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: () })?