[flang][hlfir] Fixed nullptr dereference.

[vzakhari]

Summary

In case of unlimited polymorphic type, there is no derived type
spec, so use NoneType explicitly.

[tblah]

LGTM, thanks!

flang/lib/Lower/ConvertExprToHLFIR.cpp

if constexpr (R::category == Fortran::common::TypeCategory::Character) {
       unaryOp.genResultTypeParams(loc, builder, left, typeParams);
     }
     if (rank == 0)
       return unaryOp.gen(loc, builder, op.derived(), left);
 
     // Elemental expression.
     mlir::Type elementType;
     if constexpr (R::category == Fortran::common::TypeCategory::Derived) {
+      if (op.derived().GetType().IsUnlimitedPolymorphic())
+        elementType = mlir::NoneType::get(builder.getContext());
+      else
         elementType = Fortran::lower::translateDerivedTypeToFIRType(
             getConverter(), op.derived().GetType().GetDerivedTypeSpec());
     } else {
       elementType =
           Fortran::lower::getFIRType(builder.getContext(), R::category, R::kind,
                                      /*params=*/std::nullopt);
     }
     mlir::Value shape = hlfir::genShape(loc, builder, left);
     auto genKernel = [&op, &left, &unaryOp](
                          mlir::Location l, fir::FirOpBuilder &b,

flang/test/Lower/HLFIR/elemental-array-ops.f90

 ! CHECK:             %[[VAL_9:.*]] = hlfir.designate %[[VAL_3]]#0 (%[[VAL_8]])  : (!fir.class<!fir.array<?x!fir.type<_QFpolymorphic_parenthesisTt>>>, index) -> !fir.class<!fir.type<_QFpolymorphic_parenthesisTt>>
 ! CHECK:             %[[VAL_10:.*]] = hlfir.as_expr %[[VAL_9]] : (!fir.class<!fir.type<_QFpolymorphic_parenthesisTt>>) -> !hlfir.expr<!fir.type<_QFpolymorphic_parenthesisTt>?>
 ! CHECK:             hlfir.yield_element %[[VAL_10]] : !hlfir.expr<!fir.type<_QFpolymorphic_parenthesisTt>?>
 ! CHECK:           }
 ! CHECK:           hlfir.assign %[[VAL_7]] to %[[VAL_2]]#0 realloc : !hlfir.expr<?x!fir.type<_QFpolymorphic_parenthesisTt>?>, !fir.ref<!fir.class<!fir.heap<!fir.array<?x!fir.type<_QFpolymorphic_parenthesisTt>>>>>
 ! CHECK:           hlfir.destroy %[[VAL_7]] : !hlfir.expr<?x!fir.type<_QFpolymorphic_parenthesisTt>?>
 ! CHECK:           return
 ! CHECK:         }
+
+subroutine unlimited_polymorphic_parenthesis(x, y)
+  class(*), allocatable :: x(:)
+  class(*), intent(in) :: y(:)
+  x = (y)
+end subroutine unlimited_polymorphic_parenthesis
+! CHECK-LABEL:   func.func @_QPunlimited_polymorphic_parenthesis(
+! CHECK-SAME:        %[[VAL_0:.*]]: !fir.ref<!fir.class<!fir.heap<!fir.array<?xnone>>>> {fir.bindc_name = "x"},
+! CHECK-SAME:        %[[VAL_1:.*]]: !fir.class<!fir.array<?xnone>> {fir.bindc_name = "y"}) {
+! CHECK:           %[[VAL_2:.*]]:2 = hlfir.declare %[[VAL_0]] {fortran_attrs = #fir.var_attrs<allocatable>, uniq_name = "_QFunlimited_polymorphic_parenthesisEx"} : (!fir.ref<!fir.class<!fir.heap<!fir.array<?xnone>>>>) -> (!fir.ref<!fir.class<!fir.heap<!fir.array<?xnone>>>>, !fir.ref<!fir.class<!fir.heap<!fir.array<?xnone>>>>)
+! CHECK:           %[[VAL_3:.*]]:2 = hlfir.declare %[[VAL_1]] {fortran_attrs = #fir.var_attrs<intent_in>, uniq_name = "_QFunlimited_polymorphic_parenthesisEy"} : (!fir.class<!fir.array<?xnone>>) -> (!fir.class<!fir.array<?xnone>>, !fir.class<!fir.array<?xnone>>)
+! CHECK:           %[[VAL_4:.*]] = arith.constant 0 : index
+! CHECK:           %[[VAL_5:.*]]:3 = fir.box_dims %[[VAL_3]]#0, %[[VAL_4]] : (!fir.class<!fir.array<?xnone>>, index) -> (index, index, index)
+! CHECK:           %[[VAL_6:.*]] = fir.shape %[[VAL_5]]#1 : (index) -> !fir.shape<1>
+! CHECK:           %[[VAL_7:.*]] = hlfir.elemental %[[VAL_6]] mold %[[VAL_3]]#0 unordered : (!fir.shape<1>, !fir.class<!fir.array<?xnone>>) -> !hlfir.expr<?xnone?> {
+! CHECK:           ^bb0(%[[VAL_8:.*]]: index):
+! CHECK:             %[[VAL_9:.*]] = hlfir.designate %[[VAL_3]]#0 (%[[VAL_8]])  : (!fir.class<!fir.array<?xnone>>, index) -> !fir.class<none>
+! CHECK:             %[[VAL_10:.*]] = hlfir.as_expr %[[VAL_9]] : (!fir.class<none>) -> !hlfir.expr<none?>
+! CHECK:             hlfir.yield_element %[[VAL_10]] : !hlfir.expr<none?>
+! CHECK:           }
+! CHECK:           hlfir.assign %[[VAL_7]] to %[[VAL_2]]#0 realloc : !hlfir.expr<?xnone?>, !fir.ref<!fir.class<!fir.heap<!fir.array<?xnone>>>>
+! CHECK:           hlfir.destroy %[[VAL_7]] : !hlfir.expr<?xnone?>
+! CHECK:           return
+! CHECK:         }