PR26547: alignof should return ABI alignment, not preferred alignment
Summary:
- Add `UETT_PreferredAlignOf` to account for the difference between `__alignof` and `alignof`
- `AlignOfType` now returns ABI alignment instead of preferred alignment iff clang-abi-compat > 7, and one uses _Alignof or alignof
Patch by Nicole Mazzuca!
Differential Revision: https://reviews.llvm.org/D53207
llvm-svn: 345419
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7e79849..c6ddbfd 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -77,6 +77,11 @@
Modified Compiler Flags
-----------------------
+- As of clang 8, `alignof` and `_Alignof` return the ABI alignment of a type,
+ as opposed to the preferred alignment. `__alignof` still returns the
+ preferred alignment. `-fclang-abi-compat=7` (and previous) will make
+ `alignof` and `_Alignof` return preferred alignment again.
+
New Pragmas in Clang
--------------------
@@ -132,6 +137,21 @@
...
+ABI Changes in Clang
+--------------------
+
+- `_Alignof` and `alignof` now return the ABI alignment of a type, as opposed
+ to the preferred alignment.
+ - This is more in keeping with the language of the standards, as well as
+ being compatible with gcc
+ - `__alignof` and `__alignof__` still return the preferred alignment of
+ a type
+ - This shouldn't break any ABI except for things that explicitly ask for
+ `alignas(alignof(T))`.
+ - If you have interfaces that break with this change, you may wish to switch
+ to `alignas(__alignof(T))`, instead of using the `-fclang-abi-compat`
+ switch.
+
OpenMP Support in Clang
----------------------------------