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From: "sam at gentoo dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/108250] New: [12/13 regression] llvm-tblgen miscompiled on
 powerpc-unknown-linux-gnu since r12-5383-g22c242342e38eb
Date: Wed, 28 Dec 2022 23:35:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108250

            Bug ID: 108250
           Summary: [12/13 regression] llvm-tblgen miscompiled on
                    powerpc-unknown-linux-gnu since
                    r12-5383-g22c242342e38eb
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sam at gentoo dot org
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---
              Host: powerpc-unknown-linux-gnu
            Target: powerpc-unknown-linux-gnu
             Build: powerpc-unknown-linux-gnu

Originally reported downstream in Gentoo at https://bugs.gentoo.org/880677.=
 I
forwarded it to LLVM at https://github.com/llvm/llvm-project/issues/59698 t=
oo.

With GCC 12 and newer, llvm-tblgen (which is built as part of the LLVM build
process and used for part of the build) is miscompiled on
powerpc-unknown-linux-gnu. GCC 11 and older are fine.

It has two failure modes:
1. When producing a description for the PPC target in LLVM as:
```
bin/llvm-tblgen -I ~/llvm-project/llvm/lib/TargetPowerPC \
                -I ~/llvm-project/llvm/include/ \
                -I ~/llvm-project/llvm/lib/Target/PowerPC/ \
                ~/llvm-project/llvm/lib/Target/PowerPC/PPC.td \
                -o /dev/null \
                --gen-dag-isel \
                -d /dev/null \
                --time-phases \
                --write-if-changed
```
it'll regularly hang (not on all runs, but if you run it 10 times, it'll ha=
ng
for several of them).
2. For X86, it'll give invalid output which later causes the LLVM compilati=
on
to fail.

For the purposes of tracking down which GCC commit caused it, we bisected by
checking for timeouts in a loop. The result was r12-5383-g22c242342e38eb.

Reverting 22c242342e38ebffa6bbf7e86e7a1e4abdf0d686 on top of releases/gcc-12
(at a3fbfc1027e9edcd14bb290b5702504d80d9e8fe) results in a built llvm-tblgen
which doesn't hang.

Please let me know what further information you require. Access to the
environment is also available (it's purely a testing machine for this kind =
of
bug, no personal data on it).=