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