1 //===--- DAGDeltaAlgorithm.cpp - A DAG Minimization Algorithm --*- C++ -*--===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //===----------------------------------------------------------------------===//
9 // The algorithm we use attempts to exploit the dependency information by
10 // minimizing top-down. We start by constructing an initial root set R, and
13 // 1. Minimize the set R using the test predicate:
14 // P'(S) = P(S union pred*(S))
16 // 2. Extend R to R' = R union pred(R).
18 // until a fixed point is reached.
20 // The idea is that we want to quickly prune entire portions of the graph, so we
21 // try to find high-level nodes that can be eliminated with all of their
24 // FIXME: The current algorithm doesn't actually provide a strong guarantee
25 // about the minimality of the result. The problem is that after adding nodes to
26 // the required set, we no longer consider them for elimination. For strictly
27 // well formed predicates, this doesn't happen, but it commonly occurs in
28 // practice when there are unmodelled dependencies. I believe we can resolve
29 // this by allowing the required set to be minimized as well, but need more test
32 //===----------------------------------------------------------------------===//
34 #include "llvm/ADT/DAGDeltaAlgorithm.h"
35 #include "llvm/ADT/DeltaAlgorithm.h"
36 #include "llvm/Support/Debug.h"
37 #include "llvm/Support/Format.h"
38 #include "llvm/Support/raw_ostream.h"
47 class DAGDeltaAlgorithmImpl {
48 friend class DeltaActiveSetHelper;
51 typedef DAGDeltaAlgorithm::change_ty change_ty;
52 typedef DAGDeltaAlgorithm::changeset_ty changeset_ty;
53 typedef DAGDeltaAlgorithm::changesetlist_ty changesetlist_ty;
54 typedef DAGDeltaAlgorithm::edge_ty edge_ty;
57 typedef std::vector<change_ty>::iterator pred_iterator_ty;
58 typedef std::vector<change_ty>::iterator succ_iterator_ty;
59 typedef std::set<change_ty>::iterator pred_closure_iterator_ty;
60 typedef std::set<change_ty>::iterator succ_closure_iterator_ty;
62 DAGDeltaAlgorithm &DDA;
64 const changeset_ty &Changes;
65 const std::vector<edge_ty> &Dependencies;
67 std::vector<change_ty> Roots;
69 /// Cache of failed test results. Successful test results are never cached
70 /// since we always reduce following a success. We maintain an independent
71 /// cache from that used by the individual delta passes because we may get
72 /// hits across multiple individual delta invocations.
73 mutable std::set<changeset_ty> FailedTestsCache;
76 std::map<change_ty, std::vector<change_ty> > Predecessors;
77 std::map<change_ty, std::vector<change_ty> > Successors;
79 std::map<change_ty, std::set<change_ty> > PredClosure;
80 std::map<change_ty, std::set<change_ty> > SuccClosure;
83 pred_iterator_ty pred_begin(change_ty Node) {
84 assert(Predecessors.count(Node) && "Invalid node!");
85 return Predecessors[Node].begin();
87 pred_iterator_ty pred_end(change_ty Node) {
88 assert(Predecessors.count(Node) && "Invalid node!");
89 return Predecessors[Node].end();
92 pred_closure_iterator_ty pred_closure_begin(change_ty Node) {
93 assert(PredClosure.count(Node) && "Invalid node!");
94 return PredClosure[Node].begin();
96 pred_closure_iterator_ty pred_closure_end(change_ty Node) {
97 assert(PredClosure.count(Node) && "Invalid node!");
98 return PredClosure[Node].end();
101 succ_iterator_ty succ_begin(change_ty Node) {
102 assert(Successors.count(Node) && "Invalid node!");
103 return Successors[Node].begin();
105 succ_iterator_ty succ_end(change_ty Node) {
106 assert(Successors.count(Node) && "Invalid node!");
107 return Successors[Node].end();
110 succ_closure_iterator_ty succ_closure_begin(change_ty Node) {
111 assert(SuccClosure.count(Node) && "Invalid node!");
112 return SuccClosure[Node].begin();
114 succ_closure_iterator_ty succ_closure_end(change_ty Node) {
115 assert(SuccClosure.count(Node) && "Invalid node!");
116 return SuccClosure[Node].end();
119 void UpdatedSearchState(const changeset_ty &Changes,
120 const changesetlist_ty &Sets,
121 const changeset_ty &Required) {
122 DDA.UpdatedSearchState(Changes, Sets, Required);
125 /// ExecuteOneTest - Execute a single test predicate on the change set \arg S.
