[Bug fortran/126517] New: Assigning an unallocated allocatable function result array to an allocatable causes segmentation fault

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126517

            Bug ID: 126517
           Summary: Assigning an unallocated allocatable function result
                    array to an allocatable causes segmentation fault
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mikael at gcc dot gnu.org
  Target Milestone: ---

Example assigning (unallocated) allocatable function results to allocatable
variables:

program p
  implicit none
  type :: t1
    integer :: c1
  end type
  type, extends(t1) :: t2
    integer :: c2
  end type
  type(t1), allocatable :: ta(:)
  class(t1), allocatable :: ca(:), ca2(:)

  print *, allocated(ta)
  ta = t1_alloc()
  !print *, allocated(ta)
  !allocate(ta(5))
  !ta = t1_alloc()
  !print *, allocated(ta)

  print *, allocated(ca)
  ca = t1_alloc()
  print *, allocated(ca)
  allocate(ca(5))
  ca = t1_alloc()
  print *, allocated(ca)

  print *, allocated(ca2)
  !ca2 = class_alloc()
  !print *, allocated(ca2)
  !allocate(t2 :: ca2(5))
  !ca2 = class_alloc()
  !print *, allocated(ca2)

contains
  function t1_alloc()
    type(t1), allocatable :: t1_alloc(:)
  end function
  function class_alloc()
    class(t1), allocatable :: class_alloc(:)
  end function
end program


The non commented lines are the ones that work.
Uncommenting the lines either in the first block or in the third one cause a
segfault at runtime.
My expectation is that with all the lines enabled it should print False nine
times.

I think the program is valid, but I can't find anything in the standard
explicitly allowing an allocatable function to return an unallocated value.