[llvm] [CycleAnalysis] Methods to verify cycles and their nesting. (PR #102300)

[Sameer Sahasrabuddhe via llvm-commits]

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@@ -119,6 +120,104 @@ auto GenericCycle<ContextT>::getCyclePredecessor() const -> BlockT * {
   return Out;
 }
 
+/// \brief Verify that this is actually a well-formed cycle in the CFG.
+template <typename ContextT> void GenericCycle<ContextT>::verifyCycle() const {
+#ifndef NDEBUG
+  assert(!Blocks.empty() && "Cycle cannot be empty.");
+  DenseSet<BlockT *> Blocks;
+  for (BlockT *BB : blocks()) {
+    assert(Blocks.insert(BB).second); // duplicates in block list?
+  }
+  assert(!Entries.empty() && "Cycle must have one or more entries.");
+
+  DenseSet<BlockT *> Entries;
+  for (BlockT *Entry : entries()) {
+    assert(Entries.insert(Entry).second); // duplicate entry?
+    assert(contains(Entry));
+  }
+
+  // Setup for using a depth-first iterator to visit every block in the cycle.
+  SmallVector<BlockT *, 8> ExitBBs;
+  getExitBlocks(ExitBBs);
+  df_iterator_default_set<BlockT *> VisitSet;
+  VisitSet.insert(ExitBBs.begin(), ExitBBs.end());
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ssahasra wrote:

That constructor exists in SmallPtrSet, but turns out that it is not exposed in df_iterator, which is a derived class. So have to go with the default constructor instead.

https://github.com/llvm/llvm-project/pull/102300