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-rw-r--r--rust/alloc/raw_vec.rs18
1 files changed, 12 insertions, 6 deletions
diff --git a/rust/alloc/raw_vec.rs b/rust/alloc/raw_vec.rs
index 5db87eac53b7..65d5ce15828e 100644
--- a/rust/alloc/raw_vec.rs
+++ b/rust/alloc/raw_vec.rs
@@ -6,7 +6,6 @@ use core::alloc::LayoutError;
use core::cmp;
use core::intrinsics;
use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
-use core::ops::Drop;
use core::ptr::{self, NonNull, Unique};
use core::slice;
@@ -274,10 +273,15 @@ 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))
}
}
@@ -465,11 +469,13 @@ 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: () })?