Revert "[CodeGen] Remove applySplitCriticalEdges in `MachineDominat…

…orTree` (llvm#97055)"

This reverts commit c5e5088.

Causes large compile-time regressions.

llvm/include/llvm/CodeGen/MachineDominators.h

@@ -73,22 +73,86 @@ extern template bool Verify<MBBDomTree>(const MBBDomTree &DT,
 /// compute a normal dominator tree.
 ///
 class MachineDominatorTree : public DomTreeBase<MachineBasicBlock> {
+  /// Helper structure used to hold all the basic blocks
+  /// involved in the split of a critical edge.
+  struct CriticalEdge {
+    MachineBasicBlock *FromBB;
+    MachineBasicBlock *ToBB;
+    MachineBasicBlock *NewBB;
+  };
+
+  /// Pile up all the critical edges to be split.
+  /// The splitting of a critical edge is local and thus, it is possible
+  /// to apply several of those changes at the same time.
+  mutable SmallVector<CriticalEdge, 32> CriticalEdgesToSplit;
+
+  /// Remember all the basic blocks that are inserted during
+  /// edge splitting.
+  /// Invariant: NewBBs == all the basic blocks contained in the NewBB
+  /// field of all the elements of CriticalEdgesToSplit.
+  /// I.e., forall elt in CriticalEdgesToSplit, it exists BB in NewBBs
+  /// such as BB == elt.NewBB.
+  mutable SmallSet<MachineBasicBlock *, 32> NewBBs;
+
+  /// Apply all the recorded critical edges to the DT.
+  /// This updates the underlying DT information in a way that uses
+  /// the fast query path of DT as much as possible.
+  /// FIXME: This method should not be a const member!
+  ///
+  /// \post CriticalEdgesToSplit.empty().
+  void applySplitCriticalEdges() const;
 
 public:
   using Base = DomTreeBase<MachineBasicBlock>;
 
   MachineDominatorTree() = default;
-  explicit MachineDominatorTree(MachineFunction &MF) { recalculate(MF); }
+  explicit MachineDominatorTree(MachineFunction &MF) { calculate(MF); }
 
   /// Handle invalidation explicitly.
   bool invalidate(MachineFunction &, const PreservedAnalyses &PA,
                   MachineFunctionAnalysisManager::Invalidator &);
 
-  using Base::dominates;
+  // FIXME: If there is an updater for MachineDominatorTree,
+  // migrate to this updater and remove these wrappers.
+
+  MachineDominatorTree &getBase() {
+    applySplitCriticalEdges();
+    return *this;
+  }
+
+  MachineBasicBlock *getRoot() const {
+    applySplitCriticalEdges();
+    return Base::getRoot();
+  }
+
+  MachineDomTreeNode *getRootNode() const {
+    applySplitCriticalEdges();
+    return const_cast<MachineDomTreeNode *>(Base::getRootNode());
+  }
+
+  void calculate(MachineFunction &F);
+
+  bool dominates(const MachineDomTreeNode *A,
+                 const MachineDomTreeNode *B) const {
+    applySplitCriticalEdges();
+    return Base::dominates(A, B);
+  }
+
+  void getDescendants(MachineBasicBlock *A,
+                      SmallVectorImpl<MachineBasicBlock *> &Result) {
+    applySplitCriticalEdges();
+    Base::getDescendants(A, Result);
+  }
+
+  bool dominates(const MachineBasicBlock *A, const MachineBasicBlock *B) const {
+    applySplitCriticalEdges();
+    return Base::dominates(A, B);
+  }
 
   // dominates - Return true if A dominates B. This performs the
   // special checks necessary if A and B are in the same basic block.
   bool dominates(const MachineInstr *A, const MachineInstr *B) const {
+    applySplitCriticalEdges();
     const MachineBasicBlock *BBA = A->getParent(), *BBB = B->getParent();
     if (BBA != BBB)
       return Base::dominates(BBA, BBB);
@@ -100,6 +164,107 @@ class MachineDominatorTree : public DomTreeBase<MachineBasicBlock> {
 
