https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113565
--- Comment #4 from Jan Schultke <janschultke at googlemail dot com> --- I would expect an error here because things that are undefined behavior are generally supposed to fail in constant expressions. I don't see a good reason why builtins should be exempt from that rule. The lack of diagnostic has cost me a few minutes of debugging yesterday. I had a static_assert: > static_assert(my_function(0u) == 32); This succeeded at compile time, but my_function(0) would return 0 at run-time as a result of passing through to __builtin_clz. UBSan may have caught it, but regardless, it's not sane to have different results inside/outside constant expressions like that.
