
 
 // inputBytes scans a byte slice.
@@ -389,7 +389,7 @@ func (i *inputBytes) index(re *Regexp, pos int) int {
 	return bytes.Index(i.str[pos:], re.prefixBytes)
 }
 
-func (i *inputBytes) context(pos int) syntax.EmptyOp {
+func (i *inputBytes) context(pos int) lazyFlag {
 	r1, r2 := endOfText, endOfText
 	// 0 < pos && pos <= len(i.str)
 	if uint(pos-1) < uint(len(i.str)) {
@@ -405,7 +405,7 @@ func (i *inputBytes) context(pos int) syntax.EmptyOp {
 			r2, _ = utf8.DecodeRune(i.str[pos:])
 		}
 	}
-	return syntax.EmptyOpContext(r1, r2)
+	return newLazyFlag(r1, r2)
 }
 
 // inputReader scans a RuneReader.
@@ -441,8 +441,8 @@ func (i *inputReader) index(re *Regexp, pos int) int {
 	return -1
 }
 
-func (i *inputReader) context(pos int) syntax.EmptyOp {
-	return 0
+func (i *inputReader) context(pos int) lazyFlag {
+	return 0 // not used
 }
 
 // LiteralPrefix returns a literal string that must begin any match