[Bug middle-end/92120] New: OpenMP 5 – implicit mapping of this->member variable access – "this[:1]" shall be mapped

[burnus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92120

            Bug ID: 92120
           Summary: OpenMP 5 – implicit mapping of this->member variable
                    access – "this[:1]" shall be mapped
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org
  Target Milestone: ---

Loosely related to PR 66053 which is about explicit mapping.

The original code boils down to:
  this->j = this->i[1] + this->i[2]

This ends up in omp_notice_variable (via gimplify_var_or_parm_decl) as "this",
but it is – in line with OpenMP 4.5 – only mapped as:

map(alloc:MEM[(char *)this] [len: 0]) map(firstprivate:this [pointer assign,
bias: 0])

However, for OpenMP 5 – and to be usable – one also needs the actual data, i.e.
map(tofrom:this[:1]).


OpenMP 4.5, "2.15.5 Data-mapping Attribute Rules and Clauses":
"A variable that is of type reference to pointer is treated as if it had
appeared in a map clause as a1zero-length array section."

OpenMP 5.0: "If the target construct is within a class non-static member
function, and a variable is an accessible data member of the object for which
the non-static data member function is invoked, the variable is treated as if
the this[:1] expression had appeared in a map clause with a map-type of tofrom.
[…]"


#include <stdlib.h>  // For abort.

class foo {
public:
  int i[2], j;

  void func() {
    int k[2];
    #pragma omp target
    j = i[1]+i[2];
  }
};

int bar(int x)
{
  foo cl;
  cl.i[1] = x;
  cl.i[2] = 42;
  cl.func();
  return cl.j;
}

int main()
{
  if (bar(3) != 45)
    abort();
  return 0;
}