diff options
Diffstat (limited to 'library')
| -rw-r--r-- | library/core/src/num/uint_macros.rs | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/library/core/src/num/uint_macros.rs b/library/core/src/num/uint_macros.rs index ffe2ca2440e..cd74cece0d1 100644 --- a/library/core/src/num/uint_macros.rs +++ b/library/core/src/num/uint_macros.rs @@ -454,8 +454,19 @@ macro_rules! uint_impl { without modifying the original"] #[inline] pub const fn checked_add(self, rhs: Self) -> Option<Self> { - let (a, b) = self.overflowing_add(rhs); - if unlikely!(b) { None } else { Some(a) } + // This used to use `overflowing_add`, but that means it ends up being + // a `wrapping_add`, losing some optimization opportunities. Notably, + // phrasing it this way helps `.checked_add(1)` optimize to a check + // against `MAX` and a `add nuw`. + // Per <https://github.com/rust-lang/rust/pull/124114#issuecomment-2066173305>, + // LLVM is happy to re-form the intrinsic later if useful. + + if unlikely!(intrinsics::add_with_overflow(self, rhs).1) { + None + } else { + // SAFETY: Just checked it doesn't overflow + Some(unsafe { intrinsics::unchecked_add(self, rhs) }) + } } /// Strict integer addition. Computes `self + rhs`, panicking |