[llvm] [FixIrreducible] Use CycleInfo instead of a custom SCC traversal (PR #101386)

[Jakub Kuderski via llvm-commits]

================
@@ -189,6 +195,21 @@ template <typename ContextT> class GenericCycle {
   //@{
   using const_entry_iterator =
       typename SmallVectorImpl<BlockT *>::const_iterator;
+  const_entry_iterator entry_begin() const {
+    return const_entry_iterator{Entries.begin()};
----------------
kuhar wrote:

nit: you should be able to drop the redundant return types here and below
```suggestion
    return {Entries.begin()};
```

https://github.com/llvm/llvm-project/pull/101386