     return &*I == A;
   }
+
+  bool properlyDominates(const MachineDomTreeNode *A,
+                         const MachineDomTreeNode *B) const {
+    applySplitCriticalEdges();
+    return Base::properlyDominates(A, B);
+  }
+
+  bool properlyDominates(const MachineBasicBlock *A,
+                         const MachineBasicBlock *B) const {
+    applySplitCriticalEdges();
+    return Base::properlyDominates(A, B);
+  }
+
+  /// findNearestCommonDominator - Find nearest common dominator basic block
+  /// for basic block A and B. If there is no such block then return NULL.
+  MachineBasicBlock *findNearestCommonDominator(MachineBasicBlock *A,
+                                                MachineBasicBlock *B) {
+    applySplitCriticalEdges();
+    return Base::findNearestCommonDominator(A, B);
+  }
+
+  MachineDomTreeNode *operator[](MachineBasicBlock *BB) const {
+    applySplitCriticalEdges();
+    return Base::getNode(BB);
+  }
+
+  /// getNode - return the (Post)DominatorTree node for the specified basic
+  /// block.  This is the same as using operator[] on this class.
+  ///
+  MachineDomTreeNode *getNode(MachineBasicBlock *BB) const {
+    applySplitCriticalEdges();
+    return Base::getNode(BB);
+  }
+
+  /// addNewBlock - Add a new node to the dominator tree information.  This
+  /// creates a new node as a child of DomBB dominator node,linking it into
+  /// the children list of the immediate dominator.
+  MachineDomTreeNode *addNewBlock(MachineBasicBlock *BB,
+                                  MachineBasicBlock *DomBB) {
+    applySplitCriticalEdges();
+    return Base::addNewBlock(BB, DomBB);
+  }
+
+  /// changeImmediateDominator - This method is used to update the dominator
+  /// tree information when a node's immediate dominator changes.
+  ///
+  void changeImmediateDominator(MachineBasicBlock *N,
+                                MachineBasicBlock *NewIDom) {
+    applySplitCriticalEdges();
+    Base::changeImmediateDominator(N, NewIDom);
+  }
+
+  void changeImmediateDominator(MachineDomTreeNode *N,
+                                MachineDomTreeNode *NewIDom) {
+    applySplitCriticalEdges();
+    Base::changeImmediateDominator(N, NewIDom);
+  }
+
+  /// eraseNode - Removes a node from  the dominator tree. Block must not
+  /// dominate any other blocks. Removes node from its immediate dominator's
+  /// children list. Deletes dominator node associated with basic block BB.
+  void eraseNode(MachineBasicBlock *BB) {
+    applySplitCriticalEdges();
+    Base::eraseNode(BB);
+  }
+
+  /// splitBlock - BB is split and now it has one successor. Update dominator
+  /// tree to reflect this change.
+  void splitBlock(MachineBasicBlock* NewBB) {
+    applySplitCriticalEdges();
+    Base::splitBlock(NewBB);
+  }
+
+  /// isReachableFromEntry - Return true if A is dominated by the entry
+  /// block of the function containing it.
+  bool isReachableFromEntry(const MachineBasicBlock *A) {
+    applySplitCriticalEdges();
+    return Base::isReachableFromEntry(A);
+  }
+
+  /// Record that the critical edge (FromBB, ToBB) has been
+  /// split with NewBB.
+  /// This is best to use this method instead of directly update the
+  /// underlying information, because this helps mitigating the
+  /// number of time the DT information is invalidated.
+  ///
+  /// \note Do not use this method with regular edges.
+  ///
+  /// \note To benefit from the compile time improvement incurred by this
+  /// method, the users of this method have to limit the queries to the DT
+  /// interface between two edges splitting. In other words, they have to
+  /// pack the splitting of critical edges as much as possible.
+  void recordSplitCriticalEdge(MachineBasicBlock *FromBB,
+                              MachineBasicBlock *ToBB,
+                              MachineBasicBlock *NewBB) {
+    bool Inserted = NewBBs.insert(NewBB).second;
+    (void)Inserted;
+    assert(Inserted &&
+           "A basic block inserted via edge splitting cannot appear twice");
+    CriticalEdgesToSplit.push_back({FromBB, ToBB, NewBB});
+  }
 };
 
 /// \brief Analysis pass which computes a \c MachineDominatorTree.

