Optimization to regexp _CharClass: keep track of overall range of

    charclass to avoid unnecessarily iterating over ranges.
    Also, use the fact that IntVector is an []int to avoid method calls.
    On my machine, this brings us from ~27500 ns/op to ~17500 ns/op in the benchmark I've added (it is also faster in the case where a range check
    doesn't help, added a benchmark for this too.)

    I'd also like to propose that "[]", and "[^]" be disallowed. They aren't useful as far as I can tell, they aren't widely supported, and they make reasoning about character classes a bit more complicated.

R=r
CC=golang-dev
https://golang.org/cl/1495041

2 files changed, 48 insertions, 10 deletions

diff --git a/src/pkg/regexp/all_test.go b/src/pkg/regexp/all_test.go
index 62dad3aa01..fd7ee2acb6 100644
--- a/src/pkg/regexp/all_test.go
+++ b/src/pkg/regexp/all_test.go
@@ -519,7 +519,7 @@ var numSubexpCases = []numSubexpCase{
 
 func TestNumSubexp(t *testing.T) {
 	for _, c := range numSubexpCases {
-		re, _ := Compile(c.input)
+		re := MustCompile(c.input)
 		n := re.NumSubexp()
 		if n != c.expected {
 			t.Errorf("NumSubexp for %q returned %d, expected %d", c.input, n, c.expected)
@@ -530,7 +530,7 @@ func TestNumSubexp(t *testing.T) {
 func BenchmarkLiteral(b *testing.B) {
 	x := strings.Repeat("x", 50)
 	b.StopTimer()
-	re, _ := Compile(x)
+	re := MustCompile(x)
 	b.StartTimer()
 	for i := 0; i < b.N; i++ {
 		if !re.MatchString(x) {
@@ -543,7 +543,35 @@ func BenchmarkLiteral(b *testing.B) {
 func BenchmarkNotLiteral(b *testing.B) {
 	x := strings.Repeat("x", 49)
 	b.StopTimer()
-	re, _ := Compile("^" + x)
+	re := MustCompile("^" + x)
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		if !re.MatchString(x) {
+			println("no match!")
+			break
+		}
+	}
+}
+
+func BenchmarkMatchClass(b *testing.B) {
+	b.StopTimer()
+	x := strings.Repeat("xxxx", 20) + "w"
+	re := MustCompile("[abcdw]")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		if !re.MatchString(x) {
+			println("no match!")
+			break
+		}
+	}
+}
+
+func BenchmarkMatchClass_InRange(b *testing.B) {
+	b.StopTimer()
+	// 'b' is betwen 'a' and 'c', so the charclass
+	// range checking is no help here.
+	x := strings.Repeat("bbbb", 20) + "c"
+	re := MustCompile("[ac]")
 	b.StartTimer()
 	for i := 0; i < b.N; i++ {
 		if !re.MatchString(x) {
@@ -556,7 +584,7 @@ func BenchmarkNotLiteral(b *testing.B) {
 func BenchmarkReplaceAll(b *testing.B) {
 	x := "abcdefghijklmnopqrstuvwxyz"
 	b.StopTimer()
-	re, _ := Compile("[cjrw]")
+	re := MustCompile("[cjrw]")
 	b.StartTimer()
 	for i := 0; i < b.N; i++ {
 		re.ReplaceAllString(x, "")
diff --git a/src/pkg/regexp/regexp.go b/src/pkg/regexp/regexp.go
index cdd5cacdda..edf91531de 100644
--- a/src/pkg/regexp/regexp.go
+++ b/src/pkg/regexp/regexp.go
@@ -152,10 +152,10 @@ func newChar(char int) *_Char {
 
 type _CharClass struct {
 	common
-	char   int
 	negate bool // is character class negated? ([^a-z])
 	// vector of int, stored pairwise: [a-z] is (a,z); x is (x,x):
-	ranges *vector.IntVector
+	ranges     *vector.IntVector
+	cmin, cmax int
 }
 
 func (cclass *_CharClass) kind() int { return _CHARCLASS }
@@ -180,13 +180,21 @@ func (cclass *_CharClass) addRange(a, b int) {
 	// range is a through b inclusive
 	cclass.ranges.Push(a)
 	cclass.ranges.Push(b)
+	if a < cclass.cmin {
+		cclass.cmin = a
+	}
+	if b > cclass.cmax {
+		cclass.cmax = b
+	}
 }
 
 func (cclass *_CharClass) matches(c int) bool {
-	for i := 0; i < cclass.ranges.Len(); i = i + 2 {
-		min := cclass.ranges.At(i)
-		max := cclass.ranges.At(i + 1)
-		if min <= c && c <= max {
+	if c < cclass.cmin || c > cclass.cmax {
+		return cclass.negate
+	}
+	ranges := []int(*cclass.ranges)
+	for i := 0; i < len(ranges); i = i + 2 {
+		if ranges[i] <= c && c <= ranges[i+1] {
 			return !cclass.negate
 		}
 	}
@@ -196,6 +204,8 @@ func (cclass *_CharClass) matches(c int) bool {
 func newCharClass() *_CharClass {
 	c := new(_CharClass)
 	c.ranges = new(vector.IntVector)
+	c.cmin = 0x10FFFF + 1 // MaxRune + 1
+	c.cmax = -1
 	return c
 }