[flang][openmp] compiler crash when private clause is used with SIMD

[shivaramaarao]

consider the following program

PROGRAM MAIN
REAL(KIND=4) :: A(10,10), B(10,10), C(10,10)
!$OMP SIMD PRIVATE(I,J)
  DO I=1, SIZE(A,1)
    DO J=1, SIZE(A,2)
      C(I,J) = A(I,J) + B(I,J)
    ENDDO
  ENDDO
!$OMP END SIMD
END PROGRAM

$flang -openmp t1.f90

flang: /mnt/extendedspace2/shivaram/llvm_trunk2/llvm-project/flang/lib/Lower/OpenMP/OpenMP.cpp:753: mlir::Operation* createAndSetPrivatizedLoopVar(Fortran::lower::AbstractConverter&, mlir::Location, mlir::Value, const Fortran::semantics::Symbol*): Assertion `converter.isPresentShallowLookup(*sym) && "Expected symbol to be in symbol table."' failed.

[llvmbot]

@llvm/issue-subscribers-flang-ir

Author: None (shivaramaarao)

consider the following program ``` PROGRAM MAIN REAL(KIND=4) :: A(10,10), B(10,10), C(10,10) !$OMP SIMD PRIVATE(I,J) DO I=1, SIZE(A,1) DO J=1, SIZE(A,2) C(I,J) = A(I,J) + B(I,J) ENDDO ENDDO !$OMP END SIMD END PROGRAM ``` $flang -openmp t1.f90 ``` flang: /mnt/extendedspace2/shivaram/llvm_trunk2/llvm-project/flang/lib/Lower/OpenMP/OpenMP.cpp:753: mlir::Operation* createAndSetPrivatizedLoopVar(Fortran::lower::AbstractConverter&, mlir::Location, mlir::Value, const Fortran::semantics::Symbol*): Assertion `converter.isPresentShallowLookup(*sym) && "Expected symbol to be in symbol table."' failed. ```

[NimishMishra]

I have been investigating this. I am unable to fully grasp whyi has the OmpLinear flag. Is there something obvious I am missing here?

This also explains why this test (which seemingly has no relation with my linear clause PR) hits an assertion failure with the same.

!DEF: /main MainProgram
program main
 !DEF: /main/a ObjectEntity REAL(4)
 !DEF: /main/b ObjectEntity REAL(4)
 !DEF: /main/c ObjectEntity REAL(4)
 real(kind=4) a(10,10), b(10,10), c(10,10)
!$omp simd  private(i,j)
 !DEF: /main/OtherConstruct1/i (OmpPrivate, OmpLinear, OmpPreDetermined, OmpExplicit) HostAssoc INTEGER(4)
 !DEF: /main/size INTRINSIC, PURE (Function) ProcEntity
 !REF: /main/a
 do i=1,size(a, 1)
  !DEF: /main/OtherConstruct1/j (OmpPrivate, OmpExplicit) HostAssoc INTEGER(4)
  !REF: /main/size
  !REF: /main/a
  do j=1,size(a, 2)
   !REF: /main/c
   !REF: /main/OtherConstruct1/i
   !REF: /main/OtherConstruct1/j
   !REF: /main/a
   !REF: /main/b
   c(i,j) = a(i,j)+b(i,j)
  end do
 end do
!$omp end simd
end program

[mrkajetanp]

I have been investigating this. I am unable to fully grasp whyi has the OmpLinear flag. Is there something obvious I am missing here?

It's required by the openmp standard, the section for simd (iirc) says that if you have a nested loop inside a simd construct then the outer induction variable becomes linear.