[Bug c++/66571] New: Template substitution causes some OpenMP rejects-valid

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66571

            Bug ID: 66571
           Summary: Template substitution causes some OpenMP rejects-valid
           Product: gcc
           Version: 5.1.1
            Status: UNCONFIRMED
          Keywords: openmp
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
                CC: jason at gcc dot gnu.org
  Target Milestone: ---

template <typename T, typename U>
extern void bar (T, T, U);

template <typename T, typename U>
void
foo (T a, T b, U c)
{
  #pragma omp parallel for simd shared (a, c) reduction (+:b)
  for (int i = 0; i < 10; i++)
    bar<T> (a, b, c);
  #pragma omp target map(tofrom:a, c[0:5])
    ;
  #pragma omp task depend(inout:c[4:2])
    ;
  T d = a;
  T e = b;
  U f = c;
  #pragma omp parallel for simd shared (d, f) reduction (+:e)
  for (int i = 0; i < 10; i++)
    bar<T> (d, e, f);
  #pragma omp target map(tofrom:d, f[0:5])
    ;
  #pragma omp task depend(inout:f[4:2])
    ;
}

void
baz ()
{
  int a = 0, b = 0, cb[10] = {}, *c = cb;
  foo <int, int *> (a, b, c);
  foo <int &, int *&> (a, b, c);
}

is rejected with -fopenmp right now, because during tsubst_omp_clauses if
changing a non-REFERENCE_TYPE decl into a REFERENCE_TYPE decl
convert_from_reference is called, while finish_omp_clauses (and later code)
checks if OMP_CLAUSE_DECL is a decl (and later code relies on it).