LLVM API Documentation

Main Page | Namespace List | Class Hierarchy | Alphabetical List | Class List | Directories | File List | Namespace Members | Class Members | File Members | Related Pages

AliasSetTracker.cpp

Go to the documentation of this file.
00001 //===- AliasSetTracker.cpp - Alias Sets Tracker implementation-------------===//
00002 // 
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by the LLVM research group and is distributed under
00006 // the University of Illinois Open Source License. See LICENSE.TXT for details.
00007 // 
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This file implements the AliasSetTracker and AliasSet classes.
00011 // 
00012 //===----------------------------------------------------------------------===//
00013 
00014 #include "llvm/Analysis/AliasSetTracker.h"
00015 #include "llvm/Analysis/AliasAnalysis.h"
00016 #include "llvm/Instructions.h"
00017 #include "llvm/Pass.h"
00018 #include "llvm/Target/TargetData.h"
00019 #include "llvm/Assembly/Writer.h"
00020 #include "llvm/Support/InstIterator.h"
00021 #include <iostream>
00022 using namespace llvm;
00023 
00024 /// mergeSetIn - Merge the specified alias set into this alias set.
00025 ///
00026 void AliasSet::mergeSetIn(AliasSet &AS, AliasSetTracker &AST) {
00027   assert(!AS.Forward && "Alias set is already forwarding!");
00028   assert(!Forward && "This set is a forwarding set!!");
00029 
00030   // Update the alias and access types of this set...
00031   AccessTy |= AS.AccessTy;
00032   AliasTy  |= AS.AliasTy;
00033 
00034   if (AliasTy == MustAlias) {
00035     // Check that these two merged sets really are must aliases.  Since both
00036     // used to be must-alias sets, we can just check any pointer from each set
00037     // for aliasing.
00038     AliasAnalysis &AA = AST.getAliasAnalysis();
00039     HashNodePair *L = getSomePointer();
00040     HashNodePair *R = AS.getSomePointer();
00041 
00042     // If the pointers are not a must-alias pair, this set becomes a may alias.
00043     if (AA.alias(L->first, L->second.getSize(), R->first, R->second.getSize())
00044         != AliasAnalysis::MustAlias)
00045       AliasTy = MayAlias;
00046   }
00047 
00048   if (CallSites.empty()) {            // Merge call sites...
00049     if (!AS.CallSites.empty())
00050       std::swap(CallSites, AS.CallSites);
00051   } else if (!AS.CallSites.empty()) {
00052     CallSites.insert(CallSites.end(), AS.CallSites.begin(), AS.CallSites.end());
00053     AS.CallSites.clear();
00054   }
00055   
00056   AS.Forward = this;  // Forward across AS now...
00057   addRef();           // AS is now pointing to us...
00058 
00059   // Merge the list of constituent pointers...
00060   if (AS.PtrList) {
00061     *PtrListEnd = AS.PtrList;
00062     AS.PtrList->second.setPrevInList(PtrListEnd);
00063     PtrListEnd = AS.PtrListEnd;
00064 
00065     AS.PtrList = 0;
00066     AS.PtrListEnd = &AS.PtrList;
00067     assert(*AS.PtrListEnd == 0 && "End of list is not null?");
00068   }
00069 }
00070 
00071 void AliasSetTracker::removeAliasSet(AliasSet *AS) {
00072   if (AliasSet *Fwd = AS->Forward) {
00073     Fwd->dropRef(*this);
00074     AS->Forward = 0;
00075   }
00076   AliasSets.erase(AS);
00077 }
00078 
00079 void AliasSet::removeFromTracker(AliasSetTracker &AST) {
00080   assert(RefCount == 0 && "Cannot remove non-dead alias set from tracker!");
00081   AST.removeAliasSet(this);
00082 }
00083 
00084 void AliasSet::addPointer(AliasSetTracker &AST, HashNodePair &Entry,
00085                           unsigned Size, bool KnownMustAlias) {
00086   assert(!Entry.second.hasAliasSet() && "Entry already in set!");
00087 
00088   // Check to see if we have to downgrade to _may_ alias.
