lib/Support/DAGDeltaAlgorithm.cpp

   1 //===--- DAGDeltaAlgorithm.cpp - A DAG Minimization Algorithm --*- 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 // 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
  11 // then iteratively:
  12 //
  13 //   1. Minimize the set R using the test predicate:
  14 //       P'(S) = P(S union pred*(S))
  15 //
  16 //   2. Extend R to R' = R union pred(R).
  17 //
  18 // until a fixed point is reached.
  19 //
  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
  22 // dependents.
  23 //
  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
  30 // cases first.
  31 //
  32 //===----------------------------------------------------------------------===//
  33
  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"
  39 #include <algorithm>
  40 #include <cassert>
  41 #include <iterator>
  42 #include <map>
  43 using namespace llvm;
  44
  45 #define DEBUG_TYPE "dag-delta"
  46
  47 namespace {
  48
  49 class DAGDeltaAlgorithmImpl {
  50   friend class DeltaActiveSetHelper;
  51
  52 public:
  53   typedef DAGDeltaAlgorithm::change_ty change_ty;
  54   typedef DAGDeltaAlgorithm::changeset_ty changeset_ty;
  55   typedef DAGDeltaAlgorithm::changesetlist_ty changesetlist_ty;
  56   typedef DAGDeltaAlgorithm::edge_ty edge_ty;
  57
  58 private:
  59   typedef std::vector<change_ty>::iterator pred_iterator_ty;
  60   typedef std::vector<change_ty>::iterator succ_iterator_ty;
  61   typedef std::set<change_ty>::iterator pred_closure_iterator_ty;
  62   typedef std::set<change_ty>::iterator succ_closure_iterator_ty;
  63
  64   DAGDeltaAlgorithm &DDA;
  65
  66   std::vector<change_ty> Roots;
  67
  68   /// Cache of failed test results. Successful test results are never cached
  69   /// since we always reduce following a success. We maintain an independent
  70   /// cache from that used by the individual delta passes because we may get
  71   /// hits across multiple individual delta invocations.
  72   mutable std::set<changeset_ty> FailedTestsCache;
  73
  74   // FIXME: Gross.
  75   std::map<change_ty, std::vector<change_ty> > Predecessors;
  76   std::map<change_ty, std::vector<change_ty> > Successors;
  77
  78   std::map<change_ty, std::set<change_ty> > PredClosure;
  79   std::map<change_ty, std::set<change_ty> > SuccClosure;
  80
  81 private:
  82   pred_iterator_ty pred_begin(change_ty Node) {
  83     assert(Predecessors.count(Node) && "Invalid node!");
  84     return Predecessors[Node].begin();
  85   }
  86   pred_iterator_ty pred_end(change_ty Node) {
  87     assert(Predecessors.count(Node) && "Invalid node!");
  88     return Predecessors[Node].end();
  89   }
  90
  91   pred_closure_iterator_ty pred_closure_begin(change_ty Node) {
  92     assert(PredClosure.count(Node) && "Invalid node!");
  93     return PredClosure[Node].begin();
  94   }
  95   pred_closure_iterator_ty pred_closure_end(change_ty Node) {
  96     assert(PredClosure.count(Node) && "Invalid node!");
  97     return PredClosure[Node].end();
  98   }
  99
 100   succ_iterator_ty succ_begin(change_ty Node) {
 101     assert(Successors.count(Node) && "Invalid node!");
 102     return Successors[Node].begin();
 103   }
 104   succ_iterator_ty succ_end(change_ty Node) {
 105     assert(Successors.count(Node) && "Invalid node!");
 106     return Successors[Node].end();
 107   }
 108
 109   succ_closure_iterator_ty succ_closure_begin(change_ty Node) {
 110     assert(SuccClosure.count(Node) && "Invalid node!");
 111     return SuccClosure[Node].begin();
 112   }
 113   succ_closure_iterator_ty succ_closure_end(change_ty Node) {
 114     assert(SuccClosure.count(Node) && "Invalid node!");
 115     return SuccClosure[Node].end();
 116   }
 117
 118   void UpdatedSearchState(const changeset_ty &Changes,
 119                           const changesetlist_ty &Sets,
 120                           const changeset_ty &Required) {
 121     DDA.UpdatedSearchState(Changes, Sets, Required);
 122   }
 123
 124   /// ExecuteOneTest - Execute a single test predicate on the change set \p S.
 125   bool ExecuteOneTest(const changeset_ty &S) {
 126     // Check dependencies invariant.
