[Bug c++/98641] Feature request: implement pointer alignment builtins

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98641

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #3)
> assume_aligned is something different, I guess __builtin_is_aligned expands
> to an actual runtime check (perhaps optimized away if the pointer can't be
> misaligned).

But we could do this:

--- a/libstdc++-v3/include/bits/align.h
+++ b/libstdc++-v3/include/bits/align.h
@@ -98,7 +98,7 @@ align(size_t __align, size_t __size, void*& __ptr, size_t&
__space) noexcept
        {
          // This function is expected to be used in hot code, where
          // __glibcxx_assert would add unwanted overhead.
-         _GLIBCXX_DEBUG_ASSERT((uintptr_t)__ptr % _Align == 0);
+         _GLIBCXX_DEBUG_ASSERT(__builtin_is_aligned(__ptr, _Align));
          return static_cast<_Tp*>(__builtin_assume_aligned(__ptr, _Align));
        }
     }