1 //===- Dominators.h - Dominator Info 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 the DominatorTree class, which provides fast and efficient 10 // dominance queries. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_IR_DOMINATORS_H 15 #define LLVM_IR_DOMINATORS_H 16 17 #include "llvm/ADT/DenseMapInfo.h" 18 #include "llvm/ADT/DepthFirstIterator.h" 19 #include "llvm/ADT/GraphTraits.h" 20 #include "llvm/ADT/Hashing.h" 21 #include "llvm/IR/BasicBlock.h" 22 #include "llvm/IR/CFG.h" 23 #include "llvm/IR/PassManager.h" 24 #include "llvm/Pass.h" 25 #include "llvm/Support/GenericDomTree.h" 26 #include <utility> 27 28 namespace llvm { 29 30 class Function; 31 class Instruction; 32 class Module; 33 class raw_ostream; 34 35 extern template class DomTreeNodeBase<BasicBlock>; 36 extern template class DominatorTreeBase<BasicBlock, false>; // DomTree 37 extern template class DominatorTreeBase<BasicBlock, true>; // PostDomTree 38 39 extern template class cfg::Update<BasicBlock *>; 40 41 namespace DomTreeBuilder { 42 using BBDomTree = DomTreeBase<BasicBlock>; 43 using BBPostDomTree = PostDomTreeBase<BasicBlock>; 44 45 using BBUpdates = ArrayRef<llvm::cfg::Update<BasicBlock *>>; 46 47 using BBDomTreeGraphDiff = GraphDiff<BasicBlock *, false>; 48 using BBPostDomTreeGraphDiff = GraphDiff<BasicBlock *, true>; 49 50 extern template void Calculate<BBDomTree>(BBDomTree &DT); 51 extern template void CalculateWithUpdates<BBDomTree>(BBDomTree &DT, 52 BBUpdates U); 53 54 extern template void Calculate<BBPostDomTree>(BBPostDomTree &DT); 55 56 extern template void InsertEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From, 57 BasicBlock *To); 58 extern template void InsertEdge<BBPostDomTree>(BBPostDomTree &DT, 59 BasicBlock *From, 60 BasicBlock *To); 61 62 extern template void DeleteEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From, 63 BasicBlock *To); 64 extern template void DeleteEdge<BBPostDomTree>(BBPostDomTree &DT, 65 BasicBlock *From, 66 BasicBlock *To); 67 68 extern template void ApplyUpdates<BBDomTree>(BBDomTree &DT, 69 BBDomTreeGraphDiff &, 70 BBDomTreeGraphDiff *); 71 extern template void ApplyUpdates<BBPostDomTree>(BBPostDomTree &DT, 72 BBPostDomTreeGraphDiff &, 73 BBPostDomTreeGraphDiff *); 74 75 extern template bool Verify<BBDomTree>(const BBDomTree &DT, 76 BBDomTree::VerificationLevel VL); 77 extern template bool Verify<BBPostDomTree>(const BBPostDomTree &DT, 78 BBPostDomTree::VerificationLevel VL); 79 } // namespace DomTreeBuilder 80 81 using DomTreeNode = DomTreeNodeBase<BasicBlock>; 82 83 class BasicBlockEdge { 84 const BasicBlock *Start; 85 const BasicBlock *End; 86 87 public: 88 BasicBlockEdge(const BasicBlock *Start_, const BasicBlock *End_) : 89 Start(Start_), End(End_) {} 90 91 BasicBlockEdge(const std::pair<BasicBlock *, BasicBlock *> &Pair) 92 : Start(Pair.first), End(Pair.second) {} 93 94 BasicBlockEdge(const std::pair<const BasicBlock *, const BasicBlock *> &Pair) 95 : Start(Pair.first), End(Pair.second) {} 96 97 const BasicBlock *getStart() const { 98 return Start; 99 } 100 101 const BasicBlock *getEnd() const { 102 return End; 103 } 104 105 /// Check if this is the only edge between Start and End. 106 bool isSingleEdge() const; 107 }; 108 109 template <> struct DenseMapInfo<BasicBlockEdge> { 110 using BBInfo = DenseMapInfo<const BasicBlock *>; 111 112 static unsigned getHashValue(const BasicBlockEdge *V); 113 114 static inline BasicBlockEdge getEmptyKey() { 115 return BasicBlockEdge(BBInfo::getEmptyKey(), BBInfo::getEmptyKey()); 116 } 117 118 static inline BasicBlockEdge getTombstoneKey() { 119 return