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/CodeGen/MachineInstrBundleIterator.h" 23 #include "llvm/Support/GenericDomTree.h" 24 #include "llvm/Support/GenericDomTreeConstruction.h" 25 #include <cassert> 26 #include <memory> 27 28 namespace llvm { 29 class AnalysisUsage; 30 class MachineFunction; 31 class Module; 32 class raw_ostream; 33 34 template <> 35 inline void DominatorTreeBase<MachineBasicBlock, false>::addRoot( 36 MachineBasicBlock *MBB) { 37 this->Roots.push_back(MBB); 38 } 39 40 extern template class DomTreeNodeBase<MachineBasicBlock>; 41 extern template class DominatorTreeBase<MachineBasicBlock, false>; // DomTree 42 extern template class DominatorTreeBase<MachineBasicBlock, true>; // PostDomTree 43 44 using MachineDomTree = DomTreeBase<MachineBasicBlock>; 45 using MachineDomTreeNode = DomTreeNodeBase<MachineBasicBlock>; 46 47 //===------------------------------------- 48 /// DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to 49 /// compute a normal dominator tree. 50 /// 51 class MachineDominatorTree : public MachineFunctionPass { 52 /// Helper structure used to hold all the basic blocks 53 /// involved in the split of a critical edge. 54 struct CriticalEdge { 55 MachineBasicBlock *FromBB; 56 MachineBasicBlock *ToBB; 57 MachineBasicBlock *NewBB; 58 }; 59 60 /// Pile up all the critical edges to be split. 61 /// The splitting of a critical edge is local and thus, it is possible 62 /// to apply several of those changes at the same time. 63 mutable SmallVector<CriticalEdge, 32> CriticalEdgesToSplit; 64 65 /// Remember all the basic blocks that are inserted during 66 /// edge splitting. 67 /// Invariant: NewBBs == all the basic blocks contained in the NewBB 68 /// field of all the elements of CriticalEdgesToSplit. 69 /// I.e., forall elt in CriticalEdgesToSplit, it exists BB in NewBBs 70 /// such as BB == elt.NewBB. 71 mutable SmallSet<MachineBasicBlock *, 32> NewBBs; 72 73 /// The DominatorTreeBase that is used to compute a normal dominator tree. 74 std::unique_ptr<MachineDomTree> DT; 75 76 /// Apply all the recorded critical edges to the DT. 77 /// This updates the underlying DT information in a way that uses 78 /// the fast query path of DT as much as possible. 79 /// 80 /// \post CriticalEdgesToSplit.empty(). 81 void applySplitCriticalEdges() const; 82 83 public: 84 static char ID; // Pass ID, replacement for typeid 85 86 MachineDominatorTree(); 87 explicit MachineDominatorTree(MachineFunction &MF) : MachineFunctionPass(ID) { 88 calculate(MF); 89 } 90 91 MachineDomTree &getBase() { 92 if (!DT) 93 DT.reset(new MachineDomTree()); 94 applySplitCriticalEdges(); 95 return *DT; 96 } 97 98 void getAnalysisUsage(AnalysisUsage &AU) const override; 99 100 MachineBasicBlock *getRoot() const { 101 applySplitCriticalEdges(); 102 return DT->getRoot(); 103 } 104 105 MachineDomTreeNode *getRootNode() const { 106 applySplitCriticalEdges(); 107 return DT->getRootNode(); 108 } 109 110 bool runOnMachineFunction(MachineFunction &F) override; 111 112 void calculate(MachineFunction &F); 113 114 bool dominates(const MachineDomTreeNode *A, 115 const MachineDomTreeNode *B) const { 116 applySplitCriticalEdges(); 117 return DT->dominates(A, B); 118 } 119 120 void getDescendants(MachineBasicBlock *A, 121 SmallVectorImpl<MachineBasicBlock *> &Result) { 122 applySplitCriticalEdges(); 123 DT->getDescendants(A, Result); 124 } 125 126 bool dominates(const MachineBasicBlock *A, const MachineBasicBlock *B) const { 127 applySplitCriticalEdges(); 128 return DT->dominates(A, B); 129 } 130 131 // dominates - Return true if A dominates B. This performs the 132 // special checks necessary if A and B are in the same basic block. 133 bool dominates(const MachineInstr *A, const MachineInstr *B) const { 134 applySplitCriticalEdges(); 135 const MachineBasicBlock *BBA = A->getParent(), *BBB = B->getParent(); 136 if (BBA != BBB) return DT->dominates(BBA, BBB); 137 138 // Loop through the basic block until we find A or B. 139 MachineBasicBlock::const_iterator I = BBA->begin(); 140 for (; &*I != A && &*I != B; ++I) 141 /*empty*/ ; 142 143 return &*I == A; 144 } 145 146 bool properlyDominates(const MachineDomTreeNode *A, 147 const MachineDomTreeNode *B) const { 148 applySplitCriticalEdges(); 149 return DT->properlyDominates(A, B); 150 } 151 152 bool properlyDominates(const MachineBasicBlock *A, 153 const MachineBasicBlock *B) const { 154 applySplitCriticalEdges(); 155 return DT->properlyDominates(A, B); 156 } 157 158 /// findNearestCommonDominator - Find nearest common dominator basic block 159 /// for basic block A and B. If there is no such block then return NULL. 160 MachineBasicBlock *findNearestCommonDominator(MachineBasicBlock *A, 161 MachineBasicBlock *B) { 162 applySplitCriticalEdges(); 163 return DT->findNearestCommonDominator(A, B); 164 } 165 166 MachineDomTreeNode *operator[](MachineBasicBlock *BB) const { 167 applySplitCriticalEdges(); 168 return DT->getNode(BB); 169 } 170 171 /// getNode - return the (Post)DominatorTree node for the specified basic 172 /// block. This is the same as using operator[] on this class. 