Commit f1c2b28

committed

Simplify select_unpredictable guard selection

Instead of a tuple, select the dropped value and its guard with two separate calls to the intrinsic which makes both calls have a pointer-valued argument that should be simpler in codegen. Use the same condition on all (not an inverted condition) to clarify the intent of parallel selection. This should also be a simpler value-dependency chain if the guard is deduced unused (i.e. drop_in_place a noop for the type).

1 parent f6afd2e commit f1c2b28Copy full SHA for f1c2b28

File tree

1 file changed

-6

lines changed

library/core/src
- hint.rs

1 file changed

-6

lines changed

`‎library/core/src/hint.rs`

Lines changed: 6 additions & 6 deletions

Original file line number	Diff line number	Diff line change
`@@ -788,6 +788,7 @@ pub fn select_unpredictable<T>(condition: bool, true_val: T, false_val: T) -> T`
`788`	`788`	`let mut false_val = MaybeUninit::new(false_val);`
`789`	`789`
`790`	`790`	`struct DropOnPanic<T> {`
	`791`	+ // Invariant: valid pointer and points to an initialized `MaybeUninit`.
`791`	`792`	`inner: *mut MaybeUninit<T>,`
`792`	`793`	`}`
`793`	`794`
`@@ -806,12 +807,11 @@ pub fn select_unpredictable<T>(condition: bool, true_val: T, false_val: T) -> T`
`806`	`807`	`// value that is not selected.`
`807`	`808`	`unsafe {`
`808`	`809`	`// Extract the selected value first, ensure it is dropped as well if dropping the unselected`
`809`		`- // value panics.`
`810`		`- let (guard, drop) = crate::intrinsics::select_unpredictable(`
`811`		`- condition,`
`812`		`- (true_ptr, false_ptr),`
`813`		`- (false_ptr, true_ptr),`
`814`		`- );`
	`810`	`+ // value panics. We construct a temporary by-pointer guard around the selected value while`
	`811`	`+ // dropping the unselected value. Arguments overlap here, so we can not use mutable`
	`812`	`+ // reference for these arguments.`
	`813`	`+ let guard = crate::intrinsics::select_unpredictable(condition, true_ptr, false_ptr);`
	`814`	`+ let drop = crate::intrinsics::select_unpredictable(condition, false_ptr, true_ptr);`
`815`	`815`
`816`	`816`	// SAFETY: both pointers are to valid `MaybeUninit`, in both variants they do not alias but
`817`	`817`	`// the two arguments we have selected from did alias each other.`

0 commit comments

Comments

(0)

Navigation Menu

Search code, repositories, users, issues, pull requests...

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Commit f1c2b28

File tree

1 file changed

1 file changed

`‎library/core/src/hint.rs`

0 commit comments