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

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