include/llvm/CodeGen/MachineDominators.h

   1 //==- llvm/CodeGen/MachineDominators.h - Machine Dom Calculation -*- C++ -*-==//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file defines classes mirroring those in llvm/Analysis/Dominators.h,
  10 // but for target-specific code rather than target-independent IR.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #ifndef LLVM_CODEGEN_MACHINEDOMINATORS_H
  15 #define LLVM_CODEGEN_MACHINEDOMINATORS_H
  16
  17 #include "llvm/ADT/SmallSet.h"
  18 #include "llvm/ADT/SmallVector.h"
  19 #include "llvm/CodeGen/MachineBasicBlock.h"
  20 #include "llvm/CodeGen/MachineFunctionPass.h"
  21 #include "llvm/CodeGen/MachineInstr.h"
  22 #include "llvm/Support/GenericDomTree.h"
  23 #include "llvm/Support/GenericDomTreeConstruction.h"
  24 #include <cassert>
  25 #include <memory>
  26 #include <vector>
  27
  28 namespace llvm {
  29
  30 template <>
  31 inline void DominatorTreeBase<MachineBasicBlock, false>::addRoot(
  32     MachineBasicBlock *MBB) {
  33   this->Roots.push_back(MBB);
  34 }
  35
  36 extern template class DomTreeNodeBase<MachineBasicBlock>;
  37 extern template class DominatorTreeBase<MachineBasicBlock, false>; // DomTree
  38 extern template class DominatorTreeBase<MachineBasicBlock, true>; // PostDomTree
  39
  40 using MachineDomTreeNode = DomTreeNodeBase<MachineBasicBlock>;
  41
  42 //===-------------------------------------
  43 /// DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to
  44 /// compute a normal dominator tree.
  45 ///
  46 class MachineDominatorTree : public MachineFunctionPass {
  47   using DomTreeT = DomTreeBase<MachineBasicBlock>;
  48
  49   /// Helper structure used to hold all the basic blocks
  50   /// involved in the split of a critical edge.
  51   struct CriticalEdge {
  52     MachineBasicBlock *FromBB;
  53     MachineBasicBlock *ToBB;
  54     MachineBasicBlock *NewBB;
  55   };
  56
  57   /// Pile up all the critical edges to be split.
  58   /// The splitting of a critical edge is local and thus, it is possible
  59   /// to apply several of those changes at the same time.
  60   mutable SmallVector<CriticalEdge, 32> CriticalEdgesToSplit;
  61
  62   /// Remember all the basic blocks that are inserted during
  63   /// edge splitting.
  64   /// Invariant: NewBBs == all the basic blocks contained in the NewBB
  65   /// field of all the elements of CriticalEdgesToSplit.
  66   /// I.e., forall elt in CriticalEdgesToSplit, it exists BB in NewBBs
  67   /// such as BB == elt.NewBB.
  68   mutable SmallSet<MachineBasicBlock *, 32> NewBBs;
  69
  70   /// The DominatorTreeBase that is used to compute a normal dominator tree.
  71   std::unique_ptr<DomTreeT> DT;
  72
  73   /// Apply all the recorded critical edges to the DT.
  74   /// This updates the underlying DT information in a way that uses
  75   /// the fast query path of DT as much as possible.
  76   ///
  77   /// \post CriticalEdgesToSplit.empty().
  78   void applySplitCriticalEdges() const;
  79
  80 public:
  81   static char ID; // Pass ID, replacement for typeid
  82
  83   MachineDominatorTree();
  84
  85   DomTreeT &getBase() {
  86     if (!DT) DT.reset(new DomTreeT());
  87     applySplitCriticalEdges();
  88     return *DT;
  89   }
  90
  91   void getAnalysisUsage(AnalysisUsage &AU) const override;
  92
  93   /// getRoots -  Return the root blocks of the current CFG.  This may include
  94   /// multiple blocks if we are computing post dominators.  For forward
  95   /// dominators, this will always be a single block (the entry node).
