[Bug c++/100703] New: __vector_pair and __vector_quad cannot be passed by reference

["alexander.grund@tu-dresden.de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100703

            Bug ID: 100703
           Summary: __vector_pair and __vector_quad cannot be passed by
                    reference
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: alexander.grund@tu-dresden.de
  Target Milestone: ---

The PowerPC intrinsic types __vector_pair and __vector_quad cannot be passed by
reference but only by pointer.

Reproducer code:

void ploadRhsMMA(__vector_pair&){}
int main(){
  __vector_pair p;
  ploadRhsMMA(p);
}

This creates an error "invalid conversion from type »* __vector_pair«"

This error looks wrong to me: Why wouldn't I be able to pass a type by
reference when I can pass it by pointer? GCC can handle both the same so it is
at least inconsistent.

Furthermore this breaks the commonly used assumption, that the following
functions can take any argument:

template<typename T>
void foo(T&&);
template<typename T>
void bar(const T&);

This now breaks for those intrinsics and a workaround is painful as everything
needs to be covnerted to pointers when those are part of an overload set (for
example)