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/APInt.h" 18 #include "llvm/ADT/ArrayRef.h" 19 #include "llvm/ADT/DenseMap.h" 20 #include "llvm/ADT/DenseMapInfo.h" 21 #include "llvm/ADT/DepthFirstIterator.h" 22 #include "llvm/ADT/Hashing.h" 23 #include "llvm/ADT/PointerIntPair.h" 24 #include "llvm/ADT/SmallVector.h" 25 #include "llvm/ADT/Twine.h" 26 #include "llvm/ADT/ilist_iterator.h" 27 #include "llvm/ADT/iterator_range.h" 28 #include "llvm/IR/BasicBlock.h" 29 #include "llvm/IR/CFG.h" 30 #include "llvm/IR/PassManager.h" 31 #include "llvm/IR/Use.h" 32 #include "llvm/Pass.h" 33 #include "llvm/Support/CFGDiff.h" 34 #include "llvm/Support/CFGUpdate.h" 35 #include "llvm/Support/GenericDomTree.h" 36 #include "llvm/Support/GenericDomTreeConstruction.h" 37 #include <algorithm> 38 #include <utility> 39 #include <vector> 40 41 namespace llvm { 42 43 class Function; 44 class Instruction; 45 class Module; 46 class Value; 47 class raw_ostream; 48 template <class GraphType> struct GraphTraits; 49 50 extern template class DomTreeNodeBase<BasicBlock>; 51 extern template class DominatorTreeBase<BasicBlock, false>; // DomTree 52 extern template class DominatorTreeBase<BasicBlock, true>; // PostDomTree 53 54 extern template class cfg::Update<BasicBlock *>; 55 56 namespace DomTreeBuilder { 57 using BBDomTree = DomTreeBase<BasicBlock>; 58 using BBPostDomTree = PostDomTreeBase<BasicBlock>; 59 60 using BBUpdates = ArrayRef<llvm::cfg::Update<BasicBlock *>>; 61 62 using BBDomTreeGraphDiff = GraphDiff<BasicBlock *, false>; 63 using BBPostDomTreeGraphDiff = GraphDiff<BasicBlock *, true>; 64 65 extern template void Calculate<BBDomTree>(BBDomTree &DT); 66 extern template void CalculateWithUpdates<BBDomTree>(BBDomTree &DT, 67 BBUpdates U); 68 69 extern template void Calculate<BBPostDomTree>(BBPostDomTree &DT); 70 71 extern template void InsertEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From, 72 BasicBlock *To); 73 extern template void InsertEdge<BBPostDomTree>(BBPostDomTree &DT, 74 BasicBlock *From, 75 BasicBlock *To); 76 77 extern template void DeleteEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From, 78 BasicBlock *To); 79 extern template void DeleteEdge<BBPostDomTree>(BBPostDomTree &DT, 80 BasicBlock *From, 81 BasicBlock *To); 82 83 extern template void ApplyUpdates<BBDomTree>(BBDomTree &DT, 84 BBDomTreeGraphDiff &, 85 BBDomTreeGraphDiff *); 86 extern template void ApplyUpdates<BBPostDomTree>(BBPostDomTree &DT, 87 BBPostDomTreeGraphDiff &, 88 BBPostDomTreeGraphDiff *); 89 90 extern template bool Verify<BBDomTree>(const BBDomTree &DT, 91 BBDomTree::VerificationLevel VL); 92 extern template bool Verify<BBPostDomTree>(const BBPostDomTree &DT, 93 BBPostDomTree::VerificationLevel VL); 94 } // namespace DomTreeBuilder 95 96 using DomTreeNode = DomTreeNodeBase<BasicBlock>; 97 98 class BasicBlockEdge { 99 const BasicBlock *Start; 100 const BasicBlock *End; 101 102 public: 103 BasicBlockEdge(const BasicBlock *Start_, const BasicBlock *End_) : 104 Start(Start_), End(End_) {} 105 106 BasicBlockEdge(const std::pair<BasicBlock *, BasicBlock *> &Pair) 107 : Start(Pair.first), End(Pair.second) {} 108 109 BasicBlockEdge(const std::pair<const BasicBlock *, const BasicBlock *> &Pair) 110 : Start(Pair.first), End(Pair.second) {} 111 112 const BasicBlock *getStart() const { 113 return Start; 114 } 115 116 const BasicBlock *getEnd() const { 117 return End; 118 } 119 120 /// Check if this is the only edge between Start and End. 121 bool isSingleEdge() const; 122 }; 123 124 template <> struct DenseMapInfo<BasicBlockEdge> { 125 using BBInfo = DenseMapInfo<const BasicBlock *>; 126 127 static unsigned getHashValue(const BasicBlockEdge *V); 128 129 static inline BasicBlockEdge getEmptyKey() { 130 return BasicBlockEdge(BBInfo::getEmptyKey(), BBInfo::getEmptyKey()); 131 } 132 133 static inline BasicBlockEdge getTombstoneKey() { 134 return BasicBlockEdge(BBInfo::getTombstoneKey(), BBInfo::getTombstoneKey()); 135 } 136 137 static unsigned