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();
266 
267   DominatorTree &getDomTree() { return DT; }
268   const DominatorTree &getDomTree() const { return DT; }
269 
270   bool runOnFunction(Function &F) override;
271 
272   void verifyAnalysis() const override;
273 
274   void getAnalysisUsage(AnalysisUsage &AU) const override {
275     AU.setPreservesAll();
276   }
277 
278   void releaseMemory() override { DT.releaseMemory(); }
279 
280   void print(raw_ostream &OS, const Module *M = nullptr) const override;
281 };
282 } // end namespace llvm
283 
284 #endif // LLVM_IR_DOMINATORS_H
285