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1 : //===- llvm/ADT/PostOrderIterator.h - PostOrder iterator --------*- C++ -*-===//
2 : //
3 : // The LLVM Compiler Infrastructure
4 : //
5 : // This file is distributed under the University of Illinois Open Source
6 : // License. See LICENSE.TXT for details.
7 : //
8 : //===----------------------------------------------------------------------===//
9 : //
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/Optional.h"
21 : #include "llvm/ADT/SmallPtrSet.h"
22 : #include "llvm/ADT/iterator_range.h"
23 : #include <iterator>
24 : #include <set>
25 : #include <utility>
26 : #include <vector>
27 :
28 : namespace llvm {
29 :
30 : // The po_iterator_storage template provides access to the set of already
31 : // visited nodes during the po_iterator's depth-first traversal.
32 : //
33 : // The default implementation simply contains a set of visited nodes, while
34 : // the External=true version uses a reference to an external set.
35 : //
36 : // It is possible to prune the depth-first traversal in several ways:
37 : //
38 : // - When providing an external set that already contains some graph nodes,
39 : // those nodes won't be visited again. This is useful for restarting a
40 : // post-order traversal on a graph with nodes that aren't dominated by a
41 : // single node.
42 : //
43 : // - By providing a custom SetType class, unwanted graph nodes can be excluded
44 : // by having the insert() function return false. This could for example
45 : // confine a CFG traversal to blocks in a specific loop.
46 : //
47 : // - Finally, by specializing the po_iterator_storage template itself, graph
48 : // edges can be pruned by returning false in the insertEdge() function. This
49 : // could be used to remove loop back-edges from the CFG seen by po_iterator.
50 : //
51 : // A specialized po_iterator_storage class can observe both the pre-order and
52 : // the post-order. The insertEdge() function is called in a pre-order, while
53 : // the finishPostorder() function is called just before the po_iterator moves
54 : // on to the next node.
55 :
56 : /// Default po_iterator_storage implementation with an internal set object.
57 : template<class SetType, bool External>
58 : class po_iterator_storage {
59 : SetType Visited;
60 :
61 : public:
62 : // Return true if edge destination should be visited.
63 : template <typename NodeRef>
64 0 : bool insertEdge(Optional<NodeRef> From, NodeRef To) {
65 22226691 : return Visited.insert(To).second;
66 : }
67 0 :
68 0 : // Called after all children of BB have been visited.
69 0 : template <typename NodeRef> void finishPostorder(NodeRef BB) {}
70 0 : };
71 0 :
72 : /// Specialization of po_iterator_storage that references an external set.
73 : template<class SetType>
74 : class po_iterator_storage<SetType, true> {
75 0 : SetType &Visited;
76 :
77 : public:
78 3693125 : po_iterator_storage(SetType &VSet) : Visited(VSet) {}
79 126 : po_iterator_storage(const po_iterator_storage &S) : Visited(S.Visited) {}
80 :
81 : // Return true if edge destination should be visited, called with From = 0 for
82 : // the root node.
83 : // Graph edges can be pruned by specializing this function.
84 0 : template <class NodeRef> bool insertEdge(Optional<NodeRef> From, NodeRef To) {
85 3693146 : return Visited.insert(To).second;
86 : }
87 :
88 : // Called after all children of BB have been visited.
89 0 : template <class NodeRef> void finishPostorder(NodeRef BB) {}
90 0 : };
91 1 :
92 : template <class GraphT,
93 : class SetType =
94 : SmallPtrSet<typename GraphTraits<GraphT>::NodeRef, 8>,
95 : bool ExtStorage = false, class GT = GraphTraits<GraphT>>
96 16179915 : class po_iterator
97 : : public std::iterator<std::forward_iterator_tag, typename GT::NodeRef>,
98 : public po_iterator_storage<SetType, ExtStorage> {
99 : using super = std::iterator<std::forward_iterator_tag, typename GT::NodeRef>;
100 : using NodeRef = typename GT::NodeRef;
101 : using ChildItTy = typename GT::ChildIteratorType;
102 11876722 :
103 : // VisitStack - Used to maintain the ordering. Top = current block
104 : // First element is basic block pointer, second is the 'next child' to visit
105 : std::vector<std::pair<NodeRef, ChildItTy>> VisitStack;
106 :
107 6012938 : po_iterator(NodeRef BB) {
108 : this->insertEdge(Optional<NodeRef>(), BB);
109 3006470 : VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
110 3006470 : traverseChild();
111 3006470 : }
112 :
113 10635014 : po_iterator() = default; // End is when stack is empty.
