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From: "hubicka at ucw dot cz" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug ipa/99309] [10/11 Regression] Segmentation fault with
 __builtin_constant_p usage at -O2
Date: Wed, 31 Mar 2021 18:46:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99309

--- Comment #7 from Jan Hubicka <hubicka at ucw dot cz> ---
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99309
>=20
> --- 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 hit=
ting
> > unreachable when late optimizations forget to make the transformation.
>=20
> 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 coul=
d 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=