llvm/lib/Analysis/AliasSetTracker.cpp

   1 //===- AliasSetTracker.cpp - Alias Sets Tracker implementation-------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements the AliasSetTracker and AliasSet classes.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/Analysis/AliasSetTracker.h"
  14 #include "llvm/Analysis/AliasAnalysis.h"
  15 #include "llvm/Analysis/GuardUtils.h"
  16 #include "llvm/Analysis/LoopInfo.h"
  17 #include "llvm/Analysis/MemoryLocation.h"
  18 #include "llvm/Config/llvm-config.h"
  19 #include "llvm/IR/Constants.h"
  20 #include "llvm/IR/DataLayout.h"
  21 #include "llvm/IR/Function.h"
  22 #include "llvm/IR/InstIterator.h"
  23 #include "llvm/IR/Instructions.h"
  24 #include "llvm/IR/IntrinsicInst.h"
  25 #include "llvm/IR/Module.h"
  26 #include "llvm/IR/PassManager.h"
  27 #include "llvm/IR/PatternMatch.h"
  28 #include "llvm/IR/Value.h"
  29 #include "llvm/InitializePasses.h"
  30 #include "llvm/Pass.h"
  31 #include "llvm/Support/AtomicOrdering.h"
  32 #include "llvm/Support/CommandLine.h"
  33 #include "llvm/Support/Compiler.h"
  34 #include "llvm/Support/Debug.h"
  35 #include "llvm/Support/ErrorHandling.h"
  36 #include "llvm/Support/raw_ostream.h"
  37
  38 using namespace llvm;
  39
  40 static cl::opt<unsigned>
  41     SaturationThreshold("alias-set-saturation-threshold", cl::Hidden,
  42                         cl::init(250),
  43                         cl::desc("The maximum number of pointers may-alias "
  44                                  "sets may contain before degradation"));
  45
  46 /// mergeSetIn - Merge the specified alias set into this alias set.
  47 ///
  48 void AliasSet::mergeSetIn(AliasSet &AS, AliasSetTracker &AST) {
  49   assert(!AS.Forward && "Alias set is already forwarding!");
  50   assert(!Forward && "This set is a forwarding set!!");
  51
  52   bool WasMustAlias = (Alias == SetMustAlias);
  53   // Update the alias and access types of this set...
  54   Access |= AS.Access;
  55   Alias  |= AS.Alias;
  56
  57   if (Alias == SetMustAlias) {
  58     // Check that these two merged sets really are must aliases.  Since both
  59     // used to be must-alias sets, we can just check any pointer from each set
  60     // for aliasing.
  61     AliasAnalysis &AA = AST.getAliasAnalysis();
  62     PointerRec *L = getSomePointer();
  63     PointerRec *R = AS.getSomePointer();
  64
  65     // If the pointers are not a must-alias pair, this set becomes a may alias.
  66     if (!AA.isMustAlias(
  67             MemoryLocation(L->getValue(), L->getSize(), L->getAAInfo()),
  68             MemoryLocation(R->getValue(), R->getSize(), R->getAAInfo())))
  69       Alias = SetMayAlias;
  70   }
  71
  72   if (Alias == SetMayAlias) {
  73     if (WasMustAlias)
  74       AST.TotalMayAliasSetSize += size();
  75     if (AS.Alias == SetMustAlias)
  76       AST.TotalMayAliasSetSize += AS.size();
  77   }
  78
  79   bool ASHadUnknownInsts = !AS.UnknownInsts.empty();
  80   if (UnknownInsts.empty()) {            // Merge call sites...
  81     if (ASHadUnknownInsts) {
  82       std::swap(UnknownInsts, AS.UnknownInsts);
  83       addRef();
  84     }
  85   } else if (ASHadUnknownInsts) {
  86     llvm::append_range(UnknownInsts, AS.UnknownInsts);
  87     AS.UnknownInsts.clear();
  88   }
  89
  90   AS.Forward = this; // Forward across AS now...
  91   addRef();          // AS is now pointing to us...
  92
  93   // Merge the list of constituent pointers...
