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/DenseMapInfo.h" |
20 | #include "llvm/ADT/DepthFirstIterator.h" |
21 | #include "llvm/ADT/Hashing.h" |
22 | #include "llvm/ADT/PointerIntPair.h" |
23 | #include "llvm/ADT/SmallVector.h" |
24 | #include "llvm/ADT/Twine.h" |
25 | #include "llvm/ADT/ilist_iterator.h" |
26 | #include "llvm/IR/BasicBlock.h" |
27 | #include "llvm/IR/CFG.h" |
28 | #include "llvm/IR/PassManager.h" |
29 | #include "llvm/IR/Use.h" |
30 | #include "llvm/Pass.h" |
31 | #include "llvm/Support/CFGDiff.h" |
32 | #include "llvm/Support/CFGUpdate.h" |
33 | #include "llvm/Support/GenericDomTree.h" |
34 | #include <algorithm> |
35 | #include <utility> |
36 | |
37 | namespace llvm { |
38 | |
39 | class Function; |
40 | class Instruction; |
41 | class Module; |
42 | class Value; |
43 | class raw_ostream; |
44 | template <class GraphType> struct GraphTraits; |
45 | |
46 | extern template class DomTreeNodeBase<BasicBlock>; |
47 | extern template class DominatorTreeBase<BasicBlock, false>; // DomTree |
48 | extern template class DominatorTreeBase<BasicBlock, true>; // PostDomTree |
49 | |
50 | extern template class cfg::Update<BasicBlock *>; |
51 | |
52 | namespace DomTreeBuilder { |
53 | using BBDomTree = DomTreeBase<BasicBlock>; |
54 | using BBPostDomTree = PostDomTreeBase<BasicBlock>; |
55 | |
56 | using BBUpdates = ArrayRef<llvm::cfg::Update<BasicBlock *>>; |
57 | |
58 | using BBDomTreeGraphDiff = GraphDiff<BasicBlock *, false>; |
59 | using BBPostDomTreeGraphDiff = GraphDiff<BasicBlock *, true>; |
60 | |
61 | extern template void Calculate<BBDomTree>(BBDomTree &DT); |
62 | extern template void CalculateWithUpdates<BBDomTree>(BBDomTree &DT, |
63 | BBUpdates U); |
64 | |
65 | extern template void Calculate<BBPostDomTree>(BBPostDomTree &DT); |
66 | |
67 | extern template void InsertEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From, |
68 | BasicBlock *To); |
69 | extern template void InsertEdge<BBPostDomTree>(BBPostDomTree &DT, |
70 | BasicBlock *From, |
71 | BasicBlock *To); |
72 | |
73 | extern template void DeleteEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From, |
74 | BasicBlock *To); |
75 | extern template void DeleteEdge<BBPostDomTree>(BBPostDomTree &DT, |
76 | BasicBlock *From, |
77 | BasicBlock *To); |
78 | |
79 | extern template void ApplyUpdates<BBDomTree>(BBDomTree &DT, |
80 | BBDomTreeGraphDiff &, |
81 | BBDomTreeGraphDiff *); |
82 | extern template void ApplyUpdates<BBPostDomTree>(BBPostDomTree &DT, |
83 | BBPostDomTreeGraphDiff &, |
84 | BBPostDomTreeGraphDiff *); |
85 | |
86 | extern template bool Verify<BBDomTree>(const BBDomTree &DT, |
87 | BBDomTree::VerificationLevel VL); |
88 | extern template bool Verify<BBPostDomTree>(const BBPostDomTree &DT, |
89 | BBPostDomTree::VerificationLevel VL); |
90 | } // namespace DomTreeBuilder |
91 | |
92 | using DomTreeNode = DomTreeNodeBase<BasicBlock>; |
93 | |
94 | class BasicBlockEdge { |
95 | const BasicBlock *Start; |
96 | const BasicBlock *End; |
97 | |
98 | public: |
99 | BasicBlockEdge(const BasicBlock *Start_, const BasicBlock *End_) : |
100 | Start(Start_), End(End_) {} |
101 | |
102 | BasicBlockEdge(const std::pair<BasicBlock *, BasicBlock *> &Pair) |
103 | : Start(Pair.first), End(Pair.second) {} |
104 | |
105 | BasicBlockEdge(const std::pair<const BasicBlock *, const BasicBlock *> &Pair) |
106 | : Start(Pair.first), End(Pair.second) {} |
107 | |
108 | const BasicBlock *getStart() const { |
109 | return Start; |
110 | } |
111 | |
112 | const BasicBlock *getEnd() const { |
113 | return End; |
114 | } |
115 | |
116 | /// Check if this is the only edge between Start and End. |
117 | bool isSingleEdge() const; |
118 | }; |
119 | |
120 | template <> struct DenseMapInfo<BasicBlockEdge> { |
121 | using BBInfo = DenseMapInfo<const BasicBlock *>; |
122 | |
123 | static unsigned getHashValue(const BasicBlockEdge *V); |
124 | |
125 | static inline BasicBlockEdge getEmptyKey() { |
126 | return BasicBlockEdge(BBInfo::getEmptyKey(), BBInfo::getEmptyKey()); |
127 | } |
128 | |
129 | static inline BasicBlockEdge getTombstoneKey() { |