126 bool ExecuteOneTest(const changeset_ty &S) {
127 // Check dependencies invariant.
129 for (changeset_ty::const_iterator it = S.begin(),
130 ie = S.end(); it != ie; ++it)
131 for (succ_iterator_ty it2 = succ_begin(*it),
132 ie2 = succ_end(*it); it2 != ie2; ++it2)
133 assert(S.count(*it2) && "Attempt to run invalid changeset!");
136 return DDA.ExecuteOneTest(S);
140 DAGDeltaAlgorithmImpl(DAGDeltaAlgorithm &_DDA,
141 const changeset_ty &_Changes,
142 const std::vector<edge_ty> &_Dependencies);
146 /// GetTestResult - Get the test result for the active set \arg Changes with
147 /// \arg Required changes from the cache, executing the test if necessary.
149 /// \param Changes - The set of active changes being minimized, which should
150 /// have their pred closure included in the test.
151 /// \param Required - The set of changes which have previously been
152 /// established to be required.
153 /// \return - The test result.
154 bool GetTestResult(const changeset_ty &Changes, const changeset_ty &Required);
157 /// Helper object for minimizing an active set of changes.
158 class DeltaActiveSetHelper : public DeltaAlgorithm {
159 DAGDeltaAlgorithmImpl &DDAI;
161 const changeset_ty &Required;
164 /// UpdatedSearchState - Callback used when the search state changes.
165 virtual void UpdatedSearchState(const changeset_ty &Changes,
166 const changesetlist_ty &Sets) {
167 DDAI.UpdatedSearchState(Changes, Sets, Required);
170 virtual bool ExecuteOneTest(const changeset_ty &S) {
171 return DDAI.GetTestResult(S, Required);
175 DeltaActiveSetHelper(DAGDeltaAlgorithmImpl &_DDAI,
176 const changeset_ty &_Required)
177 : DDAI(_DDAI), Required(_Required) {}
182 DAGDeltaAlgorithmImpl::DAGDeltaAlgorithmImpl(DAGDeltaAlgorithm &_DDA,
183 const changeset_ty &_Changes,
184 const std::vector<edge_ty>
188 Dependencies(_Dependencies)
190 for (changeset_ty::const_iterator it = Changes.begin(),
191 ie = Changes.end(); it != ie; ++it) {
192 Predecessors.insert(std::make_pair(*it, std::vector<change_ty>()));
193 Successors.insert(std::make_pair(*it, std::vector<change_ty>()));
195 for (std::vector<edge_ty>::const_iterator it = Dependencies.begin(),
196 ie = Dependencies.end(); it != ie; ++it) {
197 Predecessors[it->second].push_back(it->first);
198 Successors[it->first].push_back(it->second);
201 // Compute the roots.
202 for (changeset_ty::const_iterator it = Changes.begin(),
203 ie = Changes.end(); it != ie; ++it)
204 if (succ_begin(*it) == succ_end(*it))
205 Roots.push_back(*it);
207 // Pre-compute the closure of the successor relation.
208 std::vector<change_ty> Worklist(Roots.begin(), Roots.end());
209 while (!Worklist.empty()) {
210 change_ty Change = Worklist.back();
213 std::set<change_ty> &ChangeSuccs = SuccClosure[Change];
214 for (pred_iterator_ty it = pred_begin(Change),
215 ie = pred_end(Change); it != ie; ++it) {
216 SuccClosure[*it].insert(Change);
217 SuccClosure[*it].insert(ChangeSuccs.begin(), ChangeSuccs.end());
218 Worklist.push_back(*it);
222 // Invert to form the predecessor closure map.
223 for (changeset_ty::const_iterator it = Changes.begin(),
224 ie = Changes.end(); it != ie; ++it)
225 PredClosure.insert(std::make_pair(*it, std::set<change_ty>()));
226 for (changeset_ty::const_iterator it = Changes.begin(),
227 ie = Changes.end(); it != ie; ++it)
228 for (succ_closure_iterator_ty it2 = succ_closure_begin(*it),
229 ie2 = succ_closure_end(*it); it2 != ie2; ++it2)
230 PredClosure[*it2].insert(*it);
232 // Dump useful debug info.
