Fortran: fix bounds-checking errors for CLASS array dummies [PR104908]

Commit r11-1235 addressed issues with bounds of unlimited polymorphic array
dummies.  However, using the descriptor from sym->backend_decl does break
the case of CLASS array dummies.  The obvious solution is to restrict the
fix to the unlimited polymorphic case, thus keeping the original descriptor
in the ordinary case.

gcc/fortran/ChangeLog:

	PR fortran/104908
	* trans-array.cc (gfc_conv_array_ref): Restrict use of transformed
	descriptor (sym->backend_decl) to the unlimited polymorphic case.

gcc/testsuite/ChangeLog:

	PR fortran/104908
	* gfortran.dg/pr104908.f90: New test.

gcc/fortran/trans-array.cc

@@ -4063,7 +4063,10 @@ gfc_conv_array_ref (gfc_se * se, gfc_array_ref * ar, gfc_expr *expr,
     }
 
   decl = se->expr;
-  if (IS_CLASS_ARRAY (sym) && sym->attr.dummy && ar->as->type != AS_DEFERRED)
+  if (UNLIMITED_POLY(sym)
+      && IS_CLASS_ARRAY (sym)
+      && sym->attr.dummy
+      && ar->as->type != AS_DEFERRED)
     decl = sym->backend_decl;
 
   cst_offset = offset = gfc_index_zero_node;

gcc/testsuite/gfortran.dg/pr104908.f90

@@ -0,0 +1,32 @@
+! { dg-do compile }
+! { dg-additional-options "-fcheck=bounds -fdump-tree-original" }
+!
+! PR fortran/104908 - incorrect out-of-bounds runtime error
+
+program test
+  implicit none
+  type vec
+     integer :: x(3) = [2,4,6]
+  end type vec
+  type(vec) :: w(2)
+  call sub(w)
+contains
+  subroutine sub (v)
+    class(vec), intent(in) :: v(:)
+    integer :: k, q(3)
+    q = [ (v(1)%x(k), k = 1, 3) ]   ! <-- was failing here after r11-1235
+    print *, q
+  end
+end
+
+subroutine sub2 (zz)
+  implicit none
+  type vec
+     integer :: x(2,1)
+  end type vec
+  class(vec), intent(in) :: zz(:)   ! used to ICE after r11-1235
+  integer :: k
+  k = zz(1)%x(2,1)
+end
+
+! { dg-final { scan-tree-dump-times " above upper bound " 4 "original" } }