[Bug fortran/97920] New: [FINAL] -O2 segment fault due to extend derive type's member being partially allocated

[xin.liu@compiler-dev.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97920

            Bug ID: 97920
           Summary: [FINAL] -O2  segment fault due to extend derive type's
                    member being partially allocated
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: xin.liu@compiler-dev.com
  Target Milestone: ---

Consider the following Fortran testcase:
module m
  type t1
    real, dimension(:), pointer :: a
  contains
    final :: t1f
  end type

  type, extends(t1) :: t2
    real, dimension(:), pointer :: b
  contains
    final :: t2f
  end type

contains
  subroutine t1f(x)
    type(t1) :: x
    if (associated(x%a)) deallocate(x%a)
  end subroutine

  subroutine t2f(x)
    type(t2) :: x
    if (associated(x%b)) deallocate(x%b)
  end subroutine
end module

subroutine test
  use m
  implicit none
  type(t1) :: a
  type(t2) :: b

  allocate(b%a(3))
!  allocate(b%b(3))
end subroutine

program p
  use m
  call test()
end program

Compiled with gfortran 10.1.0 in -O2, the testcase prints:

Program received signal SIGSEGV: Segmentation fault - invalid memory reference.

If add a statement as 'allocate(b%b(3))', it will pass with no segment fault.I
guess this segment fault maybe due to extend derive type's member being
partially allocated.