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
28namespace llvm {
29
30class Function;
31class Instruction;
32class Module;
33class raw_ostream;
34
35extern template class DomTreeNodeBase<BasicBlock>;
36extern template class DominatorTreeBase<BasicBlock, false>; // DomTree
37extern template class DominatorTreeBase<BasicBlock, true>; // PostDomTree
38
39extern template class cfg::Update<BasicBlock *>;
40
41namespace DomTreeBuilder {
42using BBDomTree = DomTreeBase<BasicBlock>;
43using BBPostDomTree = PostDomTreeBase<BasicBlock>;
44
45using BBUpdates = ArrayRef<llvm::cfg::Update<BasicBlock *>>;
46
47using BBDomTreeGraphDiff = GraphDiff<BasicBlock *, false>;
48using BBPostDomTreeGraphDiff = GraphDiff<BasicBlock *, true>;
49
50extern template void Calculate<BBDomTree>(BBDomTree &DT);
51extern template void CalculateWithUpdates<BBDomTree>(BBDomTree &DT,
52 BBUpdates U);
53
54extern template void Calculate<BBPostDomTree>(BBPostDomTree &DT);
55
56extern template void InsertEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From,
57 BasicBlock *To);
58extern template void InsertEdge<BBPostDomTree>(BBPostDomTree &DT,
59 BasicBlock *From,
60 BasicBlock *To);
61
62extern template void DeleteEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From,
63 BasicBlock *To);
64extern template void DeleteEdge<BBPostDomTree>(BBPostDomTree &DT,
65 BasicBlock *From,
66 BasicBlock *To);
67
68extern template void ApplyUpdates<BBDomTree>(BBDomTree &DT,
69 BBDomTreeGraphDiff &,
70 BBDomTreeGraphDiff *);
71extern template void ApplyUpdates<BBPostDomTree>(BBPostDomTree &DT,
72 BBPostDomTreeGraphDiff &,
73 BBPostDomTreeGraphDiff *);
74
75extern template bool Verify<BBDomTree>(const BBDomTree &DT,
76 BBDomTree::VerificationLevel VL);
77extern template bool Verify<BBPostDomTree>(const BBPostDomTree &DT,
78 BBPostDomTree::VerificationLevel VL);
79} // namespace DomTreeBuilder
80
81using DomTreeNode = DomTreeNodeBase<BasicBlock>;
82
83class BasicBlockEdge {
84 const BasicBlock *Start;
85 const BasicBlock *End;
86
87public:
88 BasicBlockEdge(const BasicBlock *Start_, const BasicBlock *End_) :
89 Start(Start_), End(End_) {}
90
91 BasicBlockEdge(const std::pair<BasicBlock *, BasicBlock *> &Pair)
92 : Start(Pair.first), End(Pair.second) {}
93
94 BasicBlockEdge(const std::pair<const BasicBlock *, const BasicBlock *> &Pair)
95 : Start(Pair.first), End(Pair.second) {}
96
97 const BasicBlock *getStart() const {
98 return Start;
99 }
100
101 const BasicBlock *getEnd() const {
102 return End;
103 }
104
105 /// Check if this is the only edge between Start and End.
106 bool isSingleEdge() const;
107};
108
109template <> struct DenseMapInfo<BasicBlockEdge> {
110 using BBInfo = DenseMapInfo<const BasicBlock *>;
111
112 static unsigned getHashValue(const BasicBlockEdge *V);
113
114 static inline BasicBlockEdge getEmptyKey() {
115 return BasicBlockEdge(BBInfo::getEmptyKey(), BBInfo::getEmptyKey());
116 }
117
118 static inline BasicBlockEdge getTombstoneKey() {
119 return BasicBlockEdge(BBInfo::getTombstoneKey(), BBInfo::getTombstoneKey());
120 }
121
122 static unsigned getHashValue(const BasicBlockEdge &Edge) {
123 return hash_combine(BBInfo::getHashValue(Edge.getStart()),
124 BBInfo::getHashValue(Edge.getEnd()));
125 }
126
127 static bool isEqual(const BasicBlockEdge &LHS, const BasicBlockEdge &RHS) {
128 return BBInfo::isEqual(LHS.getStart(), RHS.getStart()) &&
129 BBInfo::isEqual(LHS.getEnd(), RHS.getEnd());
130 }
131};
132
133/// Concrete subclass of DominatorTreeBase that is used to compute a
134/// normal dominator tree.
135///
136/// Definition: A block is said to be forward statically reachable if there is
137/// a path from the entry of the function to the block. A statically reachable
138/// block may become statically unreachable during optimization.
139///
140/// A forward unreachable block may appear in the dominator tree, or it may
141/// not. If it does, dominance queries will return results as if all reachable
142/// blocks dominate it. When asking for a Node corresponding to a potentially
143/// unreachable block, calling code must handle the case where the block was
144/// unreachable and the result of getNode() is nullptr.
145///
146/// Generally, a block known to be unreachable when the dominator tree is
147/// constructed will not be in the tree. One which becomes unreachable after
148/// the dominator tree is initially constructed may still exist in the tree,
149/// even if the tree is properly updated. Calling code should not rely on the
150/// preceding statements; this is stated only to assist human understanding.
151class DominatorTree : public DominatorTreeBase<BasicBlock, false> {
152 public:
153 using Base = DominatorTreeBase<BasicBlock, false>;
154
155 DominatorTree() = default;
156 explicit DominatorTree(Function &F) { recalculate(F); }
157 explicit DominatorTree(DominatorTree &DT, DomTreeBuilder::BBUpdates U) {
158 recalculate(*DT.Parent, U);
159 }
160
161 /// Handle invalidation explicitly.
