[flang] Keep a fir.box type when doing an array of derived type component

[clementval]

Summary

When referencing a single component from a polymorphic array in an expression,
the rebox operation should output a boxed array of that component type and
not a polymorphic boxed array as it was done.

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/lib/Lower/ConvertExpr.cpp

CC genarr(const ExtValue &extMemref, ComponentPath &components) {
     if (destShape.empty())
       destShape = getShape(arrayOperands.back());
     if (isBoxValue()) {
       // Semantics are a reference to a boxed array.
       // This case just requires that an embox operation be created to box the
       // value. The value of the box is forwarded in the continuation.
       mlir::Type reduceTy = reduceRank(arrTy, slice);
       mlir::Type boxTy = fir::BoxType::get(reduceTy);
-      if (memref.getType().isa<fir::ClassType>())
+      if (memref.getType().isa<fir::ClassType>() && !components.hasComponents())
         boxTy = fir::ClassType::get(reduceTy);
       if (components.substring) {
         // Adjust char length to substring size.
         fir::CharacterType charTy =
             fir::factory::CharacterExprHelper::getCharType(reduceTy);
         auto seqTy = reduceTy.cast<fir::SequenceType>();
         // TODO: Use a constant for fir.char LEN if we can compute it.
         boxTy = fir::BoxType::get(

flang/test/Lower/polymorphic.f90

 
 ! CHECK-LABEL: func.func @_QMpolymorphic_testPtest_poly_pointer_null() {
 ! CHECK: %[[ALLOCA:.*]] = fir.alloca !fir.class<!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>
 ! CHECK: %[[ZERO:.*]] = fir.zero_bits !fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>
 ! CHECK: %[[EMBOX:.*]] = fir.embox %[[ZERO]] : (!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>) -> !fir.class<!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>
 ! CHECK: fir.store %[[EMBOX]] to %[[ALLOCA]] : !fir.ref<!fir.class<!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>>
 ! CHECK: fir.call @_QMpolymorphic_testPpass_poly_pointer_optional(%[[ALLOCA]]) fastmath<contract> : (!fir.ref<!fir.class<!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>>) -> ()
 
+  subroutine test_poly_array_component_output(p)
+    class(p1), pointer :: p(:)
+    print*, p(:)%a
+  end subroutine
+
+! CHECK-LABEL: func.func @_QMpolymorphic_testPtest_poly_array_component_output(
+! CHECK-SAME: %[[P]]: !fir.ref<!fir.class<!fir.ptr<!fir.array<?x!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>>> {fir.bindc_name = "p"}) {
+! CHECK: %[[LOAD_P:.*]] = fir.load %[[P]] : !fir.ref<!fir.class<!fir.ptr<!fir.array<?x!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>>>
+! CHECK: %[[FIELD_INDEX_A:.*]] = fir.field_index a, !fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>
+! CHECK: %[[SLICE:.*]] = fir.slice %{{.*}}#0, %{{.*}}, %{{.*}} path %[[FIELD_INDEX_A]] : (index, index, index, !fir.field) -> !fir.slice<1>
+! CHECK: %[[REBOX:.*]] = fir.rebox %[[LOAD_P]](%{{.*}}) [%[[SLICE]]] : (!fir.class<!fir.ptr<!fir.array<?x!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>>, !fir.shift<1>, !fir.slice<1>) -> !fir.box<!fir.array<?xi32>>
+! CHECK: %[[BOX_NONE:.*]] = fir.convert %[[REBOX]] : (!fir.box<!fir.array<?xi32>>) -> !fir.box<none>
+! CHECK: %{{.*}} = fir.call @_FortranAioOutputDescriptor(%{{.*}}, %[[BOX_NONE]]) fastmath<contract> : (!fir.ref<i8>, !fir.box<none>) -> i1
+
 end module
 
 program test
   use polymorphic_test
   type(outer), allocatable :: o
   integer :: i(5)
   logical :: l(5)
   allocate(o)