[Bug ipa/99309] [10/11 Regression] Segmentation fault with __builtin_constant_p usage at -O2

["hubicka at ucw dot cz" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99309

--- Comment #7 from Jan Hubicka <hubicka at ucw dot cz> ---
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99309
> 
> --- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
> (In reply to Jan Hubicka from comment #5)
> > As discussed, I can prepare patch to make inliner to redirect
> > __builtin_constant_p to __builtin_true whenever inliner detect that the
> > expression is compile time ocnstant.  This will avoid us eventually hitting
> > unreachable when late optimizations forget to make the transformation.
> 
> I'm quite worried about that, the point of guarding something with
> __builtin_constant_p is about the hope that the argument of that builtin will
> evaluate to constant in the conditional block guarded by it.
> By folding __builtin_constant_p to true if it sees it as constant but not
> actually propagating that constant to all uses of that expression we could have
> the condition folded to true, but if SRA or FRE etc. is disabled or isn't able
> to optimize it, we wouldn't have it constant.
Yes, it is not good (this is why I did not implement it earlier).
However you can trigger same problem without inline.  Just put enough
statements between the conditional and use so AO walk oracles gives
up...

Honza