lib/Analysis/AliasSetTracker.cpp

   1 //===- AliasSetTracker.cpp - Alias Sets Tracker implementation-------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file was developed by the LLVM research group and is distributed under
   6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements the AliasSetTracker and AliasSet classes.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Analysis/AliasSetTracker.h"
  15 #include "llvm/Analysis/AliasAnalysis.h"
  16 #include "llvm/Instructions.h"
  17 #include "llvm/Pass.h"
  18 #include "llvm/Type.h"
  19 #include "llvm/Target/TargetData.h"
  20 #include "llvm/Assembly/Writer.h"
  21 #include "llvm/Support/InstIterator.h"
  22 #include <iostream>
  23 using namespace llvm;
  24
  25 /// mergeSetIn - Merge the specified alias set into this alias set.
  26 ///
  27 void AliasSet::mergeSetIn(AliasSet &AS, AliasSetTracker &AST) {
  28   assert(!AS.Forward && "Alias set is already forwarding!");
  29   assert(!Forward && "This set is a forwarding set!!");
  30
  31   // Update the alias and access types of this set...
  32   AccessTy |= AS.AccessTy;
  33   AliasTy  |= AS.AliasTy;
  34
  35   if (AliasTy == MustAlias) {
  36     // Check that these two merged sets really are must aliases.  Since both
  37     // used to be must-alias sets, we can just check any pointer from each set
  38     // for aliasing.
  39     AliasAnalysis &AA = AST.getAliasAnalysis();
  40     HashNodePair *L = getSomePointer();
  41     HashNodePair *R = AS.getSomePointer();
  42
  43     // If the pointers are not a must-alias pair, this set becomes a may alias.
  44     if (AA.alias(L->first, L->second.getSize(), R->first, R->second.getSize())
  45         != AliasAnalysis::MustAlias)
  46       AliasTy = MayAlias;
  47   }
  48
  49   if (CallSites.empty()) {            // Merge call sites...
  50     if (!AS.CallSites.empty())
  51       std::swap(CallSites, AS.CallSites);
  52   } else if (!AS.CallSites.empty()) {
  53     CallSites.insert(CallSites.end(), AS.CallSites.begin(), AS.CallSites.end());
  54     AS.CallSites.clear();
  55   }
  56
  57   AS.Forward = this;  // Forward across AS now...
  58   addRef();           // AS is now pointing to us...
  59
  60   // Merge the list of constituent pointers...
  61   if (AS.PtrList) {
  62     *PtrListEnd = AS.PtrList;
  63     AS.PtrList->second.setPrevInList(PtrListEnd);
  64     PtrListEnd = AS.PtrListEnd;
  65
  66     AS.PtrList = 0;
  67     AS.PtrListEnd = &AS.PtrList;
  68     assert(*AS.PtrListEnd == 0 && "End of list is not null?");
  69   }
  70 }
  71
  72 void AliasSetTracker::removeAliasSet(AliasSet *AS) {
  73   if (AliasSet *Fwd = AS->Forward) {
  74     Fwd->dropRef(*this);
  75     AS->Forward = 0;
  76   }
  77   AliasSets.erase(AS);
  78 }
  79
  80 void AliasSet::removeFromTracker(AliasSetTracker &AST) {
  81   assert(RefCount == 0 && "Cannot remove non-dead alias set from tracker!");
  82   AST.removeAliasSet(this);
  83 }
  84
  85 void AliasSet::addPointer(AliasSetTracker &AST, HashNodePair &Entry,
  86                           unsigned Size, bool KnownMustAlias) {
  87   assert(!Entry.second.hasAliasSet() && "Entry already in set!");
  88
  89   // Check to see if we have to downgrade to _may_ alias.
  90   if (isMustAlias() && !KnownMustAlias)
  91     if (HashNodePair *P = getSomePointer()) {
  92       AliasAnalysis &AA = AST.getAliasAnalysis();
  93       AliasAnalysis::AliasResult Result =
  94         AA.alias(P->first, P->second.getSize(), Entry.first, Size);
  95       if (Result == AliasAnalysis::MayAlias)
  96         AliasTy = MayAlias;
  97       else                  // First entry of must alias must have maximum size!
