1//===- CFG.h ----------------------------------------------------*- 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/// \file
9///
10/// This file provides various utilities for inspecting and working with the
11/// control flow graph in LLVM IR. This includes generic facilities for
12/// iterating successors and predecessors of basic blocks, the successors of
13/// specific terminator instructions, etc. It also defines specializations of
14/// GraphTraits that allow Function and BasicBlock graphs to be treated as
15/// proper graphs for generic algorithms.
16///
17//===----------------------------------------------------------------------===//
18
19#ifndef LLVM_IR_CFG_H
20#define LLVM_IR_CFG_H
21
22#include "llvm/ADT/GraphTraits.h"
23#include "llvm/ADT/iterator.h"
24#include "llvm/ADT/iterator_range.h"
25#include "llvm/IR/Function.h"
26#include "llvm/IR/Value.h"
27#include "llvm/Support/Casting.h"
28#include <cassert>
29#include <cstddef>
30#include <iterator>
31
32namespace llvm {
33
34class BasicBlock;
35class Instruction;
36class Use;
37
38//===----------------------------------------------------------------------===//
39// BasicBlock pred_iterator definition
40//===----------------------------------------------------------------------===//
41
42template <class Ptr, class USE_iterator> // Predecessor Iterator
43class PredIterator {
44public:
45 using iterator_category = std::forward_iterator_tag;
46 using value_type = Ptr;
47 using difference_type = std::ptrdiff_t;
48 using pointer = Ptr *;
49 using reference = Ptr *;
50
51private:
52 using Self = PredIterator<Ptr, USE_iterator>;
53 USE_iterator It;
54
55 inline void advancePastNonTerminators() {
56 // Loop to ignore non-terminator uses (for example BlockAddresses).
57 while (!It.atEnd()) {
58 if (auto *Inst = dyn_cast<Instruction>(*It))
59 if (Inst->isTerminator())
60 break;
61
62 ++It;
63 }
64 }
65
66public:
67 PredIterator() = default;
68 explicit inline PredIterator(Ptr *bb) : It(bb->user_begin()) {
69 advancePastNonTerminators();
70 }
71 inline PredIterator(Ptr *bb, bool) : It(bb->user_end()) {}
72
73 inline bool operator==(const Self& x) const { return It == x.It; }
74 inline bool operator!=(const Self& x) const { return !operator==(x); }
75
76 inline reference operator*() const {
77 assert(!It.atEnd() && "pred_iterator out of range!");
78 return cast<Instruction>(*It)->getParent();
79 }
80 inline pointer *operator->() const { return &operator*(); }
81
82 inline Self& operator++() { // Preincrement
83 assert(!It.atEnd() && "pred_iterator out of range!");
84 ++It; advancePastNonTerminators();
85 return *this;
86 }
87
88 inline Self operator++(int) { // Postincrement
89 Self tmp = *this; ++*this; return tmp;
90 }
91
92 /// getOperandNo - Return the operand number in the predecessor's
93 /// terminator of the successor.
94 unsigned getOperandNo() const {
95 return It.getOperandNo();
96 }
97
98 /// getUse - Return the operand Use in the predecessor's terminator
99 /// of the successor.
100 Use &getUse() const {
101 return It.getUse();
102 }
103};
104
105using pred_iterator = PredIterator<BasicBlock, Value::user_iterator>;
106using const_pred_iterator =
107 PredIterator<const BasicBlock, Value::const_user_iterator>;
108using pred_range = iterator_range<pred_iterator>;
109using const_pred_range = iterator_range<const_pred_iterator>;
110
111inline pred_iterator pred_begin(BasicBlock *BB) { return pred_iterator(BB); }
112inline const_pred_iterator pred_begin(const BasicBlock *BB) {
113 return const_pred_iterator(BB);
114}
115inline pred_iterator pred_end(BasicBlock *BB) { return pred_iterator(BB, true);}
116inline const_pred_iterator pred_end(const BasicBlock *BB) {
117 return const_pred_iterator(BB, true);
118}
119inline bool pred_empty(const BasicBlock *BB) {
120 return pred_begin(BB) == pred_end(BB);
121}
122/// Get the number of predecessors of \p BB. This is a linear time operation.