234 llvm::errs() << "-- DAGDeltaAlgorithmImpl --\n";
235 llvm::errs() << "Changes: [";
236 for (changeset_ty::const_iterator it = Changes.begin(),
237 ie = Changes.end(); it != ie; ++it) {
238 if (it != Changes.begin()) llvm::errs() << ", ";
241 if (succ_begin(*it) != succ_end(*it)) {
243 for (succ_iterator_ty it2 = succ_begin(*it),
244 ie2 = succ_end(*it); it2 != ie2; ++it2) {
245 if (it2 != succ_begin(*it)) llvm::errs() << ", ";
246 llvm::errs() << "->" << *it2;
251 llvm::errs() << "]\n";
253 llvm::errs() << "Roots: [";
254 for (std::vector<change_ty>::const_iterator it = Roots.begin(),
255 ie = Roots.end(); it != ie; ++it) {
256 if (it != Roots.begin()) llvm::errs() << ", ";
259 llvm::errs() << "]\n";
261 llvm::errs() << "Predecessor Closure:\n";
262 for (changeset_ty::const_iterator it = Changes.begin(),
263 ie = Changes.end(); it != ie; ++it) {
264 llvm::errs() << format(" %-4d: [", *it);
265 for (pred_closure_iterator_ty it2 = pred_closure_begin(*it),
266 ie2 = pred_closure_end(*it); it2 != ie2; ++it2) {
267 if (it2 != pred_closure_begin(*it)) llvm::errs() << ", ";
268 llvm::errs() << *it2;
270 llvm::errs() << "]\n";
273 llvm::errs() << "Successor Closure:\n";
274 for (changeset_ty::const_iterator it = Changes.begin(),
275 ie = Changes.end(); it != ie; ++it) {
276 llvm::errs() << format(" %-4d: [", *it);
277 for (succ_closure_iterator_ty it2 = succ_closure_begin(*it),
278 ie2 = succ_closure_end(*it); it2 != ie2; ++it2) {
279 if (it2 != succ_closure_begin(*it)) llvm::errs() << ", ";
280 llvm::errs() << *it2;
282 llvm::errs() << "]\n";
285 llvm::errs() << "\n\n";
289 bool DAGDeltaAlgorithmImpl::GetTestResult(const changeset_ty &Changes,
290 const changeset_ty &Required) {
291 changeset_ty Extended(Required);
292 Extended.insert(Changes.begin(), Changes.end());
293 for (changeset_ty::const_iterator it = Changes.begin(),
294 ie = Changes.end(); it != ie; ++it)
295 Extended.insert(pred_closure_begin(*it), pred_closure_end(*it));
297 if (FailedTestsCache.count(Extended))
300 bool Result = ExecuteOneTest(Extended);
302 FailedTestsCache.insert(Extended);
307 DAGDeltaAlgorithm::changeset_ty
308 DAGDeltaAlgorithmImpl::Run() {
309 // The current set of changes we are minimizing, starting at the roots.
310 changeset_ty CurrentSet(Roots.begin(), Roots.end());
312 // The set of required changes.
313 changeset_ty Required;
315 // Iterate until the active set of changes is empty. Convergence is guaranteed
316 // assuming input was a DAG.
318 // Invariant: CurrentSet intersect Required == {}
319 // Invariant: Required == (Required union succ*(Required))
320 while (!CurrentSet.empty()) {
322 llvm::errs() << "DAG_DD - " << CurrentSet.size() << " active changes, "
323 << Required.size() << " required changes\n";
326 // Minimize the current set of changes.
327 DeltaActiveSetHelper Helper(*this, Required);
328 changeset_ty CurrentMinSet = Helper.Run(CurrentSet);
330 // Update the set of required changes. Since
331 // CurrentMinSet subset CurrentSet
332 // and after the last iteration,
333 // succ(CurrentSet) subset Required
335 // succ(CurrentMinSet) subset Required
336 // and our invariant on Required is maintained.
337 Required.insert(CurrentMinSet.begin(), CurrentMinSet.end());
339 // Replace the current set with the predecssors of the minimized set of
342 for (changeset_ty::const_iterator it = CurrentMinSet.begin(),
343 ie = CurrentMinSet.end(); it != ie; ++it)
344 CurrentSet.insert(pred_begin(*it), pred_end(*it));
346 // FIXME: We could enforce CurrentSet intersect Required == {} here if we
347 // wanted to protect against cyclic graphs.
353 DAGDeltaAlgorithm::changeset_ty
354 DAGDeltaAlgorithm::Run(const changeset_ty &Changes,
355 const std::vector<edge_ty> &Dependencies) {
356 return DAGDeltaAlgorithmImpl(*this, Changes, Dependencies).Run();