00089   if (isMustAlias() && !KnownMustAlias)
00090     if (HashNodePair *P = getSomePointer()) {
00091       AliasAnalysis &AA = AST.getAliasAnalysis();
00092       AliasAnalysis::AliasResult Result =
00093         AA.alias(P->first, P->second.getSize(), Entry.first, Size);
00094       if (Result == AliasAnalysis::MayAlias)
00095         AliasTy = MayAlias;
00096       else                  // First entry of must alias must have maximum size!
00097         P->second.updateSize(Size);
00098       assert(Result != AliasAnalysis::NoAlias && "Cannot be part of must set!");
00099     }
00100 
00101   Entry.second.setAliasSet(this);
00102   Entry.second.updateSize(Size);
00103 
00104   // Add it to the end of the list...
00105   assert(*PtrListEnd == 0 && "End of list is not null?");
00106   *PtrListEnd = &Entry;
00107   PtrListEnd = Entry.second.setPrevInList(PtrListEnd);
00108   assert(*PtrListEnd == 0 && "End of list is not null?");
00109   addRef();               // Entry points to alias set...
00110 }
00111 
00112 void AliasSet::addCallSite(CallSite CS, AliasAnalysis &AA) {
00113   CallSites.push_back(CS);
00114 
00115   if (Function *F = CS.getCalledFunction()) {
00116     if (AA.doesNotAccessMemory(F))
00117       return;
00118     else if (AA.onlyReadsMemory(F)) {
00119       AliasTy = MayAlias;
00120       AccessTy |= Refs;
00121       return;
00122     }
00123   }
00124 
00125   // FIXME: This should use mod/ref information to make this not suck so bad
00126   AliasTy = MayAlias;
00127   AccessTy = ModRef;
00128 }
00129 
00130 /// aliasesPointer - Return true if the specified pointer "may" (or must)
00131 /// alias one of the members in the set.
00132 ///
00133 bool AliasSet::aliasesPointer(const Value *Ptr, unsigned Size,
00134                               AliasAnalysis &AA) const {
00135   if (AliasTy == MustAlias) {
00136     assert(CallSites.empty() && "Illegal must alias set!");
00137 
00138     // If this is a set of MustAliases, only check to see if the pointer aliases
00139     // SOME value in the set...
00140     HashNodePair *SomePtr = getSomePointer();
00141     assert(SomePtr && "Empty must-alias set??");
00142     return AA.alias(SomePtr->first, SomePtr->second.getSize(), Ptr, Size);
00143   }
00144 
00145   // If this is a may-alias set, we have to check all of the pointers in the set
00146   // to be sure it doesn't alias the set...
00147   for (iterator I = begin(), E = end(); I != E; ++I)
00148     if (AA.alias(Ptr, Size, I.getPointer(), I.getSize()))
00149       return true;
00150 
00151   // Check the call sites list and invoke list...
00152   if (!CallSites.empty()) {
00153     if (AA.hasNoModRefInfoForCalls())
00154       return true;
00155 
00156     for (unsigned i = 0, e = CallSites.size(); i != e; ++i)
00157       if (AA.getModRefInfo(CallSites[i], const_cast<Value*>(Ptr), Size)
00158                    != AliasAnalysis::NoModRef)
00159         return true;
00160   }
00161 
00162   return false;
00163 }
00164 
00165 bool AliasSet::aliasesCallSite(CallSite CS, AliasAnalysis &AA) const {
00166   if (Function *F = CS.getCalledFunction())
00167     if (AA.doesNotAccessMemory(F))
00168       return false;
00169 
00170   if (AA.hasNoModRefInfoForCalls())
00171     return true;
00172 
00173   for (unsigned i = 0, e = CallSites.size(); i != e; ++i)
00174     if (AA.getModRefInfo(CallSites[i], CS) != AliasAnalysis::NoModRef ||
00175         AA.getModRefInfo(CS, CallSites[i]) != AliasAnalysis::NoModRef)
00176       return true;
00177 
00178   for (iterator I = begin(), E = end(); I != E; ++I)
00179     if (AA.getModRefInfo(CS, I.getPointer(), I.getSize()) !=
00180            AliasAnalysis::NoModRef)
00181       return true;
00182 
00183   return false;
00184 }
00185 
00186 
00187 /// findAliasSetForPointer - Given a pointer, find the one alias set to put the
00188 /// instruction referring to the pointer into.  If there are multiple alias sets
00189 /// that may alias the pointer, merge them together and return the unified set.