173 /// 174 MachineDomTreeNode *getNode(MachineBasicBlock *BB) const { 175 applySplitCriticalEdges(); 176 return DT->getNode(BB); 177 } 178 179 /// addNewBlock - Add a new node to the dominator tree information. This 180 /// creates a new node as a child of DomBB dominator node,linking it into 181 /// the children list of the immediate dominator. 182 MachineDomTreeNode *addNewBlock(MachineBasicBlock *BB, 183 MachineBasicBlock *DomBB) { 184 applySplitCriticalEdges(); 185 return DT->addNewBlock(BB, DomBB); 186 } 187 188 /// changeImmediateDominator - This method is used to update the dominator 189 /// tree information when a node's immediate dominator changes. 190 /// 191 void changeImmediateDominator(MachineBasicBlock *N, 192 MachineBasicBlock *NewIDom) { 193 applySplitCriticalEdges(); 194 DT->changeImmediateDominator(N, NewIDom); 195 } 196 197 void changeImmediateDominator(MachineDomTreeNode *N, 198 MachineDomTreeNode *NewIDom) { 199 applySplitCriticalEdges(); 200 DT->changeImmediateDominator(N, NewIDom); 201 } 202 203 /// eraseNode - Removes a node from the dominator tree. Block must not 204 /// dominate any other blocks. Removes node from its immediate dominator's 205 /// children list. Deletes dominator node associated with basic block BB. 206 void eraseNode(MachineBasicBlock *BB) { 207 applySplitCriticalEdges(); 208 DT->eraseNode(BB); 209 } 210 211 /// splitBlock - BB is split and now it has one successor. Update dominator 212 /// tree to reflect this change. 213 void splitBlock(MachineBasicBlock* NewBB) { 214 applySplitCriticalEdges(); 215 DT->splitBlock(NewBB); 216 } 217 218 /// isReachableFromEntry - Return true if A is dominated by the entry 219 /// block of the function containing it. 220 bool isReachableFromEntry(const MachineBasicBlock *A) { 221 applySplitCriticalEdges(); 222 return DT->isReachableFromEntry(A); 223 } 224 225 void releaseMemory() override; 226 227 void verifyAnalysis() const override; 228 229 void print(raw_ostream &OS, const Module*) const override; 230 231 /// Record that the critical edge (FromBB, ToBB) has been 232 /// split with NewBB. 233 /// This is best to use this method instead of directly update the 234 /// underlying information, because this helps mitigating the 235 /// number of time the DT information is invalidated. 236 /// 237 /// \note Do not use this method with regular edges. 238 /// 239 /// \note To benefit from the compile time improvement incurred by this 240 /// method, the users of this method have to limit the queries to the DT 241 /// interface between two edges splitting. In other words, they have to 242 /// pack the splitting of critical edges as much as possible. 243 void recordSplitCriticalEdge(MachineBasicBlock *FromBB, 244 MachineBasicBlock *ToBB, 245 MachineBasicBlock *NewBB) { 246 bool Inserted = NewBBs.insert(NewBB).second; 247 (void)Inserted; 248 assert(Inserted && 249 "A basic block inserted via edge splitting cannot appear twice"); 250 CriticalEdgesToSplit.push_back({FromBB, ToBB, NewBB}); 251 } 252 }; 253 254 //===------------------------------------- 255 /// DominatorTree GraphTraits specialization so the DominatorTree can be 256 /// iterable by generic graph iterators. 257 /// 258 259 template <class Node, class ChildIterator> 260 struct MachineDomTreeGraphTraitsBase { 261 using NodeRef = Node *; 262 using ChildIteratorType = ChildIterator; 263 264 static NodeRef getEntryNode(NodeRef N) { return N; } 265 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); } 266 static ChildIteratorType child_end(NodeRef N) { return N->end(); } 267 }; 268 269 template <class T> struct GraphTraits; 270 271 template <> 272 struct GraphTraits<MachineDomTreeNode *> 273 : public MachineDomTreeGraphTraitsBase<MachineDomTreeNode, 274 MachineDomTreeNode::const_iterator> { 275 }; 276 277 template <> 278 struct GraphTraits<const MachineDomTreeNode *> 279 : public MachineDomTreeGraphTraitsBase<const MachineDomTreeNode, 280 MachineDomTreeNode::const_iterator> { 281 }; 282 283 template <> struct GraphTraits<MachineDominatorTree*> 284 : public GraphTraits<MachineDomTreeNode *> { 285 static NodeRef getEntryNode(MachineDominatorTree *DT) { 286 return DT->getRootNode(); 287 } 288 }; 289 290 } // end namespace llvm 291 292 #endif // LLVM_CODEGEN_MACHINEDOMINATORS_H 293