  94   if (AS.PtrList) {
  95     SetSize += AS.size();
  96     AS.SetSize = 0;
  97     *PtrListEnd = AS.PtrList;
  98     AS.PtrList->setPrevInList(PtrListEnd);
  99     PtrListEnd = AS.PtrListEnd;
 100
 101     AS.PtrList = nullptr;
 102     AS.PtrListEnd = &AS.PtrList;
 103     assert(*AS.PtrListEnd == nullptr && "End of list is not null?");
 104   }
 105   if (ASHadUnknownInsts)
 106     AS.dropRef(AST);
 107 }
 108
 109 void AliasSetTracker::removeAliasSet(AliasSet *AS) {
 110   if (AliasSet *Fwd = AS->Forward) {
 111     Fwd->dropRef(*this);
 112     AS->Forward = nullptr;
 113   } else // Update TotalMayAliasSetSize only if not forwarding.
 114       if (AS->Alias == AliasSet::SetMayAlias)
 115         TotalMayAliasSetSize -= AS->size();
 116
 117   AliasSets.erase(AS);
 118   // If we've removed the saturated alias set, set saturated marker back to
 119   // nullptr and ensure this tracker is empty.
 120   if (AS == AliasAnyAS) {
 121     AliasAnyAS = nullptr;
 122     assert(AliasSets.empty() && "Tracker not empty");
 123   }
 124 }
 125
 126 void AliasSet::removeFromTracker(AliasSetTracker &AST) {
 127   assert(RefCount == 0 && "Cannot remove non-dead alias set from tracker!");
 128   AST.removeAliasSet(this);
 129 }
 130
 131 void AliasSet::addPointer(AliasSetTracker &AST, PointerRec &Entry,
 132                           LocationSize Size, const AAMDNodes &AAInfo,
 133                           bool KnownMustAlias, bool SkipSizeUpdate) {
 134   assert(!Entry.hasAliasSet() && "Entry already in set!");
 135
 136   // Check to see if we have to downgrade to _may_ alias.
 137   if (isMustAlias())
 138     if (PointerRec *P = getSomePointer()) {
 139       if (!KnownMustAlias) {
 140         AliasAnalysis &AA = AST.getAliasAnalysis();
 141         AliasResult Result = AA.alias(
 142             MemoryLocation(P->getValue(), P->getSize(), P->getAAInfo()),
 143             MemoryLocation(Entry.getValue(), Size, AAInfo));
 144         if (Result != AliasResult::MustAlias) {
 145           Alias = SetMayAlias;
 146           AST.TotalMayAliasSetSize += size();
 147         }
 148         assert(Result != AliasResult::NoAlias && "Cannot be part of must set!");
 149       } else if (!SkipSizeUpdate)
 150         P->updateSizeAndAAInfo(Size, AAInfo);
 151     }
 152
 153   Entry.setAliasSet(this);
 154   Entry.updateSizeAndAAInfo(Size, AAInfo);
 155
 156   // Add it to the end of the list...
 157   ++SetSize;
 158   assert(*PtrListEnd == nullptr && "End of list is not null?");
 159   *PtrListEnd = &Entry;
 160   PtrListEnd = Entry.setPrevInList(PtrListEnd);
 161   assert(*PtrListEnd == nullptr && "End of list is not null?");
 162   // Entry points to alias set.
 163   addRef();
 164
 165   if (Alias == SetMayAlias)
 166     AST.TotalMayAliasSetSize++;
 167 }
 168
 169 void AliasSet::addUnknownInst(Instruction *I, AliasAnalysis &AA) {
 170   if (UnknownInsts.empty())
 171     addRef();
 172   UnknownInsts.emplace_back(I);
 173
 174   // Guards are marked as modifying memory for control flow modelling purposes,
 175   // but don't actually modify any specific memory location.
 176   using namespace PatternMatch;
 177   bool MayWriteMemory = I->mayWriteToMemory() && !isGuard(I) &&
 178     !(I->use_empty() && match(I, m_Intrinsic<Intrinsic::invariant_start>()));
 179   if (!MayWriteMemory) {
 180     Alias = SetMayAlias;
 181     Access |= RefAccess;
 182     return;
 183   }
 184
 185   // FIXME: This should use mod/ref information to make this not suck so bad
 186   Alias = SetMayAlias;
 187   Access = ModRefAccess;
 188 }
 189
 190 /// aliasesPointer - If the specified pointer "may" (or must) alias one of the
 191 /// members in the set return the appropriate AliasResult. Otherwise return
 192 /// NoAlias.
