[Bug fortran/105807] New: ICE / error when defining a class containing polymorphic components

["bourdin at mcmaster dot ca" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105807

            Bug ID: 105807
           Summary: ICE / error when defining a class containing
                    polymorphic components
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bourdin at mcmaster dot ca
  Target Milestone: ---

defining a class whose components are polymorphic variables fails:

Consider the following (legal) source code:
module Vect_class
    type, abstract :: Vect_Type
    end type
end module Vect_class

module Elem_class
    use Vect_class
    type, abstract :: Elem_Type
        integer                      :: numDof
        class(Vect_type),allocatable :: v
    end type
end module Elem_class

module Vect
    use Vect_class

    type, extends(Vect_Type) :: Vect2D 
       real :: X,Y
    end type Vect2D   

    type, extends(Vect_Type) :: Vect3D 
       real :: X,Y,Z
    end type Vect3D   
end module Vect

module Elem
    use Elem_class

    type, extends(Elem_type)  :: elem2D
    end type
end module Elem

program testElem
    use Vect_class
    use Vect
    use Elem_class
    use Elem

    type(Vect2D) :: a
    type(Vect3D) :: b
    class(Vect_type),allocatable :: c,d
    class(Elem_type),allocatable :: e
    real       :: x,y,z

    x = 1.0
    y =-2.0
    z = 3.0

    a = Vect2D(x,y)
    b = Vect3D(x,y,z)
    c = Vect2D(x,y)
    d = Vect3D(x,y,z)
    e = Elem2D(10,b)
    write(*,*) e%numDof
end program testElem

It fails to compile with error message with GNU Fortran (GCC) 11.2.1 20210728
(Red Hat 11.2.1-1) (RHEL7 devtoolset 11)

   53 |     e = Elem2D(10,b)
      |                  1
Error: Cannot convert TYPE(vect3d) to CLASS(__class_vect_class_Vect_type_a) at
(1)

Under macOS (monterey, M1 processor) GNU Fortran (Homebrew GCC 11.3.0_1)
11.3.0, I get an ICE:

TestNestedClass3.f90:53:20:

   53 |     e = Elem2D(10,b)
      |                    1
internal compiler error: in fold_convert_loc, at fold-const.c:2563