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -1698,7 +1698,7 @@ void AsmPrinter::emitFunctionBody() {
     MDT = MDTWrapper ? &MDTWrapper->getDomTree() : nullptr;
     if (!MDT) {
       OwnedMDT = std::make_unique<MachineDominatorTree>();
-      OwnedMDT->recalculate(*MF);
+      OwnedMDT->getBase().recalculate(*MF);
       MDT = OwnedMDT.get();
     }
 
@@ -1707,7 +1707,7 @@ void AsmPrinter::emitFunctionBody() {
     MLI = MLIWrapper ? &MLIWrapper->getLI() : nullptr;
     if (!MLI) {
       OwnedMLI = std::make_unique<MachineLoopInfo>();
-      OwnedMLI->analyze(*MDT);
+      OwnedMLI->analyze(MDT->getBase());
       MLI = OwnedMLI.get();
     }
   }

llvm/lib/CodeGen/LazyMachineBlockFrequencyInfo.cpp

@@ -78,13 +78,13 @@ LazyMachineBlockFrequencyInfoPass::calculateIfNotAvailable() const {
     if (!MDT) {
       LLVM_DEBUG(dbgs() << "Building DominatorTree on the fly\n");
       OwnedMDT = std::make_unique<MachineDominatorTree>();
-      OwnedMDT->recalculate(*MF);
+      OwnedMDT->getBase().recalculate(*MF);
       MDT = OwnedMDT.get();
     }
 
     // Generate LoopInfo from it.
     OwnedMLI = std::make_unique<MachineLoopInfo>();
-    OwnedMLI->analyze(*MDT);
+    OwnedMLI->analyze(MDT->getBase());
     MLI = OwnedMLI.get();
   }
 

llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp

@@ -2754,7 +2754,7 @@ void InstrRefBasedLDV::BlockPHIPlacement(
   // Apply IDF calculator to the designated set of location defs, storing
   // required PHIs into PHIBlocks. Uses the dominator tree stored in the
   // InstrRefBasedLDV object.
-  IDFCalculatorBase<MachineBasicBlock, false> IDF(*DomTree);
+  IDFCalculatorBase<MachineBasicBlock, false> IDF(DomTree->getBase());
 
   IDF.setLiveInBlocks(AllBlocks);
   IDF.setDefiningBlocks(DefBlocks);

llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp

@@ -120,7 +120,7 @@ bool LiveDebugValues::runOnMachineFunction(MachineFunction &MF) {
   MachineDominatorTree *DomTree = nullptr;
   if (InstrRefBased) {
     DomTree = &MDT;
-    MDT.recalculate(MF);
+    MDT.calculate(MF);
     TheImpl = &*InstrRefImpl;
   }
 

llvm/lib/CodeGen/MachineBasicBlock.cpp

@@ -16,13 +16,11 @@
 #include "llvm/CodeGen/LiveIntervals.h"
 #include "llvm/CodeGen/LivePhysRegs.h"
 #include "llvm/CodeGen/LiveVariables.h"
-#include "llvm/CodeGen/MachineDomTreeUpdater.h"
 #include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineJumpTableInfo.h"
 #include "llvm/CodeGen/MachineLoopInfo.h"
-#include "llvm/CodeGen/MachinePostDominators.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/SlotIndexes.h"
 #include "llvm/CodeGen/TargetInstrInfo.h"
@@ -1341,17 +1339,9 @@ MachineBasicBlock *MachineBasicBlock::SplitCriticalEdge(
     LIS->repairIntervalsInRange(this, getFirstTerminator(), end(), UsedRegs);
   }
 
-  auto *MDTWrapper =
-      P.getAnalysisIfAvailable<MachineDominatorTreeWrapperPass>();
-  auto *MPDTWrapper =
-      P.getAnalysisIfAvailable<MachinePostDominatorTreeWrapperPass>();
-  auto *MDT = MDTWrapper ? &MDTWrapper->getDomTree() : nullptr;
-  auto *MPDT = MPDTWrapper ? &MPDTWrapper->getPostDomTree() : nullptr;
-  MachineDomTreeUpdater MDTU(MDT, MPDT,
-                             MachineDomTreeUpdater::UpdateStrategy::Eager);
-  MDTU.applyUpdates({{MachineDominatorTree::Insert, this, NMBB},
-                     {MachineDominatorTree::Insert, NMBB, Succ},
-                     {MachineDominatorTree::Delete, this, Succ}});
+  if (auto *MDTWrapper =
+          P.getAnalysisIfAvailable<MachineDominatorTreeWrapperPass>())
+    MDTWrapper->getDomTree().recordSplitCriticalEdge(this, Succ, NMBB);
 