 193 ///
 194 AliasResult AliasSet::aliasesPointer(const Value *Ptr, LocationSize Size,
 195                                      const AAMDNodes &AAInfo,
 196                                      AliasAnalysis &AA) const {
 197   if (AliasAny)
 198     return AliasResult::MayAlias;
 199
 200   if (Alias == SetMustAlias) {
 201     assert(UnknownInsts.empty() && "Illegal must alias set!");
 202
 203     // If this is a set of MustAliases, only check to see if the pointer aliases
 204     // SOME value in the set.
 205     PointerRec *SomePtr = getSomePointer();
 206     assert(SomePtr && "Empty must-alias set??");
 207     return AA.alias(MemoryLocation(SomePtr->getValue(), SomePtr->getSize(),
 208                                    SomePtr->getAAInfo()),
 209                     MemoryLocation(Ptr, Size, AAInfo));
 210   }
 211
 212   // If this is a may-alias set, we have to check all of the pointers in the set
 213   // to be sure it doesn't alias the set...
 214   for (iterator I = begin(), E = end(); I != E; ++I) {
 215     AliasResult AR =
 216         AA.alias(MemoryLocation(Ptr, Size, AAInfo),
 217                  MemoryLocation(I.getPointer(), I.getSize(), I.getAAInfo()));
 218     if (AR != AliasResult::NoAlias)
 219       return AR;
 220   }
 221
 222   // Check the unknown instructions...
 223   if (!UnknownInsts.empty()) {
 224     for (unsigned i = 0, e = UnknownInsts.size(); i != e; ++i)
 225       if (auto *Inst = getUnknownInst(i))
 226         if (isModOrRefSet(
 227                 AA.getModRefInfo(Inst, MemoryLocation(Ptr, Size, AAInfo))))
 228           return AliasResult::MayAlias;
 229   }
 230
 231   return AliasResult::NoAlias;
 232 }
 233
 234 bool AliasSet::aliasesUnknownInst(const Instruction *Inst,
 235                                   AliasAnalysis &AA) const {
 236
 237   if (AliasAny)
 238     return true;
 239
 240   assert(Inst->mayReadOrWriteMemory() &&
 241          "Instruction must either read or write memory.");
 242
 243   for (unsigned i = 0, e = UnknownInsts.size(); i != e; ++i) {
 244     if (auto *UnknownInst = getUnknownInst(i)) {
 245       const auto *C1 = dyn_cast<CallBase>(UnknownInst);
 246       const auto *C2 = dyn_cast<CallBase>(Inst);
 247       if (!C1 || !C2 || isModOrRefSet(AA.getModRefInfo(C1, C2)) ||
 248           isModOrRefSet(AA.getModRefInfo(C2, C1)))
 249         return true;
 250     }
 251   }
 252
 253   for (iterator I = begin(), E = end(); I != E; ++I)
 254     if (isModOrRefSet(AA.getModRefInfo(
 255             Inst, MemoryLocation(I.getPointer(), I.getSize(), I.getAAInfo()))))
 256       return true;
 257
 258   return false;
 259 }
 260
 261 Instruction* AliasSet::getUniqueInstruction() {
 262   if (AliasAny)
 263     // May have collapses alias set
 264     return nullptr;
 265   if (begin() != end()) {
 266     if (!UnknownInsts.empty())
 267       // Another instruction found
 268       return nullptr;
 269     if (std::next(begin()) != end())
 270       // Another instruction found
 271       return nullptr;
 272     Value *Addr = begin()->getValue();
 273     assert(!Addr->user_empty() &&
 274            "where's the instruction which added this pointer?");
 275     if (std::next(Addr->user_begin()) != Addr->user_end())
 276       // Another instruction found -- this is really restrictive
 277       // TODO: generalize!
 278       return nullptr;
 279     return cast<Instruction>(*(Addr->user_begin()));
 280   }
 281   if (1 != UnknownInsts.size())
 282     return nullptr;
 283   return cast<Instruction>(UnknownInsts[0]);
 284 }
 285
 286 void AliasSetTracker::clear() {
 287   // Delete all the PointerRec entries.
 288   for (auto &I : PointerMap)
 289     I.second->eraseFromList();
 290
 291   PointerMap.clear();
 292
 293   // The alias sets should all be clear now.
