libgo: update to go1.9

    
    Reviewed-on: https://go-review.googlesource.com/63753

From-SVN: r252767

7 files changed, 452 insertions, 110 deletions

diff --git a/libgo/go/strings/example_test.go b/libgo/go/strings/example_test.go
index 3f9d63b5a4a..e9621522ef2 100644
--- a/libgo/go/strings/example_test.go
+++ b/libgo/go/strings/example_test.go
@@ -23,6 +23,16 @@ func ExampleFieldsFunc() {
 	// Output: Fields are: ["foo1" "bar2" "baz3"]
 }
 
+func ExampleCompare() {
+	fmt.Println(strings.Compare("a", "b"))
+	fmt.Println(strings.Compare("a", "a"))
+	fmt.Println(strings.Compare("b", "a"))
+	// Output:
+	// -1
+	// 0
+	// 1
+}
+
 func ExampleContains() {
 	fmt.Println(strings.Contains("seafood", "foo"))
 	fmt.Println(strings.Contains("seafood", "bar"))
@@ -47,6 +57,16 @@ func ExampleContainsAny() {
 	// false
 }
 
+func ExampleContainsRune() {
+	// Finds whether a string contains a particular Unicode code point.
+	// The code point for the lowercase letter "a", for example, is 97.
+	fmt.Println(strings.ContainsRune("aardvark", 97))
+	fmt.Println(strings.ContainsRune("timeout", 97))
+	// Output:
+	// true
+	// false
+}
+
 func ExampleCount() {
 	fmt.Println(strings.Count("cheese", "e"))
 	fmt.Println(strings.Count("five", "")) // before & after each rune
@@ -109,6 +129,15 @@ func ExampleIndexAny() {
 	// -1
 }
 
+func ExampleIndexByte() {
+	fmt.Println(strings.IndexByte("golang", 'g'))
+	fmt.Println(strings.IndexByte("gophers", 'h'))
+	fmt.Println(strings.IndexByte("golang", 'x'))
+	// Output:
+	// 0
+	// 3
+	// -1
+}
 func ExampleIndexRune() {
 	fmt.Println(strings.IndexRune("chicken", 'k'))
 	fmt.Println(strings.IndexRune("chicken", 'd'))
@@ -127,6 +156,16 @@ func ExampleLastIndex() {
 	// -1
 }
 
+func ExampleLastIndexAny() {
+	fmt.Println(strings.LastIndexAny("go gopher", "go"))
+	fmt.Println(strings.LastIndexAny("go gopher", "rodent"))
+	fmt.Println(strings.LastIndexAny("go gopher", "fail"))
+	// Output:
+	// 4
+	// 8
+	// -1
+}
+
 func ExampleJoin() {
 	s := []string{"foo", "bar", "baz"}
 	fmt.Println(strings.Join(s, ", "))
@@ -195,6 +234,14 @@ func ExampleTrim() {
 	// Output: ["Achtung! Achtung"]
 }
 
