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