00190 ///
00191 AliasSet *AliasSetTracker::findAliasSetForPointer(const Value *Ptr,
00192                                                   unsigned Size) {
00193   AliasSet *FoundSet = 0;
00194   for (iterator I = begin(), E = end(); I != E; ++I)
00195     if (!I->Forward && I->aliasesPointer(Ptr, Size, AA)) {
00196       if (FoundSet == 0) {  // If this is the first alias set ptr can go into.
00197         FoundSet = I;       // Remember it.
00198       } else {              // Otherwise, we must merge the sets.
00199         FoundSet->mergeSetIn(*I, *this);     // Merge in contents.
00200       }
00201     }
00202 
00203   return FoundSet;
00204 }
00205 
00206 /// containsPointer - Return true if the specified location is represented by
00207 /// this alias set, false otherwise.  This does not modify the AST object or
00208 /// alias sets.
00209 bool AliasSetTracker::containsPointer(Value *Ptr, unsigned Size) const {
00210   for (const_iterator I = begin(), E = end(); I != E; ++I)
00211     if (!I->Forward && I->aliasesPointer(Ptr, Size, AA))
00212       return true;
00213   return false;
00214 }
00215 
00216 
00217 
00218 AliasSet *AliasSetTracker::findAliasSetForCallSite(CallSite CS) {
00219   AliasSet *FoundSet = 0;
00220   for (iterator I = begin(), E = end(); I != E; ++I)
00221     if (!I->Forward && I->aliasesCallSite(CS, AA)) {
00222       if (FoundSet == 0) {  // If this is the first alias set ptr can go into.
00223         FoundSet = I;       // Remember it.
00224       } else if (!I->Forward) {     // Otherwise, we must merge the sets.
00225         FoundSet->mergeSetIn(*I, *this);     // Merge in contents.
00226       }
00227     }
00228 
00229   return FoundSet;
00230 }
00231 
00232 
00233 
00234 
00235 /// getAliasSetForPointer - Return the alias set that the specified pointer
00236 /// lives in...
00237 AliasSet &AliasSetTracker::getAliasSetForPointer(Value *Pointer, unsigned Size,
00238                                                  bool *New) {
00239   AliasSet::HashNodePair &Entry = getEntryFor(Pointer);
00240 
00241   // Check to see if the pointer is already known...
00242   if (Entry.second.hasAliasSet()) {
00243     Entry.second.updateSize(Size);
00244     // Return the set!
00245     return *Entry.second.getAliasSet(*this)->getForwardedTarget(*this);
00246   } else if (AliasSet *AS = findAliasSetForPointer(Pointer, Size)) {
00247     // Add it to the alias set it aliases...
00248     AS->addPointer(*this, Entry, Size);
00249     return *AS;
00250   } else {
00251     if (New) *New = true;
00252     // Otherwise create a new alias set to hold the loaded pointer...
