[Bug libgomp/69555] New: libgomp.c++/target-6.C fails because of undefined behaviour

[vogt at linux dot vnet.ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69555

            Bug ID: 69555
           Summary: libgomp.c++/target-6.C fails because of undefined
                    behaviour
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgomp
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vogt at linux dot vnet.ibm.com
                CC: jakub at gcc dot gnu.org, krebbel at gcc dot gnu.org
  Target Milestone: ---
            Target: s390x

The test case libgomp.c++/target-6.C fails on s390x, and I think that's because
it uses a reference type variable in a "private" construct:

-- snip --
...
  int a[y - 2], b[y - 2]; 
  int (&c)[y - 2] = a, (&d)[y - 2] = b;
  ^^^^^^^^^^^^^^^
  ...
  #pragma omp target private (x, u, s, c, i) firstprivate (y, v, t, d)
map(from\
:err)
                                      ^^^
  { 
    ...
    for (i = 0; i < y - 2; i++) 
      c[i] = d[i];
    ...
  }
  ...
-- snip --

Depending on optimisations and the rest of the code, this leads to either
incorrect values in the array "a" or accessing a pointer to random memory.

As far as I understand it, the "OpenMP Application Program Interface, Version
4.0 - July 2013" explicitly forbids this on page 161:

28 • A variable that appears in a private clause must not have an incomplete
type or a
29   reference type.