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From: "hubicka at gcc dot gnu.org" <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 18:18:07 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99309

--- Comment #5 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
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 was worried about this idea since this will still lead to some inconsiste=
ncy
since uses guarded by the __builtin_constnat_p may or may not be constant
propagated and it seems logical to assume that in the block guarded by
builtin_constnat_p the expression will indeed evaluate to compile time
constant.

However we can get similar inconsistencies with alias oracle walking limits=
 as
well, so these constructions are generally fragile (but seems increasingly
common in C++ codebases).

It would be still nice to have fre5 to constant propagate this. IPA analysis
are very simplistics.
Richi, any idea on this?=