user0/rust
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Switch select_unpredictable guard to raw pointer

Browse source
This commit is contained in:
Aurelia Molzer 2025-08-30 13:00:02 +02:00 • committed by Aurelia Molzer
parent 354787b5ba
commit ee9803a244
1 changed files with 11 additions and 8 deletions
Download patch file Download diff file Expand all files Collapse all files

19
library/core/src/hint.rs
View file

@ -788,19 +788,20 @@ pub fn select_unpredictable<T>(condition: bool, true_val: T, false_val: T) -> T
let mut false_val = MaybeUninit::new(false_val);
struct DropOnPanic<T> {
// Invariant: valid pointer and points to an initialized `MaybeUninit`.
inner: *mut MaybeUninit<T>,
// Invariant: valid pointer and points to an initialized value that is not further used,
// i.e. it can be dropped by this guard.
inner: *mut T,
}
impl<T> Drop for DropOnPanic<T> {
fn drop(&mut self) {
// SAFETY: Must be guaranteed on construction of local type `DropOnPanic`.
unsafe { (*self.inner).assume_init_drop() }
unsafe { self.inner.drop_in_place() }
}
}
let true_ptr = (&mut true_val) as *mut _;
let false_ptr = (&mut false_val) as *mut _;
let true_ptr = true_val.as_mut_ptr();
let false_ptr = false_val.as_mut_ptr();
// SAFETY: The value that is not selected is dropped, and the selected one
// is returned. This is necessary because the intrinsic doesn't drop the
@ -813,10 +814,12 @@ pub fn select_unpredictable<T>(condition: bool, true_val: T, false_val: T) -> T
let guard = crate::intrinsics::select_unpredictable(condition, true_ptr, false_ptr);
let drop = crate::intrinsics::select_unpredictable(condition, false_ptr, true_ptr);
// SAFETY: both pointers are to valid `MaybeUninit`, in both variants they do not alias but
// the two arguments we have selected from did alias each other.
// SAFETY: both pointers are well-aligned and point to initialized values inside a
// `MaybeUninit` each. In both possible values for `condition` the pointer `guard` and
// `drop` do not alias (even though the two argument pairs we have selected from did alias
// each other).
let guard = DropOnPanic { inner: guard };
(*drop).assume_init_drop();
drop.drop_in_place();
crate::mem::forget(guard);
// Note that it is important to use the values here. Reading from the pointer we got makes