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 // Does not accept Value to avoid ambiguity with dominance checks between 200 // two basic blocks. 201 bool dominates(const Instruction *Def, const BasicBlock *BB) const; 202 203 /// Return true if an edge dominates a use. 204 /// 205 /// If BBE is not a unique edge between start and end of the edge, it can 206 /// never dominate the use. 207 bool dominates(const BasicBlockEdge &BBE, const Use &U) const; 208 bool dominates(const BasicBlockEdge &BBE, const BasicBlock *BB) const; 209 /// Returns true if edge \p BBE1 dominates edge \p BBE2. 210 bool dominates(const BasicBlockEdge &BBE1, const BasicBlockEdge &BBE2) const; 211 212 // Ensure base class overloads are visible. 213 using Base::isReachableFromEntry; 214 215 /// Provide an overload for a Use. 216 bool isReachableFromEntry(const Use &U) const; 217 218 // Pop up a GraphViz/gv window with the Dominator Tree rendered using `dot`. 219 void viewGraph(const Twine &Name, const Twine &Title); 220 void viewGraph(); 221 }; 222 223 //===------------------------------------- 224 // DominatorTree GraphTraits specializations so the DominatorTree can be 225 // iterable by generic graph iterators. 226 227 template <class Node, class ChildIterator> struct DomTreeGraphTraitsBase { 228 using NodeRef = Node *; 229 using ChildIteratorType = ChildIterator; 230 using nodes_iterator = df_iterator<Node *, df_iterator_default_set<Node*>>; 231 232 static NodeRef getEntryNode(NodeRef N) { return N; } 233 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); } 234 static ChildIteratorType child_end(NodeRef N) { return N->end(); } 235 236 static nodes_iterator nodes_begin(NodeRef N) { 237 return df_begin(getEntryNode(N)); 238 } 239 240 static nodes_iterator nodes_end(NodeRef N) { return df_end(getEntryNode(N)); } 241 }; 242 243 template <> 244 struct GraphTraits<DomTreeNode *> 245 : public DomTreeGraphTraitsBase<DomTreeNode, DomTreeNode::const_iterator> { 246 }; 247 248 template <> 249 struct GraphTraits<const DomTreeNode *> 250 : public DomTreeGraphTraitsBase<const DomTreeNode, 251 DomTreeNode::const_iterator> {}; 252 253 template <> struct GraphTraits<DominatorTree*> 254 : public GraphTraits<DomTreeNode*> { 255 static NodeRef getEntryNode(DominatorTree *DT) { return DT->getRootNode(); } 256 257 static nodes_iterator nodes_begin(DominatorTree *N) { 258 return df_begin(getEntryNode(N)); 259 } 260 261 static nodes_iterator nodes_end(DominatorTree *N) { 262 return df_end(getEntryNode(N)); 263 } 264 }; 265 266 /// Analysis pass which computes a \c DominatorTree. 267 class DominatorTreeAnalysis : public AnalysisInfoMixin<DominatorTreeAnalysis> { 268 friend AnalysisInfoMixin<DominatorTreeAnalysis>; 269 static AnalysisKey Key; 270 271 public: 272 /// Provide the result typedef for this analysis pass. 273 using Result = DominatorTree; 274 275 /// Run the analysis pass over a function and produce a dominator tree. 276 DominatorTree run(Function &F, FunctionAnalysisManager &); 277 }; 278 279 /// Printer pass for the \c DominatorTree. 280 class DominatorTreePrinterPass 281 : public PassInfoMixin<DominatorTreePrinterPass> { 282 raw_ostream &OS; 283 284 public: 285 explicit DominatorTreePrinterPass(raw_ostream &OS); 286 287 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); 288 }; 289 290 /// Verifier pass for the \c DominatorTree. 291 struct DominatorTreeVerifierPass : PassInfoMixin<DominatorTreeVerifierPass> { 292 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); 293 }; 294 295 /// Enables verification of dominator trees. 296 /// 297 /// This check is expensive and is disabled by default. `-verify-dom-info` 298 /// allows selectively enabling the check without needing to recompile. 299 extern bool VerifyDomInfo; 300 301 /// Legacy analysis pass which computes a \c DominatorTree. 302 class DominatorTreeWrapperPass : public FunctionPass { 303 DominatorTree DT; 304 305 public: 306 static char ID; 307 308 DominatorTreeWrapperPass(); 309 310 DominatorTree &getDomTree() { return DT; } 311 const DominatorTree &getDomTree() const { return DT; } 312 313 bool runOnFunction(Function &F) override; 314 315 void verifyAnalysis() const override; 316 317 void getAnalysisUsage(AnalysisUsage &AU) const override { 318 AU.setPreservesAll(); 319 } 320 321 void releaseMemory() override { DT.reset(); } 322 323 void print(raw_ostream &OS, const Module *M = nullptr) const override; 324 }; 325 } // end namespace llvm 326 327 #endif // LLVM_IR_DOMINATORS_H 328