| Issue |
169229
|
| Summary |
[Flang] [OpenMP] New OpenMP and Compiler directive incompatibility causes large apps buildability regression.
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
scamp-nvidia
|
Recently, it appears that #168884 introduced a change that caused an incompatiblity between having openmp structures and compiler directives. Consider the following:
```
program omp_cdir_crash
implicit none
integer, parameter :: n = 10
real :: a(n)
integer :: i
!$OMP PARALLEL DO
!dir$ anything goes here
do i = 1, n
a(i) = real(i)
end do
!$OMP END PARALLEL DO
print *, 'a(1)=', a(1), ' a(n)=', a(n)
end program omp_cdir_crash
```
The above compiles fine with GCC and NVHPC
```
scamp$ nvfortran test.F90 -o test -mp
scamp$ gfortran test.F90 -o test -fopenmp
```
However, after the recent change, Flang now chokes on this:
```
scamp$ flang test.F90 -o test -fopenmp
error: Semantic errors in test.F90
./test.F90:7:7: error: A DO loop must follow the PARALLEL DO directive
!$OMP PARALLEL DO
^^^^^^^^^^^
./test.F90:8:7: warning: Unrecognized compiler directive was ignored [-Wignored-directive]
!dir$ anything goes here
^^^^^^^^^^^^^^^^^^^
./test.F90:8:7: error: Compiler directives are not allowed inside OpenMP loop constructs
!dir$ anything goes here
^^^^^^^^^^^^^^^^^^^
```
This immediately popped up in our nightly testing for some large applications used by ECWMF and MeteoFrance, along with OpenRadioss - all of which make use of compiler directives nested inside an openmp region. I'm not positive what NVHPC and Gfortran do in those situations, but I do know that they compile the code and that to support similar behavior and portability, Flang should likely compile it as well. Tagging @kiranchandramohan too for an OpenMP supporting break.
Note that I talked with some people working on OpenACC parsing things, and they highlighted they ran into a similar issue and resolved it with this sort of handling, where they move the directive prior to the parallel region, so it's preserved:
https://github.com/llvm/llvm-project/blob/e6f60a61cdaae8fcf79d4f001096f2c826628074/flang/lib/Semantics/canonicalize-acc.cpp#L114
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