123/// Use \ref BasicBlock::hasNPredecessors() or hasNPredecessorsOrMore if able.
124inline unsigned pred_size(const BasicBlock *BB) {
125 return std::distance(pred_begin(BB), pred_end(BB));
126}
127inline pred_range predecessors(BasicBlock *BB) {
128 return pred_range(pred_begin(BB), pred_end(BB));
129}
130inline const_pred_range predecessors(const BasicBlock *BB) {
131 return const_pred_range(pred_begin(BB), pred_end(BB));
132}
133
134//===----------------------------------------------------------------------===//
135// Instruction and BasicBlock succ_iterator helpers
136//===----------------------------------------------------------------------===//
137
138template <class InstructionT, class BlockT>
139class SuccIterator
140 : public iterator_facade_base<SuccIterator<InstructionT, BlockT>,
141 std::random_access_iterator_tag, BlockT, int,
142 BlockT *, BlockT *> {
143public:
144 using difference_type = int;
145 using pointer = BlockT *;
146 using reference = BlockT *;
147
148private:
149 InstructionT *Inst;
150 int Idx;
151 using Self = SuccIterator<InstructionT, BlockT>;
152
153 inline bool index_is_valid(int Idx) {
154 // Note that we specially support the index of zero being valid even in the
155 // face of a null instruction.
156 return Idx >= 0 && (Idx == 0 || Idx <= (int)Inst->getNumSuccessors());
157 }
158
159 /// Proxy object to allow write access in operator[]
160 class SuccessorProxy {
161 Self It;
162
163 public:
164 explicit SuccessorProxy(const Self &It) : It(It) {}
165
166 SuccessorProxy(const SuccessorProxy &) = default;
167
168 SuccessorProxy &operator=(SuccessorProxy RHS) {
169 *this = reference(RHS);
170 return *this;
171 }
172
173 SuccessorProxy &operator=(reference RHS) {
174 It.Inst->setSuccessor(It.Idx, RHS);
175 return *this;
176 }
177
178 operator reference() const { return *It; }
179 };
180
181public:
182 // begin iterator
183 explicit inline SuccIterator(InstructionT *Inst) : Inst(Inst), Idx(0) {}
184 // end iterator
185 inline SuccIterator(InstructionT *Inst, bool) : Inst(Inst) {
186 if (Inst)
187 Idx = Inst->getNumSuccessors();
188 else
189 // Inst == NULL happens, if a basic block is not fully constructed and
190 // consequently getTerminator() returns NULL. In this case we construct
191 // a SuccIterator which describes a basic block that has zero
192 // successors.
193 // Defining SuccIterator for incomplete and malformed CFGs is especially
194 // useful for debugging.
195 Idx = 0;
196 }
197
198 /// This is used to interface between code that wants to
199 /// operate on terminator instructions directly.
200 int getSuccessorIndex() const { return Idx; }
201
202 inline bool operator==(const Self &x) const { return Idx == x.Idx; }
203
204 inline BlockT *operator*() const { return Inst->getSuccessor(Idx); }
205
206 // We use the basic block pointer directly for operator->.
207 inline BlockT *operator->() const { return operator*(); }
208
209 inline bool operator<(const Self &RHS) const {
210 assert(Inst == RHS.Inst && "Cannot compare iterators of different blocks!");
211 return Idx < RHS.Idx;
212 }
213
214 int operator-(const Self &RHS) const {
215 assert(Inst == RHS.Inst && "Cannot compare iterators of different blocks!");
216 return Idx - RHS.Idx;
217 }
218
219 inline Self &operator+=(int RHS) {
220 int NewIdx = Idx + RHS;
221 assert(index_is_valid(NewIdx) && "Iterator index out of bound");
222 Idx = NewIdx;
223 return *this;
224 }
225
226 inline Self &operator-=(int RHS) { return operator+=(-RHS); }
227
228 // Specially implement the [] operation using a proxy object to support
229 // assignment.