 294   AliasSets.clear();
 295 }
 296
 297 /// mergeAliasSetsForPointer - Given a pointer, merge all alias sets that may
 298 /// alias the pointer. Return the unified set, or nullptr if no set that aliases
 299 /// the pointer was found. MustAliasAll is updated to true/false if the pointer
 300 /// is found to MustAlias all the sets it merged.
 301 AliasSet *AliasSetTracker::mergeAliasSetsForPointer(const Value *Ptr,
 302                                                     LocationSize Size,
 303                                                     const AAMDNodes &AAInfo,
 304                                                     bool &MustAliasAll) {
 305   AliasSet *FoundSet = nullptr;
 306   MustAliasAll = true;
 307   for (AliasSet &AS : llvm::make_early_inc_range(*this)) {
 308     if (AS.Forward)
 309       continue;
 310
 311     AliasResult AR = AS.aliasesPointer(Ptr, Size, AAInfo, AA);
 312     if (AR == AliasResult::NoAlias)
 313       continue;
 314
 315     if (AR != AliasResult::MustAlias)
 316       MustAliasAll = false;
 317
 318     if (!FoundSet) {
 319       // If this is the first alias set ptr can go into, remember it.
 320       FoundSet = &AS;
 321     } else {
 322       // Otherwise, we must merge the sets.
 323       FoundSet->mergeSetIn(AS, *this);
 324     }
 325   }
 326
 327   return FoundSet;
 328 }
 329
 330 AliasSet *AliasSetTracker::findAliasSetForUnknownInst(Instruction *Inst) {
 331   AliasSet *FoundSet = nullptr;
 332   for (AliasSet &AS : llvm::make_early_inc_range(*this)) {
 333     if (AS.Forward || !AS.aliasesUnknownInst(Inst, AA))
 334       continue;
 335     if (!FoundSet) {
 336       // If this is the first alias set ptr can go into, remember it.
 337       FoundSet = &AS;
 338     } else {
 339       // Otherwise, we must merge the sets.
 340       FoundSet->mergeSetIn(AS, *this);
 341     }
 342   }
 343   return FoundSet;
 344 }
 345
 346 AliasSet &AliasSetTracker::getAliasSetFor(const MemoryLocation &MemLoc) {
 347
 348   Value * const Pointer = const_cast<Value*>(MemLoc.Ptr);
 349   const LocationSize Size = MemLoc.Size;
 350   const AAMDNodes &AAInfo = MemLoc.AATags;
 351
 352   AliasSet::PointerRec &Entry = getEntryFor(Pointer);
 353
 354   if (AliasAnyAS) {
 355     // At this point, the AST is saturated, so we only have one active alias
 356     // set. That means we already know which alias set we want to return, and
 357     // just need to add the pointer to that set to keep the data structure
 358     // consistent.
 359     // This, of course, means that we will never need a merge here.
 360     if (Entry.hasAliasSet()) {
 361       Entry.updateSizeAndAAInfo(Size, AAInfo);
 362       assert(Entry.getAliasSet(*this) == AliasAnyAS &&
 363              "Entry in saturated AST must belong to only alias set");
 364     } else {
 365       AliasAnyAS->addPointer(*this, Entry, Size, AAInfo);
 366     }
 367     return *AliasAnyAS;
 368   }
 369
 370   bool MustAliasAll = false;
 371   // Check to see if the pointer is already known.
 372   if (Entry.hasAliasSet()) {
 373     // If the size changed, we may need to merge several alias sets.
 374     // Note that we can *not* return the result of mergeAliasSetsForPointer
 375     // due to a quirk of alias analysis behavior. Since alias(undef, undef)
 376     // is NoAlias, mergeAliasSetsForPointer(undef, ...) will not find the
 377     // the right set for undef, even if it exists.
 378     if (Entry.updateSizeAndAAInfo(Size, AAInfo))
 379       mergeAliasSetsForPointer(Pointer, Size, AAInfo, MustAliasAll);
 380     // Return the set!
 381     return *Entry.getAliasSet(*this)->getForwardedTarget(*this);
 382   }
 383
 384   if (AliasSet *AS =
 385           mergeAliasSetsForPointer(Pointer, Size, AAInfo, MustAliasAll)) {
 386     // Add it to the alias set it aliases.
