LLVM: include/llvm/ADT/PostOrderIterator.h Source File

LLVM 22.0.0git
PostOrderIterator.h
Go to the documentation of this file.
1//===- llvm/ADT/PostOrderIterator.h - PostOrder iterator --------*- 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/// \file
10/// This file builds on the ADT/GraphTraits.h file to build a generic graph
11/// post order iterator. This should work over any graph type that has a
12/// GraphTraits specialization.
13///
14//===----------------------------------------------------------------------===//
15
16#ifndef LLVM_ADT_POSTORDERITERATOR_H
17#define LLVM_ADT_POSTORDERITERATOR_H
18
19#include "llvm/ADT/GraphTraits.h"
20#include "llvm/ADT/SmallPtrSet.h"
21#include "llvm/ADT/SmallVector.h"
22#include "llvm/ADT/iterator_range.h"
23#include <iterator>
24#include <optional>
25#include <set>
26#include <type_traits>
27#include <utility>
28
29namespace llvm {
30
31// The po_iterator_storage template provides access to the set of already
32// visited nodes during the po_iterator's depth-first traversal.
33//
34// The default implementation simply contains a set of visited nodes, while
35// the External=true version uses a reference to an external set.
36//
37// It is possible to prune the depth-first traversal in several ways:
38//
39// - When providing an external set that already contains some graph nodes,
40// those nodes won't be visited again. This is useful for restarting a
41// post-order traversal on a graph with nodes that aren't dominated by a
42// single node.
43//
44// - By providing a custom SetType class, unwanted graph nodes can be excluded
45// by having the insert() function return false. This could for example
46// confine a CFG traversal to blocks in a specific loop.
47//
48// - Finally, by specializing the po_iterator_storage template itself, graph
49// edges can be pruned by returning false in the insertEdge() function. This
50// could be used to remove loop back-edges from the CFG seen by po_iterator.
51//
52// A specialized po_iterator_storage class can observe both the pre-order and
53// the post-order. The insertEdge() function is called in a pre-order, while
54// the finishPostorder() function is called just before the po_iterator moves
55// on to the next node.
56
57/// Default po_iterator_storage implementation with an internal set object.
58template<class SetType, bool External>
60 SetType Visited;
61
62public:
63 // Return true if edge destination should be visited.
64 template <typename NodeRef>
65 bool insertEdge(std::optional<NodeRef> From, NodeRef To) {
66 return Visited.insert(To).second;
67 }
68
69 // Called after all children of BB have been visited.
70 template <typename NodeRef> void finishPostorder(NodeRef BB) {}
71};
72
73/// Specialization of po_iterator_storage that references an external set.
74template<class SetType>
75 class po_iterator_storage<SetType, true> {
76 SetType &Visited;
77
78public:
79 po_iterator_storage(SetType &VSet) : Visited(VSet) {}
80 po_iterator_storage(const po_iterator_storage &S) : Visited(S.Visited) {}
81
82 // Return true if edge destination should be visited, called with From = 0 for
83 // the root node.
84 // Graph edges can be pruned by specializing this function.
85 template <class NodeRef>
86 bool insertEdge(std::optional<NodeRef> From, NodeRef To) {
87 return Visited.insert(To).second;
88 }
89
90 // Called after all children of BB have been visited.
91 template <class NodeRef> void finishPostorder(NodeRef BB) {}
92};
93
94template <class GraphT,
95 class SetType = SmallPtrSet<typename GraphTraits<GraphT>::NodeRef, 8>,
96 bool ExtStorage = false, class GT = GraphTraits<GraphT>>
97 class po_iterator : public po_iterator_storage<SetType, ExtStorage> {
98public:
99 // When External storage is used we are not multi-pass safe.
101 std::conditional_t<ExtStorage, std::input_iterator_tag,
102 std::forward_iterator_tag>;
103 using value_type = typename GT::NodeRef;
104 using difference_type = std::ptrdiff_t;
106 using reference = const value_type &;
107
108private:
109 using NodeRef = typename GT::NodeRef;
110 using ChildItTy = typename GT::ChildIteratorType;
111
112 /// Used to maintain the ordering.
113 /// First element is basic block pointer, second is iterator for the next
114 /// child to visit, third is the end iterator.
116
117 po_iterator(NodeRef BB) {
118 this->insertEdge(std::optional<NodeRef>(), BB);
119 VisitStack.emplace_back(BB, GT::child_begin(BB), GT::child_end(BB));
120 traverseChild();
121 }
122
123 po_iterator() = default; // End is when stack is empty.
124
125 po_iterator(NodeRef BB, SetType &S)
126 : po_iterator_storage<SetType, ExtStorage>(S) {
127 if (this->insertEdge(std::optional<NodeRef>(), BB)) {
128 VisitStack.emplace_back(BB, GT::child_begin(BB), GT::child_end(BB));
129 traverseChild();
130 }
131 }
132
133 po_iterator(SetType &S)
134 : po_iterator_storage<SetType, ExtStorage>(S) {
135 } // End is when stack is empty.
