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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/106498] [13 Regression] ICE in
 check_loop_closed_ssa_def, at tree-ssa-loop-manip.cc:645 since
 r13-1450-gd2a89866660945
Date: Mon, 01 Aug 2022 13:57:24 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106498

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  Before OMP expansion the loops do not define virtual operands.=
=20
After OMP expansion there's (useless) loop-around virtual operands.

SSA form is updated at

#0  update_ssa (update_flags=3D2048)
    at /space/rguenther/src/gcc-clean/gcc/tree-into-ssa.cc:3377
#1  0x00000000023fad6d in expand_omp_taskreg (region=3D0x3614bb0)
    at /space/rguenther/src/gcc-clean/gcc/omp-expand.cc:1511
#2  0x000000000242a485 in expand_omp (region=3D0x3614bb0)
    at /space/rguenther/src/gcc-clean/gcc/omp-expand.cc:10353
#3  0x000000000242aac4 in execute_expand_omp ()
    at /space/rguenther/src/gcc-clean/gcc/omp-expand.cc:10592
#4  0x000000000242ac3f in (anonymous namespace)::pass_expand_omp_ssa::execu=
te (
    this=3D0x349c290) at /space/rguenther/src/gcc-clean/gcc/omp-expand.cc:1=
0681
#5  0x000000000126d265 in execute_one_pass (
    pass=3D<opt_pass* 0x349c290 "ompexpssa"(174)>)

which ends up adding this virtual def.  The reason is a __builtin_GOMP_para=
llel
but the use is in a if (0 !=3D 0) guarded region (that's possibly outlined
afterwards?).

It's quite ugly, SSA omp-expansion performs update_ssa sometimes per stmt!

SSA omp-expansion test coverage is quite weak and autopar isn't well mainta=
ined
:/

I do have a patch for this particular case though.=