00253     AliasSets.push_back(new AliasSet());
00254     AliasSets.back().addPointer(*this, Entry, Size);
00255     return AliasSets.back();
00256   }
00257 }
00258 
00259 bool AliasSetTracker::add(Value *Ptr, unsigned Size) {
00260   bool NewPtr;
00261   addPointer(Ptr, Size, AliasSet::NoModRef, NewPtr);
00262   return NewPtr;
00263 }
00264 
00265 
00266 bool AliasSetTracker::add(LoadInst *LI) {
00267   bool NewPtr;
00268   AliasSet &AS = addPointer(LI->getOperand(0),
00269                             AA.getTargetData().getTypeSize(LI->getType()),
00270                             AliasSet::Refs, NewPtr);
00271   if (LI->isVolatile()) AS.setVolatile();
00272   return NewPtr;
00273 }
00274 
00275 bool AliasSetTracker::add(StoreInst *SI) {
00276   bool NewPtr;
00277   Value *Val = SI->getOperand(0);
00278   AliasSet &AS = addPointer(SI->getOperand(1),
00279                             AA.getTargetData().getTypeSize(Val->getType()),
00280                             AliasSet::Mods, NewPtr);
00281   if (SI->isVolatile()) AS.setVolatile();
00282   return NewPtr;
00283 }
00284 
00285 bool AliasSetTracker::add(FreeInst *FI) {
00286   bool NewPtr;
00287   AliasSet &AS = addPointer(FI->getOperand(0), ~0,
00288                             AliasSet::Mods, NewPtr);
00289   return NewPtr;
00290 }
00291 
00292 
00293 bool AliasSetTracker::add(CallSite CS) {
00294   if (Function *F = CS.getCalledFunction())
00295     if (AA.doesNotAccessMemory(F))
00296       return true; // doesn't alias anything
00297 
00298   AliasSet *AS = findAliasSetForCallSite(CS);
00299   if (!AS) {
00300     AliasSets.push_back(new AliasSet());
00301     AS = &AliasSets.back();
00302     AS->addCallSite(CS, AA);
00303     return true;
00304   } else {
00305     AS->addCallSite(CS, AA);
00306     return false;
00307   }
00308 }
00309 
00310 bool AliasSetTracker::add(Instruction *I) {
00311   // Dispatch to one of the other add methods...
00312   if (LoadInst *LI = dyn_cast<LoadInst>(I))
00313     return add(LI);
00314   else if (StoreInst *SI = dyn_cast<StoreInst>(I))
00315     return add(SI);
00316   else if (CallInst *CI = dyn_cast<CallInst>(I))
00317     return add(CI);
00318   else if (InvokeInst *II = dyn_cast<InvokeInst>(I))
00319     return add(II);
00320   else if (FreeInst *FI = dyn_cast<FreeInst>(I))
00321     return add(FI);
00322   return true;
00323 }
00324 
00325 void AliasSetTracker::add(BasicBlock &BB) {
00326   for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
00327     add(I);
00328 }
00329 
00330 void AliasSetTracker::add(const AliasSetTracker &AST) {
00331   assert(&AA == &AST.AA &&
00332          "Merging AliasSetTracker objects with different Alias Analyses!");
00333 
00334   // Loop over all of the alias sets in AST, adding the pointers contained
00335   // therein into the current alias sets.  This can cause alias sets to be
00336   // merged together in the current AST.
00337   for (const_iterator I = AST.begin(), E = AST.end(); I != E; ++I)
00338     if (!I->Forward) {   // Ignore forwarding alias sets
00339       AliasSet &AS = const_cast<AliasSet&>(*I);
00340 
00341       // If there are any call sites in the alias set, add them to this AST.
00342       for (unsigned i = 0, e = AS.CallSites.size(); i != e; ++i)
00343         add(AS.CallSites[i]);
00344 
00345       // Loop over all of the pointers in this alias set...
00346       AliasSet::iterator I = AS.begin(), E = AS.end();
00347       bool X;
00348       for (; I != E; ++I)
00349         addPointer(I.getPointer(), I.getSize(),
00350                    (AliasSet::AccessType)AS.AccessTy, X);
00351     }
00352 }
00353 
00354 /// remove - Remove the specified (potentially non-empty) alias set from the
00355 /// tracker.
00356 void AliasSetTracker::remove(AliasSet &AS) {
00357   bool SetDead;
00358   do {
00359     AliasSet::iterator I = AS.begin();
00360     Value *Ptr = I.getPointer(); ++I;
00361 
00362     // deleteValue will delete the set automatically when the last pointer
00363     // reference is destroyed.  "Predict" when this will happen.
