At the moment, ReversePostOrderTraversal performs a post-order walk on
the entry node of the passed in graph, rather than the graph type
itself.
If GT::NodeRef is the same as GraphT, everything works as expected and
this is the case for the current uses in-tree. But it does not work as
expected if GraphT != GT::NodeRef. In that case, we either fail to build
(if there is no GraphTrait specialization for GT:NodeRef) or we pick the
GraphTrait specialization for GT::NodeRef, instead of the specialization
of GraphT.
Both the depth-first and post-order iterators pick the expected
specalization and this patch updates ReversePostOrderTraversal to
delegate to po_begin & po_end to pick the right specialization, rather
than forcing using GraphTraits<GT::NodeRef>, by first getting the entry
node.
This makes `ReversePostOrderTraversal<Graph<6>> RPOT(G);` build and
work as expected in the test.
Reviewed By: dexonsmith
Differential Revision: https://reviews.llvm.org/D100169
bd2bad88ac