include/llvm/IR/Dominators.h

   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 extern template void Calculate<BBDomTree>(BBDomTree &DT);
  48 extern template void CalculateWithUpdates<BBDomTree>(BBDomTree &DT,
  49                                                      BBUpdates U);
  50
  51 extern template void Calculate<BBPostDomTree>(BBPostDomTree &DT);
  52
  53 extern template void InsertEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From,
  54                                            BasicBlock *To);
  55 extern template void InsertEdge<BBPostDomTree>(BBPostDomTree &DT,
  56                                                BasicBlock *From,
  57                                                BasicBlock *To);
  58
  59 extern template void DeleteEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From,
  60                                            BasicBlock *To);
  61 extern template void DeleteEdge<BBPostDomTree>(BBPostDomTree &DT,
  62                                                BasicBlock *From,
  63                                                BasicBlock *To);
  64
  65 extern template void ApplyUpdates<BBDomTree>(BBDomTree &DT, BBUpdates);
  66 extern template void ApplyUpdates<BBPostDomTree>(BBPostDomTree &DT, BBUpdates);
  67
  68 extern template bool Verify<BBDomTree>(const BBDomTree &DT,
  69                                        BBDomTree::VerificationLevel VL);
  70 extern template bool Verify<BBPostDomTree>(const BBPostDomTree &DT,
  71                                            BBPostDomTree::VerificationLevel VL);
  72 }  // namespace DomTreeBuilder
  73
  74 using DomTreeNode = DomTreeNodeBase<BasicBlock>;
  75
  76 class BasicBlockEdge {
  77   const BasicBlock *Start;
  78   const BasicBlock *End;
  79
  80 public:
  81   BasicBlockEdge(const BasicBlock *Start_, const BasicBlock *End_) :
  82     Start(Start_), End(End_) {}
  83
  84   BasicBlockEdge(const std::pair<BasicBlock *, BasicBlock *> &Pair)
  85       : Start(Pair.first), End(Pair.second) {}
  86
  87   BasicBlockEdge(const std::pair<const BasicBlock *, const BasicBlock *> &Pair)
  88       : Start(Pair.first), End(Pair.second) {}
  89
  90   const BasicBlock *getStart() const {
  91     return Start;
  92   }
  93
  94   const BasicBlock *getEnd() const {
  95     return End;
  96   }
  97
  98   /// Check if this is the only edge between Start and End.
  99   bool isSingleEdge() const;
 100 };
 101
 102 template <> struct DenseMapInfo<BasicBlockEdge> {
 103   using BBInfo = DenseMapInfo<const BasicBlock *>;
 104
 105   static unsigned getHashValue(const BasicBlockEdge *V);
 106
 107   static inline BasicBlockEdge getEmptyKey() {
 108     return BasicBlockEdge(BBInfo::getEmptyKey(), BBInfo::getEmptyKey());
 109   }
 110
 111   static inline BasicBlockEdge getTombstoneKey() {
 112     return BasicBlockEdge(BBInfo::getTombstoneKey(), BBInfo::getTombstoneKey());
 113   }
 114
 115   static unsigned getHashValue(const BasicBlockEdge &Edge) {
 116     return hash_combine(BBInfo::getHashValue(Edge.getStart()),
 117                         BBInfo::getHashValue(Edge.getEnd()));
 118   }
 119
 120   static bool isEqual(const BasicBlockEdge &LHS, const BasicBlockEdge &RHS) {
 121     return BBInfo::isEqual(LHS.getStart(), RHS.getStart()) &&
 122            BBInfo::isEqual(LHS.getEnd(), RHS.getEnd());
 123   }
 124 };
 125
 126 /// Concrete subclass of DominatorTreeBase that is used to compute a
 127 /// normal dominator tree.
 128 ///
 129 /// Definition: A block is said to be forward statically reachable if there is
 130 /// a path from the entry of the function to the block.  A statically reachable
 131 /// block may become statically unreachable during optimization.
 132 ///
 133 /// A forward unreachable block may appear in the dominator tree, or it may
 134 /// not.  If it does, dominance queries will return results as if all reachable
 135 /// blocks dominate it.  When asking for a Node corresponding to a potentially
 136 /// unreachable block, calling code must handle the case where the block was
 137 /// unreachable and the result of getNode() is nullptr.
 138 ///
 139 /// Generally, a block known to be unreachable when the dominator tree is
 140 /// constructed will not be in the tree.  One which becomes unreachable after
 141 /// the dominator tree is initially constructed may still exist in the tree,
 142 /// even if the tree is properly updated. Calling code should not rely on the
 143 /// preceding statements; this is stated only to assist human understanding.
 144 class DominatorTree : public DominatorTreeBase<BasicBlock, false> {
 145  public:
 146   using Base = DominatorTreeBase<BasicBlock, false>;
 147
 148   DominatorTree() = default;
 149   explicit DominatorTree(Function &F) { recalculate(F); }
 150   explicit DominatorTree(DominatorTree &DT, DomTreeBuilder::BBUpdates U) {
 151     recalculate(*DT.Parent, U);
 152   }
 153
 154   /// Handle invalidation explicitly.
 155   bool invalidate(Function &F, const PreservedAnalyses &PA,
 156                   FunctionAnalysisManager::Invalidator &);
 157
 158   // Ensure base-class overloads are visible.