 387     AS->addPointer(*this, Entry, Size, AAInfo, MustAliasAll);
 388     return *AS;
 389   }
 390
 391   // Otherwise create a new alias set to hold the loaded pointer.
 392   AliasSets.push_back(new AliasSet());
 393   AliasSets.back().addPointer(*this, Entry, Size, AAInfo, true);
 394   return AliasSets.back();
 395 }
 396
 397 void AliasSetTracker::add(Value *Ptr, LocationSize Size,
 398                           const AAMDNodes &AAInfo) {
 399   addPointer(MemoryLocation(Ptr, Size, AAInfo), AliasSet::NoAccess);
 400 }
 401
 402 void AliasSetTracker::add(LoadInst *LI) {
 403   if (isStrongerThanMonotonic(LI->getOrdering()))
 404     return addUnknown(LI);
 405   addPointer(MemoryLocation::get(LI), AliasSet::RefAccess);
 406 }
 407
 408 void AliasSetTracker::add(StoreInst *SI) {
 409   if (isStrongerThanMonotonic(SI->getOrdering()))
 410     return addUnknown(SI);
 411   addPointer(MemoryLocation::get(SI), AliasSet::ModAccess);
 412 }
 413
 414 void AliasSetTracker::add(VAArgInst *VAAI) {
 415   addPointer(MemoryLocation::get(VAAI), AliasSet::ModRefAccess);
 416 }
 417
 418 void AliasSetTracker::add(AnyMemSetInst *MSI) {
 419   addPointer(MemoryLocation::getForDest(MSI), AliasSet::ModAccess);
 420 }
 421
 422 void AliasSetTracker::add(AnyMemTransferInst *MTI) {
 423   addPointer(MemoryLocation::getForDest(MTI), AliasSet::ModAccess);
 424   addPointer(MemoryLocation::getForSource(MTI), AliasSet::RefAccess);
 425 }
 426
 427 void AliasSetTracker::addUnknown(Instruction *Inst) {
 428   if (isa<DbgInfoIntrinsic>(Inst))
 429     return; // Ignore DbgInfo Intrinsics.
 430
 431   if (auto *II = dyn_cast<IntrinsicInst>(Inst)) {
 432     // These intrinsics will show up as affecting memory, but they are just
 433     // markers.
 434     switch (II->getIntrinsicID()) {
 435     default:
 436       break;
 437       // FIXME: Add lifetime/invariant intrinsics (See: PR30807).
 438     case Intrinsic::assume:
 439     case Intrinsic::experimental_noalias_scope_decl:
 440     case Intrinsic::sideeffect:
 441     case Intrinsic::pseudoprobe:
 442       return;
 443     }
 444   }
 445   if (!Inst->mayReadOrWriteMemory())
 446     return; // doesn't alias anything
 447
 448   if (AliasSet *AS = findAliasSetForUnknownInst(Inst)) {
 449     AS->addUnknownInst(Inst, AA);
 450     return;
 451   }
 452   AliasSets.push_back(new AliasSet());
 453   AliasSets.back().addUnknownInst(Inst, AA);
 454 }
 455
 456 void AliasSetTracker::add(Instruction *I) {
 457   // Dispatch to one of the other add methods.
 458   if (LoadInst *LI = dyn_cast<LoadInst>(I))
 459     return add(LI);
 460   if (StoreInst *SI = dyn_cast<StoreInst>(I))
 461     return add(SI);
 462   if (VAArgInst *VAAI = dyn_cast<VAArgInst>(I))
 463     return add(VAAI);
 464   if (AnyMemSetInst *MSI = dyn_cast<AnyMemSetInst>(I))
 465     return add(MSI);
 466   if (AnyMemTransferInst *MTI = dyn_cast<AnyMemTransferInst>(I))
 467     return add(MTI);
 468
 469   // Handle all calls with known mod/ref sets genericall
 470   if (auto *Call = dyn_cast<CallBase>(I))
 471     if (Call->onlyAccessesArgMemory()) {
 472       auto getAccessFromModRef = [](ModRefInfo MRI) {
 473         if (isRefSet(MRI) && isModSet(MRI))
 474           return AliasSet::ModRefAccess;
 475         else if (isModSet(MRI))
 476           return AliasSet::ModAccess;
 477         else if (isRefSet(MRI))
 478           return AliasSet::RefAccess;
 479         else
 480           return AliasSet::NoAccess;
 481       };
 482
 483       ModRefInfo CallMask = createModRefInfo(AA.getModRefBehavior(Call));
 484
 485       // Some intrinsics are marked as modifying memory for control flow
 486       // modelling purposes, but don't actually modify any specific memory
 487       // location.
