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| author | Matthias Krüger <matthias.krueger@famsik.de> | 2022-08-07 01:19:34 +0200 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2022-08-07 01:19:34 +0200 |
| commit | f0ff31fa09a144b1c24099e7b93be87522200caf (patch) | |
| tree | b08e89a6fe55744e5b5046ee9ac2bdd8ce90730b | |
| parent | 1a96f31f763142942adf7f15421b2d59494c2af4 (diff) | |
| parent | c195f7c0a432d1d77aed3c490509895add77f93f (diff) | |
| download | rust-f0ff31fa09a144b1c24099e7b93be87522200caf.tar.gz rust-f0ff31fa09a144b1c24099e7b93be87522200caf.zip | |
Rollup merge of #100169 - WaffleLapkin:optimize_is_aligned_to, r=workingjubilee
Optimize `pointer::as_aligned_to` This PR replaces `addr % align` with `addr & align - 1`, which is correct due to `align` being a power of two. Here is a proof that this makes things better: [[godbolt]](https://godbolt.org/z/Wbq3hx6YG). This PR also removes `assume(align != 0)`, with the new impl it does not improve anything anymore ([[godbolt]](https://rust.godbolt.org/z/zcnrG4777), [[original concern]](https://github.com/rust-lang/rust/pull/95643#discussion_r843326903)).
| -rw-r--r-- | library/core/src/ptr/const_ptr.rs | 5 | ||||
| -rw-r--r-- | library/core/src/ptr/mut_ptr.rs | 5 |
2 files changed, 2 insertions, 8 deletions
diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs index e0655d68d2c..2cd6e23c71a 100644 --- a/library/core/src/ptr/const_ptr.rs +++ b/library/core/src/ptr/const_ptr.rs @@ -1336,11 +1336,8 @@ impl<T: ?Sized> *const T { panic!("is_aligned_to: align is not a power-of-two"); } - // SAFETY: `is_power_of_two()` will return `false` for zero. - unsafe { core::intrinsics::assume(align != 0) }; - // Cast is needed for `T: !Sized` - self.cast::<u8>().addr() % align == 0 + self.cast::<u8>().addr() & align - 1 == 0 } } diff --git a/library/core/src/ptr/mut_ptr.rs b/library/core/src/ptr/mut_ptr.rs index fc3dd2a9b25..56ad5f7658e 100644 --- a/library/core/src/ptr/mut_ptr.rs +++ b/library/core/src/ptr/mut_ptr.rs @@ -1614,11 +1614,8 @@ impl<T: ?Sized> *mut T { panic!("is_aligned_to: align is not a power-of-two"); } - // SAFETY: `is_power_of_two()` will return `false` for zero. - unsafe { core::intrinsics::assume(align != 0) }; - // Cast is needed for `T: !Sized` - self.cast::<u8>().addr() % align == 0 + self.cast::<u8>().addr() & align - 1 == 0 } } |