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