Don't unleash NRVO const-eval test

Author: ecstatic-morse

src/test/ui/consts/miri_unleashed/nrvo.rs renamed to src/test/ui/consts/const-eval/nrvo.rs

@@ -1,20 +1,23 @@
-// compile-flags: -Zunleash-the-miri-inside-of-you
 // run-pass
 
+// When the NRVO is applied, the return place (`_0`) gets treated like a normal local. For example,
+// its address may be taken and it may be written to indirectly. Ensure that MIRI can handle this.
+
+#![feature(const_mut_refs)]
+
+#[inline(never)] // Try to ensure that MIR optimizations don't optimize this away.
 const fn init(buf: &mut [u8; 1024]) {
     buf[33] = 3;
     buf[444] = 4;
 }
 
-const fn nrvo(init: fn(&mut [u8; 1024])) -> [u8; 1024] {
+const fn nrvo() -> [u8; 1024] {
     let mut buf = [0; 1024];
     init(&mut buf);
     buf
 }
 
-// When the NRVO is applied, the return place (`_0`) gets treated like a normal local. For example,
-// its address may be taken and it may be written to indirectly. Ensure that MIRI can handle this.
-const BUF: [u8; 1024] = nrvo(init);
+const BUF: [u8; 1024] = nrvo();
 
 fn main() {
     assert_eq!(BUF[33], 3);