+func ExampleTrimFunc() {
+	f := func(c rune) bool {
+		return !unicode.IsLetter(c) && !unicode.IsNumber(c)
+	}
+	fmt.Printf("[%q]", strings.TrimFunc("  Achtung1! Achtung2,...", f))
+	// Output: ["Achtung1! Achtung2"]
+}
+
 func ExampleMap() {
 	rot13 := func(r rune) rune {
 		switch {
diff --git a/libgo/go/strings/replace_test.go b/libgo/go/strings/replace_test.go
index 77e48b988bc..34b5badfadf 100644
--- a/libgo/go/strings/replace_test.go
+++ b/libgo/go/strings/replace_test.go
@@ -540,3 +540,44 @@ func BenchmarkByteByteMap(b *testing.B) {
 		Map(fn, str)
 	}
 }
+
+var mapdata = []struct{ name, data string }{
+	{"ASCII", "a b c d e f g h i j k l m n o p q r s t u v w x y z"},
+	{"Greek", "α β γ δ ε ζ η θ ι κ λ μ ν ξ ο π ρ ς σ τ υ φ χ ψ ω"},
+}
+
+func BenchmarkMap(b *testing.B) {
+	mapidentity := func(r rune) rune {
+		return r
+	}
+
+	b.Run("identity", func(b *testing.B) {
+		for _, md := range mapdata {
+			b.Run(md.name, func(b *testing.B) {
+				for i := 0; i < b.N; i++ {
+					Map(mapidentity, md.data)
+				}
+			})
+		}
+	})
+
+	mapchange := func(r rune) rune {
+		if 'a' <= r && r <= 'z' {
+			return r + 'A' - 'a'
+		}
+		if 'α' <= r && r <= 'ω' {
+			return r + 'Α' - 'α'
+		}
+		return r
+	}
+
+	b.Run("change", func(b *testing.B) {
+		for _, md := range mapdata {
+			b.Run(md.name, func(b *testing.B) {
+				for i := 0; i < b.N; i++ {
+					Map(mapchange, md.data)
+				}
+			})
+		}
+	})
+}
diff --git a/libgo/go/strings/strings.go b/libgo/go/strings/strings.go
index 60a281a6ac5..0c836c09d46 100644
--- a/libgo/go/strings/strings.go
+++ b/libgo/go/strings/strings.go
@@ -72,22 +72,20 @@ func hashStrRev(sep string) (uint32, uint32) {
 	return hash, pow
 }
 
-// Count counts the number of non-overlapping instances of sep in s.
-// If sep is an empty string, Count returns 1 + the number of Unicode code points in s.
-func Count(s, sep string) int {
-	n := 0
-	// special cases
-	if len(sep) == 0 {
+// countGeneric implements Count.
+func countGeneric(s, substr string) int {
+	// special case
+	if len(substr) == 0 {
 		return utf8.RuneCountInString(s) + 1
 	}
-	offset := 0
+	n := 0
 	for {
-		i := Index(s[offset:], sep)
+		i := Index(s, substr)
 		if i == -1 {
 			return n
 		}
 		n++
-		offset += i + len(sep)
+		s = s[i+len(substr):]
 	}
 }
 
@@ -106,16 +104,16 @@ func ContainsRune(s string, r rune) bool {
 	return IndexRune(s, r) >= 0
 }
 
-// LastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s.
-func LastIndex(s, sep string) int {
-	n := len(sep)
+// LastIndex returns the index of the last instance of substr in s, or -1 if substr is not present in s.
+func LastIndex(s, substr string) int {
+	n := len(substr)
 	switch {
 	case n == 0:
 		return len(s)
 	case n == 1:
-		return LastIndexByte(s, sep[0])
+		return LastIndexByte(s, substr[0])
 	case n == len(s):
-		if sep == s {
+		if substr == s {
 			return 0
 		}
 		return -1
@@ -123,20 +121,20 @@ func LastIndex(s, sep string) int {
 		return -1
 	}
 	// Rabin-Karp search from the end of the string
-	hashsep, pow := hashStrRev(sep)
+	hashss, pow := hashStrRev(substr)
 	last := len(s) - n
 	var h uint32
 	for i := len(s) - 1; i >= last; i-- {
 		h = h*primeRK + uint32(s[i])
 	}
-	if h == hashsep && s[last:] == sep {
+	if h == hashss && s[last:] == substr {
 		return last
 	}
 	for i := last - 1; i >= 0; i-- {
 		h *= primeRK
 		h += uint32(s[i])
 		h -= pow * uint32(s[i+n])
-		if h == hashsep && s[i:i+n] == sep {
+		if h == hashss && s[i:i+n] == substr {
 			return i
 		}
 	}
@@ -240,61 +238,187 @@ func genSplit(s, sep string, sepSave, n int) []string {
 	if n < 0 {
 		n = Count(s, sep) + 1
 	}
-	c := sep[0]
-	start := 0
+
 	a := make([]string, n)
-	na := 0
-	for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ {
-		if s[i] == c && (len(sep) == 1 || s[i:i+len(sep)] == sep) {
-			a[na] = s[start : i+sepSave]
-			na++
-			start = i + len(sep)
-			i += len(sep) - 1
-		}
+	n--
+	i := 0
+	for i < n {
+		m := Index(s, sep)
+		if m < 0 {
+			break
+		}
+		a[i] = s[:m+sepSave]
+		s = s[m+len(sep):]
+		i++
 	}
-	a[na] = s[start:]
-	return a[0 : na+1]
+	a[i] = s
+	return a[:i+1]
 }
 
