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Date: Fri, 12 May 2023 16:29:10 +0200
From: Jan Hubicka <hubicka@ucw.cz>
To: "amonakov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
Cc: gcc-bugs@gcc.gnu.org
Subject: Re: [Bug c++/106943] GCC building clang/llvm with LTO flags causes
 ICE in clang
Message-ID: <ZF5NNmRodBUxPNY2@kam.mff.cuni.cz>
References: <bug-106943-4@http.gcc.gnu.org/bugzilla/>
 <bug-106943-4-xZLBVwM0gY@http.gcc.gnu.org/bugzilla/>
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> > Indeed it is quite long time problem with clang not building with lifetime
> > DSE and strict aliasing.  I wonder why this is not fixed on clang side?
> 
> Because the problems were not communicated? I knew that Firefox needed
> -flifetime-dse=1, but it's the first time I hear that any such problems in
> Clang/LLVM were identified.
> 
> 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 not manifesting
> because LLVM is built without LTO?

I think opensuse package outs-out LTO probably for this reason.  I am
sometimes using LLVM as benchmark of LTO and PGO, so it would be great
to have this enabled in the packages, but I had no time to do that so
far.  LLVM built with LTO and PGO builds quite a lot faster.  I was
filling bugreport for that some time ago and it seems that the bugreport
linked above has quite good analysis about what breaks.