[flang][OpenMP]Flang crashes with implicit none and undeclared variables

[Leporacanthicus]

program omp_examples
  implicit none
  integer, parameter :: n = 100
  real :: values(n)
  integer :: i
!  real :: sum
  
  call random_number(values)

  sum = 0
  !$omp parallel do reduction(+:sum)
  do i = 1, n
     sum = sum + values(i)
  end do

  
  print *, values
  print *, "sum=", sum
end program omp_examples

Uncomment the declaration for sum and it compiles fine.

To reproduce, save the sample above and compile with flang -fc1 -fopenmp sample.f90

The crash appears in the following code, where GetLastName(*desg).symbol is NULL.

const Symbol *OmpStructureChecker::GetObjectSymbol(
    const parser::OmpObject &object) {
  if (auto *name{std::get_if<parser::Name>(&object.u)}) {
    return &name->symbol->GetUltimate();
  } else if (auto *desg{std::get_if<parser::Designator>(&object.u)}) {
    return &GetLastName(*desg).symbol->GetUltimate();
  }
  return nullptr;
}

I'm recording this now, as I found it broken the other day. I may well fix this in the next day or two, but I'd rather report a bug and fix it quickly, than find that someone else found the same bug, and it wasn't fixed for ages... :)

[tblah]

Fixed by #139559

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: Mats Petersson (Leporacanthicus)

program omp_examples
  implicit none
  integer, parameter :: n = 100
  real :: values(n)
  integer :: i
!  real :: sum
  
  call random_number(values)

  sum = 0
  !$omp parallel do reduction(+:sum)
  do i = 1, n
     sum = sum + values(i)
  end do

  
  print *, values
  print *, "sum=", sum
end program omp_examples

Uncomment the declaration for sum and it compiles fine.

To reproduce, save the sample above and compile with flang -fc1 -fopenmp sample.f90

The crash appears in the following code, where GetLastName(*desg).symbol is NULL.

const Symbol *OmpStructureChecker::GetObjectSymbol(
    const parser::OmpObject &object) {
  if (auto *name{std::get_if<parser::Name>(&object.u)}) {
    return &name->symbol->GetUltimate();
  } else if (auto *desg{std::get_if<parser::Designator>(&object.u)}) {
    return &GetLastName(*desg).symbol->GetUltimate();
  }
  return nullptr;
}

I'm recording this now, as I found it broken the other day. I may well fix this in the next day or two, but I'd rather report a bug and fix it quickly, than find that someone else found the same bug, and it wasn't fixed for ages... :)