 // SplitN slices s into substrings separated by sep and returns a slice of
 // the substrings between those separators.
-// If sep is empty, SplitN splits after each UTF-8 sequence.
+//
 // The count determines the number of substrings to return:
 //   n > 0: at most n substrings; the last substring will be the unsplit remainder.
 //   n == 0: the result is nil (zero substrings)
 //   n < 0: all substrings
+//
+// Edge cases for s and sep (for example, empty strings) are handled
+// as described in the documentation for Split.
 func SplitN(s, sep string, n int) []string { return genSplit(s, sep, 0, n) }
 
 // SplitAfterN slices s into substrings after each instance of sep and
 // returns a slice of those substrings.
-// If sep is empty, SplitAfterN splits after each UTF-8 sequence.
+//
 // The count determines the number of substrings to return:
 //   n > 0: at most n substrings; the last substring will be the unsplit remainder.
 //   n == 0: the result is nil (zero substrings)
 //   n < 0: all substrings
+//
+// Edge cases for s and sep (for example, empty strings) are handled
+// as described in the documentation for SplitAfter.
 func SplitAfterN(s, sep string, n int) []string {
 	return genSplit(s, sep, len(sep), n)
 }
 
 // Split slices s into all substrings separated by sep and returns a slice of
 // the substrings between those separators.
-// If sep is empty, Split splits after each UTF-8 sequence.
+//
+// If s does not contain sep and sep is not empty, Split returns a
+// slice of length 1 whose only element is s.
+//
+// If sep is empty, Split splits after each UTF-8 sequence. If both s
+// and sep are empty, Split returns an empty slice.
+//
 // It is equivalent to SplitN with a count of -1.
 func Split(s, sep string) []string { return genSplit(s, sep, 0, -1) }
 
 // SplitAfter slices s into all substrings after each instance of sep and
 // returns a slice of those substrings.
-// If sep is empty, SplitAfter splits after each UTF-8 sequence.
+//
+// If s does not contain sep and sep is not empty, SplitAfter returns
+// a slice of length 1 whose only element is s.
+//
+// If sep is empty, SplitAfter splits after each UTF-8 sequence. If
+// both s and sep are empty, SplitAfter returns an empty slice.
+//
 // It is equivalent to SplitAfterN with a count of -1.
 func SplitAfter(s, sep string) []string {
 	return genSplit(s, sep, len(sep), -1)
 }
 