00364     SetDead = I == AS.end();
00365     deleteValue(Ptr);  // Delete all of the pointers from the set
00366   } while (!SetDead);
00367 }
00368 
00369 bool AliasSetTracker::remove(Value *Ptr, unsigned Size) {
00370   AliasSet *AS = findAliasSetForPointer(Ptr, Size);
00371   if (!AS) return false;
00372   remove(*AS);
00373   return true;
00374 }
00375 
00376 bool AliasSetTracker::remove(LoadInst *LI) {
00377   unsigned Size = AA.getTargetData().getTypeSize(LI->getType());
00378   AliasSet *AS = findAliasSetForPointer(LI->getOperand(0), Size);
00379   if (!AS) return false;
00380   remove(*AS);
00381   return true;
00382 }
00383 
00384 bool AliasSetTracker::remove(StoreInst *SI) {
00385   unsigned Size = AA.getTargetData().getTypeSize(SI->getOperand(0)->getType());
00386   AliasSet *AS = findAliasSetForPointer(SI->getOperand(1), Size);
00387   if (!AS) return false;
00388   remove(*AS);
00389   return true;
00390 }
00391 
00392 bool AliasSetTracker::remove(FreeInst *FI) {
00393   AliasSet *AS = findAliasSetForPointer(FI->getOperand(0), ~0);
00394   if (!AS) return false;
00395   remove(*AS);
00396   return true;
00397 }
00398 
00399 bool AliasSetTracker::remove(CallSite CS) {
00400   if (Function *F = CS.getCalledFunction())
00401     if (AA.doesNotAccessMemory(F))
00402       return false; // doesn't alias anything
00403 
00404   AliasSet *AS = findAliasSetForCallSite(CS);
00405   if (!AS) return false;
00406   remove(*AS);
00407   return true;
00408 }
00409 
00410 bool AliasSetTracker::remove(Instruction *I) {
00411   // Dispatch to one of the other remove methods...
00412   if (LoadInst *LI = dyn_cast<LoadInst>(I))
00413     return remove(LI);
00414   else if (StoreInst *SI = dyn_cast<StoreInst>(I))
00415     return remove(SI);
00416   else if (CallInst *CI = dyn_cast<CallInst>(I))
00417     return remove(CI);
00418   else if (FreeInst *FI = dyn_cast<FreeInst>(I))
00419     return remove(FI);
00420   return true;
00421 }
00422 
00423 
00424 // deleteValue method - This method is used to remove a pointer value from the
00425 // AliasSetTracker entirely.  It should be used when an instruction is deleted
00426 // from the program to update the AST.  If you don't use this, you would have
00427 // dangling pointers to deleted instructions.
00428 //
00429 void AliasSetTracker::deleteValue(Value *PtrVal) {
00430   // Notify the alias analysis implementation that this value is gone.
00431   AA.deleteValue(PtrVal);
00432 
00433   // First, look up the PointerRec for this pointer.
00434   hash_map<Value*, AliasSet::PointerRec>::iterator I = PointerMap.find(PtrVal);
00435   if (I == PointerMap.end()) return;  // Noop
00436 
00437   // If we found one, remove the pointer from the alias set it is in.
00438   AliasSet::HashNodePair &PtrValEnt = *I;
00439   AliasSet *AS = PtrValEnt.second.getAliasSet(*this);
00440 
00441   // Unlink from the list of values...
00442   PtrValEnt.second.removeFromList();
00443   // Stop using the alias set
00444   AS->dropRef(*this);
00445   PointerMap.erase(I);
00446 }
00447 
00448 // copyValue - This method should be used whenever a preexisting value in the
00449 // program is copied or cloned, introducing a new value.  Note that it is ok for
00450 // clients that use this method to introduce the same value multiple times: if
00451 // the tracker already knows about a value, it will ignore the request.
00452 //
00453 void AliasSetTracker::copyValue(Value *From, Value *To) {
00454   // Notify the alias analysis implementation that this value is copied.
