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