https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72785

--- Comment #7 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #2)
> This is undesirable, iftmp.0_2 really isn't constant, so we shouldn't turn
> it into sometimes constant, sometimes non-constant.

I am not sure about that. The way I use __builtin_constant_p for optimization
purposes, I'd be happy to see the kind of threading that is going on here. The
discussion on the linux ML also doesn't clearly conclude that the code
absolutely has to be written this way.
Maybe we could get 2 separate builtins, one for optimization, and one for
checking, since the desired behavior is not the same?

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