 488       using namespace PatternMatch;
 489       if (Call->use_empty() &&
 490           match(Call, m_Intrinsic<Intrinsic::invariant_start>()))
 491         CallMask = clearMod(CallMask);
 492
 493       for (auto IdxArgPair : enumerate(Call->args())) {
 494         int ArgIdx = IdxArgPair.index();
 495         const Value *Arg = IdxArgPair.value();
 496         if (!Arg->getType()->isPointerTy())
 497           continue;
 498         MemoryLocation ArgLoc =
 499             MemoryLocation::getForArgument(Call, ArgIdx, nullptr);
 500         ModRefInfo ArgMask = AA.getArgModRefInfo(Call, ArgIdx);
 501         ArgMask = intersectModRef(CallMask, ArgMask);
 502         if (!isNoModRef(ArgMask))
 503           addPointer(ArgLoc, getAccessFromModRef(ArgMask));
 504       }
 505       return;
 506     }
 507
 508   return addUnknown(I);
 509 }
 510
 511 void AliasSetTracker::add(BasicBlock &BB) {
 512   for (auto &I : BB)
 513     add(&I);
 514 }
 515
 516 void AliasSetTracker::add(const AliasSetTracker &AST) {
 517   assert(&AA == &AST.AA &&
 518          "Merging AliasSetTracker objects with different Alias Analyses!");
 519
 520   // Loop over all of the alias sets in AST, adding the pointers contained
 521   // therein into the current alias sets.  This can cause alias sets to be
 522   // merged together in the current AST.
 523   for (const AliasSet &AS : AST) {
 524     if (AS.Forward)
 525       continue; // Ignore forwarding alias sets
 526
 527     // If there are any call sites in the alias set, add them to this AST.
 528     for (unsigned i = 0, e = AS.UnknownInsts.size(); i != e; ++i)
 529       if (auto *Inst = AS.getUnknownInst(i))
 530         add(Inst);
 531
 532     // Loop over all of the pointers in this alias set.
 533     for (AliasSet::iterator ASI = AS.begin(), E = AS.end(); ASI != E; ++ASI)
 534       addPointer(
 535           MemoryLocation(ASI.getPointer(), ASI.getSize(), ASI.getAAInfo()),
 536           (AliasSet::AccessLattice)AS.Access);
 537   }
 538 }
 539
 540 // deleteValue method - This method is used to remove a pointer value from the
 541 // AliasSetTracker entirely.  It should be used when an instruction is deleted
 542 // from the program to update the AST.  If you don't use this, you would have
 543 // dangling pointers to deleted instructions.
 544 //
 545 void AliasSetTracker::deleteValue(Value *PtrVal) {
 546   // First, look up the PointerRec for this pointer.
 547   PointerMapType::iterator I = PointerMap.find_as(PtrVal);
 548   if (I == PointerMap.end()) return;  // Noop
 549
 550   // If we found one, remove the pointer from the alias set it is in.
 551   AliasSet::PointerRec *PtrValEnt = I->second;
 552   AliasSet *AS = PtrValEnt->getAliasSet(*this);
 553
 554   // Unlink and delete from the list of values.
 555   PtrValEnt->eraseFromList();
 556
 557   if (AS->Alias == AliasSet::SetMayAlias) {
 558     AS->SetSize--;
 559     TotalMayAliasSetSize--;
 560   }
 561
 562   // Stop using the alias set.
 563   AS->dropRef(*this);
 564
 565   PointerMap.erase(I);
 566 }
 567
 568 // copyValue - This method should be used whenever a preexisting value in the
 569 // program is copied or cloned, introducing a new value.  Note that it is ok for
 570 // clients that use this method to introduce the same value multiple times: if
 571 // the tracker already knows about a value, it will ignore the request.
 572 //
 573 void AliasSetTracker::copyValue(Value *From, Value *To) {
 574   // First, look up the PointerRec for this pointer.