  98         P->second.updateSize(Size);
  99       assert(Result != AliasAnalysis::NoAlias && "Cannot be part of must set!");
 100     }
 101
 102   Entry.second.setAliasSet(this);
 103   Entry.second.updateSize(Size);
 104
 105   // Add it to the end of the list...
 106   assert(*PtrListEnd == 0 && "End of list is not null?");
 107   *PtrListEnd = &Entry;
 108   PtrListEnd = Entry.second.setPrevInList(PtrListEnd);
 109   assert(*PtrListEnd == 0 && "End of list is not null?");
 110   addRef();               // Entry points to alias set...
 111 }
 112
 113 void AliasSet::addCallSite(CallSite CS, AliasAnalysis &AA) {
 114   CallSites.push_back(CS);
 115
 116   if (Function *F = CS.getCalledFunction()) {
 117     AliasAnalysis::ModRefBehavior Behavior = AA.getModRefBehavior(F, CS);
 118     if (Behavior == AliasAnalysis::DoesNotAccessMemory)
 119       return;
 120     else if (Behavior == AliasAnalysis::OnlyReadsMemory) {
 121       AliasTy = MayAlias;
 122       AccessTy |= Refs;
 123       return;
 124     }
 125   }
 126
 127   // FIXME: This should use mod/ref information to make this not suck so bad
 128   AliasTy = MayAlias;
 129   AccessTy = ModRef;
 130 }
 131
 132 /// aliasesPointer - Return true if the specified pointer "may" (or must)
 133 /// alias one of the members in the set.
 134 ///
 135 bool AliasSet::aliasesPointer(const Value *Ptr, unsigned Size,
 136                               AliasAnalysis &AA) const {
 137   if (AliasTy == MustAlias) {
 138     assert(CallSites.empty() && "Illegal must alias set!");
 139
 140     // If this is a set of MustAliases, only check to see if the pointer aliases
 141     // SOME value in the set...
 142     HashNodePair *SomePtr = getSomePointer();
 143     assert(SomePtr && "Empty must-alias set??");
 144     return AA.alias(SomePtr->first, SomePtr->second.getSize(), Ptr, Size);
 145   }
 146
 147   // If this is a may-alias set, we have to check all of the pointers in the set
 148   // to be sure it doesn't alias the set...
 149   for (iterator I = begin(), E = end(); I != E; ++I)
 150     if (AA.alias(Ptr, Size, I.getPointer(), I.getSize()))
 151       return true;
 152
 153   // Check the call sites list and invoke list...
 154   if (!CallSites.empty()) {
 155     if (AA.hasNoModRefInfoForCalls())
 156       return true;
 157
 158     for (unsigned i = 0, e = CallSites.size(); i != e; ++i)
 159       if (AA.getModRefInfo(CallSites[i], const_cast<Value*>(Ptr), Size)
 160                    != AliasAnalysis::NoModRef)
 161         return true;
 162   }
 163
 164   return false;
 165 }
 166
 167 bool AliasSet::aliasesCallSite(CallSite CS, AliasAnalysis &AA) const {
 168   if (Function *F = CS.getCalledFunction())
 169     if (AA.doesNotAccessMemory(F))
 170       return false;
 171
 172   if (AA.hasNoModRefInfoForCalls())
 173     return true;
 174
 175   for (unsigned i = 0, e = CallSites.size(); i != e; ++i)
 176     if (AA.getModRefInfo(CallSites[i], CS) != AliasAnalysis::NoModRef ||
 177         AA.getModRefInfo(CS, CallSites[i]) != AliasAnalysis::NoModRef)
 178       return true;
 179
 180   for (iterator I = begin(), E = end(); I != E; ++I)
 181     if (AA.getModRefInfo(CS, I.getPointer(), I.getSize()) !=
 182            AliasAnalysis::NoModRef)
 183       return true;
 184
 185   return false;
 186 }
 187
 188
 189 /// findAliasSetForPointer - Given a pointer, find the one alias set to put the
 190 /// instruction referring to the pointer into.  If there are multiple alias sets
 191 /// that may alias the pointer, merge them together and return the unified set.
