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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:19:13 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:19:13 +0000 |
commit | 218caa410aa38c29984be31a5229b9fa717560ee (patch) | |
tree | c54bd55eeb6e4c508940a30e94c0032fbd45d677 /library/core/src/slice/iter/macros.rs | |
parent | Releasing progress-linux version 1.67.1+dfsg1-1~progress7.99u1. (diff) | |
download | rustc-218caa410aa38c29984be31a5229b9fa717560ee.tar.xz rustc-218caa410aa38c29984be31a5229b9fa717560ee.zip |
Merging upstream version 1.68.2+dfsg1.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'library/core/src/slice/iter/macros.rs')
-rw-r--r-- | library/core/src/slice/iter/macros.rs | 22 |
1 files changed, 6 insertions, 16 deletions
diff --git a/library/core/src/slice/iter/macros.rs b/library/core/src/slice/iter/macros.rs index ce51d48e3..0fd57b197 100644 --- a/library/core/src/slice/iter/macros.rs +++ b/library/core/src/slice/iter/macros.rs @@ -9,30 +9,20 @@ macro_rules! is_empty { }; } -// To get rid of some bounds checks (see `position`), we compute the length in a somewhat -// unexpected way. (Tested by `codegen/slice-position-bounds-check`.) macro_rules! len { ($self: ident) => {{ #![allow(unused_unsafe)] // we're sometimes used within an unsafe block let start = $self.ptr; - let size = size_from_ptr(start.as_ptr()); - if size == 0 { - // This _cannot_ use `unchecked_sub` because we depend on wrapping + if T::IS_ZST { + // This _cannot_ use `ptr_sub` because we depend on wrapping // to represent the length of long ZST slice iterators. $self.end.addr().wrapping_sub(start.as_ptr().addr()) } else { - // We know that `start <= end`, so can do better than `offset_from`, - // which needs to deal in signed. By setting appropriate flags here - // we can tell LLVM this, which helps it remove bounds checks. - // SAFETY: By the type invariant, `start <= end` - let diff = unsafe { unchecked_sub($self.end.addr(), start.as_ptr().addr()) }; - // By also telling LLVM that the pointers are apart by an exact - // multiple of the type size, it can optimize `len() == 0` down to - // `start == end` instead of `(end - start) < size`. - // SAFETY: By the type invariant, the pointers are aligned so the - // distance between them must be a multiple of pointee size - unsafe { exact_div(diff, size) } + // To get rid of some bounds checks (see `position`), we use ptr_sub instead of + // offset_from (Tested by `codegen/slice-position-bounds-check`.) + // SAFETY: by the type invariant pointers are aligned and `start <= end` + unsafe { $self.end.sub_ptr(start.as_ptr()) } } }}; } |