add benchmark

Author: the8472

library/core/benches/slice.rs

@@ -1,3 +1,4 @@
+use core::ptr::NonNull;
 use test::black_box;
 use test::Bencher;
 
@@ -162,3 +163,11 @@ fn fill_byte_sized(b: &mut Bencher) {
         black_box(slice.fill(black_box(NewType(42))));
     });
 }
+
+// Tests the ability of the compiler to recognize that only the last slice item is needed
+// based on issue #106288
+#[bench]
+fn fold_to_last(b: &mut Bencher) {
+    let slice: &[i32] = &[0; 1024];
+    b.iter(|| black_box(slice).iter().fold(None, |_, r| Some(NonNull::from(r))));
+}