136
137 void traverseChild() {
138 while (true) {
139 auto &Entry = VisitStack.back();
140 if (std::get<1>(Entry) == std::get<2>(Entry))
141 break;
142 NodeRef BB = *std::get<1>(Entry)++;
143 if (this->insertEdge(std::optional<NodeRef>(std::get<0>(Entry)), BB)) {
144 // If the block is not visited...
145 VisitStack.emplace_back(BB, GT::child_begin(BB), GT::child_end(BB));
146 }
147 }
148 }
149
150public:
151 // Provide static "constructors"...
152 static po_iterator begin(const GraphT &G) {
153 return po_iterator(GT::getEntryNode(G));
154 }
155 static po_iterator end(const GraphT &G) { return po_iterator(); }
156
157 static po_iterator begin(const GraphT &G, SetType &S) {
158 return po_iterator(GT::getEntryNode(G), S);
159 }
160 static po_iterator end(const GraphT &G, SetType &S) { return po_iterator(S); }
161
162 bool operator==(const po_iterator &x) const {
163 return VisitStack == x.VisitStack;
164 }
165 bool operator!=(const po_iterator &x) const { return !(*this == x); }
166
167 reference operator*() const { return std::get<0>(VisitStack.back()); }
168
169 // This is a nonstandard operator-> that dereferences the pointer an extra
170 // time... so that you can actually call methods ON the BasicBlock, because
171 // the contained type is a pointer. This allows BBIt->getTerminator() f.e.
172 //
173 NodeRef operator->() const { return **this; }
174
175 po_iterator &operator++() { // Preincrement
176 this->finishPostorder(std::get<0>(VisitStack.back()));
177 VisitStack.pop_back();
178 if (!VisitStack.empty())
179 traverseChild();
180 return *this;
181 }
182
183 po_iterator operator++(int) { // Postincrement
184 po_iterator tmp = *this;
185 ++*this;
186 return tmp;
187 }
188};
189
190// Provide global constructors that automatically figure out correct types...
191//
192template <class T>
193 po_iterator<T> po_begin(const T &G) { return po_iterator<T>::begin(G); }
194template <class T>
195 po_iterator<T> po_end (const T &G) { return po_iterator<T>::end(G); }
196
197 template <class T> iterator_range<po_iterator<T>> post_order(const T &G) {
198 return make_range(po_begin(G), po_end(G));
199}
200
201// Provide global definitions of external postorder iterators...
202template <class T, class SetType = std::set<typename GraphTraits<T>::NodeRef>>
203 struct po_ext_iterator : po_iterator<T, SetType, true> {
204 po_ext_iterator(const po_iterator<T, SetType, true> &V) :
205 po_iterator<T, SetType, true>(V) {}
206};
207
208template<class T, class SetType>
212
213template<class T, class SetType>
217
218template <class T, class SetType>
222
223// Provide global definitions of inverse post order iterators...
224template <class T, class SetType = std::set<typename GraphTraits<T>::NodeRef>,
225 bool External = false>
226 struct ipo_iterator : po_iterator<Inverse<T>, SetType, External> {
227 ipo_iterator(const po_iterator<Inverse<T>, SetType, External> &V) :
228 po_iterator<Inverse<T>, SetType, External> (V) {}
229};
230
231template <class T>
235
236template <class T>
238 return ipo_iterator<T>::end(G);
239}
240
241template <class T>
245
246// Provide global definitions of external inverse postorder iterators...
247template <class T, class SetType = std::set<typename GraphTraits<T>::NodeRef>>
248 struct ipo_ext_iterator : ipo_iterator<T, SetType, true> {
251 ipo_ext_iterator(const po_iterator<Inverse<T>, SetType, true> &V) :
252 ipo_iterator<T, SetType, true>(V) {}
253};
254
255template <class T, class SetType>
259
260template <class T, class SetType>
264
265template <class T, class SetType>
266iterator_range<ipo_ext_iterator<T, SetType>>
267 inverse_post_order_ext(const T &G, SetType &S) {
268 return make_range(ipo_ext_begin(G, S), ipo_ext_end(G, S));
269}
270
271//===--------------------------------------------------------------------===//
272// Reverse Post Order CFG iterator code
273//===--------------------------------------------------------------------===//
274//
275// This is used to visit basic blocks in a method in reverse post order. This
276// class is awkward to use because I don't know a good incremental algorithm to
277// computer RPO from a graph. Because of this, the construction of the
278// ReversePostOrderTraversal object is expensive (it must walk the entire graph
279// with a postorder iterator to build the data structures). The moral of this
280// story is: Don't create more ReversePostOrderTraversal classes than necessary.