 575   PointerMapType::iterator I = PointerMap.find_as(From);
 576   if (I == PointerMap.end())
 577     return;  // Noop
 578   assert(I->second->hasAliasSet() && "Dead entry?");
 579
 580   AliasSet::PointerRec &Entry = getEntryFor(To);
 581   if (Entry.hasAliasSet()) return;    // Already in the tracker!
 582
 583   // getEntryFor above may invalidate iterator \c I, so reinitialize it.
 584   I = PointerMap.find_as(From);
 585   // Add it to the alias set it aliases...
 586   AliasSet *AS = I->second->getAliasSet(*this);
 587   AS->addPointer(*this, Entry, I->second->getSize(), I->second->getAAInfo(),
 588                  true, true);
 589 }
 590
 591 AliasSet &AliasSetTracker::mergeAllAliasSets() {
 592   assert(!AliasAnyAS && (TotalMayAliasSetSize > SaturationThreshold) &&
 593          "Full merge should happen once, when the saturation threshold is "
 594          "reached");
 595
 596   // Collect all alias sets, so that we can drop references with impunity
 597   // without worrying about iterator invalidation.
 598   std::vector<AliasSet *> ASVector;
 599   ASVector.reserve(SaturationThreshold);
 600   for (AliasSet &AS : *this)
 601     ASVector.push_back(&AS);
 602
 603   // Copy all instructions and pointers into a new set, and forward all other
 604   // sets to it.
 605   AliasSets.push_back(new AliasSet());
 606   AliasAnyAS = &AliasSets.back();
 607   AliasAnyAS->Alias = AliasSet::SetMayAlias;
 608   AliasAnyAS->Access = AliasSet::ModRefAccess;
 609   AliasAnyAS->AliasAny = true;
 610
 611   for (auto Cur : ASVector) {
 612     // If Cur was already forwarding, just forward to the new AS instead.
 613     AliasSet *FwdTo = Cur->Forward;
 614     if (FwdTo) {
 615       Cur->Forward = AliasAnyAS;
 616       AliasAnyAS->addRef();
 617       FwdTo->dropRef(*this);
 618       continue;
 619     }
 620
 621     // Otherwise, perform the actual merge.
 622     AliasAnyAS->mergeSetIn(*Cur, *this);
 623   }
 624
 625   return *AliasAnyAS;
 626 }
 627
 628 AliasSet &AliasSetTracker::addPointer(MemoryLocation Loc,
 629                                       AliasSet::AccessLattice E) {
 630   AliasSet &AS = getAliasSetFor(Loc);
 631   AS.Access |= E;
 632
 633   if (!AliasAnyAS && (TotalMayAliasSetSize > SaturationThreshold)) {
 634     // The AST is now saturated. From here on, we conservatively consider all
 635     // pointers to alias each-other.
 636     return mergeAllAliasSets();
 637   }
 638
 639   return AS;
 640 }
 641
 642 //===----------------------------------------------------------------------===//
 643 //               AliasSet/AliasSetTracker Printing Support
 644 //===----------------------------------------------------------------------===//
 645
 646 void AliasSet::print(raw_ostream &OS) const {
 647   OS << "  AliasSet[" << (const void*)this << ", " << RefCount << "] ";
 648   OS << (Alias == SetMustAlias ? "must" : "may") << " alias, ";
 649   switch (Access) {
 650   case NoAccess:     OS << "No access "; break;
 651   case RefAccess:    OS << "Ref       "; break;
 652   case ModAccess:    OS << "Mod       "; break;
 653   case ModRefAccess: OS << "Mod/Ref   "; break;
 654   default: llvm_unreachable("Bad value for Access!");
 655   }
 656   if (Forward)
 657     OS << " forwarding to " << (void*)Forward;
 658
 659   if (!empty()) {
 660     OS << "Pointers: ";
 661     for (iterator I = begin(), E = end(); I != E; ++I) {
 662       if (I != begin()) OS << ", ";
 663       I.getPointer()->printAsOperand(OS << "(");
 664       if (I.getSize() == LocationSize::afterPointer())
 665         OS << ", unknown after)";
 666       else if (I.getSize() == LocationSize::beforeOrAfterPointer())
 667         OS << ", unknown before-or-after)";
 668       else
 669         OS << ", " << I.getSize() << ")";
 670     }
 671   }
 672   if (!UnknownInsts.empty()) {
