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   /// Helper structure used to hold all the basic blocks
  48   /// involved in the split of a critical edge.
  49   struct CriticalEdge {
  50     MachineBasicBlock *FromBB;
  51     MachineBasicBlock *ToBB;
  52     MachineBasicBlock *NewBB;
  53   };
  54
  55   /// Pile up all the critical edges to be split.
  56   /// The splitting of a critical edge is local and thus, it is possible
  57   /// to apply several of those changes at the same time.
  58   mutable SmallVector<CriticalEdge, 32> CriticalEdgesToSplit;
  59
  60   /// Remember all the basic blocks that are inserted during
  61   /// edge splitting.
  62   /// Invariant: NewBBs == all the basic blocks contained in the NewBB
  63   /// field of all the elements of CriticalEdgesToSplit.
  64   /// I.e., forall elt in CriticalEdgesToSplit, it exists BB in NewBBs
  65   /// such as BB == elt.NewBB.
  66   mutable SmallSet<MachineBasicBlock *, 32> NewBBs;
  67
  68   /// The DominatorTreeBase that is used to compute a normal dominator tree
  69   std::unique_ptr<DomTreeBase<MachineBasicBlock>> DT;
  70
  71   /// Apply all the recorded critical edges to the DT.
  72   /// This updates the underlying DT information in a way that uses
  73   /// the fast query path of DT as much as possible.
  74   ///
  75   /// \post CriticalEdgesToSplit.empty().
  76   void applySplitCriticalEdges() const;
  77
  78 public:
  79   static char ID; // Pass ID, replacement for typeid
  80
  81   MachineDominatorTree();
  82
  83   DomTreeBase<MachineBasicBlock> &getBase() {
  84     if (!DT) DT.reset(new DomTreeBase<MachineBasicBlock>());
  85     applySplitCriticalEdges();
  86     return *DT;
  87   }
  88
  89   void getAnalysisUsage(AnalysisUsage &AU) const override;
  90
  91   /// getRoots -  Return the root blocks of the current CFG.  This may include
  92   /// multiple blocks if we are computing post dominators.  For forward
  93   /// dominators, this will always be a single block (the entry node).
  94   ///
  95   inline const SmallVectorImpl<MachineBasicBlock*> &getRoots() const {
  96     applySplitCriticalEdges();
  97     return DT->getRoots();
  98   }
  99
 100   inline MachineBasicBlock *getRoot() const {
 101     applySplitCriticalEdges();
 102     return DT->getRoot();
 103   }
 104
 105   inline MachineDomTreeNode *getRootNode() const {
 106     applySplitCriticalEdges();
 107     return DT->getRootNode();
 108   }
 109
 110   bool runOnMachineFunction(MachineFunction &F) override;
 111
 112   inline bool dominates(const MachineDomTreeNode* A,
 113                         const MachineDomTreeNode* B) const {
 114     applySplitCriticalEdges();
 115     return DT->dominates(A, B);
 116   }
 117
 118   inline bool dominates(const MachineBasicBlock* A,
 119                         const MachineBasicBlock* B) const {
 120     applySplitCriticalEdges();
 121     return DT->dominates(A, B);
 122   }
 123
 124   // dominates - Return true if A dominates B. This performs the
 125   // special checks necessary if A and B are in the same basic block.
 126   bool dominates(const MachineInstr *A, const MachineInstr *B) const {
 127     applySplitCriticalEdges();
 128     const MachineBasicBlock *BBA = A->getParent(), *BBB = B->getParent();
 129     if (BBA != BBB) return DT->dominates(BBA, BBB);
 130
 131     // Loop through the basic block until we find A or B.
 132     MachineBasicBlock::const_iterator I = BBA->begin();
 133     for (; &*I != A && &*I != B; ++I)
 134       /*empty*/ ;
 135
 136     //if(!DT.IsPostDominators) {
 137       // A dominates B if it is found first in the basic block.
 138       return &*I == A;
 139     //} else {
 140     //  // A post-dominates B if B is found first in the basic block.
 141     //  return &*I == B;
 142     //}
 143   }
 144
 145   inline bool properlyDominates(const MachineDomTreeNode* A,
 146                                 const MachineDomTreeNode* B) const {
 147     applySplitCriticalEdges();
 148     return DT->properlyDominates(A, B);
 149   }
 150
 151   inline bool properlyDominates(const MachineBasicBlock* A,
 152                                 const MachineBasicBlock* B) const {
 153     applySplitCriticalEdges();
 154     return DT->properlyDominates(A, B);
 155   }
 156
 157   /// findNearestCommonDominator - Find nearest common dominator basic block
 158   /// for basic block A and B. If there is no such block then return NULL.
 159   inline MachineBasicBlock *findNearestCommonDominator(MachineBasicBlock *A,
 160                                                        MachineBasicBlock *B) {
 161     applySplitCriticalEdges();
 162     return DT->findNearestCommonDominator(A, B);
 163   }
 164
 165   inline MachineDomTreeNode *operator[](MachineBasicBlock *BB) const {
 166     applySplitCriticalEdges();
 167     return DT->getNode(BB);
 168   }
 169
 170   /// getNode - return the (Post)DominatorTree node for the specified basic
 171   /// block.  This is the same as using operator[] on this class.
