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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/107424] [13 Regression] ICE in gfc_trans_omp_do, at
 fortran/trans-openmp.cc:5397 - and wrong code - with non-rectangular loops
Date: Fri, 13 Jan 2023 11:51:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107424

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
For the non-simple loops, I guess the questions are if
do i =3D x, y, 10000
is equivalent to
for (i =3D x; i <=3D y; i +=3D 10000)
or not (especially regarding the in C UB cases of y being above INT_MAX -
10000),
and also what to do about
do i =3D x, y, z
where the step is variable - in C/C++, we always know if the iterator is
increasing or decreasing from the condition, except for !=3D condition but =
in
that case OpenMP requires
the step to be compile time known 1 or -1.  I'm afraid for Fortran we have =
no
idea.
And for non-rectangular loops like:
!$omp do collapse(2)
do i =3D x, y, s1
  do j =3D z, 2 * i + w, s2
that is quite important...=