diff options
Diffstat (limited to '')
| -rw-r--r-- | library/alloc/src/raw_vec.rs | 17 |
1 files changed, 12 insertions, 5 deletions
diff --git a/library/alloc/src/raw_vec.rs b/library/alloc/src/raw_vec.rs index 5a10121bb..3751f2a24 100644 --- a/library/alloc/src/raw_vec.rs +++ b/library/alloc/src/raw_vec.rs @@ -241,10 +241,15 @@ impl<T, A: Allocator> RawVec<T, A> { if T::IS_ZST || self.cap == 0 { None } else { - // We have an allocated chunk of memory, so we can bypass runtime - // checks to get our current layout. + // We could use Layout::array here which ensures the absence of isize and usize overflows + // and could hypothetically handle differences between stride and size, but this memory + // has already been allocated so we know it can't overflow and currently rust does not + // support such types. So we can do better by skipping some checks and avoid an unwrap. + let _: () = const { assert!(mem::size_of::<T>() % mem::align_of::<T>() == 0) }; unsafe { - let layout = Layout::array::<T>(self.cap).unwrap_unchecked(); + let align = mem::align_of::<T>(); + let size = mem::size_of::<T>().unchecked_mul(self.cap); + let layout = Layout::from_size_align_unchecked(size, align); Some((self.ptr.cast().into(), layout)) } } @@ -426,11 +431,13 @@ impl<T, A: Allocator> RawVec<T, A> { assert!(cap <= self.capacity(), "Tried to shrink to a larger capacity"); let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) }; - + // See current_memory() why this assert is here + let _: () = const { assert!(mem::size_of::<T>() % mem::align_of::<T>() == 0) }; let ptr = unsafe { // `Layout::array` cannot overflow here because it would have // overflowed earlier when capacity was larger. - let new_layout = Layout::array::<T>(cap).unwrap_unchecked(); + let new_size = mem::size_of::<T>().unchecked_mul(cap); + let new_layout = Layout::from_size_align_unchecked(new_size, layout.align()); self.alloc .shrink(ptr, layout, new_layout) .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })? |