 192 ///
 193 AliasSet *AliasSetTracker::findAliasSetForPointer(const Value *Ptr,
 194                                                   unsigned Size) {
 195   AliasSet *FoundSet = 0;
 196   for (iterator I = begin(), E = end(); I != E; ++I)
 197     if (!I->Forward && I->aliasesPointer(Ptr, Size, AA)) {
 198       if (FoundSet == 0) {  // If this is the first alias set ptr can go into.
 199         FoundSet = I;       // Remember it.
 200       } else {              // Otherwise, we must merge the sets.
 201         FoundSet->mergeSetIn(*I, *this);     // Merge in contents.
 202       }
 203     }
 204
 205   return FoundSet;
 206 }
 207
 208 /// containsPointer - Return true if the specified location is represented by
 209 /// this alias set, false otherwise.  This does not modify the AST object or
 210 /// alias sets.
 211 bool AliasSetTracker::containsPointer(Value *Ptr, unsigned Size) const {
 212   for (const_iterator I = begin(), E = end(); I != E; ++I)
 213     if (!I->Forward && I->aliasesPointer(Ptr, Size, AA))
 214       return true;
 215   return false;
 216 }
 217
 218
 219
 220 AliasSet *AliasSetTracker::findAliasSetForCallSite(CallSite CS) {
 221   AliasSet *FoundSet = 0;
 222   for (iterator I = begin(), E = end(); I != E; ++I)
 223     if (!I->Forward && I->aliasesCallSite(CS, AA)) {
 224       if (FoundSet == 0) {  // If this is the first alias set ptr can go into.
 225         FoundSet = I;       // Remember it.
 226       } else if (!I->Forward) {     // Otherwise, we must merge the sets.
 227         FoundSet->mergeSetIn(*I, *this);     // Merge in contents.
 228       }
 229     }
 230
 231   return FoundSet;
 232 }
 233
 234
 235
 236
 237 /// getAliasSetForPointer - Return the alias set that the specified pointer
 238 /// lives in...
 239 AliasSet &AliasSetTracker::getAliasSetForPointer(Value *Pointer, unsigned Size,
 240                                                  bool *New) {
 241   AliasSet::HashNodePair &Entry = getEntryFor(Pointer);
 242
 243   // Check to see if the pointer is already known...
 244   if (Entry.second.hasAliasSet()) {
 245     Entry.second.updateSize(Size);
 246     // Return the set!
 247     return *Entry.second.getAliasSet(*this)->getForwardedTarget(*this);
 248   } else if (AliasSet *AS = findAliasSetForPointer(Pointer, Size)) {
 249     // Add it to the alias set it aliases...
 250     AS->addPointer(*this, Entry, Size);
 251     return *AS;
 252   } else {
 253     if (New) *New = true;
 254     // Otherwise create a new alias set to hold the loaded pointer...
 255     AliasSets.push_back(new AliasSet());
 256     AliasSets.back().addPointer(*this, Entry, Size);
 257     return AliasSets.back();
 258   }
 259 }
 260
 261 bool AliasSetTracker::add(Value *Ptr, unsigned Size) {
 262   bool NewPtr;
 263   addPointer(Ptr, Size, AliasSet::NoModRef, NewPtr);
 264   return NewPtr;
 265 }
 266
 267
 268 bool AliasSetTracker::add(LoadInst *LI) {
 269   bool NewPtr;
 270   AliasSet &AS = addPointer(LI->getOperand(0),
 271                             AA.getTargetData().getTypeSize(LI->getType()),
 272                             AliasSet::Refs, NewPtr);
 273   if (LI->isVolatile()) AS.setVolatile();
 274   return NewPtr;
 275 }
 276
 277 bool AliasSetTracker::add(StoreInst *SI) {
 278   bool NewPtr;
 279   Value *Val = SI->getOperand(0);
 280   AliasSet &AS = addPointer(SI->getOperand(1),
 281                             AA.getTargetData().getTypeSize(Val->getType()),
 282                             AliasSet::Mods, NewPtr);
 283   if (SI->isVolatile()) AS.setVolatile();
 284   return NewPtr;
 285 }
 286
 287 bool AliasSetTracker::add(FreeInst *FI) {
 288   bool NewPtr;
 289   AliasSet &AS = addPointer(FI->getOperand(0), ~0,
 290                             AliasSet::Mods, NewPtr);
 291
 292   // Free operations are volatile ops (cannot be moved).