230 inline SuccessorProxy operator[](int Offset) {
231 Self TmpIt = *this;
232 TmpIt += Offset;
233 return SuccessorProxy(TmpIt);
234 }
235
236 /// Get the source BlockT of this iterator.
237 inline BlockT *getSource() {
238 assert(Inst && "Source not available, if basic block was malformed");
239 return Inst->getParent();
240 }
241};
242
243using succ_iterator = SuccIterator<Instruction, BasicBlock>;
244using const_succ_iterator = SuccIterator<const Instruction, const BasicBlock>;
245using succ_range = iterator_range<succ_iterator>;
246using const_succ_range = iterator_range<const_succ_iterator>;
247
248inline succ_iterator succ_begin(Instruction *I) { return succ_iterator(I); }
249inline const_succ_iterator succ_begin(const Instruction *I) {
250 return const_succ_iterator(I);
251}
252inline succ_iterator succ_end(Instruction *I) { return succ_iterator(I, true); }
253inline const_succ_iterator succ_end(const Instruction *I) {
254 return const_succ_iterator(I, true);
255}
256inline bool succ_empty(const Instruction *I) {
257 return succ_begin(I) == succ_end(I);
258}
259inline unsigned succ_size(const Instruction *I) {
260 return std::distance(succ_begin(I), succ_end(I));
261}
262inline succ_range successors(Instruction *I) {
263 return succ_range(succ_begin(I), succ_end(I));
264}
265inline const_succ_range successors(const Instruction *I) {
266 return const_succ_range(succ_begin(I), succ_end(I));
267}
268
269inline succ_iterator succ_begin(BasicBlock *BB) {
270 return succ_iterator(BB->getTerminator());
271}
272inline const_succ_iterator succ_begin(const BasicBlock *BB) {
273 return const_succ_iterator(BB->getTerminator());
274}
275inline succ_iterator succ_end(BasicBlock *BB) {
276 return succ_iterator(BB->getTerminator(), true);
277}
278inline const_succ_iterator succ_end(const BasicBlock *BB) {
279 return const_succ_iterator(BB->getTerminator(), true);
280}
281inline bool succ_empty(const BasicBlock *BB) {
282 return succ_begin(BB) == succ_end(BB);
283}
284inline unsigned succ_size(const BasicBlock *BB) {
285 return std::distance(succ_begin(BB), succ_end(BB));
286}
287inline succ_range successors(BasicBlock *BB) {
288 return succ_range(succ_begin(BB), succ_end(BB));
289}
290inline const_succ_range successors(const BasicBlock *BB) {
291 return const_succ_range(succ_begin(BB), succ_end(BB));
292}
293
294//===--------------------------------------------------------------------===//
295// GraphTraits specializations for basic block graphs (CFGs)
296//===--------------------------------------------------------------------===//
297
298// Provide specializations of GraphTraits to be able to treat a function as a
299// graph of basic blocks...
300
301template <> struct GraphTraits<BasicBlock*> {
302 using NodeRef = BasicBlock *;
303 using ChildIteratorType = succ_iterator;
304
305 static NodeRef getEntryNode(BasicBlock *BB) { return BB; }
306 static ChildIteratorType child_begin(NodeRef N) { return succ_begin(N); }
307 static ChildIteratorType child_end(NodeRef N) { return succ_end(N); }
308};
309
310template <> struct GraphTraits<const BasicBlock*> {
311 using NodeRef = const BasicBlock *;
312 using ChildIteratorType = const_succ_iterator;
313
314 static NodeRef getEntryNode(const BasicBlock *BB) { return BB; }
315
316 static ChildIteratorType child_begin(NodeRef N) { return succ_begin(N); }
317 static ChildIteratorType child_end(NodeRef N) { return succ_end(N); }
318};
319
320// Provide specializations of GraphTraits to be able to treat a function as a
321// graph of basic blocks... and to walk it in inverse order. Inverse order for
322// a function is considered to be when traversing the predecessor edges of a BB
323// instead of the successor edges.
