https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89617
--- Comment #2 from John Zwinck <jzwinck at gmail dot com> ---
Jakub, here is a similar example using structs instead of arrays. It still
generates different code, with RESTRICT giving memcpy instead of mov, but no
RESTRICT still using memmove which is suboptimal.
struct S
{
int arr[3];
};
inline void Copy(S& __restrict__ dest, const S& __restrict__ src)
{
std::copy(std::begin(src.arr), std::end(src.arr), dest.arr);
}
void f2(S& dest, const S& src)
{
if (&dest != &src)
{
#ifdef RESTRICT
Copy(dest, src);
#else
std::copy(std::begin(src.arr), std::end(src.arr), dest.arr);
#endif
}
}
Demo: https://godbolt.org/z/zmJTLU
That being said, Clang thinks that casting a larger array to a smaller one is
undefined behavior, so can you give a more specific example of when two arrays
might overlap yet not have the same starting address?