 293   AS.setVolatile();
 294   return NewPtr;
 295 }
 296
 297
 298 bool AliasSetTracker::add(CallSite CS) {
 299   if (Function *F = CS.getCalledFunction())
 300     if (AA.doesNotAccessMemory(F))
 301       return true; // doesn't alias anything
 302
 303   AliasSet *AS = findAliasSetForCallSite(CS);
 304   if (!AS) {
 305     AliasSets.push_back(new AliasSet());
 306     AS = &AliasSets.back();
 307     AS->addCallSite(CS, AA);
 308     return true;
 309   } else {
 310     AS->addCallSite(CS, AA);
 311     return false;
 312   }
 313 }
 314
 315 bool AliasSetTracker::add(Instruction *I) {
 316   // Dispatch to one of the other add methods...
 317   if (LoadInst *LI = dyn_cast<LoadInst>(I))
 318     return add(LI);
 319   else if (StoreInst *SI = dyn_cast<StoreInst>(I))
 320     return add(SI);
 321   else if (CallInst *CI = dyn_cast<CallInst>(I))
 322     return add(CI);
 323   else if (InvokeInst *II = dyn_cast<InvokeInst>(I))
 324     return add(II);
 325   else if (FreeInst *FI = dyn_cast<FreeInst>(I))
 326     return add(FI);
 327   return true;
 328 }
 329
 330 void AliasSetTracker::add(BasicBlock &BB) {
 331   for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
 332     add(I);
 333 }
 334
 335 void AliasSetTracker::add(const AliasSetTracker &AST) {
 336   assert(&AA == &AST.AA &&
 337          "Merging AliasSetTracker objects with different Alias Analyses!");
 338
 339   // Loop over all of the alias sets in AST, adding the pointers contained
 340   // therein into the current alias sets.  This can cause alias sets to be
 341   // merged together in the current AST.
 342   for (const_iterator I = AST.begin(), E = AST.end(); I != E; ++I)
 343     if (!I->Forward) {   // Ignore forwarding alias sets
 344       AliasSet &AS = const_cast<AliasSet&>(*I);
 345
 346       // If there are any call sites in the alias set, add them to this AST.
 347       for (unsigned i = 0, e = AS.CallSites.size(); i != e; ++i)
 348         add(AS.CallSites[i]);
 349
 350       // Loop over all of the pointers in this alias set...
 351       AliasSet::iterator I = AS.begin(), E = AS.end();
 352       bool X;
 353       for (; I != E; ++I)
 354         addPointer(I.getPointer(), I.getSize(),
 355                    (AliasSet::AccessType)AS.AccessTy, X);
 356     }
 357 }
 358
 359 /// remove - Remove the specified (potentially non-empty) alias set from the
 360 /// tracker.
 361 void AliasSetTracker::remove(AliasSet &AS) {
 362   // Drop all call sites.
 363   AS.CallSites.clear();
 364
 365   // Clear the alias set.
 366   unsigned NumRefs = 0;
 367   while (!AS.empty()) {
 368     AliasSet::HashNodePair *P = AS.PtrList;
 369
 370     // Unlink from the list of values.
 371     P->second.removeFromList();
 372
 373     // Remember how many references need to be dropped.
 374     ++NumRefs;
 375
 376     // Finally, remove the entry.
 377     PointerMap.erase(P->first);
 378   }
 379
 380   // Stop using the alias set, removing it.