162 bool invalidate(Function &F, const PreservedAnalyses &PA,
163 FunctionAnalysisManager::Invalidator &);
164
165 // Ensure base-class overloads are visible.
166 using Base::dominates;
167
168 /// Return true if the (end of the) basic block BB dominates the use U.
169 bool dominates(const BasicBlock *BB, const Use &U) const;
170
171 /// Return true if value Def dominates use U, in the sense that Def is
172 /// available at U, and could be substituted as the used value without
173 /// violating the SSA dominance requirement.
174 ///
175 /// In particular, it is worth noting that:
176 /// * Non-instruction Defs dominate everything.
177 /// * Def does not dominate a use in Def itself (outside of degenerate cases
178 /// like unreachable code or trivial phi cycles).
179 /// * Invoke/callbr Defs only dominate uses in their default destination.
180 bool dominates(const Value *Def, const Use &U) const;
181 /// Return true if value Def dominates all possible uses inside instruction
182 /// User. Same comments as for the Use-based API apply.
183 bool dominates(const Value *Def, const Instruction *User) const;
184 // Does not accept Value to avoid ambiguity with dominance checks between
185 // two basic blocks.
186 bool dominates(const Instruction *Def, const BasicBlock *BB) const;
187
188 /// Return true if an edge dominates a use.
189 ///
190 /// If BBE is not a unique edge between start and end of the edge, it can
191 /// never dominate the use.
192 bool dominates(const BasicBlockEdge &BBE, const Use &U) const;
193 bool dominates(const BasicBlockEdge &BBE, const BasicBlock *BB) const;
194 /// Returns true if edge \p BBE1 dominates edge \p BBE2.
195 bool dominates(const BasicBlockEdge &BBE1, const BasicBlockEdge &BBE2) const;
196
197 // Ensure base class overloads are visible.
198 using Base::isReachableFromEntry;
199
200 /// Provide an overload for a Use.
201 bool isReachableFromEntry(const Use &U) const;
202
203 // Pop up a GraphViz/gv window with the Dominator Tree rendered using `dot`.
204 void viewGraph(const Twine &Name, const Twine &Title);
205 void viewGraph();
206};
207
208//===-------------------------------------
209// DominatorTree GraphTraits specializations so the DominatorTree can be
210// iterable by generic graph iterators.
211
212template <class Node, class ChildIterator> struct DomTreeGraphTraitsBase {
213 using NodeRef = Node *;
214 using ChildIteratorType = ChildIterator;
215 using nodes_iterator = df_iterator<Node *, df_iterator_default_set<Node*>>;
216
217 static NodeRef getEntryNode(NodeRef N) { return N; }
218 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
219 static ChildIteratorType child_end(NodeRef N) { return N->end(); }
220
221 static nodes_iterator nodes_begin(NodeRef N) {
222 return df_begin(getEntryNode(N));
223 }
224
225 static nodes_iterator nodes_end(NodeRef N) { return df_end(getEntryNode(N)); }
226};
227
228template <>
229struct GraphTraits<DomTreeNode *>
230 : public DomTreeGraphTraitsBase<DomTreeNode, DomTreeNode::const_iterator> {
231};
232
233template <>
234struct GraphTraits<const DomTreeNode *>
235 : public DomTreeGraphTraitsBase<const DomTreeNode,
236 DomTreeNode::const_iterator> {};
237
238template <> struct GraphTraits<DominatorTree*>
239 : public GraphTraits<DomTreeNode*> {
240 static NodeRef getEntryNode(DominatorTree *DT) { return DT->getRootNode(); }
241
242 static nodes_iterator nodes_begin(DominatorTree *N) {
243 return df_begin(getEntryNode(N));
244 }
245
246 static nodes_iterator nodes_end(DominatorTree *N) {
247 return df_end(getEntryNode(N));
248 }
249};
250
251/// Analysis pass which computes a \c DominatorTree.
252class DominatorTreeAnalysis : public AnalysisInfoMixin<DominatorTreeAnalysis> {
253 friend AnalysisInfoMixin<DominatorTreeAnalysis>;
254 static AnalysisKey Key;
255
256public:
257 /// Provide the result typedef for this analysis pass.
258 using Result = DominatorTree;
259
260 /// Run the analysis pass over a function and produce a dominator tree.
261 DominatorTree run(Function &F, FunctionAnalysisManager &);
262};
263
264/// Printer pass for the \c DominatorTree.
265class DominatorTreePrinterPass
266 : public PassInfoMixin<DominatorTreePrinterPass> {
267 raw_ostream &OS;
268
269public:
270 explicit DominatorTreePrinterPass(raw_ostream &OS);
271
272 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
273};
274
275/// Verifier pass for the \c DominatorTree.
276struct DominatorTreeVerifierPass : PassInfoMixin<DominatorTreeVerifierPass> {
277 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
278};
279
280/// Legacy analysis pass which computes a \c DominatorTree.
281class DominatorTreeWrapperPass : public FunctionPass {
282 DominatorTree DT;
283
284public:
285 static char ID;
286
287 DominatorTreeWrapperPass();
288
289 DominatorTree &getDomTree() { return DT; }
290 const DominatorTree &getDomTree() const { return DT; }
291
292 bool runOnFunction(Function &F) override;
293
294 void verifyAnalysis() const override;
295
296 void getAnalysisUsage(AnalysisUsage &AU) const override {
297 AU.setPreservesAll();
298 }
299
300 void releaseMemory() override { DT.reset(); }
301
302 void print(raw_ostream &OS, const Module *M = nullptr) const override;
303};
304} // end namespace llvm
305
306#endif // LLVM_IR_DOMINATORS_H
307