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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/100181] hot-cold partitioned code doesn't assemble
Date: Wed, 21 Apr 2021 14:42:27 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100181

--- Comment #9 from Tobias Burnus <burnus at gcc dot gnu.org> ---
(In reply to Thomas Schwinge from comment #8)
> (In reply to Tobias Burnus from comment #7)
> > (I could not reproduce the LLVM 9 issue in PR94278 back then.)
>=20
> Hmm, but didn't you say in the LLVM issue
> <https://bugs.llvm.org/show_bug.cgi?id=3D45887> that you _did_ reproduce =
this back then?

I partially mixed it up - I could not reproduce it with a self-build LLVM b=
ut
could do so with the distro LLVM ones.

Our/my LLVM bug 45887 is similar to
https://bugs.llvm.org/show_bug.cgi?id=3D41914, which was fixed by
https://reviews.llvm.org/D79943 and the latter adds the check which causes =
the
error message: "undefined label '.L33'"

However, the other bug (41914) and the the testcase in the fix (D79943) were
about a label which was truly missing as opposed to one which is just in a
differently named .section.

 * * *

Obviously, with D79943 at place (LLVM 11, 12, ...), I can reproduce the iss=
ue
with -O2 (with < -O0 there is only .text) as then 's_branch .L33' is in
.section .text but '.L33:' is in '.section .text.unlikely'.

Whether it is intended that cross-.section s_branch are no longer permitted=
 or
whether it happened by chance by this patch or on purpose, I don't know.

Sections themselves are supported =E2=80=93 and the  LVM testsuite for GCN =
has
testcases with '.section' (under llvm/test/MC/AMDGPU/*.s) =E2=80=93 but in =
the
testsuite one at a time.

GCC guards the .text.unlikely generation by (=E2=86=92 varasm.c's
default_function_section) by

  if (!flag_reorder_functions
      || !targetm_common.have_named_sections)
    return NULL;

while the patch in PR 94278 comment 3 uses
   flag_reorder_blocks_and_partition =3D 0=