114 :
115 9011750 : po_iterator(NodeRef BB, SetType &S)
116 9012846 : : po_iterator_storage<SetType, ExtStorage>(S) {
117 9011750 : if (this->insertEdge(Optional<NodeRef>(), BB)) {
118 9416792 : VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
119 3694146 : traverseChild();
120 2861324 : }
121 6555566 : }
122 2861872 :
123 4913464 : po_iterator(SetType &S)
124 548 : : po_iterator_storage<SetType, ExtStorage>(S) {
125 2456649 : } // End is when stack is empty.
126 2456649 :
127 36296096 : void traverseChild() {
128 102236295 : while (VisitStack.back().second != GT::child_end(VisitStack.back().first)) {
129 16987273 : NodeRef BB = *VisitStack.back().second++;
130 30890535 : if (this->insertEdge(Optional<NodeRef>(VisitStack.back().first), BB)) {
131 9006 : // If the block is not visited...
132 39086685 : VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
133 8993 : }
134 8458 : }
135 33848918 : }
136 :
137 8458 : public:
138 : using pointer = typename super::pointer;
139 :
140 : // Provide static "constructors"...
141 1585 : static po_iterator begin(GraphT G) {
142 2221526 : return po_iterator(GT::getEntryNode(G));
143 8529019 : }
144 31580992 : static po_iterator end(GraphT G) { return po_iterator(); }
145 6141983 :
146 6195994 : static po_iterator begin(GraphT G, SetType &S) {
147 3693125 : return po_iterator(GT::getEntryNode(G), S);
148 11372005 : }
149 1585 : static po_iterator end(GraphT G, SetType &S) { return po_iterator(S); }
150 860 :
151 8530997 : bool operator==(const po_iterator &x) const {
152 32616260 : return VisitStack == x.VisitStack;
153 5258424 : }
154 1364281 : bool operator!=(const po_iterator &x) const { return !(*this == x); }
155 1365069 :
156 21992616 : const NodeRef &operator*() const { return VisitStack.back().first; }
157 1795150 :
158 859 : // This is a nonstandard operator-> that dereferences the pointer an extra
159 726 : // time... so that you can actually call methods ON the BasicBlock, because
160 1266568 : // the contained type is a pointer. This allows BBIt->getTerminator() f.e.
161 7234179 : //
162 24024674 : NodeRef operator->() const { return **this; }
163 4777702 :
164 4778084 : po_iterator &operator++() { // Preincrement
165 : this->finishPostorder(VisitStack.back().first);
166 9555404 : VisitStack.pop_back();
167 24652439 : if (!VisitStack.empty())
168 17952249 : traverseChild();
169 7233734 : return *this;
170 29909 : }
171 82750 :
172 : po_iterator operator++(int) { // Postincrement
173 52841 : po_iterator tmp = *this;
174 : ++*this;
175 21451 : return tmp;
176 405443 : }
177 : };
178 435352 :
179 0 : // Provide global constructors that automatically figure out correct types...
180 : //
181 0 : template <class T>
182 0 : po_iterator<T> po_begin(const T &G) { return po_iterator<T>::begin(G); }
183 : template <class T>
184 2681 : po_iterator<T> po_end (const T &G) { return po_iterator<T>::end(G); }
185 0 :
186 10660035 : template <class T> iterator_range<po_iterator<T>> post_order(const T &G) {
187 117122 : return make_range(po_begin(G), po_end(G));
188 : }
189 :
190 3226997 : // Provide global definitions of external postorder iterators...
191 : template <class T, class SetType = std::set<typename GraphTraits<T>::NodeRef>>
192 0 : struct po_ext_iterator : public po_iterator<T, SetType, true> {
193 : po_ext_iterator(const po_iterator<T, SetType, true> &V) :
194 : po_iterator<T, SetType, true>(V) {}
195 12440407 : };
196 :
197 : template<class T, class SetType>
198 1 : po_ext_iterator<T, SetType> po_ext_begin(T G, SetType &S) {
199 1585 : return po_ext_iterator<T, SetType>::begin(G, S);
200 585 : }
201 7971505 :
202 5341535 : template<class T, class SetType>
203 : po_ext_iterator<T, SetType> po_ext_end(T G, SetType &S) {
204 : return po_ext_iterator<T, SetType>::end(G, S);
205 : }
206 :
207 29909 : template <class T, class SetType>
208 29909 : iterator_range<po_ext_iterator<T, SetType>> post_order_ext(const T &G, SetType &S) {
209 0 : return make_range(po_ext_begin(G, S), po_ext_end(G, S));
210 9744411 : }
211 7048415 :
212 29909 : // Provide global definitions of inverse post order iterators...
