[PATCH] D100169: [ADT] Update RPOT to work with specializations of different types.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: dexonsmith, dblaikie, bkramer, nhaehnle.
fhahn requested review of this revision.
Herald added a project: LLVM.

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.

The patch also updates a couple of functions that unnecessarily took the
input graph by value, when it was not needed. They can take the graph by
const-reference instead, which does not require GraphT to provide a copy
constructor. This technically is a separate change, but is required to
be able to use Graph<> from TestGraph in the test, because it does not
provide a copy constructor. If desired, I can split this out as a
separate change.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D100169

Files:
  llvm/include/llvm/ADT/PostOrderIterator.h
  llvm/unittests/ADT/PostOrderIteratorTest.cpp


Index: llvm/unittests/ADT/PostOrderIteratorTest.cpp
===================================================================
--- llvm/unittests/ADT/PostOrderIteratorTest.cpp
+++ llvm/unittests/ADT/PostOrderIteratorTest.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 #include "llvm/ADT/PostOrderIterator.h"
+#include "TestGraph.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
 #include "gtest/gtest.h"
@@ -33,4 +34,40 @@
   auto PIExt = po_ext_end(NullBB, Ext);
   PIExt.insertEdge(Optional<BasicBlock *>(), NullBB);
 }
+
+// Test post-order and reverse post-order traversals for simple graph type.
+TEST(PostOrderIteratorTest, PostOrderAndReversePostOrderTraverrsal) {
+  Graph<6> G;
+  G.AddEdge(0, 1);
+  G.AddEdge(0, 2);
+  G.AddEdge(0, 3);
+  G.AddEdge(1, 4);
+  G.AddEdge(2, 5);
+  G.AddEdge(5, 2);
+  G.AddEdge(2, 4);
+  G.AddEdge(1, 4);
+
+  SmallVector<int> FromIterator;
+  for (auto N : post_order(G))
+    FromIterator.push_back(N->first);
+  EXPECT_EQ(6u, FromIterator.size());
+  EXPECT_EQ(4, FromIterator[0]);
+  EXPECT_EQ(1, FromIterator[1]);
+  EXPECT_EQ(5, FromIterator[2]);
+  EXPECT_EQ(2, FromIterator[3]);
+  EXPECT_EQ(3, FromIterator[4]);
+  EXPECT_EQ(0, FromIterator[5]);
+  FromIterator.clear();
+
+  ReversePostOrderTraversal<Graph<6>> RPOT(G);
+  for (auto N : RPOT)
+    FromIterator.push_back(N->first);
+  EXPECT_EQ(6u, FromIterator.size());
+  EXPECT_EQ(0, FromIterator[0]);
+  EXPECT_EQ(3, FromIterator[1]);
+  EXPECT_EQ(2, FromIterator[2]);
+  EXPECT_EQ(5, FromIterator[3]);
+  EXPECT_EQ(1, FromIterator[4]);
+  EXPECT_EQ(4, FromIterator[5]);
+}
 }
Index: llvm/include/llvm/ADT/PostOrderIterator.h
===================================================================
--- llvm/include/llvm/ADT/PostOrderIterator.h
+++ llvm/include/llvm/ADT/PostOrderIterator.h
@@ -138,15 +138,15 @@
   using pointer = typename super::pointer;
 
   // Provide static "constructors"...
-  static po_iterator begin(GraphT G) {
+  static po_iterator begin(const GraphT &G) {
     return po_iterator(GT::getEntryNode(G));
   }
-  static po_iterator end(GraphT G) { return po_iterator(); }
+  static po_iterator end(const GraphT &G) { return po_iterator(); }
 
-  static po_iterator begin(GraphT G, SetType &S) {
+  static po_iterator begin(const GraphT &G, SetType &S) {
     return po_iterator(GT::getEntryNode(G), S);
   }
-  static po_iterator end(GraphT G, SetType &S) { return po_iterator(S); }
+  static po_iterator end(const GraphT &G, SetType &S) { return po_iterator(S); }
 
   bool operator==(const po_iterator &x) const {
     return VisitStack == x.VisitStack;
@@ -290,15 +290,15 @@
 
   std::vector<NodeRef> Blocks; // Block list in normal PO order
 
-  void Initialize(NodeRef BB) {
-    std::copy(po_begin(BB), po_end(BB), std::back_inserter(Blocks));
+  void Initialize(const GraphT &G) {
+    std::copy(po_begin(G), po_end(G), std::back_inserter(Blocks));
   }
 
 public:
   using rpo_iterator = typename std::vector<NodeRef>::reverse_iterator;
   using const_rpo_iterator = typename std::vector<NodeRef>::const_reverse_iterator;
 
-  ReversePostOrderTraversal(GraphT G) { Initialize(GT::getEntryNode(G)); }
+  ReversePostOrderTraversal(const GraphT &G) { Initialize(G); }
 
   // Because we want a reverse post order, use reverse iterators from the vector
   rpo_iterator begin() { return Blocks.rbegin(); }


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