getHashValue(const BasicBlockEdge &Edge) { 138 return hash_combine(BBInfo::getHashValue(Edge.getStart()), 139 BBInfo::getHashValue(Edge.getEnd())); 140 } 141 142 static bool isEqual(const BasicBlockEdge &LHS, const BasicBlockEdge &RHS) { 143 return BBInfo::isEqual(LHS.getStart(), RHS.getStart()) && 144 BBInfo::isEqual(LHS.getEnd(), RHS.getEnd()); 145 } 146 }; 147 148 /// Concrete subclass of DominatorTreeBase that is used to compute a 149 /// normal dominator tree. 150 /// 151 /// Definition: A block is said to be forward statically reachable if there is 152 /// a path from the entry of the function to the block. A statically reachable 153 /// block may become statically unreachable during optimization. 154 /// 155 /// A forward unreachable block may appear in the dominator tree, or it may 156 /// not. If it does, dominance queries will return results as if all reachable 157 /// blocks dominate it. When asking for a Node corresponding to a potentially 158 /// unreachable block, calling code must handle the case where the block was 159 /// unreachable and the result of getNode() is nullptr. 160 /// 161 /// Generally, a block known to be unreachable when the dominator tree is 162 /// constructed will not be in the tree. One which becomes unreachable after 163 /// the dominator tree is initially constructed may still exist in the tree, 164 /// even if the tree is properly updated. Calling code should not rely on the 165 /// preceding statements; this is stated only to assist human understanding. 166 class DominatorTree : public DominatorTreeBase<BasicBlock, false> { 167 public: 168 using Base = DominatorTreeBase<BasicBlock, false>; 169 170 DominatorTree() = default; 171 explicit DominatorTree(Function &F) { recalculate(F); } 172 explicit DominatorTree(DominatorTree &DT, DomTreeBuilder::BBUpdates U) { 173 recalculate(*DT.Parent, U); 174 } 175 176 /// Handle invalidation explicitly. 177 bool invalidate(Function &F, const PreservedAnalyses &PA, 178 FunctionAnalysisManager::Invalidator &); 179 180 // Ensure base-class overloads are visible. 181 using Base::dominates; 182 183 /// Return true if the (end of the) basic block BB dominates the use U. 184 bool dominates(const BasicBlock *BB, const Use &U) const; 185 186 /// Return true if value Def dominates use U, in the sense that Def is 187 /// available at U, and could be substituted as the used value without 188 /// violating the SSA dominance requirement. 189 /// 190 /// In particular, it is worth noting that: 191 /// * Non-instruction Defs dominate everything. 192 /// * Def does not dominate a use in Def itself (outside of degenerate cases 193 /// like unreachable code or trivial phi cycles). 194 /// * Invoke/callbr Defs only dominate uses in their default destination. 195 bool dominates(const Value *Def, const Use &U) const; 196 /// Return true if value Def dominates all possible uses inside instruction 197 /// User. Same comments as for the Use-based API apply. 198 bool dominates(const Value *Def, const Instruction *User) const; 199 200 /// Returns true if Def would dominate a use in any instruction in BB. 201 /// If Def is an instruction in BB, then Def does not dominate BB. 202 /// 203 /// Does not accept Value to avoid ambiguity with dominance checks between 204 /// two basic blocks. 205 bool dominates(const Instruction *Def, const BasicBlock *BB) const; 206 207 /// Return true if an edge dominates a use. 208 /// 209 /// If BBE is not a unique edge between start and end of the edge, it can 210 /// never dominate the use. 211 bool dominates(const BasicBlockEdge &BBE, const Use &U) const; 212 bool dominates(const BasicBlockEdge &BBE, const BasicBlock *BB) const; 213 /// Returns true if edge \p BBE1 dominates edge \p BBE2. 214 bool dominates(const BasicBlockEdge &BBE1, const BasicBlockEdge &BBE2) const; 215 216 // Ensure base class overloads are visible. 217 using Base::isReachableFromEntry; 218 219 /// Provide an overload for a Use. 220 bool isReachableFromEntry(const Use &U) const; 221 222 // Ensure base class overloads are visible. 