https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36685
--- Comment #5 from James Y Knight <foom at fuhm dot net> --- (oops submitted commit by mistake, continuing...) Strangely, it appears that Clang and GCC both have odd behaviors currently, but somewhat opposites: - GCC appears to evaluate weak constants _only_ in frontend constant evaluation. It does not treat them as known during backend optimizations. (However, GCC does not allow you to use such a variable in a context that is required to be constant by language rules). - Clang evaluates weak constants _only_ in backend optimizations, and never in frontend constant evaluation. Clang will be changing to stop optimizing based on weak constant value, so that they are consistently treated as unknown values. I'd suggest that GCC probably ought to do the same (by no longer constant evaluating such variables).
