Add benchmarks for string::insert(_str)

src/liballoc/benches/string.rs

@@ -122,3 +122,43 @@ fn bench_to_string(b: &mut Bencher) {
              Lorem ipsum dolor sit amet, consectetur. ";
     b.iter(|| s.to_string())
 }
+
+#[bench]
+fn bench_insert_char_short(b: &mut Bencher) {
+    let s = "Hello, World!";
+    b.iter(|| {
+        let mut x = String::from(s);
+        black_box(&mut x).insert(6, black_box(' '));
+        x
+    })
+}
+
+#[bench]
+fn bench_insert_char_long(b: &mut Bencher) {
+    let s = "Hello, World!";
+    b.iter(|| {
+        let mut x = String::from(s);
+        black_box(&mut x).insert(6, black_box('❤'));
+        x
+    })
+}
+
+#[bench]
+fn bench_insert_str_short(b: &mut Bencher) {
+    let s = "Hello, World!";
+    b.iter(|| {
+        let mut x = String::from(s);
+        black_box(&mut x).insert_str(6, black_box(" "));
+        x
+    })
+}
+
+#[bench]
+fn bench_insert_str_long(b: &mut Bencher) {
+    let s = "Hello, World!";
+    b.iter(|| {
+        let mut x = String::from(s);
+        black_box(&mut x).insert_str(6, black_box(" rustic "));
+        x
+    })
+}