[Bug fortran/108921] New: ICE: using the result of an impure function in automatic character allocation

["vterzi1996 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108921

            Bug ID: 108921
           Summary: ICE: using the result of an impure function in
                    automatic character allocation
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vterzi1996 at gmail dot com
  Target Milestone: ---

Created attachment 54527
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54527&action=edit
Complete backtrace

Consider the following minimal working example:
```
module lib
    type t
    contains
        procedure::f,g
    end type
contains
    integer function f(this)
        class(t),intent(in)::this
        f=10
    end
    function g(this)result(r)
        class(t),intent(in)::this
        character(len=this%f())::r  ! problem appears here
        r='42'
    end
end

program prog
    use lib
    type(t)::o
    print*,o%g()
end
```

This example was already discussed here:
https://stackoverflow.com/questions/75544072/using-function-result-as-character-length-in-fortran

The compilation of this code with the GNU compiler (gfortran 12.2.0 on Rocky
Linux 8.7) fails with the message `f951: internal compiler error: Segmentation
fault` (full output is in the attachment). It also fails with 7.5.0, 9.4.0, and
11.1.0 on Ubuntu 18.04.2 LTS. The reason for this problem is the unallowed
usage of the result of an impure function (here: `f`) in the automatic
allocation of the CHARACTER variable, but the compiler fails to identify the
mistake in the code.