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

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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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2
library/core/src/hint.rs
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@ -44,7 +44,7 @@ use crate::intrinsics;
/// ``` /// ```
#[inline] #[inline]
#[stable(feature = "unreachable", since = "1.27.0")] #[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() -> ! { pub const unsafe fn unreachable_unchecked() -> ! {
// SAFETY: the safety contract for `intrinsics::unreachable` must // SAFETY: the safety contract for `intrinsics::unreachable` must
// be upheld by the caller. // be upheld by the caller.

2
library/core/src/intrinsics.rs
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@ -735,7 +735,7 @@ extern "rust-intrinsic" {
/// reach code marked with this function. /// reach code marked with this function.
/// ///
/// The stabilized version of this intrinsic is [`core::hint::unreachable_unchecked`]. /// 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() -> !; pub fn unreachable() -> !;
/// Informs the optimizer that a condition is always true. /// Informs the optimizer that a condition is always true.

1
library/core/src/lib.rs
View file

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

4
src/test/ui/consts/const_unsafe_unreachable.rs
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@ -1,7 +1,5 @@
// run-pass // run-pass
#![feature(const_unreachable_unchecked)]
const unsafe fn foo(x: bool) -> bool { const unsafe fn foo(x: bool) -> bool {
match x { match x {
true => true, true => true,
@ -12,5 +10,5 @@ const unsafe fn foo(x: bool) -> bool {
const BAR: bool = unsafe { foo(true) }; const BAR: bool = unsafe { foo(true) };
fn main() { fn main() {
assert_eq!(BAR, true); assert_eq!(BAR, true);
} }

3
src/test/ui/consts/const_unsafe_unreachable_ub.rs
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@ -1,5 +1,4 @@
// error-pattern: evaluation of constant value failed // error-pattern: evaluation of constant value failed
#![feature(const_unreachable_unchecked)]
const unsafe fn foo(x: bool) -> bool { const unsafe fn foo(x: bool) -> bool {
match x { match x {
@ -11,5 +10,5 @@ const unsafe fn foo(x: bool) -> bool {
const BAR: bool = unsafe { foo(false) }; const BAR: bool = unsafe { foo(false) };
fn main() { fn main() {
assert_eq!(BAR, true); assert_eq!(BAR, true);
} }

6
src/test/ui/consts/const_unsafe_unreachable_ub.stderr
View file

@ -7,13 +7,13 @@ LL | unsafe { intrinsics::unreachable() }
| entering unreachable code | entering unreachable code
| inside `unreachable_unchecked` at $SRC_DIR/core/src/hint.rs:LL:COL | 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(), 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) }; 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 error: aborting due to previous error