[flang][fir] handle poly to non poly case in rebox_assumed_rank (#95240)

Dynamic type and element size of the descriptor dummy must match the
dummy static type when the dummy is not polymorphic, otherwise
IS_CONTIGUOUS, C_SIZEOF.... won't work properly inside the callee.

When the actual argument is polymorphic the descriptor of the actual may
have a different dynamic type/element size. Hence, the dummy argument
cannot simply take or copy the descriptor of the actual argument.

Author: jeanPerier

flang/lib/Optimizer/Transforms/AssumedRankOpConversion.cpp

@@ -84,7 +84,9 @@ class ReboxAssumedRankConv
     auto oldBoxType = mlir::cast<fir::BaseBoxType>(
         fir::unwrapRefType(rebox.getBox().getType()));
     auto newDerivedType = mlir::dyn_cast<fir::RecordType>(newEleType);
-    if (newDerivedType && (newEleType != oldBoxType.unwrapInnerType()) &&
+    if (newDerivedType && !fir::isPolymorphicType(newBoxType) &&
+        (fir::isPolymorphicType(oldBoxType) ||
+         (newEleType != oldBoxType.unwrapInnerType())) &&
         !fir::isPolymorphicType(newBoxType)) {
       newDtype = builder.create<fir::TypeDescOp>(
           loc, mlir::TypeAttr::get(newDerivedType));

flang/test/Fir/rebox_assumed_rank_codegen.fir

@@ -34,10 +34,18 @@ func.func @test_new_dtype(%arg0: !fir.box<!fir.array<*:!t2>> ) {
   return
 }
 
+!sometype = !fir.type<sometype{i:i32}>
+func.func @test_poly_to_nonepoly(%arg0: !fir.class<!fir.array<*:!sometype>>) {
+  %1 = fir.rebox_assumed_rank %arg0 lbs ones : (!fir.class<!fir.array<*:!sometype>>) -> !fir.box<!fir.array<*:!sometype>>
+  fir.call @takes_assumed_rank_t(%1) : (!fir.box<!fir.array<*:!sometype>>) -> ()
+  return
+}
+
 func.func private @somefunc(!fir.box<!fir.array<*:f32>>)
 func.func private @somefuncalloc(!fir.box<!fir.heap<!fir.array<*:f32>>>)
 func.func private @somefuncpointer(!fir.box<!fir.ptr<!fir.array<*:f32>>>)
 func.func private @somefunct1(!fir.box<!fir.array<*:!t1>>)
+func.func private @takes_assumed_rank_t(!fir.box<!fir.array<*:!sometype>>)
 
 // CHECK-LABEL:   func.func @test_simple(
 // CHECK-SAME:                           %[[VAL_0:.*]]: !fir.box<!fir.array<*:f32>>) {
@@ -108,4 +116,9 @@ func.func private @somefunct1(!fir.box<!fir.array<*:!t1>>)
 // CHECK:           return
 // CHECK:         }
 
+// CHECK-LABEL:   func.func @test_poly_to_nonepoly(
+// CHECK:           %[[VAL_4:.*]] = fir.type_desc !fir.type<sometype{i:i32}>
+// CHECK:           %[[VAL_7:.*]] = fir.convert %[[VAL_4]] : (!fir.tdesc<!fir.type<sometype{i:i32}>>) -> !fir.ref<none>
+// CHECK:           %[[VAL_8:.*]] = fir.call @_FortranACopyAndUpdateDescriptor(%{{.*}}, %{{.*}}, %[[VAL_7]],
+
 // CHECK:         func.func private @_FortranACopyAndUpdateDescriptor(!fir.ref<!fir.box<none>> {llvm.nocapture}, !fir.box<none> {llvm.nocapture}, !fir.ref<none>, i8, i32) -> none attributes {fir.runtime}