  96   ///
  97   const SmallVectorImpl<MachineBasicBlock*> &getRoots() const {
  98     applySplitCriticalEdges();
  99     return DT->getRoots();
 100   }
 101
 102   MachineBasicBlock *getRoot() const {
 103     applySplitCriticalEdges();
 104     return DT->getRoot();
 105   }
 106
 107   MachineDomTreeNode *getRootNode() const {
 108     applySplitCriticalEdges();
 109     return DT->getRootNode();
 110   }
 111
 112   bool runOnMachineFunction(MachineFunction &F) override;
 113
 114   bool dominates(const MachineDomTreeNode *A,
 115                  const MachineDomTreeNode *B) const {
 116     applySplitCriticalEdges();
 117     return DT->dominates(A, B);
 118   }
 119
 120   bool dominates(const MachineBasicBlock *A, const MachineBasicBlock *B) const {
 121     applySplitCriticalEdges();
 122     return DT->dominates(A, B);
 123   }
 124
 125   // dominates - Return true if A dominates B. This performs the
 126   // special checks necessary if A and B are in the same basic block.
 127   bool dominates(const MachineInstr *A, const MachineInstr *B) const {
 128     applySplitCriticalEdges();
 129     const MachineBasicBlock *BBA = A->getParent(), *BBB = B->getParent();
 130     if (BBA != BBB) return DT->dominates(BBA, BBB);
 131
 132     // Loop through the basic block until we find A or B.
 133     MachineBasicBlock::const_iterator I = BBA->begin();
 134     for (; &*I != A && &*I != B; ++I)
 135       /*empty*/ ;
 136
 137     return &*I == A;
 138   }
 139
 140   bool properlyDominates(const MachineDomTreeNode *A,
 141                          const MachineDomTreeNode *B) const {
 142     applySplitCriticalEdges();
 143     return DT->properlyDominates(A, B);
 144   }
 145
 146   bool properlyDominates(const MachineBasicBlock *A,
 147                          const MachineBasicBlock *B) const {
 148     applySplitCriticalEdges();
 149     return DT->properlyDominates(A, B);
 150   }
 151
 152   /// findNearestCommonDominator - Find nearest common dominator basic block
 153   /// for basic block A and B. If there is no such block then return NULL.
 154   MachineBasicBlock *findNearestCommonDominator(MachineBasicBlock *A,
 155                                                 MachineBasicBlock *B) {
 156     applySplitCriticalEdges();
 157     return DT->findNearestCommonDominator(A, B);
 158   }
 159
 160   MachineDomTreeNode *operator[](MachineBasicBlock *BB) const {
 161     applySplitCriticalEdges();
 162     return DT->getNode(BB);
 163   }
 164
 165   /// getNode - return the (Post)DominatorTree node for the specified basic
 166   /// block.  This is the same as using operator[] on this class.
 167   ///
 168   MachineDomTreeNode *getNode(MachineBasicBlock *BB) const {
 169     applySplitCriticalEdges();
 170     return DT->getNode(BB);
 171   }
 172
 173   /// addNewBlock - Add a new node to the dominator tree information.  This
 174   /// creates a new node as a child of DomBB dominator node,linking it into
 175   /// the children list of the immediate dominator.
 176   MachineDomTreeNode *addNewBlock(MachineBasicBlock *BB,
 177                                   MachineBasicBlock *DomBB) {
 178     applySplitCriticalEdges();
 179     return DT->addNewBlock(BB, DomBB);
 180   }
 181
 182   /// changeImmediateDominator - This method is used to update the dominator
 183   /// tree information when a node's immediate dominator changes.
