diff options
Diffstat (limited to '')
-rw-r--r-- | library/core/src/slice/iter.rs | 12 | ||||
-rw-r--r-- | library/core/src/slice/iter/macros.rs | 22 |
2 files changed, 9 insertions, 25 deletions
diff --git a/library/core/src/slice/iter.rs b/library/core/src/slice/iter.rs index 062289767..90ab43d12 100644 --- a/library/core/src/slice/iter.rs +++ b/library/core/src/slice/iter.rs @@ -6,7 +6,7 @@ mod macros; use crate::cmp; use crate::cmp::Ordering; use crate::fmt; -use crate::intrinsics::{assume, exact_div, unchecked_sub}; +use crate::intrinsics::assume; use crate::iter::{FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce}; use crate::marker::{PhantomData, Send, Sized, Sync}; use crate::mem::{self, SizedTypeProperties}; @@ -35,12 +35,6 @@ impl<'a, T> IntoIterator for &'a mut [T] { } } -// Macro helper functions -#[inline(always)] -fn size_from_ptr<T>(_: *const T) -> usize { - mem::size_of::<T>() -} - /// Immutable slice iterator /// /// This struct is created by the [`iter`] method on [slices]. @@ -65,7 +59,7 @@ fn size_from_ptr<T>(_: *const T) -> usize { #[must_use = "iterators are lazy and do nothing unless consumed"] pub struct Iter<'a, T: 'a> { ptr: NonNull<T>, - end: *const T, // If T is a ZST, this is actually ptr+len. This encoding is picked so that + end: *const T, // If T is a ZST, this is actually ptr+len. This encoding is picked so that // ptr == end is a quick test for the Iterator being empty, that works // for both ZST and non-ZST. _marker: PhantomData<&'a T>, @@ -186,7 +180,7 @@ impl<T> AsRef<[T]> for Iter<'_, T> { #[must_use = "iterators are lazy and do nothing unless consumed"] pub struct IterMut<'a, T: 'a> { ptr: NonNull<T>, - end: *mut T, // If T is a ZST, this is actually ptr+len. This encoding is picked so that + end: *mut T, // If T is a ZST, this is actually ptr+len. This encoding is picked so that // ptr == end is a quick test for the Iterator being empty, that works // for both ZST and non-ZST. _marker: PhantomData<&'a mut T>, 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()) } } }}; } |