[flang] OpenMP default private clause does not work as expected

[shivaramaarao]

consider the following program

PROGRAM main
INTEGER:: NEL
!$OMP PARALLEL DO DEFAULT(PRIVATE) !PRIVATE(NEL)
DO I=1, 4
NEL=I
PRINT *, I, NEL
ENDDO
!$OMP END PARALLEL DO
END PROGRAM

$flang-new -fopenmp test.f90
$a.out
2 4
4 4
3 4
1 4

NEL variable is expected to be private, but it is not considered so. uncommenting PRIVATE(NEL) clause makes the program work.

[kparzysz]

The handling of DEFAULT isn't really fully implemented yet: https://github.com/llvm/llvm-project/blob/main/flang/lib/Lower/OpenMP.cpp#L1356-L1376

[shivaramaarao]

Thanks for the reply. The testcase is extracted from 362.fma3d omp2012 benchmark suite.

if I comment the following line, the testcase passes. Should the function defaultPrivatize need to handle this case better?

https://github.com/llvm/llvm-project/blob/main/flang/lib/Lower/OpenMP.cpp#L517

[NimishMishra]

@shivaramaarao This check was added in #71922, to fix #65569. I will do some analysis and get back with more details by EOD on this, on why this check is causing the current issue.

[llvmbot]

@llvm/issue-subscribers-flang-ir

Author: None (shivaramaarao)

consider the following program

PROGRAM main
INTEGER:: NEL
!$OMP PARALLEL DO DEFAULT(PRIVATE) !PRIVATE(NEL)
DO I=1, 4
NEL=I
PRINT *, I, NEL
ENDDO
!$OMP END PARALLEL DO
END PROGRAM

$flang-new -fopenmp test.f90
$a.out
2 4
4 4
3 4
1 4

NEL variable is expected to be private, but it is not considered so. uncommenting PRIVATE(NEL) clause makes the program work.

[NimishMishra]

Hello @shivaramaarao,

I re-looked at the issue with rebased llvm flang. The issue is no longer existent with #72510 applied atop 4235e44. Could you check once? I get the following IR, which seems to be correct:

omp.parallel {
      %4 = fir.alloca i32 {adapt.valuebyref, pinned}
      %5 = fir.declare %4 {uniq_name = "_QFEi"} : (!fir.ref<i32>) -> !fir.ref<i32>
      %6 = fir.alloca i32 {bindc_name = "nel", pinned, uniq_name = "_QFEnel"}
      %7 = fir.declare %6 {uniq_name = "_QFEnel"} : (!fir.ref<i32>) -> !fir.ref<i32>
      omp.wsloop  for  (%arg0) : i32 = (%c1_i32) to (%c4_i32) inclusive step (%c1_i32) {
        fir.store %arg0 to %5 : !fir.ref<i32>
        %8 = fir.load %5 : !fir.ref<i32>
        fir.store %8 to %7 : !fir.ref<i32>
        omp.yield
      }
      omp.terminator
    }

[kiranchandramohan]

@NimishMishra if this works now, can you close the issue?

[NimishMishra]

Validated the application from which this reproducer arose, and it is working fine. Closing this hence.