Assume same alignment in RawVec

Author: TimDiekmann

library/alloc/src/raw_vec.rs

@@ -3,6 +3,7 @@
 
 use core::alloc::LayoutErr;
 use core::cmp;
+use core::intrinsics;
 use core::mem::{self, ManuallyDrop, MaybeUninit};
 use core::ops::Drop;
 use core::ptr::{NonNull, Unique};
@@ -495,7 +496,11 @@ where
 
     let memory = if let Some((ptr, old_layout)) = current_memory {
         debug_assert_eq!(old_layout.align(), new_layout.align());
-        unsafe { alloc.grow(ptr, old_layout, new_layout) }
+        unsafe {
+            // The allocator checks for alignment equality
+            intrinsics::assume(old_layout.align() == new_layout.align());
+            alloc.grow(ptr, old_layout, new_layout)
+        }
     } else {
         alloc.alloc(new_layout)
     };