[DomTreeUpdater] Move critical edge splitting code to updater (#115111)

Support critical edge splitting in dominator tree updater. Continue the
work in #100856.

Compile time check:
https://llvm-compile-time-tracker.com/compare.php?from=87c35d782795b54911b3e3a91a5b738d4d870e55&to=42b3e5623a9ab4c3648564dc0926b36f3b438a3a&stat=instructions%3Au

Author: paperchalice

llvm/include/llvm/Analysis/DomTreeUpdater.h

@@ -81,6 +81,9 @@ class DomTreeUpdater
 
   ///@}
 
+  /// Debug method to help view the internal state of this class.
+  LLVM_DUMP_METHOD void dump() const;
+
 private:
   class CallBackOnDeletion final : public CallbackVH {
   public:
@@ -109,9 +112,6 @@ class DomTreeUpdater
 
   /// Returns true if at least one BasicBlock is deleted.
   bool forceFlushDeletedBB();
-
-  /// Debug method to help view the internal state of this class.
-  LLVM_DUMP_METHOD void dump() const;
 };
 
 extern template class GenericDomTreeUpdater<DomTreeUpdater, DominatorTree,
@@ -120,6 +120,13 @@ extern template class GenericDomTreeUpdater<DomTreeUpdater, DominatorTree,
 extern template void
 GenericDomTreeUpdater<DomTreeUpdater, DominatorTree,
                       PostDominatorTree>::recalculate(Function &F);
+
+extern template void
+GenericDomTreeUpdater<DomTreeUpdater, DominatorTree, PostDominatorTree>::
+    applyUpdatesImpl</*IsForward=*/true>();
+extern template void
+GenericDomTreeUpdater<DomTreeUpdater, DominatorTree, PostDominatorTree>::
+    applyUpdatesImpl</*IsForward=*/false>();
 } // namespace llvm
 
 #endif // LLVM_ANALYSIS_DOMTREEUPDATER_H

llvm/include/llvm/Analysis/GenericDomTreeUpdater.h

@@ -30,6 +30,7 @@ class GenericDomTreeUpdater {
 public:
   enum class UpdateStrategy : unsigned char { Eager = 0, Lazy = 1 };
   using BasicBlockT = typename DomTreeT::NodeType;
+  using UpdateT = typename DomTreeT::UpdateType;
 
   explicit GenericDomTreeUpdater(UpdateStrategy Strategy_)
       : Strategy(Strategy_) {}
@@ -146,7 +147,12 @@ class GenericDomTreeUpdater {
   /// 2. It is illegal to submit any update that has already been submitted,
   /// i.e., you are supposed not to insert an existent edge or delete a
   /// nonexistent edge.
-  void applyUpdates(ArrayRef<typename DomTreeT::UpdateType> Updates);
+  void applyUpdates(ArrayRef<UpdateT> Updates);
+
+  /// Apply updates that the critical edge (FromBB, ToBB) has been
+  /// split with NewBB.
+  void splitCriticalEdge(BasicBlockT *FromBB, BasicBlockT *ToBB,
+                         BasicBlockT *NewBB);
 
   /// Submit updates to all available trees. It will also
   /// 1. discard duplicated updates,
@@ -169,7 +175,7 @@ class GenericDomTreeUpdater {
   /// 3. It is only legal to submit updates to an edge in the order CFG changes
   /// are made. The order you submit updates on different edges is not
   /// restricted.
-  void applyUpdatesPermissive(ArrayRef<typename DomTreeT::UpdateType> Updates);
+  void applyUpdatesPermissive(ArrayRef<UpdateT> Updates);
 
   ///@}
 
@@ -205,7 +211,25 @@ class GenericDomTreeUpdater {
   LLVM_DUMP_METHOD void dump() const;
 
 protected:
-  SmallVector<typename DomTreeT::UpdateType, 16> PendUpdates;
+  /// Helper structure used to hold all the basic blocks
+  /// involved in the split of a critical edge.
+  struct CriticalEdge {
+    BasicBlockT *FromBB;
+    BasicBlockT *ToBB;
+    BasicBlockT *NewBB;
+  };
+
+  struct DomTreeUpdate {
+    bool IsCriticalEdgeSplit = false;
+    union {
+      UpdateT Update;
+      CriticalEdge EdgeSplit;
+    };
+    DomTreeUpdate(UpdateT Update) : Update(Update) {}
+    DomTreeUpdate(CriticalEdge E) : IsCriticalEdgeSplit(true), EdgeSplit(E) {}
+  };
+
+  SmallVector<DomTreeUpdate, 16> PendUpdates;
   size_t PendDTUpdateIndex = 0;
   size_t PendPDTUpdateIndex = 0;
   DomTreeT *DT = nullptr;
@@ -216,21 +240,21 @@ class GenericDomTreeUpdater {
   bool IsRecalculatingPostDomTree = false;
 
   /// Returns true if the update is self dominance.
-  bool isSelfDominance(typename DomTreeT::UpdateType Update) const {
+  bool isSelfDominance(UpdateT Update) const {
     // Won't affect DomTree and PostDomTree.
     return Update.getFrom() == Update.getTo();
   }
 
   /// Helper function to apply all pending DomTree updates.
-  void applyDomTreeUpdates();
+  void applyDomTreeUpdates() { applyUpdatesImpl<true>(); }
 
   /// Helper function to apply all pending PostDomTree updates.
-  void applyPostDomTreeUpdates();
+  void applyPostDomTreeUpdates() { applyUpdatesImpl<false>(); }
 
   /// Returns true if the update appears in the LLVM IR.
   /// It is used to check whether an update is valid in
   /// insertEdge/deleteEdge or is unnecessary in the batch update.
-  bool isUpdateValid(typename DomTreeT::UpdateType Update) const;
+  bool isUpdateValid(UpdateT Update) const;
 
   /// Erase Basic Block node before it is unlinked from Function
   /// in the DomTree and PostDomTree.
@@ -243,6 +267,11 @@ class GenericDomTreeUpdater {
   /// Drop all updates applied by all available trees and delete BasicBlocks if
   /// all available trees are up-to-date.
   void dropOutOfDateUpdates();
+
+private:
+  void splitDTCriticalEdges(ArrayRef<CriticalEdge> Updates);
+  void splitPDTCriticalEdges(ArrayRef<CriticalEdge> Updates);
+  template <bool IsForward> void applyUpdatesImpl();
 };
 
 } // namespace llvm