[Flang][OpenMP] FIRSTPRIVATE clause specified within DO SIMD construct does not become active

[ohno-fj]

Version of flang : 22.0.0(63fe60f830ec00cb44fb7354291a74ddc1a7c513)/AArch64

In the attached program (test011.f90), FIRSTPRIVATE clause and LASTPRIVATE clause are specified within DO SIMD construct, and the same variable (a) is specified in both clauses.
When checking the variable's value, LASTPRIVATE clause appears to be active, but FIRSTPRIVATE clause seems inactive.
The values for main1 : a = and sub1 : a = are expected to output 10.

The result is correct in the following cases:

• Change DO SIMD construct to DO construct, or
• Specify only FIRSTPRIVATE clause (remove LASTPRIVATE clause)

This issue relates to the closed #155195.
The compilation error in the above issue #155195 has been fixed. However, since the current execution result is incorrect, I issue this new issue.

The following are the test program, Flang, Gfortran and ifx compilation/execution results.

test011.f90:

subroutine sub
  integer a
  a=10
!$omp do simd lastprivate(a) firstprivate(a)
  do i=1,1
     write(6,*) "sub1  : a = ", a
     a=20
  end do
!$omp end do simd
  write(6,*) "sub2  : a = ", a
end subroutine sub

program main
  integer a
  a=10
!$omp do simd lastprivate(a) firstprivate(a)
  do i=1,1
     write(6,*) "main1 : a = ", a
     a=20
  end do
!$omp end do simd
  write(6,*) "main2 : a = ", a
  call sub
  print *,'pass'
end program main

$ export OMP_NUM_THREADS=2; flang -fopenmp test011.f90; ./a.out
 main1 : a =  0
 main2 : a =  20
 sub1  : a =  -45698304
 sub2  : a =  20
 pass
$

$ gfortran -fopenmp test011.f90
test011.f90:4:44:

    4 | !$omp do simd lastprivate(a) firstprivate(a)
      |                                            ^
Error: firstprivate variable ‘a’ is private in outer context
test011.f90:4:44: Error: lastprivate variable ‘a’ is private in outer context
test011.f90:16:44:

   16 | !$omp do simd lastprivate(a) firstprivate(a)
      |                                            ^
Error: firstprivate variable ‘a’ is private in outer context
test011.f90:16:44: Error: lastprivate variable ‘a’ is private in outer context
$

$ export OMP_NUM_THREADS=2; ifx -qopenmp test011.f90; ./a.out
 main1 : a =           10
 main2 : a =           20
 sub1  : a =           10
 sub2  : a =           20
$

[KrxGu]

I would like to work on this issue.

My plan is:

• Reproduce the bug on current main using the test case from the description.
• Inspect the lowering of composite do simd in flang/lib/Lower/OpenMP/OpenMP.cpp
  (specifically genCompositeDoSimd) and the clause splitting in
  flang/lib/Lower/OpenMP/Decomposer.cpp.
• Align the data-sharing handling for do simd with the existing
  same_var_first_lastprivate.f90 test (where a variable appears in both
  FIRSTPRIVATE and LASTPRIVATE) by making sure the DataSharingProcessor used
  for the loop nest sees both clauses for the same symbol.
• Add a new lowering test under flang/test/Lower/OpenMP that covers
  !$omp do simd firstprivate(a) lastprivate(a) and verifies the generated
  MLIR matches the expected FIRSTPRIVATE and LASTPRIVATE semantics.

If there are no objections, I’ll start working on a patch and open a PR referencing this issue. It would be great if this issue could be assigned to me.

[llvmbot]

@llvm/issue-subscribers-flang-ir

Author: ohno-fj (ohno-fj)

``` Version of flang : 22.0.0(63fe60f)/AArch64 ```

In the attached program (test011.f90), FIRSTPRIVATE clause and LASTPRIVATE clause are specified within DO SIMD construct, and the same variable (a) is specified in both clauses.
When checking the variable's value, LASTPRIVATE clause appears to be active, but FIRSTPRIVATE clause seems inactive.
The values for main1 : a = and sub1 : a = are expected to output 10.

The result is correct in the following cases:

• Change DO SIMD construct to DO construct, or
• Specify only FIRSTPRIVATE clause (remove LASTPRIVATE clause)

This issue relates to the closed #155195.
The compilation error in the above issue #155195 has been fixed. However, since the current execution result is incorrect, I issue this new issue.

The following are the test program, Flang, Gfortran and ifx compilation/execution results.

test011.f90:

subroutine sub
  integer a
  a=10
!$omp do simd lastprivate(a) firstprivate(a)
  do i=1,1
     write(6,*) "sub1  : a = ", a
     a=20
  end do
!$omp end do simd
  write(6,*) "sub2  : a = ", a
end subroutine sub

program main
  integer a
  a=10
!$omp do simd lastprivate(a) firstprivate(a)
  do i=1,1
     write(6,*) "main1 : a = ", a
     a=20
  end do
!$omp end do simd
  write(6,*) "main2 : a = ", a
  call sub
  print *,'pass'
end program main

$ export OMP_NUM_THREADS=2; flang -fopenmp test011.f90; ./a.out
 main1 : a =  0
 main2 : a =  20
 sub1  : a =  -45698304
 sub2  : a =  20
 pass
$

$ gfortran -fopenmp test011.f90
test011.f90:4:44:

    4 | !$omp do simd lastprivate(a) firstprivate(a)
      |                                            ^
Error: firstprivate variable ‘a’ is private in outer context
test011.f90:4:44: Error: lastprivate variable ‘a’ is private in outer context
test011.f90:16:44:

   16 | !$omp do simd lastprivate(a) firstprivate(a)
      |                                            ^
Error: firstprivate variable ‘a’ is private in outer context
test011.f90:16:44: Error: lastprivate variable ‘a’ is private in outer context
$

$ export OMP_NUM_THREADS=2; ifx -qopenmp test011.f90; ./a.out
 main1 : a =           10
 main2 : a =           20
 sub1  : a =           10
 sub2  : a =           20
$