4 files changed, 29 insertions, 12 deletions
diff --git a/libgo/go/regexp/syntax/parse.go b/libgo/go/regexp/syntax/parse.go
index d579a40..f38bbf6 100644
--- a/libgo/go/regexp/syntax/parse.go
+++ b/libgo/go/regexp/syntax/parse.go
@@ -470,9 +470,14 @@ func (p *parser) factor(sub []*Regexp, flags Flags) []*Regexp {
 	}
 	sub = out
 
-	// Round 2: Factor out common complex prefixes,
-	// just the first piece of each concatenation,
-	// whatever it is.  This is good enough a lot of the time.
+	// Round 2: Factor out common simple prefixes,
+	// just the first piece of each concatenation.
+	// This will be good enough a lot of the time.
+	//
+	// Complex subexpressions (e.g. involving quantifiers)
+	// are not safe to factor because that collapses their
+	// distinct paths through the automaton, which affects
+	// correctness in some cases.
 	start = 0
 	out = sub[:0]
 	var first *Regexp
@@ -485,7 +490,9 @@ func (p *parser) factor(sub []*Regexp, flags Flags) []*Regexp {
 		var ifirst *Regexp
 		if i < len(sub) {
 			ifirst = p.leadingRegexp(sub[i])
-			if first != nil && first.Equal(ifirst) {
+			if first != nil && first.Equal(ifirst) &&
+				// first must be a character class OR a fixed repeat of a character class.
+				(isCharClass(first) || (first.Op == OpRepeat && first.Min == first.Max && isCharClass(first.Sub[0]))) {
 				continue
 			}
 		}
@@ -830,7 +837,14 @@ func Parse(s string, flags Flags) (*Regexp, error) {
 						lit = t[2:i]
 						t = t[i+2:]
 					}
-					p.push(literalRegexp(lit, p.flags))
+					for lit != "" {
+						c, rest, err := nextRune(lit)
+						if err != nil {
+							return nil, err
+						}
+						p.literal(c)
+						lit = rest
+					}
 					break BigSwitch
 				case 'z':
 					p.op(OpEndText)
diff --git a/libgo/go/regexp/syntax/parse_test.go b/libgo/go/regexp/syntax/parse_test.go
index c4a1117..5ca54bb 100644
--- a/libgo/go/regexp/syntax/parse_test.go
+++ b/libgo/go/regexp/syntax/parse_test.go
@@ -144,6 +144,7 @@ var parseTests = []parseTest{
 	// Test Perl quoted literals
 	{`\Q+|*?{[\E`, `str{+|*?{[}`},
 	{`\Q+\E+`, `plus{lit{+}}`},
+	{`\Qab\E+`, `cat{lit{a}plus{lit{b}}}`},
 	{`\Q\\E`, `lit{\}`},
 	{`\Q\\\E`, `str{\\}`},
 
@@ -171,7 +172,7 @@ var parseTests = []parseTest{
 
 	// Factoring.
 	{`abc|abd|aef|bcx|bcy`, `alt{cat{lit{a}alt{cat{lit{b}cc{0x63-0x64}}str{ef}}}cat{str{bc}cc{0x78-0x79}}}`},
-	{`ax+y|ax+z|ay+w`, `cat{lit{a}alt{cat{plus{lit{x}}cc{0x79-0x7a}}cat{plus{lit{y}}lit{w}}}}`},
+	{`ax+y|ax+z|ay+w`, `cat{lit{a}alt{cat{plus{lit{x}}lit{y}}cat{plus{lit{x}}lit{z}}cat{plus{lit{y}}lit{w}}}}`},
 
 	// Bug fixes.
 	{`(?:.)`, `dot{}`},
@@ -194,12 +195,13 @@ var parseTests = []parseTest{
 	{`abc|x|abd`, `alt{str{abc}lit{x}str{abd}}`},
 	{`(?i)abc|ABD`, `cat{strfold{AB}cc{0x43-0x44 0x63-0x64}}`},
 	{`[ab]c|[ab]d`, `cat{cc{0x61-0x62}cc{0x63-0x64}}`},
-	{`(?:xx|yy)c|(?:xx|yy)d`,
-		`cat{alt{str{xx}str{yy}}cc{0x63-0x64}}`},
+	{`.c|.d`, `cat{dot{}cc{0x63-0x64}}`},
 	{`x{2}|x{2}[0-9]`,
 		`cat{rep{2,2 lit{x}}alt{emp{}cc{0x30-0x39}}}`},
 	{`x{2}y|x{2}[0-9]y`,
 		`cat{rep{2,2 lit{x}}alt{lit{y}cat{cc{0x30-0x39}lit{y}}}}`},
+	{`a.*?c|a.*?b`,
+		`cat{lit{a}alt{cat{nstar{dot{}}lit{c}}cat{nstar{dot{}}lit{b}}}}`},
 
 	// Valid repetitions.
 	{`((((((((((x{2}){2}){2}){2}){2}){2}){2}){2}){2}))`, ``},
@@ -479,6 +481,7 @@ var invalidRegexps = []string{
 	`a{100000}`,
 	`a{100000,}`,
 	"((((((((((x{2}){2}){2}){2}){2}){2}){2}){2}){2}){2})",
+	`\Q\E*`,
 }
 
 var onlyPerl = []string{
diff --git a/libgo/go/regexp/syntax/regexp.go b/libgo/go/regexp/syntax/regexp.go
index cea7d9e..75822cf 100644
--- a/libgo/go/regexp/syntax/regexp.go
+++ b/libgo/go/regexp/syntax/regexp.go
@@ -166,9 +166,9 @@ func writeRegexp(b *bytes.Buffer, re *Regexp) {
 	case OpAnyChar:
 		b.WriteString(`(?s:.)`)
 	case OpBeginLine:
-		b.WriteRune('^')
+		b.WriteString(`(?m:^)`)
 	case OpEndLine:
-		b.WriteRune('$')
+		b.WriteString(`(?m:$)`)
 	case OpBeginText:
 		b.WriteString(`\A`)
 	case OpEndText:
diff --git a/libgo/go/regexp/syntax/simplify_test.go b/libgo/go/regexp/syntax/simplify_test.go
index 879eff5..5d0f1de 100644
--- a/libgo/go/regexp/syntax/simplify_test.go
+++ b/libgo/go/regexp/syntax/simplify_test.go
@@ -19,8 +19,8 @@ var simplifyTests = []struct {
 	{`(ab)+`, `(ab)+`},
 	{`(ab)?`, `(ab)?`},
 	{`.`, `(?s:.)`},
-	{`^`, `^`},
-	{`$`, `$`},
+	{`^`, `(?m:^)`},
+	{`$`, `(?m:$)`},
 	{`[ac]`, `[ac]`},
 	{`[^ac]`, `[^ac]`},