+var asciiSpace = [256]uint8{'\t': 1, '\n': 1, '\v': 1, '\f': 1, '\r': 1, ' ': 1}
+
 // Fields splits the string s around each instance of one or more consecutive white space
 // characters, as defined by unicode.IsSpace, returning an array of substrings of s or an
 // empty list if s contains only white space.
 func Fields(s string) []string {
-	return FieldsFunc(s, unicode.IsSpace)
+	// First count the fields.
+	// This is an exact count if s is ASCII, otherwise it is an approximation.
+	n := 0
+	wasSpace := 1
+	// setBits is used to track which bits are set in the bytes of s.
+	setBits := uint8(0)
+	for i := 0; i < len(s); i++ {
+		r := s[i]
+		setBits |= r
+		isSpace := int(asciiSpace[r])
+		n += wasSpace & ^isSpace
+		wasSpace = isSpace
+	}
+
+	if setBits < utf8.RuneSelf { // ASCII fast path
+		a := make([]string, n)
+		na := 0
+		fieldStart := 0
+		i := 0
+		// Skip spaces in the front of the input.
+		for i < len(s) && asciiSpace[s[i]] != 0 {
+			i++
+		}
+		fieldStart = i
+		for i < len(s) {
+			if asciiSpace[s[i]] == 0 {
+				i++
+				continue
+			}
+			a[na] = s[fieldStart:i]
+			na++
+			i++
+			// Skip spaces in between fields.
+			for i < len(s) && asciiSpace[s[i]] != 0 {
+				i++
+			}
+			fieldStart = i
+		}
+		if fieldStart < len(s) { // Last field might end at EOF.
+			a[na] = s[fieldStart:]
+		}
+		return a
+	}
+
+	// Some runes in the input string are not ASCII.
+	// Same general approach as in the ASCII path but
+	// uses DecodeRuneInString and unicode.IsSpace if
+	// a non-ASCII rune needs to be decoded and checked
+	// if it corresponds to a space.
+	a := make([]string, 0, n)
+	fieldStart := 0
+	i := 0
+	// Skip spaces in the front of the input.
+	for i < len(s) {
+		if c := s[i]; c < utf8.RuneSelf {
+			if asciiSpace[c] == 0 {
+				break
+			}
+			i++
+		} else {
+			r, w := utf8.DecodeRuneInString(s[i:])
+			if !unicode.IsSpace(r) {
+				break
+			}
+			i += w
+		}
+	}
+	fieldStart = i
+	for i < len(s) {
+		if c := s[i]; c < utf8.RuneSelf {
+			if asciiSpace[c] == 0 {
+				i++
+				continue
+			}
+			a = append(a, s[fieldStart:i])
+			i++
+		} else {
+			r, w := utf8.DecodeRuneInString(s[i:])
+			if !unicode.IsSpace(r) {
+				i += w
+				continue
+			}
+			a = append(a, s[fieldStart:i])
+			i += w
+		}
+		// Skip spaces in between fields.
+		for i < len(s) {
+			if c := s[i]; c < utf8.RuneSelf {
+				if asciiSpace[c] == 0 {
+					break
+				}
+				i++
+			} else {
+				r, w := utf8.DecodeRuneInString(s[i:])
+				if !unicode.IsSpace(r) {
+					break
+				}
+				i += w
+			}
+		}
+		fieldStart = i
+	}
+	if fieldStart < len(s) { // Last field might end at EOF.
+		a = append(a, s[fieldStart:])
+	}
+	return a
 }
 
 // FieldsFunc splits the string s at each run of Unicode code points c satisfying f(c)
@@ -383,40 +507,71 @@ func Map(mapping func(rune) rune, s string) string {
 	// In the worst case, the string can grow when mapped, making
 	// things unpleasant. But it's so rare we barge in assuming it's
 	// fine. It could also shrink but that falls out naturally.
-	maxbytes := len(s) // length of b
-	nbytes := 0        // number of bytes encoded in b
+
 	// The output buffer b is initialized on demand, the first
 	// time a character differs.
 	var b []byte
+	// nbytes is the number of bytes encoded in b.
+	var nbytes int
 
 	for i, c := range s {
 		r := mapping(c)
-		if b == nil {
-			if r == c {
-				continue
-			}
-			b = make([]byte, maxbytes)
-			nbytes = copy(b, s[:i])
+		if r == c {
+			continue
 		}
+
+		b = make([]byte, len(s)+utf8.UTFMax)
+		nbytes = copy(b, s[:i])
 		if r >= 0 {
-			wid := 1
-			if r >= utf8.RuneSelf {
-				wid = utf8.RuneLen(r)
+			if r <= utf8.RuneSelf {
+				b[nbytes] = byte(r)
+				nbytes++
+			} else {
+				nbytes += utf8.EncodeRune(b[nbytes:], r)
 			}
-			if nbytes+wid > maxbytes {
-				// Grow the buffer.
-				maxbytes = maxbytes*2 + utf8.UTFMax
-				nb := make([]byte, maxbytes)
-				copy(nb, b[0:nbytes])
-				b = nb
-			}
-			nbytes += utf8.EncodeRune(b[nbytes:maxbytes], r)
 		}
+
+		if c == utf8.RuneError {
+			// RuneError is the result of either decoding
+			// an invalid sequence or '\uFFFD'. Determine
+			// the correct number of bytes we need to advance.
+			_, w := utf8.DecodeRuneInString(s[i:])
+			i += w
+		} else {
+			i += utf8.RuneLen(c)
+		}
+
+		s = s[i:]
+		break
 	}
+
 	if b == nil {
 		return s
 	}
-	return string(b[0:nbytes])
+
+	for _, c := range s {
+		r := mapping(c)
+
+		// common case
+		if (0 <= r && r <= utf8.RuneSelf) && nbytes < len(b) {
+			b[nbytes] = byte(r)
+			nbytes++
+			continue
+		}
+
+		// b is not big enough or r is not a ASCII rune.
+		if r >= 0 {
+			if nbytes+utf8.UTFMax >= len(b) {
+				// Grow the buffer.
+				nb := make([]byte, 2*len(b))
+				copy(nb, b[:nbytes])
+				b = nb
+			}
+			nbytes += utf8.EncodeRune(b[nbytes:], r)
+		}
+	}
+
+	return string(b[:nbytes])
 }
 
