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:
BasicBlockEdge(const BasicBlock * Start_,const BasicBlock * End_)54   BasicBlockEdge(const BasicBlock *Start_, const BasicBlock *End_) :
55     Start(Start_), End(End_) { }
getStart()56   const BasicBlock *getStart() const {
57     return Start;
58   }
getEnd()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 
DominatorTree()87   DominatorTree() : DominatorTreeBase<BasicBlock>(false) {}
DominatorTree(Function & F)88   explicit DominatorTree(Function &F) : DominatorTreeBase<BasicBlock>(false) {
89     recalculate(F);
90   }
91 
DominatorTree(DominatorTree && Arg)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.
compare(const DominatorTree & Other)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 
getEntryNodeDomTreeGraphTraitsBase149   static NodeType *getEntryNode(NodeType *N) { return N; }
child_beginDomTreeGraphTraitsBase150   static inline ChildIteratorType child_begin(NodeType *N) {
151     return N->begin();
152   }
child_endDomTreeGraphTraitsBase153   static inline ChildIteratorType child_end(NodeType *N) { return N->end(); }
154 
nodes_beginDomTreeGraphTraitsBase155   static nodes_iterator nodes_begin(NodeType *N) {
156     return df_begin(getEntryNode(N));
157   }
158 
nodes_endDomTreeGraphTraitsBase159   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