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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
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	[thread overview]
Message-ID: <bug-99309-4-zJNNnUguVi@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-99309-4@http.gcc.gnu.org/bugzilla/>

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

--- 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 inconsistency
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?

  parent reply	other threads:[~2021-03-31 18:18 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-28 10:33 [Bug c++/99309] New: " gcc at mailinator dot com
2021-03-01  9:31 ` [Bug c++/99309] [10/11 Regression] " rguenth at gcc dot gnu.org
2021-03-01  9:44 ` jakub at gcc dot gnu.org
2021-03-08 15:45 ` [Bug ipa/99309] " mpolacek at gcc dot gnu.org
2021-03-29 14:07 ` jakub at gcc dot gnu.org
2021-03-31 18:18 ` hubicka at gcc dot gnu.org [this message]
2021-03-31 18:29 ` jakub at gcc dot gnu.org
2021-03-31 18:46 ` hubicka at ucw dot cz
2021-04-08 12:02 ` rguenth at gcc dot gnu.org
2021-04-15  9:49 ` hubicka at gcc dot gnu.org
2022-03-24 13:59 ` [Bug ipa/99309] [10/11/12 " rguenth at gcc dot gnu.org
2022-06-28 10:43 ` [Bug ipa/99309] [10/11/12/13 " jakub at gcc dot gnu.org
2023-07-07 10:39 ` [Bug ipa/99309] [11/12/13/14 " rguenth at gcc dot gnu.org
2023-08-17  0:19 ` pinskia at gcc dot gnu.org

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