On Wed, Apr 5, 2017 at 1:41 PM, Bernd Edlinger <bernd.edlin...@hotmail.de> wrote: > 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).
My impression is that this is how GCC 6 worked, but GCC 7 decides to ignore alias set 0 members. Is that right? > 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 Well, only the array member, not the whole structure, but it may make sense for GCC to treat the whole structure as such internally. Jason