130 | return BasicBlockEdge(BBInfo::getTombstoneKey(), BBInfo::getTombstoneKey()); |
131 | } |
132 | |
133 | static unsigned getHashValue(const BasicBlockEdge &Edge) { |
134 | return hash_combine(args: BBInfo::getHashValue(PtrVal: Edge.getStart()), |
135 | args: BBInfo::getHashValue(PtrVal: Edge.getEnd())); |
136 | } |
137 | |
138 | static bool isEqual(const BasicBlockEdge &LHS, const BasicBlockEdge &RHS) { |
139 | return BBInfo::isEqual(LHS: LHS.getStart(), RHS: RHS.getStart()) && |
140 | BBInfo::isEqual(LHS: LHS.getEnd(), RHS: RHS.getEnd()); |
141 | } |
142 | }; |
143 | |
144 | /// Concrete subclass of DominatorTreeBase that is used to compute a |
145 | /// normal dominator tree. |
146 | /// |
147 | /// Definition: A block is said to be forward statically reachable if there is |
148 | /// a path from the entry of the function to the block. A statically reachable |
149 | /// block may become statically unreachable during optimization. |
150 | /// |
151 | /// A forward unreachable block may appear in the dominator tree, or it may |
152 | /// not. If it does, dominance queries will return results as if all reachable |
153 | /// blocks dominate it. When asking for a Node corresponding to a potentially |
154 | /// unreachable block, calling code must handle the case where the block was |
155 | /// unreachable and the result of getNode() is nullptr. |
156 | /// |
157 | /// Generally, a block known to be unreachable when the dominator tree is |
158 | /// constructed will not be in the tree. One which becomes unreachable after |
159 | /// the dominator tree is initially constructed may still exist in the tree, |
160 | /// even if the tree is properly updated. Calling code should not rely on the |
161 | /// preceding statements; this is stated only to assist human understanding. |
162 | class DominatorTree : public DominatorTreeBase<BasicBlock, false> { |
163 | public: |
164 | using Base = DominatorTreeBase<BasicBlock, false>; |
165 | |
166 | DominatorTree() = default; |
167 | explicit DominatorTree(Function &F) { recalculate(Func&: F); } |
168 | explicit DominatorTree(DominatorTree &DT, DomTreeBuilder::BBUpdates U) { |
169 | recalculate(Func&: *DT.Parent, Updates: U); |
170 | } |
171 | |
172 | /// Handle invalidation explicitly. |
173 | bool invalidate(Function &F, const PreservedAnalyses &PA, |
174 | FunctionAnalysisManager::Invalidator &); |
175 | |
176 | // Ensure base-class overloads are visible. |
177 | using Base::dominates; |
178 | |
179 | /// Return true if the (end of the) basic block BB dominates the use U. |
180 | bool dominates(const BasicBlock *BB, const Use &U) const; |
181 | |
182 | /// Return true if value Def dominates use U, in the sense that Def is |
183 | /// available at U, and could be substituted as the used value without |
184 | /// violating the SSA dominance requirement. |
185 | /// |
186 | /// In particular, it is worth noting that: |
187 | /// * Non-instruction Defs dominate everything. |
188 | /// * Def does not dominate a use in Def itself (outside of degenerate cases |
189 | /// like unreachable code or trivial phi cycles). |
190 | /// * Invoke Defs only dominate uses in their default destination. |
191 | bool dominates(const Value *Def, const Use &U) const; |
192 | /// Return true if value Def dominates all possible uses inside instruction |
193 | /// User. Same comments as for the Use-based API apply. |
194 | bool dominates(const Value *Def, const Instruction *User) const; |
195 | |
196 | /// Returns true if Def would dominate a use in any instruction in BB. |
197 | /// If Def is an instruction in BB, then Def does not dominate BB. |
198 | /// |
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 | // Ensure base class overloads are visible. |
219 | using Base::findNearestCommonDominator; |
220 | |
221 | /// Find the nearest instruction I that dominates both I1 and I2, in the sense |
222 | /// that a result produced before I will be available at both I1 and I2. |
223 | Instruction *findNearestCommonDominator(Instruction *I1, |
224 | Instruction *I2) const; |
225 | |
226 | // Pop up a GraphViz/gv window with the Dominator Tree rendered using `dot`. |