 159   using Base::dominates;
 160
 161   /// Return true if Def dominates a use in User.
 162   ///
 163   /// This performs the special checks necessary if Def and User are in the same
 164   /// basic block. Note that Def doesn't dominate a use in Def itself!
 165   bool dominates(const Instruction *Def, const Use &U) const;
 166   bool dominates(const Instruction *Def, const Instruction *User) const;
 167   bool dominates(const Instruction *Def, const BasicBlock *BB) const;
 168
 169   /// Return true if an edge dominates a use.
 170   ///
 171   /// If BBE is not a unique edge between start and end of the edge, it can
 172   /// never dominate the use.
 173   bool dominates(const BasicBlockEdge &BBE, const Use &U) const;
 174   bool dominates(const BasicBlockEdge &BBE, const BasicBlock *BB) const;
 175
 176   // Ensure base class overloads are visible.
 177   using Base::isReachableFromEntry;
 178
 179   /// Provide an overload for a Use.
 180   bool isReachableFromEntry(const Use &U) const;
 181
 182   // Pop up a GraphViz/gv window with the Dominator Tree rendered using `dot`.
 183   void viewGraph(const Twine &Name, const Twine &Title);
 184   void viewGraph();
 185 };
 186
 187 //===-------------------------------------
 188 // DominatorTree GraphTraits specializations so the DominatorTree can be
 189 // iterable by generic graph iterators.
 190
 191 template <class Node, class ChildIterator> struct DomTreeGraphTraitsBase {
 192   using NodeRef = Node *;
 193   using ChildIteratorType = ChildIterator;
 194   using nodes_iterator = df_iterator<Node *, df_iterator_default_set<Node*>>;
 195
 196   static NodeRef getEntryNode(NodeRef N) { return N; }
 197   static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
 198   static ChildIteratorType child_end(NodeRef N) { return N->end(); }
 199
 200   static nodes_iterator nodes_begin(NodeRef N) {
 201     return df_begin(getEntryNode(N));
 202   }
 203
 204   static nodes_iterator nodes_end(NodeRef N) { return df_end(getEntryNode(N)); }
 205 };
 206
 207 template <>
 208 struct GraphTraits<DomTreeNode *>
 209     : public DomTreeGraphTraitsBase<DomTreeNode, DomTreeNode::iterator> {};
 210
 211 template <>
 212 struct GraphTraits<const DomTreeNode *>
 213     : public DomTreeGraphTraitsBase<const DomTreeNode,
 214                                     DomTreeNode::const_iterator> {};
 215
 216 template <> struct GraphTraits<DominatorTree*>
 217   : public GraphTraits<DomTreeNode*> {
 218   static NodeRef getEntryNode(DominatorTree *DT) { return DT->getRootNode(); }
 219
 220   static nodes_iterator nodes_begin(DominatorTree *N) {
 221     return df_begin(getEntryNode(N));
 222   }
 223
 224   static nodes_iterator nodes_end(DominatorTree *N) {
 225     return df_end(getEntryNode(N));
 226   }
 227 };
 228
 229 /// Analysis pass which computes a \c DominatorTree.
 230 class DominatorTreeAnalysis : public AnalysisInfoMixin<DominatorTreeAnalysis> {
 231   friend AnalysisInfoMixin<DominatorTreeAnalysis>;
 232   static AnalysisKey Key;
 233
 234 public:
 235   /// Provide the result typedef for this analysis pass.
 236   using Result = DominatorTree;
 237
 238   /// Run the analysis pass over a function and produce a dominator tree.
 239   DominatorTree run(Function &F, FunctionAnalysisManager &);
 240 };
 241
 242 /// Printer pass for the \c DominatorTree.
 243 class DominatorTreePrinterPass
 244     : public PassInfoMixin<DominatorTreePrinterPass> {
 245   raw_ostream &OS;
 246
 247 public:
 248   explicit DominatorTreePrinterPass(raw_ostream &OS);
 249
 250   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
 251 };
 252
 253 /// Verifier pass for the \c DominatorTree.
 254 struct DominatorTreeVerifierPass : PassInfoMixin<DominatorTreeVerifierPass> {
 255   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
 256 };
 257
 258 /// Legacy analysis pass which computes a \c DominatorTree.
 259 class DominatorTreeWrapperPass : public FunctionPass {
 260   DominatorTree DT;
 261
 262 public:
 263   static char ID;
 264
 265   DominatorTreeWrapperPass() : FunctionPass(ID) {
 266     initializeDominatorTreeWrapperPassPass(*PassRegistry::getPassRegistry());
 267   }
 268
 269   DominatorTree &getDomTree() { return DT; }
 270   const DominatorTree &getDomTree() const { return DT; }
 271
 272   bool runOnFunction(Function &F) override;
 273
 274   void verifyAnalysis() const override;
 275
 276   void getAnalysisUsage(AnalysisUsage &AU) const override {
 277     AU.setPreservesAll();
 278   }
 279
 280   void releaseMemory() override { DT.releaseMemory(); }
 281
 282   void print(raw_ostream &OS, const Module *M = nullptr) const override;
 283 };
 284 } // end namespace llvm
 285
 286 #endif // LLVM_IR_DOMINATORS_H