Fortran] PR91586 Fix ICE on invalid code with CLASS

        gcc/fortran/
        PR fortran/91586
        * class.c (gfc_find_derived_vtab): Return NULL
        instead of deref'ing NULL pointer.

        gcc/testsuite/
        PR fortran/91586
        * gfortran.dg/class_71.f90: New.

From-SVN: r277153

gcc/fortran/ChangeLog

+2019-10-18  Tobias Burnus  <tobias@codesourcery.com>
+
+	PR fortran/91586
+	* class.c (gfc_find_derived_vtab): Return NULL
+	instead of deref'ing NULL pointer.
+
 2019-10-15  James Norris  <jnorris@codesourcery.com>
 	    Tobias Burnus  <tobias@codesourcery.com>
 

gcc/fortran/class.c

@@ -2241,6 +2241,9 @@ gfc_find_derived_vtab (gfc_symbol *derived)
   if (!derived->attr.unlimited_polymorphic && derived->attr.is_class)
     derived = gfc_get_derived_super_type (derived);
 
+  if (!derived)
+    return NULL;
+
   /* Find the gsymbol for the module of use associated derived types.  */
   if ((derived->attr.use_assoc || derived->attr.used_in_submodule)
        && !derived->attr.vtype && !derived->attr.is_class)

gcc/testsuite/ChangeLog

+2019-10-18  Tobias Burnus  <tobias@codesourcery.com>
+
+	PR fortran/91586
+	* gfortran.dg/class_71.f90: New.
+
 2019-10-18  Georg-Johann Lay  <avr@gjlay.de>
 
 	Fix some fallout for small targets.

gcc/testsuite/gfortran.dg/class_71.f90

+! { dg-do compile }
+!
+! PR fortran/91586
+!
+! Contributed by G. Steinmetz
+!
+program p
+   type t
+      class(*), allocatable :: a
+   end type
+   class(t) :: x, y  ! { dg-error "must be dummy, allocatable or pointer" }
+   y = x  ! { dg-error "Nonallocatable variable must not be polymorphic in intrinsic assignment" }
+end