   auto *MLIWrapper = P.getAnalysisIfAvailable<MachineLoopInfoWrapperPass>();
   if (MachineLoopInfo *MLI = MLIWrapper ? &MLIWrapper->getLI() : nullptr)

llvm/lib/CodeGen/MachineDominanceFrontier.cpp

@@ -38,7 +38,8 @@ char &llvm::MachineDominanceFrontierID = MachineDominanceFrontier::ID;
 
 bool MachineDominanceFrontier::runOnMachineFunction(MachineFunction &) {
   releaseMemory();
-  Base.analyze(getAnalysis<MachineDominatorTreeWrapperPass>().getDomTree());
+  Base.analyze(
+      getAnalysis<MachineDominatorTreeWrapperPass>().getDomTree().getBase());
   return false;
 }
 

llvm/lib/CodeGen/MachineDominators.cpp

@@ -95,6 +95,12 @@ MachineDominatorTreeWrapperPass::MachineDominatorTreeWrapperPass()
       *PassRegistry::getPassRegistry());
 }
 
+void MachineDominatorTree::calculate(MachineFunction &F) {
+  CriticalEdgesToSplit.clear();
+  NewBBs.clear();
+  recalculate(F);
+}
+
 char &llvm::MachineDominatorsID = MachineDominatorTreeWrapperPass::ID;
 
 bool MachineDominatorTreeWrapperPass::runOnMachineFunction(MachineFunction &F) {
@@ -115,3 +121,71 @@ void MachineDominatorTreeWrapperPass::print(raw_ostream &OS,
   if (DT)
     DT->print(OS);
 }
+
+void MachineDominatorTree::applySplitCriticalEdges() const {
+  // Bail out early if there is nothing to do.
+  if (CriticalEdgesToSplit.empty())
+    return;
+
+  // For each element in CriticalEdgesToSplit, remember whether or not element
+  // is the new immediate domminator of its successor. The mapping is done by
+  // index, i.e., the information for the ith element of CriticalEdgesToSplit is
+  // the ith element of IsNewIDom.
+  SmallBitVector IsNewIDom(CriticalEdgesToSplit.size(), true);
+  size_t Idx = 0;
+
+  // Collect all the dominance properties info, before invalidating
+  // the underlying DT.
+  for (CriticalEdge &Edge : CriticalEdgesToSplit) {
+    // Update dominator information.
+    MachineBasicBlock *Succ = Edge.ToBB;
+    MachineDomTreeNode *SuccDTNode = Base::getNode(Succ);
+
+    for (MachineBasicBlock *PredBB : Succ->predecessors()) {
+      if (PredBB == Edge.NewBB)
+        continue;
+      // If we are in this situation:
+      // FromBB1        FromBB2
+      //    +              +
+      //   + +            + +
+      //  +   +          +   +
+      // ...  Split1  Split2 ...
+      //           +   +
+      //            + +
+      //             +
+      //            Succ
+      // Instead of checking the domiance property with Split2, we check it with
+      // FromBB2 since Split2 is still unknown of the underlying DT structure.
+      if (NewBBs.count(PredBB)) {
+        assert(PredBB->pred_size() == 1 && "A basic block resulting from a "
+                                           "critical edge split has more "
+                                           "than one predecessor!");
+        PredBB = *PredBB->pred_begin();
+      }
+      if (!Base::dominates(SuccDTNode, Base::getNode(PredBB))) {
+        IsNewIDom[Idx] = false;
+        break;
+      }
+    }
+    ++Idx;
+  }
+
+  // Now, update DT with the collected dominance properties info.
+  Idx = 0;
+  for (CriticalEdge &Edge : CriticalEdgesToSplit) {
+    // We know FromBB dominates NewBB.
+    MachineDomTreeNode *NewDTNode =
+        const_cast<MachineDominatorTree *>(this)->Base::addNewBlock(
+            Edge.NewBB, Edge.FromBB);
+
+    // If all the other predecessors of "Succ" are dominated by "Succ" itself
+    // then the new block is the new immediate dominator of "Succ". Otherwise,
+    // the new block doesn't dominate anything.
+    if (IsNewIDom[Idx])
+      const_cast<MachineDominatorTree *>(this)->Base::changeImmediateDominator(
+          Base::getNode(Edge.ToBB), NewDTNode);
+    ++Idx;
+  }
+  NewBBs.clear();
+  CriticalEdgesToSplit.clear();
+}