 673     OS << "\n    " << UnknownInsts.size() << " Unknown instructions: ";
 674     for (unsigned i = 0, e = UnknownInsts.size(); i != e; ++i) {
 675       if (i) OS << ", ";
 676       if (auto *I = getUnknownInst(i)) {
 677         if (I->hasName())
 678           I->printAsOperand(OS);
 679         else
 680           I->print(OS);
 681       }
 682     }
 683   }
 684   OS << "\n";
 685 }
 686
 687 void AliasSetTracker::print(raw_ostream &OS) const {
 688   OS << "Alias Set Tracker: " << AliasSets.size();
 689   if (AliasAnyAS)
 690     OS << " (Saturated)";
 691   OS << " alias sets for " << PointerMap.size() << " pointer values.\n";
 692   for (const AliasSet &AS : *this)
 693     AS.print(OS);
 694   OS << "\n";
 695 }
 696
 697 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 698 LLVM_DUMP_METHOD void AliasSet::dump() const { print(dbgs()); }
 699 LLVM_DUMP_METHOD void AliasSetTracker::dump() const { print(dbgs()); }
 700 #endif
 701
 702 //===----------------------------------------------------------------------===//
 703 //                     ASTCallbackVH Class Implementation
 704 //===----------------------------------------------------------------------===//
 705
 706 void AliasSetTracker::ASTCallbackVH::deleted() {
 707   assert(AST && "ASTCallbackVH called with a null AliasSetTracker!");
 708   AST->deleteValue(getValPtr());
 709   // this now dangles!
 710 }
 711
 712 void AliasSetTracker::ASTCallbackVH::allUsesReplacedWith(Value *V) {
 713   AST->copyValue(getValPtr(), V);
 714 }
 715
 716 AliasSetTracker::ASTCallbackVH::ASTCallbackVH(Value *V, AliasSetTracker *ast)
 717   : CallbackVH(V), AST(ast) {}
 718
 719 AliasSetTracker::ASTCallbackVH &
 720 AliasSetTracker::ASTCallbackVH::operator=(Value *V) {
 721   return *this = ASTCallbackVH(V, AST);
 722 }
 723
 724 //===----------------------------------------------------------------------===//
 725 //                            AliasSetPrinter Pass
 726 //===----------------------------------------------------------------------===//
 727
 728 namespace {
 729
 730   class AliasSetPrinter : public FunctionPass {
 731   public:
 732     static char ID; // Pass identification, replacement for typeid
 733
 734     AliasSetPrinter() : FunctionPass(ID) {
 735       initializeAliasSetPrinterPass(*PassRegistry::getPassRegistry());
 736     }
 737
 738     void getAnalysisUsage(AnalysisUsage &AU) const override {
 739       AU.setPreservesAll();
 740       AU.addRequired<AAResultsWrapperPass>();
 741     }
 742
 743     bool runOnFunction(Function &F) override {
 744       auto &AAWP = getAnalysis<AAResultsWrapperPass>();
 745       AliasSetTracker Tracker(AAWP.getAAResults());
 746       errs() << "Alias sets for function '" << F.getName() << "':\n";
 747       for (Instruction &I : instructions(F))
 748         Tracker.add(&I);
 749       Tracker.print(errs());
 750       return false;
 751     }
 752   };
 753
 754 } // end anonymous namespace
 755
 756 char AliasSetPrinter::ID = 0;
 757
 758 INITIALIZE_PASS_BEGIN(AliasSetPrinter, "print-alias-sets",
 759                 "Alias Set Printer", false, true)
 760 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
 761 INITIALIZE_PASS_END(AliasSetPrinter, "print-alias-sets",
 762                 "Alias Set Printer", false, true)
 763
 764 AliasSetsPrinterPass::AliasSetsPrinterPass(raw_ostream &OS) : OS(OS) {}
 765
 766 PreservedAnalyses AliasSetsPrinterPass::run(Function &F,
 767                                             FunctionAnalysisManager &AM) {
 768   auto &AA = AM.getResult<AAManager>(F);
 769   AliasSetTracker Tracker(AA);
 770   OS << "Alias sets for function '" << F.getName() << "':\n";
 771   for (Instruction &I : instructions(F))
 772     Tracker.add(&I);
 773   Tracker.print(OS);
 774   return PreservedAnalyses::all();
 775 }