 127     LLVM_DEBUG({
 128       for (changeset_ty::const_iterator it = S.begin(), ie = S.end(); it != ie;
 129            ++it)
 130         for (succ_iterator_ty it2 = succ_begin(*it), ie2 = succ_end(*it);
 131              it2 != ie2; ++it2)
 132           assert(S.count(*it2) && "Attempt to run invalid changeset!");
 133     });
 134
 135     return DDA.ExecuteOneTest(S);
 136   }
 137
 138 public:
 139   DAGDeltaAlgorithmImpl(DAGDeltaAlgorithm &DDA, const changeset_ty &Changes,
 140                         const std::vector<edge_ty> &Dependencies);
 141
 142   changeset_ty Run();
 143
 144   /// GetTestResult - Get the test result for the active set \p Changes with
 145   /// \p Required changes from the cache, executing the test if necessary.
 146   ///
 147   /// \param Changes - The set of active changes being minimized, which should
 148   /// have their pred closure included in the test.
 149   /// \param Required - The set of changes which have previously been
 150   /// established to be required.
 151   /// \return - The test result.
 152   bool GetTestResult(const changeset_ty &Changes, const changeset_ty &Required);
 153 };
 154
 155 /// Helper object for minimizing an active set of changes.
 156 class DeltaActiveSetHelper : public DeltaAlgorithm {
 157   DAGDeltaAlgorithmImpl &DDAI;
 158
 159   const changeset_ty &Required;
 160
 161 protected:
 162   /// UpdatedSearchState - Callback used when the search state changes.
 163   void UpdatedSearchState(const changeset_ty &Changes,
 164                                   const changesetlist_ty &Sets) override {
 165     DDAI.UpdatedSearchState(Changes, Sets, Required);
 166   }
 167
 168   bool ExecuteOneTest(const changeset_ty &S) override {
 169     return DDAI.GetTestResult(S, Required);
 170   }
 171
 172 public:
 173   DeltaActiveSetHelper(DAGDeltaAlgorithmImpl &DDAI,
 174                        const changeset_ty &Required)
 175       : DDAI(DDAI), Required(Required) {}
 176 };
 177
 178 }
 179
 180 DAGDeltaAlgorithmImpl::DAGDeltaAlgorithmImpl(
 181     DAGDeltaAlgorithm &DDA, const changeset_ty &Changes,
 182     const std::vector<edge_ty> &Dependencies)
 183     : DDA(DDA) {
 184   for (changeset_ty::const_iterator it = Changes.begin(),
 185          ie = Changes.end(); it != ie; ++it) {
 186     Predecessors.insert(std::make_pair(*it, std::vector<change_ty>()));
 187     Successors.insert(std::make_pair(*it, std::vector<change_ty>()));
 188   }
 189   for (std::vector<edge_ty>::const_iterator it = Dependencies.begin(),
 190          ie = Dependencies.end(); it != ie; ++it) {
 191     Predecessors[it->second].push_back(it->first);
 192     Successors[it->first].push_back(it->second);
 193   }
 194
 195   // Compute the roots.
 196   for (changeset_ty::const_iterator it = Changes.begin(),
 197          ie = Changes.end(); it != ie; ++it)
 198     if (succ_begin(*it) == succ_end(*it))
 199       Roots.push_back(*it);
 200
 201   // Pre-compute the closure of the successor relation.
 202   std::vector<change_ty> Worklist(Roots.begin(), Roots.end());
 203   while (!Worklist.empty()) {
 204     change_ty Change = Worklist.back();
 205     Worklist.pop_back();
 206
 207     std::set<change_ty> &ChangeSuccs = SuccClosure[Change];
 208     for (pred_iterator_ty it = pred_begin(Change),
 209            ie = pred_end(Change); it != ie; ++it) {
 210       SuccClosure[*it].insert(Change);
 211       SuccClosure[*it].insert(ChangeSuccs.begin(), ChangeSuccs.end());
 212       Worklist.push_back(*it);
 213     }
 214   }
 215
 216   // Invert to form the predecessor closure map.
 217   for (changeset_ty::const_iterator it = Changes.begin(),
 218          ie = Changes.end(); it != ie; ++it)
 219     PredClosure.insert(std::make_pair(*it, std::set<change_ty>()));
 220   for (changeset_ty::const_iterator it = Changes.begin(),
 221          ie = Changes.end(); it != ie; ++it)
 222     for (succ_closure_iterator_ty it2 = succ_closure_begin(*it),
 223            ie2 = succ_closure_end(*it); it2 != ie2; ++it2)
 224       PredClosure[*it2].insert(*it);
 225
 226   // Dump useful debug info.
