tree bd823fe542a37febe84d83a3597a6a48ec46ec30
parent dd429fa8c88bd8a1f416ab7a456b0ac984f99473
author Florian Hahn <flo@fhahn.com> 1618679767 +0100
committer Copybara-Service <copybara-worker@google.com> 1618720490 -0700

[ADT] Update RPOT to work with specializations of different types.

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

GitOrigin-RevId: d91f864ced6eebe8db35c092c8da29e87cd882b2