On Thu, Dec 13, 2018 at 05:04:59PM +0100, Florian Weimer wrote: > * Rich Felker: > > >> If the compiler can handle the zeroing, that would be great, though not > >> sure how (some __attribute__((zero)) which generates a type constructor > >> for such structure; it kind of departs from what the C language offers). > > > > The compiler fundamentally can't. At the very least it would require > > effective type tracking, which requires shadow memory and is even more > > controversial than -fstrict-aliasing (because in a sense it's a > > stronger version thereof). > > It's possible to do it with the right types. See _Bool on 32-bit Darwin > PowerPC for an example, which is four bytes instead of the usual one. > > Similarly, we could have integer types with trap representations. > Whether it is a good idea is a different matter, but the amount of > compiler magic required is actually limited. If you do this you just have LP64 with value range restricted to 32-bit. This does not accomplish anything useful since it uses just as much memory as normal LP64 but you don't get anything beneficial out of it. Rich