 381   AS.RefCount -= NumRefs;
 382   if (AS.RefCount == 0)
 383     AS.removeFromTracker(*this);
 384 }
 385
 386 bool AliasSetTracker::remove(Value *Ptr, unsigned Size) {
 387   AliasSet *AS = findAliasSetForPointer(Ptr, Size);
 388   if (!AS) return false;
 389   remove(*AS);
 390   return true;
 391 }
 392
 393 bool AliasSetTracker::remove(LoadInst *LI) {
 394   unsigned Size = AA.getTargetData().getTypeSize(LI->getType());
 395   AliasSet *AS = findAliasSetForPointer(LI->getOperand(0), Size);
 396   if (!AS) return false;
 397   remove(*AS);
 398   return true;
 399 }
 400
 401 bool AliasSetTracker::remove(StoreInst *SI) {
 402   unsigned Size = AA.getTargetData().getTypeSize(SI->getOperand(0)->getType());
 403   AliasSet *AS = findAliasSetForPointer(SI->getOperand(1), Size);
 404   if (!AS) return false;
 405   remove(*AS);
 406   return true;
 407 }
 408
 409 bool AliasSetTracker::remove(FreeInst *FI) {
 410   AliasSet *AS = findAliasSetForPointer(FI->getOperand(0), ~0);
 411   if (!AS) return false;
 412   remove(*AS);
 413   return true;
 414 }
 415
 416 bool AliasSetTracker::remove(CallSite CS) {
 417   if (Function *F = CS.getCalledFunction())
 418     if (AA.doesNotAccessMemory(F))
 419       return false; // doesn't alias anything
 420
 421   AliasSet *AS = findAliasSetForCallSite(CS);
 422   if (!AS) return false;
 423   remove(*AS);
 424   return true;
 425 }
 426
 427 bool AliasSetTracker::remove(Instruction *I) {
 428   // Dispatch to one of the other remove methods...
 429   if (LoadInst *LI = dyn_cast<LoadInst>(I))
 430     return remove(LI);
 431   else if (StoreInst *SI = dyn_cast<StoreInst>(I))
 432     return remove(SI);
 433   else if (CallInst *CI = dyn_cast<CallInst>(I))
 434     return remove(CI);
 435   else if (FreeInst *FI = dyn_cast<FreeInst>(I))
 436     return remove(FI);
 437   return true;
 438 }
 439
 440
 441 // deleteValue method - This method is used to remove a pointer value from the
 442 // AliasSetTracker entirely.  It should be used when an instruction is deleted
 443 // from the program to update the AST.  If you don't use this, you would have
 444 // dangling pointers to deleted instructions.
 445 //
 446 void AliasSetTracker::deleteValue(Value *PtrVal) {
 447   // Notify the alias analysis implementation that this value is gone.
 448   AA.deleteValue(PtrVal);
 449
 450   // If this is a call instruction, remove the callsite from the appropriate
 451   // AliasSet.
 452   CallSite CS = CallSite::get(PtrVal);
 453   if (CS.getInstruction()) {
 454     Function *F = CS.getCalledFunction();
 455     if (!F || !AA.doesNotAccessMemory(F)) {
 456       if (AliasSet *AS = findAliasSetForCallSite(CS))
 457         AS->removeCallSite(CS);
 458     }
 459   }
 460
 461   // First, look up the PointerRec for this pointer.
 462   hash_map<Value*, AliasSet::PointerRec>::iterator I = PointerMap.find(PtrVal);
 463   if (I == PointerMap.end()) return;  // Noop
 464
 465   // If we found one, remove the pointer from the alias set it is in.
 466   AliasSet::HashNodePair &PtrValEnt = *I;
 467   AliasSet *AS = PtrValEnt.second.getAliasSet(*this);
 468
 469   // Unlink from the list of values...
 470   PtrValEnt.second.removeFromList();
 471   // Stop using the alias set
 472   AS->dropRef(*this);
 473   PointerMap.erase(I);
 474 }
 475
 476 // copyValue - This method should be used whenever a preexisting value in the
 477 // program is copied or cloned, introducing a new value.  Note that it is ok for
 478 // clients that use this method to introduce the same value multiple times: if
 479 // the tracker already knows about a value, it will ignore the request.
