Merge commit '370c397ec9169809e5ad270079712e0043514240' into sync_cg_clif-2022-03-20

[rust.git] / library / core / src / ptr / mod.rs

diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs
index ff71fadb614182e942ce9a2d1a93a4916c211ecb..59b1b4c1367526a274b0fc1ad26aa44a12096fa8 100644 (file)
--- a/library/core/src/ptr/mod.rs
+++ b/library/core/src/ptr/mod.rs
@@ -419,6 +419,7 @@ pub const fn slice_from_raw_parts_mut<T>(data: *mut T, len: usize) -> *mut [T] {
 #[stable(feature = "swap_nonoverlapping", since = "1.27.0")]
 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
 pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) {
+    #[allow(unused)]
     macro_rules! attempt_swap_as_chunks {
         ($ChunkTy:ty) => {
             if mem::align_of::<T>() >= mem::align_of::<$ChunkTy>()
@@ -437,15 +438,21 @@ macro_rules! attempt_swap_as_chunks {
         };
     }
 
-    // Split up the slice into small power-of-two-sized chunks that LLVM is able
-    // to vectorize (unless it's a special type with more-than-pointer alignment,
-    // because we don't want to pessimize things like slices of SIMD vectors.)
-    if mem::align_of::<T>() <= mem::size_of::<usize>()
-        && (!mem::size_of::<T>().is_power_of_two()
-            || mem::size_of::<T>() > mem::size_of::<usize>() * 2)
+    // NOTE(scottmcm) MIRI is disabled here as reading in smaller units is a
+    // pessimization for it.  Also, if the type contains any unaligned pointers,
+    // copying those over multiple reads is difficult to support.
+    #[cfg(not(miri))]
     {
-        attempt_swap_as_chunks!(usize);
-        attempt_swap_as_chunks!(u8);
+        // Split up the slice into small power-of-two-sized chunks that LLVM is able
+        // to vectorize (unless it's a special type with more-than-pointer alignment,
+        // because we don't want to pessimize things like slices of SIMD vectors.)
+        if mem::align_of::<T>() <= mem::size_of::<usize>()
+            && (!mem::size_of::<T>().is_power_of_two()
+                || mem::size_of::<T>() > mem::size_of::<usize>() * 2)
+        {
+            attempt_swap_as_chunks!(usize);
+            attempt_swap_as_chunks!(u8);
+        }
     }
 
     // SAFETY: Same preconditions as this function