BasicBlockEdge(BBInfo::getTombstoneKey(), BBInfo::getTombstoneKey()); 120 } 121 122 static unsigned getHashValue(const BasicBlockEdge &Edge) { 123 return hash_combine(BBInfo::getHashValue(Edge.getStart()), 124 BBInfo::getHashValue(Edge.getEnd())); 125 } 126 127 static bool isEqual(const BasicBlockEdge &LHS, const BasicBlockEdge &RHS) { 128 return BBInfo::isEqual(LHS.getStart(), RHS.getStart()) && 129 BBInfo::isEqual(LHS.getEnd(), RHS.getEnd()); 130 } 131 }; 132 133 /// Concrete subclass of DominatorTreeBase that is used to compute a 134 /// normal dominator tree. 135 /// 136 /// Definition: A block is said to be forward statically reachable if there is 137 /// a path from the entry of the function to the block. A statically reachable 138 /// block may become statically unreachable during optimization. 139 /// 140 /// A forward unreachable block may appear in the dominator tree, or it may 141 /// not. If it does, dominance queries will return results as if all reachable 142 /// blocks dominate it. When asking for a Node corresponding to a potentially 143 /// unreachable block, calling code must handle the case where the block was 144 /// unreachable and the result of getNode() is nullptr. 145 /// 146 /// Generally, a block known to be unreachable when the dominator tree is 147 /// constructed will not be in the tree. One which becomes unreachable after 148 /// the dominator tree is initially constructed may still exist in the tree, 149 /// even if the tree is properly updated. Calling code should not rely on the 150 /// preceding statements; this is stated only to assist human understanding. 151 class DominatorTree : public DominatorTreeBase<BasicBlock, false> { 152 public: 153 using Base = DominatorTreeBase<BasicBlock, false>; 154 155 DominatorTree() = default; 156 explicit DominatorTree(Function &F) { recalculate(F); } 157 explicit DominatorTree(DominatorTree &DT, DomTreeBuilder::BBUpdates U) { 158 recalculate(*DT.Parent, U); 159 } 160 161 /// Handle invalidation explicitly. 162 bool invalidate(Function &F, const PreservedAnalyses &PA, 163 FunctionAnalysisManager::Invalidator &); 164 165 // Ensure base-class overloads are visible. 166 using Base::dominates; 167 168 /// Return true if value Def dominates use U, in the sense that Def is 169 /// available at U, and could be substituted as the used value without 170 /// violating the SSA dominance requirement. 171 /// 172 /// In particular, it is worth noting that: 173 /// * Non-instruction Defs dominate everything. 174 /// * Def does not dominate a use in Def itself (outside of degenerate cases 175 /// like unreachable code or trivial phi cycles). 176 /// * Invoke/callbr Defs only dominate uses in their default destination. 177 bool dominates(const Value *Def, const Use &U) const; 178 /// Return true if value Def dominates all possible uses inside instruction 179 /// User. Same comments as for the Use-based API apply. 180 bool dominates(const Value *Def, const Instruction *User) const; 181 // Does not accept Value to avoid ambiguity with dominance checks between 182 // two basic blocks. 183 bool dominates(const Instruction *Def, const BasicBlock *BB) const; 184 185 /// Return true if an edge dominates a use. 186 /// 187 /// If BBE is not a unique edge between start and end of the edge, it can 188 /// never dominate the use. 189 bool dominates(const BasicBlockEdge &BBE, const Use &U) const; 190 bool dominates(const BasicBlockEdge &BBE, const BasicBlock *BB) const; 191 /// Returns true if edge \p BBE1 dominates edge \p BBE2. 