 480 //
 481 void AliasSetTracker::copyValue(Value *From, Value *To) {
 482   // Notify the alias analysis implementation that this value is copied.
 483   AA.copyValue(From, To);
 484
 485   // First, look up the PointerRec for this pointer.
 486   hash_map<Value*, AliasSet::PointerRec>::iterator I = PointerMap.find(From);
 487   if (I == PointerMap.end() || !I->second.hasAliasSet())
 488     return;  // Noop
 489
 490   AliasSet::HashNodePair &Entry = getEntryFor(To);
 491   if (Entry.second.hasAliasSet()) return;    // Already in the tracker!
 492
 493   // Add it to the alias set it aliases...
 494   AliasSet *AS = I->second.getAliasSet(*this);
 495   AS->addPointer(*this, Entry, I->second.getSize(), true);
 496 }
 497
 498
 499
 500 //===----------------------------------------------------------------------===//
 501 //               AliasSet/AliasSetTracker Printing Support
 502 //===----------------------------------------------------------------------===//
 503
 504 void AliasSet::print(std::ostream &OS) const {
 505   OS << "  AliasSet[" << (void*)this << "," << RefCount << "] ";
 506   OS << (AliasTy == MustAlias ? "must" : "may ") << " alias, ";
 507   switch (AccessTy) {
 508   case NoModRef: OS << "No access "; break;
 509   case Refs    : OS << "Ref       "; break;
 510   case Mods    : OS << "Mod       "; break;
 511   case ModRef  : OS << "Mod/Ref   "; break;
 512   default: assert(0 && "Bad value for AccessTy!");
 513   }
 514   if (isVolatile()) OS << "[volatile] ";
 515   if (Forward)
 516     OS << " forwarding to " << (void*)Forward;
 517
 518
 519   if (begin() != end()) {
 520     OS << "Pointers: ";
 521     for (iterator I = begin(), E = end(); I != E; ++I) {
 522       if (I != begin()) OS << ", ";
 523       WriteAsOperand(OS << "(", I.getPointer());
 524       OS << ", " << I.getSize() << ")";
 525     }
 526   }
 527   if (!CallSites.empty()) {
 528     OS << "\n    " << CallSites.size() << " Call Sites: ";
 529     for (unsigned i = 0, e = CallSites.size(); i != e; ++i) {
 530       if (i) OS << ", ";
 531       WriteAsOperand(OS, CallSites[i].getCalledValue());
 532     }
 533   }
 534   OS << "\n";
 535 }
 536
 537 void AliasSetTracker::print(std::ostream &OS) const {
 538   OS << "Alias Set Tracker: " << AliasSets.size() << " alias sets for "
 539      << PointerMap.size() << " pointer values.\n";
 540   for (const_iterator I = begin(), E = end(); I != E; ++I)
 541     I->print(OS);
 542   OS << "\n";
 543 }
 544
 545 void AliasSet::dump() const { print (std::cerr); }
 546 void AliasSetTracker::dump() const { print(std::cerr); }
 547
 548 //===----------------------------------------------------------------------===//
 549 //                            AliasSetPrinter Pass
 550 //===----------------------------------------------------------------------===//
 551
 552 namespace {
 553   class AliasSetPrinter : public FunctionPass {
 554     AliasSetTracker *Tracker;
 555   public:
 556     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
 557       AU.setPreservesAll();
 558       AU.addRequired<AliasAnalysis>();
 559     }
 560
 561     virtual bool runOnFunction(Function &F) {
 562       Tracker = new AliasSetTracker(getAnalysis<AliasAnalysis>());
 563
 564       for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
 565         Tracker->add(&*I);
 566       Tracker->print(std::cerr);
 567       delete Tracker;
 568       return false;
 569     }
 570   };
 571   RegisterOpt<AliasSetPrinter> X("print-alias-sets", "Alias Set Printer");
 572 }