| Issue |
130308
|
| Summary |
Flang OpenMP default(private) clause fails to implicitly set the data-sharing of variables to private.
|
| Labels |
flang
|
| Assignees |
|
| Reporter |
scamp-nvidia
|
We have found that the "default(private)" clause gets ignored by the compiler when it is used on a "parallel" construct that contains a "single" construct with a "copyprivate" clause. This clause should not be ignored. Here are the relevant rules from the OpenMP 6.0 specification:
> 210:23 7.1.1 Variables Referenced in a Construct
> 213:15 * In a parallel, teams, or task-generating construct, the data-sharing attributes of these
> 213:16 variables are determined by the default clause, if present (see Section 7.5.1).
>
> 223:3 7.5.1 default Clause
> 223:12 The default clause determines the implicitly determined data-sharing attributes of certain
> 223:13 variables that are referenced in the construct, in accordance with the rules given in Section 7.1.1.
> 224:1 If data-sharing-attribute is not none, the data-sharing attributes of the selected variables will be
> 224:2 data-sharing-attribute.
We attach a simple reproducer that shows the error for scalar variables, but we have also seen it for pointers.
test.F90:
```
Program main
implicit none
integer :: x
#if defined(USE_PRIVATE)
!Explicitly set the data-sharing of x to be private
!$omp parallel private(x) default(none)
#else
!Implicitly obtain the data-sharing of x - see rule 213:15-16
!$omp parallel default(private)
#endif
!$omp single
x = 1
!$omp end single copyprivate(x)
if (x == 1) then
print *, "SUCCESS"
else
print *, "FAILURE"
end if
!$omp end parallel
End Program main
```
So compiling the code normally, without declaring "USE_PRIVATE", we get:
```
scamp@dev-sky5:~$ flang --version
flang version 21.0.0git (https://github.com/llvm/llvm-project db5e4016c0332e7e5c0950414bb0b252975663ed)
Target: x86_64-unknown-linux-gnu
Thread model: posix
...
scamp@dev-sky5:~$ flang test.F90 -o test -fopenmp
flang-21: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
error: Semantic errors in test.F90
./test.F90:13:32: error: COPYPRIVATE variable 'x' is not PRIVATE or THREADPRIVATE in outer context
!$omp end single copyprivate(x)
^
```
Whereas, if we compile with "-DUSE_PRIVATE", we get successful compilations. We believe this code should work without the "-DUSE_PRIVATE", however. We also identified this as a bug in gfortran 14.1.0.
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