 184   ///
 185   void changeImmediateDominator(MachineBasicBlock *N,
 186                                 MachineBasicBlock *NewIDom) {
 187     applySplitCriticalEdges();
 188     DT->changeImmediateDominator(N, NewIDom);
 189   }
 190
 191   void changeImmediateDominator(MachineDomTreeNode *N,
 192                                 MachineDomTreeNode *NewIDom) {
 193     applySplitCriticalEdges();
 194     DT->changeImmediateDominator(N, NewIDom);
 195   }
 196
 197   /// eraseNode - Removes a node from  the dominator tree. Block must not
 198   /// dominate any other blocks. Removes node from its immediate dominator's
 199   /// children list. Deletes dominator node associated with basic block BB.
 200   void eraseNode(MachineBasicBlock *BB) {
 201     applySplitCriticalEdges();
 202     DT->eraseNode(BB);
 203   }
 204
 205   /// splitBlock - BB is split and now it has one successor. Update dominator
 206   /// tree to reflect this change.
 207   void splitBlock(MachineBasicBlock* NewBB) {
 208     applySplitCriticalEdges();
 209     DT->splitBlock(NewBB);
 210   }
 211
 212   /// isReachableFromEntry - Return true if A is dominated by the entry
 213   /// block of the function containing it.
 214   bool isReachableFromEntry(const MachineBasicBlock *A) {
 215     applySplitCriticalEdges();
 216     return DT->isReachableFromEntry(A);
 217   }
 218
 219   void releaseMemory() override;
 220
 221   void verifyAnalysis() const override;
 222
 223   void print(raw_ostream &OS, const Module*) const override;
 224
 225   /// Record that the critical edge (FromBB, ToBB) has been
 226   /// split with NewBB.
 227   /// This is best to use this method instead of directly update the
 228   /// underlying information, because this helps mitigating the
 229   /// number of time the DT information is invalidated.
 230   ///
 231   /// \note Do not use this method with regular edges.
 232   ///
 233   /// \note To benefit from the compile time improvement incurred by this
 234   /// method, the users of this method have to limit the queries to the DT
 235   /// interface between two edges splitting. In other words, they have to
 236   /// pack the splitting of critical edges as much as possible.
 237   void recordSplitCriticalEdge(MachineBasicBlock *FromBB,
 238                               MachineBasicBlock *ToBB,
 239                               MachineBasicBlock *NewBB) {
 240     bool Inserted = NewBBs.insert(NewBB).second;
 241     (void)Inserted;
 242     assert(Inserted &&
 243            "A basic block inserted via edge splitting cannot appear twice");
 244     CriticalEdgesToSplit.push_back({FromBB, ToBB, NewBB});
 245   }
 246 };
 247
 248 //===-------------------------------------
 249 /// DominatorTree GraphTraits specialization so the DominatorTree can be
 250 /// iterable by generic graph iterators.
 251 ///
 252
 253 template <class Node, class ChildIterator>
 254 struct MachineDomTreeGraphTraitsBase {
 255   using NodeRef = Node *;
 256   using ChildIteratorType = ChildIterator;
 257
 258   static NodeRef getEntryNode(NodeRef N) { return N; }
 259   static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
 260   static ChildIteratorType child_end(NodeRef N) { return N->end(); }
 261 };
 262
 263 template <class T> struct GraphTraits;
 264
 265 template <>
 266 struct GraphTraits<MachineDomTreeNode *>
 267     : public MachineDomTreeGraphTraitsBase<MachineDomTreeNode,
 268                                            MachineDomTreeNode::iterator> {};
 269
 270 template <>
 271 struct GraphTraits<const MachineDomTreeNode *>
 272     : public MachineDomTreeGraphTraitsBase<const MachineDomTreeNode,
 273                                            MachineDomTreeNode::const_iterator> {
 274 };
 275
 276 template <> struct GraphTraits<MachineDominatorTree*>
 277   : public GraphTraits<MachineDomTreeNode *> {
 278   static NodeRef getEntryNode(MachineDominatorTree *DT) {
 279     return DT->getRootNode();
 280   }
 281 };
 282
 283 } // end namespace llvm
 284
 285 #endif // LLVM_CODEGEN_MACHINEDOMINATORS_H