 // Repeat returns a new string consisting of count copies of the string s.
@@ -561,17 +716,10 @@ func LastIndexFunc(s string, f func(rune) bool) int {
 // truth==false, the sense of the predicate function is
 // inverted.
 func indexFunc(s string, f func(rune) bool, truth bool) int {
-	start := 0
-	for start < len(s) {
-		wid := 1
-		r := rune(s[start])
-		if r >= utf8.RuneSelf {
-			r, wid = utf8.DecodeRuneInString(s[start:])
-		}
+	for i, r := range s {
 		if f(r) == truth {
-			return start
+			return i
 		}
-		start += wid
 	}
 	return -1
 }
diff --git a/libgo/go/strings/strings_amd64.go b/libgo/go/strings/strings_amd64.go
index e55afd53d01..9648912fd5b 100644
--- a/libgo/go/strings/strings_amd64.go
+++ b/libgo/go/strings/strings_amd64.go
@@ -6,44 +6,46 @@
 
 package strings
 
+import "internal/cpu"
+
 //go:noescape
 
 // indexShortStr returns the index of the first instance of c in s, or -1 if c is not present in s.
 // indexShortStr requires 2 <= len(c) <= shortStringLen
-func indexShortStr(s, c string) int // ../runtime/asm_$GOARCH.s
-func supportAVX2() bool             // ../runtime/asm_$GOARCH.s
+func indexShortStr(s, c string) int  // ../runtime/asm_amd64.s
+func countByte(s string, c byte) int // ../runtime/asm_amd64.s
 
 var shortStringLen int
 
 func init() {
-	if supportAVX2() {
+	if cpu.X86.HasAVX2 {
 		shortStringLen = 63
 	} else {
 		shortStringLen = 31
 	}
 }
 
-// Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
-func Index(s, sep string) int {
-	n := len(sep)
+// Index returns the index of the first instance of substr in s, or -1 if substr is not present in s.
+func Index(s, substr string) int {
+	n := len(substr)
 	switch {
 	case n == 0:
 		return 0
 	case n == 1:
-		return IndexByte(s, sep[0])
+		return IndexByte(s, substr[0])
 	case n == len(s):
-		if sep == s {
+		if substr == s {
 			return 0
 		}
 		return -1
 	case n > len(s):
 		return -1
 	case n <= shortStringLen:
-		// Use brute force when s and sep both are small
+		// Use brute force when s and substr both are small
 		if len(s) <= 64 {
-			return indexShortStr(s, sep)
+			return indexShortStr(s, substr)
 		}
-		c := sep[0]
+		c := substr[0]
 		i := 0
 		t := s[:len(s)-n+1]
 		fails := 0
@@ -57,7 +59,7 @@ func Index(s, sep string) int {
 				}
 				i += o
 			}
-			if s[i:i+n] == sep {
+			if s[i:i+n] == substr {
 				return i
 			}
 			fails++
@@ -66,7 +68,7 @@ func Index(s, sep string) int {
 			// Too many means more that 1 error per 8 characters.
 			// Allow some errors in the beginning.
 			if fails > (i+16)/8 {
-				r := indexShortStr(s[i:], sep)
+				r := indexShortStr(s[i:], substr)
 				if r >= 0 {
 					return r + i
 				}
@@ -76,12 +78,12 @@ func Index(s, sep string) int {
 		return -1
 	}
 	// Rabin-Karp search
-	hashsep, pow := hashStr(sep)
+	hashss, pow := hashStr(substr)
 	var h uint32
 	for i := 0; i < n; i++ {
 		h = h*primeRK + uint32(s[i])
 	}
-	if h == hashsep && s[:n] == sep {
+	if h == hashss && s[:n] == substr {
 		return 0
 	}
 	for i := n; i < len(s); {
@@ -89,9 +91,18 @@ func Index(s, sep string) int {
 		h += uint32(s[i])
 		h -= pow * uint32(s[i-n])
 		i++
-		if h == hashsep && s[i-n:i] == sep {
+		if h == hashss && s[i-n:i] == substr {
 			return i - n
 		}
 	}
 	return -1
 }
+
+// Count counts the number of non-overlapping instances of substr in s.
+// If substr is an empty string, Count returns 1 + the number of Unicode code points in s.
+func Count(s, substr string) int {
+	if len(substr) == 1 && cpu.X86.HasPOPCNT {
+		return countByte(s, byte(substr[0]))
+	}
+	return countGeneric(s, substr)
+}
diff --git a/libgo/go/strings/strings_generic.go b/libgo/go/strings/strings_generic.go
index a3ad515444b..9844201db30 100644
--- a/libgo/go/strings/strings_generic.go
+++ b/libgo/go/strings/strings_generic.go
@@ -9,16 +9,16 @@ package strings
 // TODO: implements short string optimization on non amd64 platforms
 // and get rid of strings_amd64.go
 
-// Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
-func Index(s, sep string) int {
-	n := len(sep)
+// Index returns the index of the first instance of substr in s, or -1 if substr is not present in s.
+func Index(s, substr string) int {
+	n := len(substr)
 	switch {
 	case n == 0:
 		return 0
 	case n == 1:
-		return IndexByte(s, sep[0])
+		return IndexByte(s, substr[0])
 	case n == len(s):
-		if sep == s {
+		if substr == s {
 			return 0
 		}
 		return -1
@@ -26,12 +26,12 @@ func Index(s, sep string) int {
 		return -1
 	}
 	// Rabin-Karp search
-	hashsep, pow := hashStr(sep)
+	hashss, pow := hashStr(substr)
 	var h uint32
 	for i := 0; i < n; i++ {
 		h = h*primeRK + uint32(s[i])
 	}
-	if h == hashsep && s[:n] == sep {
+	if h == hashss && s[:n] == substr {
 		return 0
 	}
 	for i := n; i < len(s); {
@@ -39,9 +39,15 @@ func Index(s, sep string) int {
 		h += uint32(s[i])
 		h -= pow * uint32(s[i-n])
 		i++
-		if h == hashsep && s[i-n:i] == sep {
+		if h == hashss && s[i-n:i] == substr {
 			return i - n
 		}
 	}
 	return -1
 }
+
+// Count counts the number of non-overlapping instances of substr in s.
+// If substr is an empty string, Count returns 1 + the number of Unicode code points in s.
+func Count(s, substr string) int {
+	return countGeneric(s, substr)
+}
diff --git a/libgo/go/strings/strings_s390x.go b/libgo/go/strings/strings_s390x.go
index b47702fd51a..b05fb2b025a 100644
--- a/libgo/go/strings/strings_s390x.go
+++ b/libgo/go/strings/strings_s390x.go
@@ -26,27 +26,27 @@ func init() {
 	}
 }
 
-// Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
-func Index(s, sep string) int {
-	n := len(sep)
+// Index returns the index of the first instance of substr in s, or -1 if substr is not present in s.
+func Index(s, substr string) int {
+	n := len(substr)
 	switch {
 	case n == 0:
 		return 0
 	case n == 1:
-		return IndexByte(s, sep[0])
+		return IndexByte(s, substr[0])
 	case n == len(s):
-		if sep == s {
+		if substr == s {
 			return 0
 		}
 		return -1
 	case n > len(s):
 		return -1
 	case n <= shortStringLen:
-		// Use brute force when s and sep both are small
+		// Use brute force when s and substr both are small
 		if len(s) <= 64 {
-			return indexShortStr(s, sep)
+			return indexShortStr(s, substr)
 		}
-		c := sep[0]
+		c := substr[0]
 		i := 0
 		t := s[:len(s)-n+1]
 		fails := 0
@@ -60,7 +60,7 @@ func Index(s, sep string) int {
 				}
 				i += o
 			}
-			if s[i:i+n] == sep {
+			if s[i:i+n] == substr {
 				return i
 			}
 			fails++
@@ -69,7 +69,7 @@ func Index(s, sep string) int {
 			// Too many means more that 1 error per 8 characters.
 			// Allow some errors in the beginning.
 			if fails > (i+16)/8 {
-				r := indexShortStr(s[i:], sep)
+				r := indexShortStr(s[i:], substr)
 				if r >= 0 {
 					return r + i
 				}
@@ -79,12 +79,12 @@ func Index(s, sep string) int {
 		return -1
 	}
 	// Rabin-Karp search
-	hashsep, pow := hashStr(sep)
+	hashss, pow := hashStr(substr)
 	var h uint32
 	for i := 0; i < n; i++ {
 		h = h*primeRK + uint32(s[i])
 	}
-	if h == hashsep && s[:n] == sep {
+	if h == hashss && s[:n] == substr {
 		return 0
 	}
 	for i := n; i < len(s); {
@@ -92,9 +92,15 @@ func Index(s, sep string) int {
 		h += uint32(s[i])
 		h -= pow * uint32(s[i-n])
 		i++
-		if h == hashsep && s[i-n:i] == sep {
+		if h == hashss && s[i-n:i] == substr {
 			return i - n
 		}
 	}
 	return -1
 }
+
+// Count counts the number of non-overlapping instances of substr in s.
+// If substr is an empty string, Count returns 1 + the number of Unicode code points in s.
+func Count(s, substr string) int {
+	return countGeneric(s, substr)
+}
diff --git a/libgo/go/strings/strings_test.go b/libgo/go/strings/strings_test.go
index 449fb502d64..0fddaf0e4a6 100644
--- a/libgo/go/strings/strings_test.go
+++ b/libgo/go/strings/strings_test.go
@@ -456,6 +456,7 @@ var fieldstests = []FieldsTest{
 	{"", []string{}},
 	{" ", []string{}},
 	{" \t ", []string{}},
+	{"\u2000", []string{}},
 	{"  abc  ", []string{"abc"}},
 	{"1 2 3 4", []string{"1", "2", "3", "4"}},
 	{"1  2  3  4", []string{"1", "2", "3", "4"}},
@@ -463,6 +464,9 @@ var fieldstests = []FieldsTest{
 	{"1\u20002\u20013\u20024", []string{"1", "2", "3", "4"}},
 	{"\u2000\u2001\u2002", []string{}},
 	{"\n™\t™\n", []string{"™", "™"}},
+	{"\n\u20001™2\u2000 \u2001 ™", []string{"1™2", "™"}},
+	{"\n1\uFFFD \uFFFD2\u20003\uFFFD4", []string{"1\uFFFD", "\uFFFD2", "3\uFFFD4"}},
+	{"1\xFF\u2000\xFF2\xFF \xFF", []string{"1\xFF", "\xFF2\xFF", "\xFF"}},
 	{faces, []string{faces}},
 }
 
@@ -629,6 +633,19 @@ func TestMap(t *testing.T) {
 		(*reflect.StringHeader)(unsafe.Pointer(&m)).Data {
 		t.Error("unexpected copy during identity map")
 	}
+
+	// 7. Handle invalid UTF-8 sequence
+	replaceNotLatin := func(r rune) rune {
+		if unicode.Is(unicode.Latin, r) {
+			return r
+		}
+		return '?'
+	}
+	m = Map(replaceNotLatin, "Hello\255World")
+	expect = "Hello?World"
+	if m != expect {
+		t.Errorf("replace invalid sequence: expected %q got %q", expect, m)
+	}
 }
 
 func TestToUpper(t *testing.T) { runStringTests(t, ToUpper, "ToUpper", upperTests) }
@@ -1444,6 +1461,24 @@ func BenchmarkCountTortureOverlapping(b *testing.B) {
 	}
 }
 