00455   AA.copyValue(From, To);
00456 
00457   // First, look up the PointerRec for this pointer.
00458   hash_map<Value*, AliasSet::PointerRec>::iterator I = PointerMap.find(From);
00459   if (I == PointerMap.end() || !I->second.hasAliasSet())
00460     return;  // Noop
00461 
00462   AliasSet::HashNodePair &Entry = getEntryFor(To);
00463   if (Entry.second.hasAliasSet()) return;    // Already in the tracker!
00464 
00465   // Add it to the alias set it aliases...
00466   AliasSet *AS = I->second.getAliasSet(*this);
00467   AS->addPointer(*this, Entry, I->second.getSize(), true);
00468 }
00469 
00470 
00471 
00472 //===----------------------------------------------------------------------===//
00473 //               AliasSet/AliasSetTracker Printing Support
00474 //===----------------------------------------------------------------------===//
00475 
00476 void AliasSet::print(std::ostream &OS) const {
00477   OS << "  AliasSet[" << (void*)this << "," << RefCount << "] ";
00478   OS << (AliasTy == MustAlias ? "must" : "may ") << " alias, ";
00479   switch (AccessTy) {
00480   case NoModRef: OS << "No access "; break;
00481   case Refs    : OS << "Ref       "; break;
00482   case Mods    : OS << "Mod       "; break;
00483   case ModRef  : OS << "Mod/Ref   "; break;
00484   default: assert(0 && "Bad value for AccessTy!");
00485   }
00486   if (isVolatile()) OS << "[volatile] ";
00487   if (Forward)
00488     OS << " forwarding to " << (void*)Forward;
00489 
00490 
00491   if (begin() != end()) {
00492     OS << "Pointers: ";
00493     for (iterator I = begin(), E = end(); I != E; ++I) {
00494       if (I != begin()) OS << ", ";
00495       WriteAsOperand(OS << "(", I.getPointer());
00496       OS << ", " << I.getSize() << ")";
00497     }
00498   }
00499   if (!CallSites.empty()) {
00500     OS << "\n    " << CallSites.size() << " Call Sites: ";
00501     for (unsigned i = 0, e = CallSites.size(); i != e; ++i) {
00502       if (i) OS << ", ";
00503       WriteAsOperand(OS, CallSites[i].getCalledValue());
00504     }      
00505   }
00506   OS << "\n";
00507 }
00508 
00509 void AliasSetTracker::print(std::ostream &OS) const {
00510   OS << "Alias Set Tracker: " << AliasSets.size() << " alias sets for "
00511      << PointerMap.size() << " pointer values.\n";
00512   for (const_iterator I = begin(), E = end(); I != E; ++I)
00513     I->print(OS);
00514   OS << "\n";
00515 }
00516 
00517 void AliasSet::dump() const { print (std::cerr); }
00518 void AliasSetTracker::dump() const { print(std::cerr); }
00519 
00520 //===----------------------------------------------------------------------===//
00521 //                            AliasSetPrinter Pass
00522 //===----------------------------------------------------------------------===//
00523 
00524 namespace {
00525   class AliasSetPrinter : public FunctionPass {
00526     AliasSetTracker *Tracker;
00527   public:
00528     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
00529       AU.setPreservesAll();
00530       AU.addRequired<AliasAnalysis>();
00531     }
00532 
00533     virtual bool runOnFunction(Function &F) {
00534       Tracker = new AliasSetTracker(getAnalysis<AliasAnalysis>());
00535 
00536       for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
00537         Tracker->add(&*I);
00538       return false;
00539     }
00540 
00541     /// print - Convert to human readable form
00542     virtual void print(std::ostream &OS) const {
00543       Tracker->print(OS);
00544     }
00545 
00546     virtual void releaseMemory() {
00547       delete Tracker;
00548     }
00549   };
00550   RegisterPass<AliasSetPrinter> X("print-alias-sets", "Alias Set Printer",
00551                                   PassInfo::Analysis | PassInfo::Optimization);
00552 }