192 bool dominates(const BasicBlockEdge &BBE1, const BasicBlockEdge &BBE2) const; 193 194 // Ensure base class overloads are visible. 195 using Base::isReachableFromEntry; 196 197 /// Provide an overload for a Use. 198 bool isReachableFromEntry(const Use &U) const; 199 200 // Pop up a GraphViz/gv window with the Dominator Tree rendered using `dot`. 201 void viewGraph(const Twine &Name, const Twine &Title); 202 void viewGraph(); 203 }; 204 205 //===------------------------------------- 206 // DominatorTree GraphTraits specializations so the DominatorTree can be 207 // iterable by generic graph iterators. 208 209 template <class Node, class ChildIterator> struct DomTreeGraphTraitsBase { 210 using NodeRef = Node *; 211 using ChildIteratorType = ChildIterator; 212 using nodes_iterator = df_iterator<Node *, df_iterator_default_set<Node*>>; 213 214 static NodeRef getEntryNode(NodeRef N) { return N; } 215 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); } 216 static ChildIteratorType child_end(NodeRef N) { return N->end(); } 217 218 static nodes_iterator nodes_begin(NodeRef N) { 219 return df_begin(getEntryNode(N)); 220 } 221 222 static nodes_iterator nodes_end(NodeRef N) { return df_end(getEntryNode(N)); } 223 }; 224 225 template <> 226 struct GraphTraits<DomTreeNode *> 227 : public DomTreeGraphTraitsBase<DomTreeNode, DomTreeNode::const_iterator> { 228 }; 229 230 template <> 231 struct GraphTraits<const DomTreeNode *> 232 : public DomTreeGraphTraitsBase<const DomTreeNode, 233 DomTreeNode::const_iterator> {}; 234 235 template <> struct GraphTraits<DominatorTree*> 236 : public GraphTraits<DomTreeNode*> { 237 static NodeRef getEntryNode(DominatorTree *DT) { return DT->getRootNode(); } 238 239 static nodes_iterator nodes_begin(DominatorTree *N) { 240 return df_begin(getEntryNode(N)); 241 } 242 243 static nodes_iterator nodes_end(DominatorTree *N) { 244 return df_end(getEntryNode(N)); 245 } 246 }; 247 248 /// Analysis pass which computes a \c DominatorTree. 249 class DominatorTreeAnalysis : public AnalysisInfoMixin<DominatorTreeAnalysis> { 250 friend AnalysisInfoMixin<DominatorTreeAnalysis>; 251 static AnalysisKey Key; 252 253 public: 254 /// Provide the result typedef for this analysis pass. 255 using Result = DominatorTree; 256 257 /// Run the analysis pass over a function and produce a dominator tree. 258 DominatorTree run(Function &F, FunctionAnalysisManager &); 259 }; 260 261 /// Printer pass for the \c DominatorTree. 262 class DominatorTreePrinterPass 263 : public PassInfoMixin<DominatorTreePrinterPass> { 264 raw_ostream &OS; 265 266 public: 267 explicit DominatorTreePrinterPass(raw_ostream &OS); 268 269 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); 270 }; 271 272 /// Verifier pass for the \c DominatorTree. 273 struct DominatorTreeVerifierPass : PassInfoMixin<DominatorTreeVerifierPass> { 274 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); 275 }; 276 277 /// Legacy analysis pass which computes a \c DominatorTree. 278 class DominatorTreeWrapperPass : public FunctionPass { 279 DominatorTree DT; 280 281 public: 282 static char ID; 283 284 DominatorTreeWrapperPass(); 285 286 DominatorTree &getDomTree() { return DT; } 287 const DominatorTree &getDomTree() const { return DT; } 288 289 bool runOnFunction(Function &F) override; 290 291 void verifyAnalysis() const override; 292 293 void getAnalysisUsage(AnalysisUsage &AU) const override { 294 AU.setPreservesAll(); 295 } 296 297 void releaseMemory() override { DT.reset(); } 298 299 void print(raw_ostream &OS, const Module *M = nullptr) const override; 300 }; 301 } // end namespace llvm 302 303 #endif // LLVM_IR_DOMINATORS_H 304