223 using Base::findNearestCommonDominator; 224 225 /// Find the nearest instruction I that dominates both I1 and I2, in the sense 226 /// that a result produced before I will be available at both I1 and I2. 227 Instruction *findNearestCommonDominator(Instruction *I1, 228 Instruction *I2) const; 229 230 // Pop up a GraphViz/gv window with the Dominator Tree rendered using `dot`. 231 void viewGraph(const Twine &Name, const Twine &Title); 232 void viewGraph(); 233 }; 234 235 //===------------------------------------- 236 // DominatorTree GraphTraits specializations so the DominatorTree can be 237 // iterable by generic graph iterators. 238 239 template <class Node, class ChildIterator> struct DomTreeGraphTraitsBase { 240 using NodeRef = Node *; 241 using ChildIteratorType = ChildIterator; 242 using nodes_iterator = df_iterator<Node *, df_iterator_default_set<Node*>>; 243 244 static NodeRef getEntryNode(NodeRef N) { return N; } 245 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); } 246 static ChildIteratorType child_end(NodeRef N) { return N->end(); } 247 248 static nodes_iterator nodes_begin(NodeRef N) { 249 return df_begin(getEntryNode(N)); 250 } 251 252 static nodes_iterator nodes_end(NodeRef N) { return df_end(getEntryNode(N)); } 253 }; 254 255 template <> 256 struct GraphTraits<DomTreeNode *> 257 : public DomTreeGraphTraitsBase<DomTreeNode, DomTreeNode::const_iterator> { 258 }; 259 260 template <> 261 struct GraphTraits<const DomTreeNode *> 262 : public DomTreeGraphTraitsBase<const DomTreeNode, 263 DomTreeNode::const_iterator> {}; 264 265 template <> struct GraphTraits<DominatorTree*> 266 : public GraphTraits<DomTreeNode*> { 267 static NodeRef getEntryNode(DominatorTree *DT) { return DT->getRootNode(); } 268 269 static nodes_iterator nodes_begin(DominatorTree *N) { 270 return df_begin(getEntryNode(N)); 271 } 272 273 static nodes_iterator nodes_end(DominatorTree *N) { 274 return df_end(getEntryNode(N)); 275 } 276 }; 277 278 /// Analysis pass which computes a \c DominatorTree. 279 class DominatorTreeAnalysis : public AnalysisInfoMixin<DominatorTreeAnalysis> { 280 friend AnalysisInfoMixin<DominatorTreeAnalysis>; 281 static AnalysisKey Key; 282 283 public: 284 /// Provide the result typedef for this analysis pass. 285 using Result = DominatorTree; 286 287 /// Run the analysis pass over a function and produce a dominator tree. 288 DominatorTree run(Function &F, FunctionAnalysisManager &); 289 }; 290 291 /// Printer pass for the \c DominatorTree. 292 class DominatorTreePrinterPass 293 : public PassInfoMixin<DominatorTreePrinterPass> { 294 raw_ostream &OS; 295 296 public: 297 explicit DominatorTreePrinterPass(raw_ostream &OS); 298 299 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); 300 }; 301 302 /// Verifier pass for the \c DominatorTree. 303 struct DominatorTreeVerifierPass : PassInfoMixin<DominatorTreeVerifierPass> { 304 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); 305 }; 306 307 /// Enables verification of dominator trees. 308 /// 309 /// This check is expensive and is disabled by default. `-verify-dom-info` 310 /// allows selectively enabling the check without needing to recompile. 311 extern bool VerifyDomInfo; 312 313 /// Legacy analysis pass which computes a \c DominatorTree. 314 class DominatorTreeWrapperPass : public FunctionPass { 315 DominatorTree DT; 316 317 public: 318 static char ID; 319 320 DominatorTreeWrapperPass(); 321 322 DominatorTree &getDomTree() { return DT; } 323 const DominatorTree &getDomTree() const { return DT; } 324 325 bool runOnFunction(Function &F) override; 326 327 void verifyAnalysis() const override; 328 329 void getAnalysisUsage(AnalysisUsage &AU) const override { 330 AU.setPreservesAll(); 331 } 332 333 void releaseMemory() override { DT.reset(); } 334 335 void print(raw_ostream &OS, const Module *M = nullptr) const override; 336 }; 337 } // end namespace llvm 338 339 #endif // LLVM_IR_DOMINATORS_H 340