 172   ///
 173   inline MachineDomTreeNode *getNode(MachineBasicBlock *BB) const {
 174     applySplitCriticalEdges();
 175     return DT->getNode(BB);
 176   }
 177
 178   /// addNewBlock - Add a new node to the dominator tree information.  This
 179   /// creates a new node as a child of DomBB dominator node,linking it into
 180   /// the children list of the immediate dominator.
 181   inline MachineDomTreeNode *addNewBlock(MachineBasicBlock *BB,
 182                                          MachineBasicBlock *DomBB) {
 183     applySplitCriticalEdges();
 184     return DT->addNewBlock(BB, DomBB);
 185   }
 186
 187   /// changeImmediateDominator - This method is used to update the dominator
 188   /// tree information when a node's immediate dominator changes.
 189   ///
 190   inline void changeImmediateDominator(MachineBasicBlock *N,
 191                                        MachineBasicBlock* NewIDom) {
 192     applySplitCriticalEdges();
 193     DT->changeImmediateDominator(N, NewIDom);
 194   }
 195
 196   inline void changeImmediateDominator(MachineDomTreeNode *N,
 197                                        MachineDomTreeNode* NewIDom) {
 198     applySplitCriticalEdges();
 199     DT->changeImmediateDominator(N, NewIDom);
 200   }
 201
 202   /// eraseNode - Removes a node from  the dominator tree. Block must not
 203   /// dominate any other blocks. Removes node from its immediate dominator's
 204   /// children list. Deletes dominator node associated with basic block BB.
 205   inline void eraseNode(MachineBasicBlock *BB) {
 206     applySplitCriticalEdges();
 207     DT->eraseNode(BB);
 208   }
 209
 210   /// splitBlock - BB is split and now it has one successor. Update dominator
 211   /// tree to reflect this change.
 212   inline void splitBlock(MachineBasicBlock* NewBB) {
 213     applySplitCriticalEdges();
 214     DT->splitBlock(NewBB);
 215   }
 216
 217   /// isReachableFromEntry - Return true if A is dominated by the entry
 218   /// block of the function containing it.
 219   bool isReachableFromEntry(const MachineBasicBlock *A) {
 220     applySplitCriticalEdges();
 221     return DT->isReachableFromEntry(A);
 222   }
 223
 224   void releaseMemory() override;
 225
 226   void verifyAnalysis() const override;
 227
 228   void print(raw_ostream &OS, const Module*) const override;
 229
 230   /// Record that the critical edge (FromBB, ToBB) has been
 231   /// split with NewBB.
 232   /// This is best to use this method instead of directly update the
 233   /// underlying information, because this helps mitigating the
 234   /// number of time the DT information is invalidated.
 235   ///
 236   /// \note Do not use this method with regular edges.
 237   ///
 238   /// \note To benefit from the compile time improvement incurred by this
 239   /// method, the users of this method have to limit the queries to the DT
 240   /// interface between two edges splitting. In other words, they have to
 241   /// pack the splitting of critical edges as much as possible.
 242   void recordSplitCriticalEdge(MachineBasicBlock *FromBB,
 243                               MachineBasicBlock *ToBB,
 244                               MachineBasicBlock *NewBB) {
 245     bool Inserted = NewBBs.insert(NewBB).second;
 246     (void)Inserted;
 247     assert(Inserted &&
 248            "A basic block inserted via edge splitting cannot appear twice");
 249     CriticalEdgesToSplit.push_back({FromBB, ToBB, NewBB});
 250   }
 251 };
 252
 253 //===-------------------------------------
 254 /// DominatorTree GraphTraits specialization so the DominatorTree can be
 255 /// iterable by generic graph iterators.
 256 ///
 257
 258 template <class Node, class ChildIterator>
 259 struct MachineDomTreeGraphTraitsBase {
 260   using NodeRef = Node *;
 261   using ChildIteratorType = ChildIterator;
 262
 263   static NodeRef getEntryNode(NodeRef N) { return N; }
 264   static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
 265   static ChildIteratorType child_end(NodeRef N) { return N->end(); }
 266 };
 267
 268 template <class T> struct GraphTraits;
 269
 270 template <>
 271 struct GraphTraits<MachineDomTreeNode *>
 272     : public MachineDomTreeGraphTraitsBase<MachineDomTreeNode,
 273                                            MachineDomTreeNode::iterator> {};
 274
 275 template <>
 276 struct GraphTraits<const MachineDomTreeNode *>
 277     : public MachineDomTreeGraphTraitsBase<const MachineDomTreeNode,
 278                                            MachineDomTreeNode::const_iterator> {
 279 };
 280
 281 template <> struct GraphTraits<MachineDominatorTree*>
 282   : public GraphTraits<MachineDomTreeNode *> {
 283   static NodeRef getEntryNode(MachineDominatorTree *DT) {
 284     return DT->getRootNode();
 285   }
 286 };
 287
 288 } // end namespace llvm
 289
 290 #endif // LLVM_CODEGEN_MACHINEDOMINATORS_H