https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92963
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu.org
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
To GCC the "mixing" makes it conservative, not assessing any 'restrict' on
r and thus not disambiguate. Then we're jump-threading the second branch
and thus instead of *r = 2 we suddenly see *p = 2 and that's _not_
aliasing the load from *q because you said so.
That is, you're trying to use 'r' as a mean to make p based on q (or the
other way around). That's probably not intended.
Of course GCC comes along and makes r which might be based on p with some
reading using q instead which clearly isn't.
So yes, all this lexical semantic reasoning easily breaks down with an
optimizing compiler. (and all this pointer provenance nonsense)
I'm not convinced this is a bug in GCC. That you do if (p == q) is a good
hint at that you're doing something not intended.
