(towards #2971) move ACC loop trans and OMP parallel loop trans

[victoria-atkinson]

No description provided.

[arporter]

Sorry to crash the party but I've just found a bug in OMPParallelTrans and, since I think you're moving it in this PR, it would be good to fix it. We have:

    def validate(self, node_list, options=None):
        '''
        Perform OpenMP-specific validation checks.

        :param node_list: list of Nodes to put within parallel region.
        :type node_list: list of :py:class:`psyclone.psyir.nodes.Node`
        :param options: a dictionary with options for transformations.
        :type options: Optional[Dict[str, Any]]
        :param bool options["node-type-check"]: this flag controls if the \
                type of the nodes enclosed in the region should be tested \
                to avoid using unsupported nodes inside a region.

        :raises TransformationError: if the target Nodes are already within \
                                     some OMP parallel region.
        '''
        if node_list[0].ancestor(OMPDirective):
            raise TransformationError("Error in OMPParallel transformation:" +
                                      " cannot create an OpenMP PARALLEL " +
                                      "region within another OpenMP region.")

and thus we fall over if the supplied node_list is a single Node. Since RegionTrans (which this class inherits from) permits node_list to be a single Node, this class should too. I think all that is needed is to add:

        node_list = self.get_node_list(node_list)
        if node_list[0].ancestor....

We'd also need to add a new test that calling OMPParallelTrans.validate works OK if provided with just a single Node rather than a list.