227 | void viewGraph(const Twine &Name, const Twine &Title); |
228 | void viewGraph(); |
229 | }; |
230 | |
231 | //===------------------------------------- |
232 | // DominatorTree GraphTraits specializations so the DominatorTree can be |
233 | // iterable by generic graph iterators. |
234 | |
235 | template <class Node, class ChildIterator> struct DomTreeGraphTraitsBase { |
236 | using NodeRef = Node *; |
237 | using ChildIteratorType = ChildIterator; |
238 | using nodes_iterator = df_iterator<Node *, df_iterator_default_set<Node*>>; |
239 | |
240 | static NodeRef getEntryNode(NodeRef N) { return N; } |
241 | static ChildIteratorType child_begin(NodeRef N) { return N->begin(); } |
242 | static ChildIteratorType child_end(NodeRef N) { return N->end(); } |
243 | |
244 | static nodes_iterator nodes_begin(NodeRef N) { |
245 | return df_begin(getEntryNode(N)); |
246 | } |
247 | |
248 | static nodes_iterator nodes_end(NodeRef N) { return df_end(getEntryNode(N)); } |
249 | }; |
250 | |
251 | template <> |
252 | struct GraphTraits<DomTreeNode *> |
253 | : public DomTreeGraphTraitsBase<DomTreeNode, DomTreeNode::const_iterator> { |
254 | }; |
255 | |
256 | template <> |
257 | struct GraphTraits<const DomTreeNode *> |
258 | : public DomTreeGraphTraitsBase<const DomTreeNode, |
259 | DomTreeNode::const_iterator> {}; |
260 | |
261 | template <> struct GraphTraits<DominatorTree*> |
262 | : public GraphTraits<DomTreeNode*> { |
263 | static NodeRef getEntryNode(DominatorTree *DT) { return DT->getRootNode(); } |
264 | |
265 | static nodes_iterator nodes_begin(DominatorTree *N) { |
266 | return df_begin(G: getEntryNode(DT: N)); |
267 | } |
268 | |
269 | static nodes_iterator nodes_end(DominatorTree *N) { |
270 | return df_end(G: getEntryNode(DT: N)); |
271 | } |
272 | }; |
273 | |
274 | /// Analysis pass which computes a \c DominatorTree. |
275 | class DominatorTreeAnalysis : public AnalysisInfoMixin<DominatorTreeAnalysis> { |
276 | friend AnalysisInfoMixin<DominatorTreeAnalysis>; |
277 | static AnalysisKey Key; |
278 | |
279 | public: |
280 | /// Provide the result typedef for this analysis pass. |
281 | using Result = DominatorTree; |
282 | |
283 | /// Run the analysis pass over a function and produce a dominator tree. |
284 | DominatorTree run(Function &F, FunctionAnalysisManager &); |
285 | }; |
286 | |
287 | /// Printer pass for the \c DominatorTree. |
288 | class DominatorTreePrinterPass |
289 | : public PassInfoMixin<DominatorTreePrinterPass> { |
290 | raw_ostream &OS; |
291 | |
292 | public: |
293 | explicit DominatorTreePrinterPass(raw_ostream &OS); |
294 | |
295 | PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); |
296 | |
297 | static bool isRequired() { return true; } |
298 | }; |
299 | |
300 | /// Verifier pass for the \c DominatorTree. |
301 | struct DominatorTreeVerifierPass : PassInfoMixin<DominatorTreeVerifierPass> { |
302 | PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); |
303 | static bool isRequired() { return true; } |
304 | }; |
305 | |
306 | /// Enables verification of dominator trees. |
307 | /// |
308 | /// This check is expensive and is disabled by default. `-verify-dom-info` |
309 | /// allows selectively enabling the check without needing to recompile. |
310 | extern bool VerifyDomInfo; |
311 | |
312 | /// Legacy analysis pass which computes a \c DominatorTree. |
313 | class DominatorTreeWrapperPass : public FunctionPass { |
314 | DominatorTree DT; |
315 | |
316 | public: |
317 | static char ID; |
318 | |
319 | DominatorTreeWrapperPass(); |
320 | |
321 | DominatorTree &getDomTree() { return DT; } |
322 | const DominatorTree &getDomTree() const { return DT; } |
323 | |
324 | bool runOnFunction(Function &F) override; |
325 | |
326 | void verifyAnalysis() const override; |
327 | |
328 | void getAnalysisUsage(AnalysisUsage &AU) const override { |
329 | AU.setPreservesAll(); |
330 | } |
331 | |
332 | void releaseMemory() override { DT.reset(); } |
333 | |
334 | void print(raw_ostream &OS, const Module *M = nullptr) const override; |
335 | }; |
336 | } // end namespace llvm |
337 | |
338 | #endif // LLVM_IR_DOMINATORS_H |
339 | |