2 files changed, 30 insertions, 11 deletions
diff --git a/src/strings/strings.go b/src/strings/strings.go
index fb53b59f2c..d07a064228 100644
--- a/src/strings/strings.go
+++ b/src/strings/strings.go
@@ -1158,19 +1158,22 @@ func Replace(s, old, new string, n int) string {
 	var b Builder
 	b.Grow(len(s) + n*(len(new)-len(old)))
 	start := 0
-	for i := 0; i < n; i++ {
-		j := start
-		if len(old) == 0 {
-			if i > 0 {
-				_, wid := utf8.DecodeRuneInString(s[start:])
-				j += wid
-			}
-		} else {
-			j += Index(s[start:], old)
+	if len(old) > 0 {
+		for range n {
+			j := start + Index(s[start:], old)
+			b.WriteString(s[start:j])
+			b.WriteString(new)
+			start = j + len(old)
 		}
-		b.WriteString(s[start:j])
+	} else { // len(old) == 0
 		b.WriteString(new)
-		start = j + len(old)
+		for range n - 1 {
+			_, wid := utf8.DecodeRuneInString(s[start:])
+			j := start + wid
+			b.WriteString(s[start:j])
+			b.WriteString(new)
+			start = j
+		}
 	}
 	b.WriteString(s[start:])
 	return b.String()
diff --git a/src/strings/strings_test.go b/src/strings/strings_test.go
index aa3458c5c9..3f228b703f 100644
--- a/src/strings/strings_test.go
+++ b/src/strings/strings_test.go
@@ -1473,6 +1473,10 @@ var ReplaceTests = []struct {
 
 func TestReplace(t *testing.T) {
 	for _, tt := range ReplaceTests {
+		allocs := testing.AllocsPerRun(10, func() { Replace(tt.in, tt.old, tt.new, tt.n) })
+		if allocs > 1 {
+			t.Errorf("Replace(%q, %q, %q, %d) allocates %.2f objects", tt.in, tt.old, tt.new, tt.n, allocs)
+		}
 		if s := Replace(tt.in, tt.old, tt.new, tt.n); s != tt.out {
 			t.Errorf("Replace(%q, %q, %q, %d) = %q, want %q", tt.in, tt.old, tt.new, tt.n, s, tt.out)
 		}
@@ -1531,6 +1535,18 @@ func FuzzReplace(f *testing.F) {
 	})
 }
 
+func BenchmarkReplace(b *testing.B) {
+	for _, tt := range ReplaceTests {
+		desc := fmt.Sprintf("%q %q %q %d", tt.in, tt.old, tt.new, tt.n)
+		b.Run(desc, func(b *testing.B) {
+			b.ReportAllocs()
+			for b.Loop() {
+				Replace(tt.in, tt.old, tt.new, tt.n)
+			}
+		})
+	}
+}
+
 var TitleTests = []struct {
 	in, out string
 }{