Rollup merge of #89509 - jhpratt:stabilize-const_unreachable_unchecked, r=oli-obk

Stabilize `unreachable_unchecked` as `const fn`

Closes #53188

This PR stabilizes `core::hint::unreachable_unchecked` as `const fn`. MIRI is able to detect when this method is called. Stabilization was delayed until `const_panic` was stabilized so as to avoid users calling this method in its place (thus resulting in runtime UB). With #89508, that is no longer an issue.

````@rustbot```` label +A-const-eval +A-const-fn +T-lang +S-blocked

(not sure why it's T-lang, but that's what the tracking issue is)
This commit is contained in:
Matthias Krüger 2021-10-16 08:02:20 +02:00 committed by GitHub
commit 9ae0804859
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6 changed files with 7 additions and 11 deletions

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@ -44,7 +44,7 @@ use crate::intrinsics;
/// ```
#[inline]
#[stable(feature = "unreachable", since = "1.27.0")]
#[rustc_const_unstable(feature = "const_unreachable_unchecked", issue = "53188")]
#[rustc_const_stable(feature = "const_unreachable_unchecked", since = "1.57.0")]
pub const unsafe fn unreachable_unchecked() -> ! {
// SAFETY: the safety contract for `intrinsics::unreachable` must
// be upheld by the caller.

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@ -735,7 +735,7 @@ extern "rust-intrinsic" {
/// reach code marked with this function.
///
/// The stabilized version of this intrinsic is [`core::hint::unreachable_unchecked`].
#[rustc_const_unstable(feature = "const_unreachable_unchecked", issue = "53188")]
#[rustc_const_stable(feature = "const_unreachable_unchecked", since = "1.57.0")]
pub fn unreachable() -> !;
/// Informs the optimizer that a condition is always true.

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@ -130,7 +130,6 @@
#![feature(const_trait_impl)]
#![feature(const_type_id)]
#![feature(const_type_name)]
#![feature(const_unreachable_unchecked)]
#![feature(const_default_impls)]
#![feature(duration_consts_2)]
#![feature(ptr_metadata)]

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@ -1,7 +1,5 @@
// run-pass
#![feature(const_unreachable_unchecked)]
const unsafe fn foo(x: bool) -> bool {
match x {
true => true,
@ -12,5 +10,5 @@ const unsafe fn foo(x: bool) -> bool {
const BAR: bool = unsafe { foo(true) };
fn main() {
assert_eq!(BAR, true);
assert_eq!(BAR, true);
}

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@ -1,5 +1,4 @@
// error-pattern: evaluation of constant value failed
#![feature(const_unreachable_unchecked)]
const unsafe fn foo(x: bool) -> bool {
match x {
@ -11,5 +10,5 @@ const unsafe fn foo(x: bool) -> bool {
const BAR: bool = unsafe { foo(false) };
fn main() {
assert_eq!(BAR, true);
assert_eq!(BAR, true);
}

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@ -7,13 +7,13 @@ LL | unsafe { intrinsics::unreachable() }
| entering unreachable code
| inside `unreachable_unchecked` at $SRC_DIR/core/src/hint.rs:LL:COL
|
::: $DIR/const_unsafe_unreachable_ub.rs:7:18
::: $DIR/const_unsafe_unreachable_ub.rs:6:18
|
LL | false => std::hint::unreachable_unchecked(),
| ---------------------------------- inside `foo` at $DIR/const_unsafe_unreachable_ub.rs:7:18
| ---------------------------------- inside `foo` at $DIR/const_unsafe_unreachable_ub.rs:6:18
...
LL | const BAR: bool = unsafe { foo(false) };
| ---------- inside `BAR` at $DIR/const_unsafe_unreachable_ub.rs:11:28
| ---------- inside `BAR` at $DIR/const_unsafe_unreachable_ub.rs:10:28
error: aborting due to previous error