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configury: test Fortran complex(real16) #13198

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configury: test Fortran complex(real16) #13198

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16 changes: 16 additions & 0 deletions config/ompi_fortran_check_iso_fortran_env_real16.m4
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Expand Up @@ -28,6 +28,22 @@ end program]])],
[AS_VAR_SET(iso_fortran_env_var_real16, no)])
AC_LANG_POP([Fortran])
])
AS_VAR_IF(iso_fortran_env_var_real16, [yes],
[AC_MSG_CHECKING([if Fortran compiler supports complex(ISO_FORTRAN_ENV:REAL16)])
AC_LANG_PUSH([Fortran])
AC_COMPILE_IFELSE([AC_LANG_SOURCE([[program check_for_iso_fortran_env_real16
use, intrinsic :: iso_fortran_env
complex(REAL16) :: var
var = 12.34
end program]])],
[AC_MSG_RESULT([yes])],
[AC_MSG_RESULT([no])
AC_MSG_WARN([*** Fortran compiler supports real(REAL16) but])
AC_MSG_WARN([*** does *not* support complex(REAL16)])
AC_MSG_WARN([*** Disabling support for ISO_FORTRAN_ENV:REAL16])
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Should we just create another type / plumb through complex(real16) such that we can support real16 and not support complex(real16)?

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@jeffhammond explained former PGI based NVHPC compiler won't support complex(REAL16), but the future is with flang (LLVM) based compilers.
I don't think this is worth the hassle unless there is a real use-case for that.
#13190 (comment)

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I saw @jeffhammond's comment, but I thought that that was exactly why we would want to do this. I.e., other compilers support REAL16 and support COMPLEX(REAL16). But the NV compiler doesn't -- and won't -- support REAL16 and COMPLEX(REAL16) -- it'll only support REAL16.

So if we test for both, and have proper test results for both, then we can handle any compiler that supports one or both. In reality, it'll only be the NV compiler that only supports one, but that's fine -- it's a generalized test.

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We can just turn OMPI_HAVE_FORTRAN_COMPLEX32 off and the datatype and op code should deal with having REAL16 but not COMPLEX32.

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But I'm fine with the solution proposed here, either you have both or none.

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I made a quick grep and unless I missed something, this is only used in MPI_Sizeof().
So though it would be ideal to handle compilers (e.g. NVHPC) that support real(REAL16) but not complex(REAL16), I do not think this is worth the hassle and fixing compilation by disabling ISO_FORTRAN_ENV:REAL16 altogether is good enough for the time being.
Of course anyone is free to improve this PR.

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It is also used in the datatype and in the MPI Op via OMPI_HAVE_FORTRAN_COMPLEX32. But I would be surprised if it had any users. For the outcome, I'm with you this PR is good enough.

AS_VAR_SET(iso_fortran_env_var_real16, no)])
AC_LANG_POP([Fortran])],
[])

AS_VAR_IF(iso_fortran_env_var_real16, [yes], [$1], [$2])
AS_VAR_POPDEF([iso_fortran_env_var_real16])
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