[flang][OpenMP] Initialize variables of omp_nest_lock_kind to a known bad value (e.g., -1)

[eugeneepshteyn]

Currently, if one declares an automatic variable of type integer(kind=omp_nest_lock_kind) and forgets to call omp_init_nest_lock(), and then proceeds to call omp_destroy_nest_lock(), there's a crash due to uninitialized nest lock variable.

Would it be possible to detect that instantiations of integer variables of omp_nest_lock_kind kind and always initialize them to some known bad value (e.g., -1)? This would allow displaying useful runtime error, instead of just crash.

[ebaskakov]

A more general approach would be a new directive, such as !dir$ initializer_hint to be associated with an numerical type. We could do something like this in omp_lib:

  integer, parameter :: omp_nest_lock_kind = int_ptr_kind()
  !dir$ initializer_hint omp_nest_lock_kind(-1)

The compiler would try to initialize variables of the type omp_nest_lock_kind with the specified value.