[flang][OpenMP] Implement better FIRSTPRIVATE/LASTPRIVATE diagnostics

[eugeneepshteyn]

Please consider implementing better FIRSTPRIVATE/LASTPRIVATE diagnostics based on comments in #143764 (comment)

In case Fujitsu fixes the tests mentioned in the above issue, here are their sources that caused the issue to be filed in the first place:

0521_0030.f90:

INTEGER :: i
i=1
i0=1
i1=1
j=2
!$OMP PARALLEL default(firstprivate)
!$OMP SECTIONS
!$OMP parallel private(i)
i=100
!$OMP END parallel
!$OMP parallel firstprivate(i0)
i0=100
!$OMP END parallel
!$OMP parallel do lastprivate(i1)
do ii=1,1
i1=100
end do
!$OMP END parallel do
!$OMP parallel shared(j)
j=200
!$OMP END parallel
!$OMP END SECTIONS
!$OMP END PARALLEL
if (i.ne.1) print *,'err var i=',i
if (i0.ne.1) print *,'err var i0=',i0
if (i1.ne.100) print *,'err var i1=',i1
if (j.ne.2) print *,'err var j=',j
print *,'pass'

END 

0686_0024.f90:

module mod0
       integer::i,ii,iii,iiii
      end module

      module mod1
       use mod0
       integer::j,jj,jjj,jjjj
       integer::k=0
      end module

      program ompv2
      use mod1
      common /com/ m,mm,mmm,mmmm

!$omp parallel num_threads(10)

!$omp do reduction(+:k),lastprivate(i,ii,iii,iiii),firstprivate(j,jj,jjj,jjjj)
      do i=1,10
      do ii=1,10
      do iii=1,10
      do iiii=1,10
        k=k+1
      enddo
      enddo
      enddo
      enddo

!$omp do reduction(+:i,ii,iii),lastprivate(j,jj,jjj,jjjj),firstprivate(m,mm,mmm,mmmm)
      do j=1,iiii-1
      do jj=1,iiii-1
      do jjj=1,iiii-1
      do jjjj=1,iiii-1
        i=i+1
        ii=ii+1
        iii=iii+1
      enddo
      enddo
      enddo
      enddo

!$omp do reduction(+:j,jj,jjj),lastprivate(m,mm,mmm,mmmm)
      do m=1,jjjj-1
      do mm=1,jjjj-1
      do mmm=1,jjjj-1
      do mmmm=1,jjjj-1
        j=j+1
        jj=jj+1
        jjj=jjj+1
      enddo
      enddo
      enddo
      enddo

!$omp end parallel
      if (k/=10000) print *,k
      if (i/=10011.or.ii/=10011.or.iii/=10011.or.iiii/=11) print *,i,ii,iii,iiii
      if (j/=10011.or.jj/=10011.or.jjj/=10011.or.jjjj/=11) print *,j,jj,jjj,jjjj
      if (m/=11.or.mm/=11.or.mmm/=11.or.mmmm/=11) print *,m,mm,mmm,mmmm

      print *,'pass'

      end

[luporl]

Thanks for filing this issue. I agree that some invalid uses of FIRSTPRIVATE/LASTPRIVATE/REDUCTION could be detected and diagnosed by Flang in 0686_0024.f90, as done by other compilers, such as GFortran (15.1.0).

But for 0521_0030.f90, I don't think diagnostics can be improved. The problem is just a wrong expectation in this line:
if (i1.ne.100) print *,'err var i1=',i1
It seems to be expecting i1 to behave as shared, or parallel do lastprivate(i1) to update the outmost i1 variable, instead of that in the enclosing scope.