On 04/05/17 17:20, Richard Biener wrote: >> Also, wonder if you need to mark all types containing such arrays, >> if you couldn't just set that flag in C++ on unsigned char/std::byte >> arrays (and on anything with that attribute), have that imply alias set >> 0 on it and then let the rest of alias machinery handle aggregate types >> containing such fields. > > Yes, I expected it to work like this (didn't look at the patch yet). >
I want to allow *only* what the C++ standard requires or what Jason says of course :), and not a single bit more, because it suppresses otherwise correct optimizations. So a struct with a std::byte member is not alias_set 0, only the std::byte itself is, but an array of std::byte is itself typeless_storage, and makes the whole structure also typeless_storage, but that is not the usual way how the alias machinery works, where such an attribute would not propagate. Currently I think the C++ FE can do the propagation when the type is declared. I would not imply that with the typeless_storage attribute, because may_alias does not do that either. Bernd.