324//
325template <> struct GraphTraits<Inverse<BasicBlock*>> {
326 using NodeRef = BasicBlock *;
327 using ChildIteratorType = pred_iterator;
328
329 static NodeRef getEntryNode(Inverse<BasicBlock *> G) { return G.Graph; }
330 static ChildIteratorType child_begin(NodeRef N) { return pred_begin(N); }
331 static ChildIteratorType child_end(NodeRef N) { return pred_end(N); }
332};
333
334template <> struct GraphTraits<Inverse<const BasicBlock*>> {
335 using NodeRef = const BasicBlock *;
336 using ChildIteratorType = const_pred_iterator;
337
338 static NodeRef getEntryNode(Inverse<const BasicBlock *> G) { return G.Graph; }
339 static ChildIteratorType child_begin(NodeRef N) { return pred_begin(N); }
340 static ChildIteratorType child_end(NodeRef N) { return pred_end(N); }
341};
342
343//===--------------------------------------------------------------------===//
344// GraphTraits specializations for function basic block graphs (CFGs)
345//===--------------------------------------------------------------------===//
346
347// Provide specializations of GraphTraits to be able to treat a function as a
348// graph of basic blocks... these are the same as the basic block iterators,
349// except that the root node is implicitly the first node of the function.
350//
351template <> struct GraphTraits<Function*> : public GraphTraits<BasicBlock*> {
352 static NodeRef getEntryNode(Function *F) { return &F->getEntryBlock(); }
353
354 // nodes_iterator/begin/end - Allow iteration over all nodes in the graph
355 using nodes_iterator = pointer_iterator<Function::iterator>;
356
357 static nodes_iterator nodes_begin(Function *F) {
358 return nodes_iterator(F->begin());
359 }
360
361 static nodes_iterator nodes_end(Function *F) {
362 return nodes_iterator(F->end());
363 }
364
365 static size_t size(Function *F) { return F->size(); }
366};
367template <> struct GraphTraits<const Function*> :
368 public GraphTraits<const BasicBlock*> {
369 static NodeRef getEntryNode(const Function *F) { return &F->getEntryBlock(); }
370
371 // nodes_iterator/begin/end - Allow iteration over all nodes in the graph
372 using nodes_iterator = pointer_iterator<Function::const_iterator>;
373
374 static nodes_iterator nodes_begin(const Function *F) {
375 return nodes_iterator(F->begin());
376 }
377
378 static nodes_iterator nodes_end(const Function *F) {
379 return nodes_iterator(F->end());
380 }
381
382 static size_t size(const Function *F) { return F->size(); }
383};
384
385// Provide specializations of GraphTraits to be able to treat a function as a
386// graph of basic blocks... and to walk it in inverse order. Inverse order for
387// a function is considered to be when traversing the predecessor edges of a BB
388// instead of the successor edges.
389//
390template <> struct GraphTraits<Inverse<Function*>> :
391 public GraphTraits<Inverse<BasicBlock*>> {
392 static NodeRef getEntryNode(Inverse<Function *> G) {
393 return &G.Graph->getEntryBlock();
394 }
395};
396template <> struct GraphTraits<Inverse<const Function*>> :
397 public GraphTraits<Inverse<const BasicBlock*>> {
398 static NodeRef getEntryNode(Inverse<const Function *> G) {
399 return &G.Graph->getEntryBlock();
400 }
401};
402
403} // end namespace llvm
404
405#endif // LLVM_IR_CFG_H
406