[FixIrreducible] Use CycleInfo instead of a custom SCC traversal

llvm/include/llvm/ADT/GenericCycleInfo.h

@@ -107,6 +107,13 @@ template <typename ContextT> class GenericCycle {
     return is_contained(Entries, Block);
   }
 
+  /// \brief Replace all entries with \p Block as single entry.
+  void setSingleEntry(BlockT *Block) {
+    assert(contains(Block));
+    Entries.clear();
+    Entries.push_back(Block);
+  }
+
   /// \brief Return whether \p Block is contained in the cycle.
   bool contains(const BlockT *Block) const { return Blocks.contains(Block); }
 
@@ -192,11 +199,16 @@ template <typename ContextT> class GenericCycle {
   //@{
   using const_entry_iterator =
       typename SmallVectorImpl<BlockT *>::const_iterator;
-
+  const_entry_iterator entry_begin() const { return Entries.begin(); }
+  const_entry_iterator entry_end() const { return Entries.end(); }
   size_t getNumEntries() const { return Entries.size(); }
   iterator_range<const_entry_iterator> entries() const {
-    return llvm::make_range(Entries.begin(), Entries.end());
+    return llvm::make_range(entry_begin(), entry_end());
   }
+  using const_reverse_entry_iterator =
+      typename SmallVectorImpl<BlockT *>::const_reverse_iterator;
+  const_reverse_entry_iterator entry_rbegin() const { return Entries.rbegin(); }
+  const_reverse_entry_iterator entry_rend() const { return Entries.rend(); }
   //@}
 
   Printable printEntries(const ContextT &Ctx) const {
@@ -255,12 +267,6 @@ template <typename ContextT> class GenericCycleInfo {
   /// the subtree.
   void moveTopLevelCycleToNewParent(CycleT *NewParent, CycleT *Child);
 
-  /// Assumes that \p Cycle is the innermost cycle containing \p Block.
-  /// \p Block will be appended to \p Cycle and all of its parent cycles.
-  /// \p Block will be added to BlockMap with \p Cycle and
-  /// BlockMapTopLevel with \p Cycle's top level parent cycle.
-  void addBlockToCycle(BlockT *Block, CycleT *Cycle);
-
 public:
   GenericCycleInfo() = default;
   GenericCycleInfo(GenericCycleInfo &&) = default;
@@ -278,6 +284,12 @@ template <typename ContextT> class GenericCycleInfo {
   unsigned getCycleDepth(const BlockT *Block) const;
   CycleT *getTopLevelParentCycle(BlockT *Block);
 
+  /// Assumes that \p Cycle is the innermost cycle containing \p Block.
+  /// \p Block will be appended to \p Cycle and all of its parent cycles.
+  /// \p Block will be added to BlockMap with \p Cycle and
+  /// BlockMapTopLevel with \p Cycle's top level parent cycle.
+  void addBlockToCycle(BlockT *Block, CycleT *Cycle);
+
   /// Methods for debug and self-test.
   //@{
   void verifyCycleNest(bool VerifyFull = false) const;