Home | History | Annotate | Download | only in IR 
      1 //===- Dominators.h - Dominator Info Calculation ----------------*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file defines the DominatorTree class, which provides fast and efficient
     11 // dominance queries.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #ifndef LLVM_IR_DOMINATORS_H
     16 #define LLVM_IR_DOMINATORS_H
     17 
     18 #include "llvm/ADT/DenseMap.h"
     19 #include "llvm/ADT/DepthFirstIterator.h"
     20 #include "llvm/ADT/GraphTraits.h"
     21 #include "llvm/ADT/SmallPtrSet.h"
     22 #include "llvm/ADT/SmallVector.h"
     23 #include "llvm/IR/BasicBlock.h"
     24 #include "llvm/IR/CFG.h"
     25 #include "llvm/IR/Function.h"
     26 #include "llvm/Pass.h"
     27 #include "llvm/Support/Compiler.h"
     28 #include "llvm/Support/GenericDomTree.h"
     29 #include "llvm/Support/raw_ostream.h"
     30 #include <algorithm>
     31 
     32 namespace llvm {
     33 
     34 // FIXME: Replace this brittle forward declaration with the include of the new
     35 // PassManager.h when doing so doesn't break the PassManagerBuilder.
     36 template <typename IRUnitT> class AnalysisManager;
     37 class PreservedAnalyses;
     38 
     39 extern template class DomTreeNodeBase<BasicBlock>;
     40 extern template class DominatorTreeBase<BasicBlock>;
     41 
     42 extern template void Calculate<Function, BasicBlock *>(
     43     DominatorTreeBase<GraphTraits<BasicBlock *>::NodeType> &DT, Function &F);
     44 extern template void Calculate<Function, Inverse<BasicBlock *>>(
     45     DominatorTreeBase<GraphTraits<Inverse<BasicBlock *>>::NodeType> &DT,
     46     Function &F);
     47 
     48 typedef DomTreeNodeBase<BasicBlock> DomTreeNode;
     49 
     50 class BasicBlockEdge {
     51   const BasicBlock *Start;
     52   const BasicBlock *End;
     53 public:
     54   BasicBlockEdge(const BasicBlock *Start_, const BasicBlock *End_) :
     55     Start(Start_), End(End_) { }
     56   const BasicBlock *getStart() const {
     57     return Start;
     58   }
     59   const BasicBlock *getEnd() const {
     60     return End;
     61   }
     62   bool isSingleEdge() const;
     63 };
     64 
     65 /// \brief Concrete subclass of DominatorTreeBase that is used to compute a
     66 /// normal dominator tree.
     67 ///
     68 /// Definition: A block is said to be forward statically reachable if there is
     69 /// a path from the entry of the function to the block.  A statically reachable
     70 /// block may become statically unreachable during optimization.
     71 ///
     72 /// A forward unreachable block may appear in the dominator tree, or it may
     73 /// not.  If it does, dominance queries will return results as if all reachable
     74 /// blocks dominate it.  When asking for a Node corresponding to a potentially
     75 /// unreachable block, calling code must handle the case where the block was
     76 /// unreachable and the result of getNode() is nullptr.
     77 ///
     78 /// Generally, a block known to be unreachable when the dominator tree is
     79 /// constructed will not be in the tree.  One which becomes unreachable after
     80 /// the dominator tree is initially constructed may still exist in the tree,
     81 /// even if the tree is properly updated. Calling code should not rely on the
     82 /// preceding statements; this is stated only to assist human understanding.
     83 class DominatorTree : public DominatorTreeBase<BasicBlock> {
     84 public:
     85   typedef DominatorTreeBase<BasicBlock> Base;
     86 
     87   DominatorTree() : DominatorTreeBase<BasicBlock>(false) {}
     88   explicit DominatorTree(Function &F) : DominatorTreeBase<BasicBlock>(false) {
     89     recalculate(F);
     90   }
     91 
     92   DominatorTree(DominatorTree &&Arg)
     93       : Base(std::move(static_cast<Base &>(Arg))) {}
     94   DominatorTree &operator=(DominatorTree &&RHS) {
     95     Base::operator=(std::move(static_cast<Base &>(RHS)));
     96     return *this;
     97   }
     98 
     99   /// \brief Returns *false* if the other dominator tree matches this dominator
    100   /// tree.
    101   inline bool compare(const DominatorTree &Other) const {
    102     const DomTreeNode *R = getRootNode();
    103     const DomTreeNode *OtherR = Other.getRootNode();
    104 
    105     if (!R || !OtherR || R->getBlock() != OtherR->getBlock())
    106       return true;
    107 
    108     if (Base::compare(Other))
    109       return true;
    110 
    111     return false;
    112   }
    113 
    114   // Ensure base-class overloads are visible.
    115   using Base::dominates;
    116 
    117   /// \brief Return true if Def dominates a use in User.
    118   ///
    119   /// This performs the special checks necessary if Def and User are in the same
    120   /// basic block. Note that Def doesn't dominate a use in Def itself!
