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
37namespace llvm {
38
39class Function;
40class Instruction;
41class Module;
42class Value;
43class raw_ostream;
44template <class GraphType> struct GraphTraits;
45
46extern template class DomTreeNodeBase<BasicBlock>;
47extern template class DominatorTreeBase<BasicBlock, false>; // DomTree
48extern template class DominatorTreeBase<BasicBlock, true>; // PostDomTree
49
50extern template class cfg::Update<BasicBlock *>;
51
52namespace DomTreeBuilder {
53using BBDomTree = DomTreeBase<BasicBlock>;
54using BBPostDomTree = PostDomTreeBase<BasicBlock>;
55
56using BBUpdates = ArrayRef<llvm::cfg::Update<BasicBlock *>>;
57
58using BBDomTreeGraphDiff = GraphDiff<BasicBlock *, false>;
59using BBPostDomTreeGraphDiff = GraphDiff<BasicBlock *, true>;
60
61extern template void Calculate<BBDomTree>(BBDomTree &DT);
62extern template void CalculateWithUpdates<BBDomTree>(BBDomTree &DT,
63 BBUpdates U);
64
65extern template void Calculate<BBPostDomTree>(BBPostDomTree &DT);
66
67extern template void InsertEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From,
68 BasicBlock *To);
69extern template void InsertEdge<BBPostDomTree>(BBPostDomTree &DT,
70 BasicBlock *From,
71 BasicBlock *To);
72
73extern template void DeleteEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From,
74 BasicBlock *To);
75extern template void DeleteEdge<BBPostDomTree>(BBPostDomTree &DT,
76 BasicBlock *From,
77 BasicBlock *To);
78
79extern template void ApplyUpdates<BBDomTree>(BBDomTree &DT,
80 BBDomTreeGraphDiff &,
81 BBDomTreeGraphDiff *);
82extern template void ApplyUpdates<BBPostDomTree>(BBPostDomTree &DT,
83 BBPostDomTreeGraphDiff &,
84 BBPostDomTreeGraphDiff *);
85
86extern template bool Verify<BBDomTree>(const BBDomTree &DT,
87 BBDomTree::VerificationLevel VL);
88extern template bool Verify<BBPostDomTree>(const BBPostDomTree &DT,
89 BBPostDomTree::VerificationLevel VL);
90} // namespace DomTreeBuilder
91
92using DomTreeNode = DomTreeNodeBase<BasicBlock>;
93
94class BasicBlockEdge {
95 const BasicBlock *Start;
96 const BasicBlock *End;
97
98public:
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
120template <> 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.
162class 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
235template <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
251template <>
252struct GraphTraits<DomTreeNode *>
253 : public DomTreeGraphTraitsBase<DomTreeNode, DomTreeNode::const_iterator> {
254};
255
256template <>
257struct GraphTraits<const DomTreeNode *>
258 : public DomTreeGraphTraitsBase<const DomTreeNode,
259 DomTreeNode::const_iterator> {};
260
261template <> 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.
275class DominatorTreeAnalysis : public AnalysisInfoMixin<DominatorTreeAnalysis> {
276 friend AnalysisInfoMixin<DominatorTreeAnalysis>;
277 static AnalysisKey Key;
278
279public:
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.
288class DominatorTreePrinterPass
289 : public PassInfoMixin<DominatorTreePrinterPass> {
290 raw_ostream &OS;
291
292public:
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.
301struct 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.
310extern bool VerifyDomInfo;
311
312/// Legacy analysis pass which computes a \c DominatorTree.
313class DominatorTreeWrapperPass : public FunctionPass {
314 DominatorTree DT;
315
316public:
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

source code of llvm/include/llvm/IR/Dominators.h