strings: add benchmarks for Replace

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
 }{