281//
282// Because it does the traversal in its constructor, it won't invalidate when
283// BasicBlocks are removed, *but* it may contain erased blocks. Some places
284// rely on this behavior (i.e. GVN).
285//
286// This class should be used like this:
287// {
288// ReversePostOrderTraversal<Function*> RPOT(FuncPtr); // Expensive to create
289// for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
290// ...
291// }
292// for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
293// ...
294// }
295// }
296//
297
298template<class GraphT, class GT = GraphTraits<GraphT>>
300 using NodeRef = typename GT::NodeRef;
301
302 using VecTy = SmallVector<NodeRef, 8>;
303 VecTy Blocks; // Block list in normal PO order
304
305 void Initialize(const GraphT &G) {
306 std::copy(po_begin(G), po_end(G), std::back_inserter(Blocks));
307 }
308
309public:
312
313 ReversePostOrderTraversal(const GraphT &G) { Initialize(G); }
314
315 // Because we want a reverse post order, use reverse iterators from the vector
316 rpo_iterator begin() { return Blocks.rbegin(); }
317 const_rpo_iterator begin() const { return Blocks.rbegin(); }
318 rpo_iterator end() { return Blocks.rend(); }
319 const_rpo_iterator end() const { return Blocks.rend(); }
320};
321
322} // end namespace llvm
323
324#endif // LLVM_ADT_POSTORDERITERATOR_H
This file defines the little GraphTraits<X> template class that should be specialized by classes that...
G
#define G(x, y, z)
Definition MD5.cpp:56
T
#define T
This file defines the SmallPtrSet class.
This file defines the SmallVector class.
const_rpo_iterator end() const
const_rpo_iterator begin() const
ReversePostOrderTraversal(const GraphT &G)
typename VecTy::reverse_iterator rpo_iterator
typename VecTy::const_reverse_iterator const_rpo_iterator
reference emplace_back(ArgTypes &&... Args)
Definition SmallVector.h:944
std::reverse_iterator< const_iterator > const_reverse_iterator
Definition SmallVector.h:258
std::reverse_iterator< iterator > reverse_iterator
Definition SmallVector.h:259
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition SmallVector.h:1203
A range adaptor for a pair of iterators.
void finishPostorder(NodeRef BB)
po_iterator_storage(const po_iterator_storage &S)
bool insertEdge(std::optional< NodeRef > From, NodeRef To)
po_iterator_storage(SetType &VSet)
Default po_iterator_storage implementation with an internal set object.
bool insertEdge(std::optional< NodeRef > From, NodeRef To)
void finishPostorder(NodeRef BB)
static po_iterator end(const GraphT &G, SetType &S)
reference operator*() const
std::ptrdiff_t difference_type
static po_iterator end(const GraphT &G)
value_type * pointer
const value_type & reference
NodeRef operator->() const
typename GT::NodeRef value_type
static po_iterator begin(const GraphT &G)
po_iterator & operator++()
po_iterator operator++(int)
std::conditional_t< ExtStorage, std::input_iterator_tag, std::forward_iterator_tag > iterator_category
bool operator==(const po_iterator &x) const
bool operator!=(const po_iterator &x) const
static po_iterator begin(const GraphT &G, SetType &S)
This provides a very simple, boring adaptor for a begin and end iterator into a range type.
@ Entry
Definition COFF.h:862
This is an optimization pass for GlobalISel generic memory operations.
Definition AddressRanges.h:18
ipo_iterator< T > ipo_end(const T &G)
iterator_range< po_ext_iterator< T, SetType > > post_order_ext(const T &G, SetType &S)
iterator_range< ipo_ext_iterator< T, SetType > > inverse_post_order_ext(const T &G, SetType &S)
ipo_ext_iterator< T, SetType > ipo_ext_begin(const T &G, SetType &S)
iterator_range< ipo_iterator< T > > inverse_post_order(const T &G)
iterator_range< T > make_range(T x, T y)
Convenience function for iterating over sub-ranges.
iterator_range< po_iterator< T > > post_order(const T &G)
po_ext_iterator< T, SetType > po_ext_end(T G, SetType &S)
po_iterator< T > po_begin(const T &G)
ipo_ext_iterator< T, SetType > ipo_ext_end(const T &G, SetType &S)
ipo_iterator< T > ipo_begin(const T &G)
iterator_range(Container &&) -> iterator_range< llvm::detail::IterOfRange< Container > >
po_iterator< T > po_end(const T &G)
po_ext_iterator< T, SetType > po_ext_begin(T G, SetType &S)
ipo_ext_iterator(const ipo_iterator< T, SetType, true > &V)
ipo_ext_iterator(const po_iterator< Inverse< T >, SetType, true > &V)
ipo_iterator(const po_iterator< Inverse< T >, SetType, External > &V)
po_ext_iterator(const po_iterator< T, SetType, true > &V)
Generated on for LLVM by doxygen 1.14.0

AltStyle によって変換されたページ (->オリジナル) /