 227   LLVM_DEBUG({
 228     llvm::errs() << "-- DAGDeltaAlgorithmImpl --\n";
 229     llvm::errs() << "Changes: [";
 230     for (changeset_ty::const_iterator it = Changes.begin(), ie = Changes.end();
 231          it != ie; ++it) {
 232       if (it != Changes.begin())
 233         llvm::errs() << ", ";
 234       llvm::errs() << *it;
 235
 236       if (succ_begin(*it) != succ_end(*it)) {
 237         llvm::errs() << "(";
 238         for (succ_iterator_ty it2 = succ_begin(*it), ie2 = succ_end(*it);
 239              it2 != ie2; ++it2) {
 240           if (it2 != succ_begin(*it))
 241             llvm::errs() << ", ";
 242           llvm::errs() << "->" << *it2;
 243         }
 244         llvm::errs() << ")";
 245       }
 246     }
 247     llvm::errs() << "]\n";
 248
 249     llvm::errs() << "Roots: [";
 250     for (std::vector<change_ty>::const_iterator it = Roots.begin(),
 251                                                 ie = Roots.end();
 252          it != ie; ++it) {
 253       if (it != Roots.begin())
 254         llvm::errs() << ", ";
 255       llvm::errs() << *it;
 256     }
 257     llvm::errs() << "]\n";
 258
 259     llvm::errs() << "Predecessor Closure:\n";
 260     for (changeset_ty::const_iterator it = Changes.begin(), ie = Changes.end();
 261          it != ie; ++it) {
 262       llvm::errs() << format("  %-4d: [", *it);
 263       for (pred_closure_iterator_ty it2 = pred_closure_begin(*it),
 264                                     ie2 = pred_closure_end(*it);
 265            it2 != ie2; ++it2) {
 266         if (it2 != pred_closure_begin(*it))
 267           llvm::errs() << ", ";
 268         llvm::errs() << *it2;
 269       }
 270       llvm::errs() << "]\n";
 271     }
 272
 273     llvm::errs() << "Successor Closure:\n";
 274     for (changeset_ty::const_iterator it = Changes.begin(), ie = Changes.end();
 275          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);
 279            it2 != ie2; ++it2) {
 280         if (it2 != succ_closure_begin(*it))
 281           llvm::errs() << ", ";
 282         llvm::errs() << *it2;
 283       }
 284       llvm::errs() << "]\n";
 285     }
 286
 287     llvm::errs() << "\n\n";
 288   });
 289 }
 290
 291 bool DAGDeltaAlgorithmImpl::GetTestResult(const changeset_ty &Changes,
 292                                           const changeset_ty &Required) {
 293   changeset_ty Extended(Required);
 294   Extended.insert(Changes.begin(), Changes.end());
 295   for (changeset_ty::const_iterator it = Changes.begin(),
 296          ie = Changes.end(); it != ie; ++it)
 297     Extended.insert(pred_closure_begin(*it), pred_closure_end(*it));
 298
 299   if (FailedTestsCache.count(Extended))
 300     return false;
 301
 302   bool Result = ExecuteOneTest(Extended);
 303   if (!Result)
 304     FailedTestsCache.insert(Extended);
 305
 306   return Result;
 307 }
 308
 309 DAGDeltaAlgorithm::changeset_ty
 310 DAGDeltaAlgorithmImpl::Run() {
 311   // The current set of changes we are minimizing, starting at the roots.
 312   changeset_ty CurrentSet(Roots.begin(), Roots.end());
 313
 314   // The set of required changes.
 315   changeset_ty Required;
 316
 317   // Iterate until the active set of changes is empty. Convergence is guaranteed
 318   // assuming input was a DAG.
 319   //
 320   // Invariant:  CurrentSet intersect Required == {}
 321   // Invariant:  Required == (Required union succ*(Required))
 322   while (!CurrentSet.empty()) {
 323     LLVM_DEBUG({
 324       llvm::errs() << "DAG_DD - " << CurrentSet.size() << " active changes, "
 325                    << Required.size() << " required changes\n";
 326     });
 327
 328     // Minimize the current set of changes.
 329     DeltaActiveSetHelper Helper(*this, Required);
 330     changeset_ty CurrentMinSet = Helper.Run(CurrentSet);
 331
 332     // Update the set of required changes. Since
 333     //   CurrentMinSet subset CurrentSet
 334     // and after the last iteration,
 335     //   succ(CurrentSet) subset Required
 336     // then
 337     //   succ(CurrentMinSet) subset Required
 338     // and our invariant on Required is maintained.
 339     Required.insert(CurrentMinSet.begin(), CurrentMinSet.end());
 340
 341     // Replace the current set with the predecssors of the minimized set of
 342     // active changes.
 343     CurrentSet.clear();
 344     for (changeset_ty::const_iterator it = CurrentMinSet.begin(),
 345            ie = CurrentMinSet.end(); it != ie; ++it)
 346       CurrentSet.insert(pred_begin(*it), pred_end(*it));
 347
 348     // FIXME: We could enforce CurrentSet intersect Required == {} here if we
 349     // wanted to protect against cyclic graphs.
 350   }
 351
 352   return Required;
 353 }
 354
 355 void DAGDeltaAlgorithm::anchor() {
 356 }
 357
 358 DAGDeltaAlgorithm::changeset_ty
 359 DAGDeltaAlgorithm::Run(const changeset_ty &Changes,
 360                        const std::vector<edge_ty> &Dependencies) {
 361   return DAGDeltaAlgorithmImpl(*this, Changes, Dependencies).Run();
 362 }