[CodeGen] Remove applySplitCriticalEdges in MachineDominatorTree

Summary:
- Remove wrappers in `MachineDominatorTree`.
- Remove `MachineDominatorTree` update code in `MachineBasicBlock::SplitCriticalEdge`
- Use `MachineDomTreeUpdater` in passes which call `MachineBasicBlock::SplitCriticalEdge`
  and preserve `MachineDominatorTreeWrapperPass` or CFG analyses.

Commit abea99f introduced related methods
in 2014. Now we have SemiNCA based dominator tree in 2017 and dominator tree updater,
the solution adopted here seems a bit outdated.

Author: paperchalice

llvm/include/llvm/CodeGen/MachineDominators.h

@@ -73,86 +73,22 @@ 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) { calculate(MF); }
+  explicit MachineDominatorTree(MachineFunction &MF) { recalculate(MF); }
 
   /// Handle invalidation explicitly.
   bool invalidate(MachineFunction &, const PreservedAnalyses &PA,
                   MachineFunctionAnalysisManager::Invalidator &);
 
-  // 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);
-  }
+  using Base::dominates;
 
   // 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);
@@ -164,107 +100,6 @@ 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

@@ -1735,15 +1735,15 @@ void AsmPrinter::emitFunctionBody() {
     MDT = MDTWrapper ? &MDTWrapper->getDomTree() : nullptr;
     if (!MDT) {
       OwnedMDT = std::make_unique<MachineDominatorTree>();
-      OwnedMDT->getBase().recalculate(*MF);
+      OwnedMDT->recalculate(*MF);
       MDT = OwnedMDT.get();
     }
 
     // Get MachineLoopInfo or compute it on the fly if it's unavailable
     MLI = getAnalysisIfAvailable<MachineLoopInfo>();
     if (!MLI) {
       OwnedMLI = std::make_unique<MachineLoopInfo>();
-      OwnedMLI->getBase().analyze(MDT->getBase());
+      OwnedMLI->getBase().analyze(*MDT);
       MLI = OwnedMLI.get();
     }
   }

llvm/lib/CodeGen/LazyMachineBlockFrequencyInfo.cpp

@@ -77,13 +77,13 @@ LazyMachineBlockFrequencyInfoPass::calculateIfNotAvailable() const {
     if (!MDT) {
       LLVM_DEBUG(dbgs() << "Building DominatorTree on the fly\n");
       OwnedMDT = std::make_unique<MachineDominatorTree>();
-      OwnedMDT->getBase().recalculate(*MF);
+      OwnedMDT->recalculate(*MF);
       MDT = OwnedMDT.get();
     }
 
     // Generate LoopInfo from it.
     OwnedMLI = std::make_unique<MachineLoopInfo>();
-    OwnedMLI->getBase().analyze(MDT->getBase());
+    OwnedMLI->getBase().analyze(*MDT);
     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->getBase());
+  IDFCalculatorBase<MachineBasicBlock, false> IDF(*DomTree);
 
   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.calculate(MF);
+    MDT.recalculate(MF);
     TheImpl = &*InstrRefImpl;
   }
 

llvm/lib/CodeGen/MachineBasicBlock.cpp

@@ -1336,10 +1336,6 @@ MachineBasicBlock *MachineBasicBlock::SplitCriticalEdge(
     LIS->repairIntervalsInRange(this, getFirstTerminator(), end(), UsedRegs);
   }
 
-  if (auto *MDTWrapper =
-          P.getAnalysisIfAvailable<MachineDominatorTreeWrapperPass>())
-    MDTWrapper->getDomTree().recordSplitCriticalEdge(this, Succ, NMBB);
-
   if (MachineLoopInfo *MLI = P.getAnalysisIfAvailable<MachineLoopInfo>())
     if (MachineLoop *TIL = MLI->getLoopFor(this)) {
       // If one or the other blocks were not in a loop, the new block is not

llvm/lib/CodeGen/MachineDominanceFrontier.cpp

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

llvm/lib/CodeGen/MachineDominators.cpp

@@ -95,12 +95,6 @@ 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) {
@@ -121,71 +115,3 @@ 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();
-}

llvm/lib/CodeGen/MachineLoopInfo.cpp

@@ -49,7 +49,7 @@ bool MachineLoopInfo::runOnMachineFunction(MachineFunction &) {
 
 void MachineLoopInfo::calculate(MachineDominatorTree &MDT) {
   releaseMemory();
-  LI.analyze(MDT.getBase());
+  LI.analyze(MDT);
 }
 
 void MachineLoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {

llvm/lib/CodeGen/MachineSink.cpp

@@ -30,6 +30,7 @@
 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
 #include "llvm/CodeGen/MachineCycleAnalysis.h"
+#include "llvm/CodeGen/MachineDomTreeUpdater.h"
 #include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
@@ -717,6 +718,8 @@ bool MachineSinking::runOnMachineFunction(MachineFunction &MF) {
   RegClassInfo.runOnMachineFunction(MF);
   TargetPassConfig *PassConfig = &getAnalysis<TargetPassConfig>();
   EnableSinkAndFold = PassConfig->getEnableSinkAndFold();
+  MachineDomTreeUpdater MDTU(DT, PDT,
+                             MachineDomTreeUpdater::UpdateStrategy::Lazy);
 
   bool EverMadeChange = false;
 
@@ -743,6 +746,11 @@ bool MachineSinking::runOnMachineFunction(MachineFunction &MF) {
         MadeChange = true;
         ++NumSplit;
         CI->splitCriticalEdge(Pair.first, Pair.second, NewSucc);
+
+        MDTU.applyUpdates(
+            {{MachineDominatorTree::Insert, Pair.first, NewSucc},
+             {MachineDominatorTree::Insert, NewSucc, Pair.second},
+             {MachineDominatorTree::Delete, Pair.first, Pair.second}});
       } else
         LLVM_DEBUG(dbgs() << " *** Not legal to break critical edge\n");
     }