213 : template <class T, class SetType = std::set<typename GraphTraits<T>::NodeRef>,
214 : bool External = false>
215 : struct ipo_iterator : public po_iterator<Inverse<T>, SetType, External> {
216 0 : ipo_iterator(const po_iterator<Inverse<T>, SetType, External> &V) :
217 : po_iterator<Inverse<T>, SetType, External> (V) {}
218 0 : };
219 :
220 0 : template <class T>
221 0 : ipo_iterator<T> ipo_begin(const T &G) {
222 : return ipo_iterator<T>::begin(G);
223 : }
224 1013 :
225 0 : template <class T>
226 : ipo_iterator<T> ipo_end(const T &G){
227 0 : return ipo_iterator<T>::end(G);
228 : }
229 0 :
230 548 : template <class T>
231 548 : iterator_range<ipo_iterator<T>> inverse_post_order(const T &G) {
232 0 : return make_range(ipo_begin(G), ipo_end(G));
233 0 : }
234 :
235 0 : // Provide global definitions of external inverse postorder iterators...
236 0 : template <class T, class SetType = std::set<typename GraphTraits<T>::NodeRef>>
237 42 : struct ipo_ext_iterator : public ipo_iterator<T, SetType, true> {
238 : ipo_ext_iterator(const ipo_iterator<T, SetType, true> &V) :
239 : ipo_iterator<T, SetType, true>(V) {}
240 548 : ipo_ext_iterator(const po_iterator<Inverse<T>, SetType, true> &V) :
241 548 : ipo_iterator<T, SetType, true>(V) {}
242 : };
243 :
244 : template <class T, class SetType>
245 0 : ipo_ext_iterator<T, SetType> ipo_ext_begin(const T &G, SetType &S) {
246 0 : return ipo_ext_iterator<T, SetType>::begin(G, S);
247 8458 : }
248 8458 :
249 : template <class T, class SetType>
250 0 : ipo_ext_iterator<T, SetType> ipo_ext_end(const T &G, SetType &S) {
251 0 : return ipo_ext_iterator<T, SetType>::end(G, S);
252 0 : }
253 0 :
254 : template <class T, class SetType>
255 : iterator_range<ipo_ext_iterator<T, SetType>>
256 21 : inverse_post_order_ext(const T &G, SetType &S) {
257 21 : return make_range(ipo_ext_begin(G, S), ipo_ext_end(G, S));
258 : }
259 :
260 : //===--------------------------------------------------------------------===//
261 : // Reverse Post Order CFG iterator code
262 : //===--------------------------------------------------------------------===//
263 : //
264 : // This is used to visit basic blocks in a method in reverse post order. This
265 : // class is awkward to use because I don't know a good incremental algorithm to
266 : // computer RPO from a graph. Because of this, the construction of the
267 : // ReversePostOrderTraversal object is expensive (it must walk the entire graph
268 : // with a postorder iterator to build the data structures). The moral of this
269 1083 : // story is: Don't create more ReversePostOrderTraversal classes than necessary.
270 : //
271 : // Because it does the traversal in its constructor, it won't invalidate when
272 : // BasicBlocks are removed, *but* it may contain erased blocks. Some places
273 : // rely on this behavior (i.e. GVN).
274 : //
275 : // This class should be used like this:
276 : // {
277 0 : // ReversePostOrderTraversal<Function*> RPOT(FuncPtr); // Expensive to create
278 0 : // for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
279 : // ...
280 : // }
281 : // for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
282 0 : // ...
283 0 : // }
284 : // }
285 : //
286 :
287 : template<class GraphT, class GT = GraphTraits<GraphT>>
288 357413 : class ReversePostOrderTraversal {
289 548 : using NodeRef = typename GT::NodeRef;
290 :
291 : std::vector<NodeRef> Blocks; // Block list in normal PO order
292 :
293 843245 : void Initialize(NodeRef BB) {
294 843245 : std::copy(po_begin(BB), po_end(BB), std::back_inserter(Blocks));
295 843244 : }
296 :
297 : public:
298 : using rpo_iterator = typename std::vector<NodeRef>::reverse_iterator;
299 : using const_rpo_iterator = typename std::vector<NodeRef>::const_reverse_iterator;
300 :
301 843245 : ReversePostOrderTraversal(GraphT G) { Initialize(GT::getEntryNode(G)); }
302 :
303 : // Because we want a reverse post order, use reverse iterators from the vector
304 : rpo_iterator begin() { return Blocks.rbegin(); }
305 : const_rpo_iterator begin() const { return Blocks.crbegin(); }
306 : rpo_iterator end() { return Blocks.rend(); }
307 : const_rpo_iterator end() const { return Blocks.crend(); }
308 : };
309 :
310 : } // end namespace llvm
311 :
312 : #endif // LLVM_ADT_POSTORDERITERATOR_H
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