    121   bool dominates(const Instruction *Def, const Use &U) const;
    122   bool dominates(const Instruction *Def, const Instruction *User) const;
    123   bool dominates(const Instruction *Def, const BasicBlock *BB) const;
    124   bool dominates(const BasicBlockEdge &BBE, const Use &U) const;
    125   bool dominates(const BasicBlockEdge &BBE, const BasicBlock *BB) const;
    126 
    127   // Ensure base class overloads are visible.
    128   using Base::isReachableFromEntry;
    129 
    130   /// \brief Provide an overload for a Use.
    131   bool isReachableFromEntry(const Use &U) const;
    132 
    133   /// \brief Verify the correctness of the domtree by re-computing it.
    134   ///
    135   /// This should only be used for debugging as it aborts the program if the
    136   /// verification fails.
    137   void verifyDomTree() const;
    138 };
    139 
    140 //===-------------------------------------
    141 // DominatorTree GraphTraits specializations so the DominatorTree can be
    142 // iterable by generic graph iterators.
    143 
    144 template <class Node, class ChildIterator> struct DomTreeGraphTraitsBase {
    145   typedef Node NodeType;
    146   typedef ChildIterator ChildIteratorType;
    147   typedef df_iterator<Node *, SmallPtrSet<NodeType *, 8>> nodes_iterator;
    148 
    149   static NodeType *getEntryNode(NodeType *N) { return N; }
    150   static inline ChildIteratorType child_begin(NodeType *N) {
    151     return N->begin();
    152   }
    153   static inline ChildIteratorType child_end(NodeType *N) { return N->end(); }
    154 
    155   static nodes_iterator nodes_begin(NodeType *N) {
    156     return df_begin(getEntryNode(N));
    157   }
    158 
    159   static nodes_iterator nodes_end(NodeType *N) {
    160     return df_end(getEntryNode(N));
    161   }
    162 };
    163 
    164 template <>
    165 struct GraphTraits<DomTreeNode *>
    166     : public DomTreeGraphTraitsBase<DomTreeNode, DomTreeNode::iterator> {};
    167 
    168 template <>
    169 struct GraphTraits<const DomTreeNode *>
    170     : public DomTreeGraphTraitsBase<const DomTreeNode,
    171                                     DomTreeNode::const_iterator> {};
    172 
    173 template <> struct GraphTraits<DominatorTree*>
    174   : public GraphTraits<DomTreeNode*> {
    175   static NodeType *getEntryNode(DominatorTree *DT) {
    176     return DT->getRootNode();
    177   }
    178 
    179   static nodes_iterator nodes_begin(DominatorTree *N) {
    180     return df_begin(getEntryNode(N));
    181   }
    182 
    183   static nodes_iterator nodes_end(DominatorTree *N) {
    184     return df_end(getEntryNode(N));
    185   }
    186 };
    187 
    188 /// \brief Analysis pass which computes a \c DominatorTree.
    189 class DominatorTreeAnalysis {
    190 public:
    191   /// \brief Provide the result typedef for this analysis pass.
    192   typedef DominatorTree Result;
    193 
    194   /// \brief Opaque, unique identifier for this analysis pass.
    195   static void *ID() { return (void *)&PassID; }
    196 
    197   /// \brief Run the analysis pass over a function and produce a dominator tree.
    198   DominatorTree run(Function &F);
    199 
    200   /// \brief Provide access to a name for this pass for debugging purposes.
    201   static StringRef name() { return "DominatorTreeAnalysis"; }
    202 
    203 private:
    204   static char PassID;
    205 };
    206 
    207 /// \brief Printer pass for the \c DominatorTree.
    208 class DominatorTreePrinterPass {
    209   raw_ostream &OS;
    210 
    211 public:
    212   explicit DominatorTreePrinterPass(raw_ostream &OS);
    213   PreservedAnalyses run(Function &F, AnalysisManager<Function> *AM);
    214 
    215   static StringRef name() { return "DominatorTreePrinterPass"; }
    216 };
    217 
    218 /// \brief Verifier pass for the \c DominatorTree.
    219 struct DominatorTreeVerifierPass {
    220   PreservedAnalyses run(Function &F, AnalysisManager<Function> *AM);
    221 
    222   static StringRef name() { return "DominatorTreeVerifierPass"; }
    223 };
    224 
    225 /// \brief Legacy analysis pass which computes a \c DominatorTree.
    226 class DominatorTreeWrapperPass : public FunctionPass {
    227   DominatorTree DT;
    228 
    229 public:
    230   static char ID;
    231 
    232   DominatorTreeWrapperPass() : FunctionPass(ID) {
    233     initializeDominatorTreeWrapperPassPass(*PassRegistry::getPassRegistry());
    234   }
    235 
    236   DominatorTree &getDomTree() { return DT; }
    237   const DominatorTree &getDomTree() const { return DT; }
    238 
    239   bool runOnFunction(Function &F) override;
    240 
    241   void verifyAnalysis() const override;
    242 
    243   void getAnalysisUsage(AnalysisUsage &AU) const override {
    244     AU.setPreservesAll();
    245   }
    246 
    247   void releaseMemory() override { DT.releaseMemory(); }
    248 
    249   void print(raw_ostream &OS, const Module *M = nullptr) const override;
    250 };
    251 
    252 } // End llvm namespace
    253 
    254 #endif
    255