+func BenchmarkCountByte(b *testing.B) {
+	indexSizes := []int{10, 32, 4 << 10, 4 << 20, 64 << 20}
+	benchStr := Repeat(benchmarkString,
+		(indexSizes[len(indexSizes)-1]+len(benchmarkString)-1)/len(benchmarkString))
+	benchFunc := func(b *testing.B, benchStr string) {
+		b.SetBytes(int64(len(benchStr)))
+		for i := 0; i < b.N; i++ {
+			Count(benchStr, "=")
+		}
+	}
+	for _, size := range indexSizes {
+		b.Run(fmt.Sprintf("%d", size), func(b *testing.B) {
+			benchFunc(b, benchStr[:size])
+		})
+	}
+
+}
+
 var makeFieldsInput = func() string {
 	x := make([]byte, 1<<20)
 	// Input is ~10% space, ~10% 2-byte UTF-8, rest ASCII non-space.
@@ -1464,40 +1499,88 @@ var makeFieldsInput = func() string {
 	return string(x)
 }
 
-var fieldsInput = makeFieldsInput()
+var makeFieldsInputASCII = func() string {
+	x := make([]byte, 1<<20)
+	// Input is ~10% space, rest ASCII non-space.
+	for i := range x {
+		if rand.Intn(10) == 0 {
+			x[i] = ' '
+		} else {
+			x[i] = 'x'
+		}
+	}
+	return string(x)
+}
+
+var stringdata = []struct{ name, data string }{
+	{"ASCII", makeFieldsInputASCII()},
+	{"Mixed", makeFieldsInput()},
+}
 
 func BenchmarkFields(b *testing.B) {
-	b.SetBytes(int64(len(fieldsInput)))
-	for i := 0; i < b.N; i++ {
-		Fields(fieldsInput)
+	for _, sd := range stringdata {
+		b.Run(sd.name, func(b *testing.B) {
+			for j := 1 << 4; j <= 1<<20; j <<= 4 {
+				b.Run(fmt.Sprintf("%d", j), func(b *testing.B) {
+					b.ReportAllocs()
+					b.SetBytes(int64(j))
+					data := sd.data[:j]
+					for i := 0; i < b.N; i++ {
+						Fields(data)
+					}
+				})
+			}
+		})
 	}
 }
 
 func BenchmarkFieldsFunc(b *testing.B) {
-	b.SetBytes(int64(len(fieldsInput)))
-	for i := 0; i < b.N; i++ {
-		FieldsFunc(fieldsInput, unicode.IsSpace)
+	for _, sd := range stringdata {
+		b.Run(sd.name, func(b *testing.B) {
+			for j := 1 << 4; j <= 1<<20; j <<= 4 {
+				b.Run(fmt.Sprintf("%d", j), func(b *testing.B) {
+					b.ReportAllocs()
+					b.SetBytes(int64(j))
+					data := sd.data[:j]
+					for i := 0; i < b.N; i++ {
+						FieldsFunc(data, unicode.IsSpace)
+					}
+				})
+			}
+		})
 	}
 }
 
-func BenchmarkSplit1(b *testing.B) {
+func BenchmarkSplitEmptySeparator(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		Split(benchInputHard, "")
 	}
 }
 
-func BenchmarkSplit2(b *testing.B) {
+func BenchmarkSplitSingleByteSeparator(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		Split(benchInputHard, "/")
 	}
 }
 
-func BenchmarkSplit3(b *testing.B) {
+func BenchmarkSplitMultiByteSeparator(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		Split(benchInputHard, "hello")
 	}
 }
 
+func BenchmarkSplitNSingleByteSeparator(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		SplitN(benchInputHard, "/", 10)
+	}
+}
+
+func BenchmarkSplitNMultiByteSeparator(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		SplitN(benchInputHard, "hello", 10)
+	}
+}
+
 func BenchmarkRepeat(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		Repeat("-", 80)