From 46b547cb5861febd3e0401acb0af6f65be775948 Mon Sep 17 00:00:00 2001
From: Tim Diekmann <tim.diekmann@3dvision.de>
Date: Thu, 20 Aug 2020 11:55:41 +0200
Subject: [PATCH] Assume same alignment in `RawVec`

---
 library/alloc/src/raw_vec.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/library/alloc/src/raw_vec.rs b/library/alloc/src/raw_vec.rs
index dafbb0acd118..05382d0b5594 100644
--- a/library/alloc/src/raw_vec.rs
+++ b/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)
     };