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From: "xry111 at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/106943] GCC building clang/llvm with LTO flags causes ICE
 in clang
Date: Fri, 12 May 2023 14:41:59 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106943

--- Comment #16 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Alexander Monakov from comment #14)
> (In reply to Jan Hubicka from comment #13)
> > Indeed it is quite long time problem with clang not building with lifet=
ime
> > DSE and strict aliasing.  I wonder why this is not fixed on clang side?
>=20
> Because the problems were not communicated? I knew that Firefox needed
> -flifetime-dse=3D1, but it's the first time I hear that any such problems=
 in
> Clang/LLVM were identified.
>=20
> I could not find any workaround for lifetime-dse in SUSE spec file for
> llvm16. Are you saying it was known and worked around somehow? Or it is n=
ot
> manifesting because LLVM is built without LTO?

I guess it's because the "official" way to build LLVM with LTO is performin=
g a
2-stage bootstrap and only enable LTO for stage 2 [1], and LLVM/Clang perfo=
rms
lifetime DSE less aggressively so it does not break itself...

[1]: https://releases.llvm.org/16.0.0/docs/BuildingADistribution.html=