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

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

[alexander.grund@tu-dresden.de]

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)

[Bug target/100703] __vector_pair and __vector_quad cannot be passed by reference

[alexander.grund@tu-dresden.de]

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

--- Comment #1 from Alexander Grund <alexander.grund@tu-dresden.de> ---
It goes further: Even the usual conversion rules for pointer types don't apply:

void foo(__vector_pair*){}
void bar(const __vector_pair*){}
int main(){
  __vector_pair p;
  foo(p); // works
  bar(p); // fails
}

[Bug target/100703] __vector_pair and __vector_quad cannot be passed by reference

[segher at gcc dot gnu.org]

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

--- Comment #2 from Segher Boessenkool <segher at gcc dot gnu.org> ---
This compiles just fine for me, even with -O0.  Does this only happen with
some older version of the compiler?  Are some special flags needed?

[Bug target/100703] __vector_pair and __vector_quad cannot be passed by reference

[alexander.grund@tu-dresden.de]

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

--- Comment #3 from Alexander Grund <alexander.grund@tu-dresden.de> ---
I found that this was fixed in 10.3 and 11.1 by
https://github.com/gcc-mirror/gcc/commit/e2882e76089cecdc268d0835c54cabfa80b5b0be

So yes only happens in 10.2. Thanks for checking that!

[Bug target/100703] __vector_pair and __vector_quad cannot be passed by reference

[wschmidt at gcc dot gnu.org]

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

Bill Schmidt <wschmidt at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #4 from Bill Schmidt <wschmidt at gcc dot gnu.org> ---
So, already fixed.  Closing.