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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/113904] [OpenMP][5.0][5.1] Dynamic context selector
 'user={condition(expr)}' not handled
Date: Tue, 13 Feb 2024 20:29:21 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113904

--- Comment #3 from Tobias Burnus <burnus at gcc dot gnu.org> ---
See comment 1 for remaining to-do items.

I also note that the Fortran resolution comes too early - during parsing - =
as
the following shows:

module m
implicit none
contains
subroutine test
  !$omp declare variant (foo) match(user=3D{condition(myTrue)})
  !$omp declare variant (bar) match(user=3D{condition(myCond(1).and.myCond(=
2))})
  logical, parameter :: myTrue =3D .true.
end
subroutine foo; end
subroutine bar; end
logical function myCond(i)
  integer :: i
  myCond =3D i < 3
end
end module m


This fails with the complete bogus:

    5 |   !$omp declare variant (foo) match(user=3D{condition(myTrue)})
      |                                                           1
Error: property must be a constant logical expression at (1)

As 'myTrue' is a scalar logical PARAMETER.

The problem is just that this is not known when parsing '!$omp' - for that
reason, Fortran separates parsing and resolution, which the current code do=
es
not handle as it comes way too early.

* * *

Otherwise: It looks as if - except for simple variable names (and probablya=
lso
for functions calls w/o arguments) - we want to introduce an internal aux
function like:

  logical function __m_MOD_test_DV_cond1() result(res)
     res =3D myCond(1).and.myCond(2)
  end

which is then called when evaluating the run-time expression.

With header files and, possibly, also C++ modules, we might be able to alwa=
ys
inline the condition - with Fortran modules probably not, such that an aux
function would be needed for the generic case.=