lib/Analysis/CFLAndersAliasAnalysis.cpp

   1 //===- CFLAndersAliasAnalysis.cpp - Unification-based Alias Analysis ------===//
   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 a CFL-based, summary-based alias analysis algorithm. It
  10 // differs from CFLSteensAliasAnalysis in its inclusion-based nature while
  11 // CFLSteensAliasAnalysis is unification-based. This pass has worse performance
  12 // than CFLSteensAliasAnalysis (the worst case complexity of
  13 // CFLAndersAliasAnalysis is cubic, while the worst case complexity of
  14 // CFLSteensAliasAnalysis is almost linear), but it is able to yield more
  15 // precise analysis result. The precision of this analysis is roughly the same
  16 // as that of an one level context-sensitive Andersen's algorithm.
  17 //
  18 // The algorithm used here is based on recursive state machine matching scheme
  19 // proposed in "Demand-driven alias analysis for C" by Xin Zheng and Radu
  20 // Rugina. The general idea is to extend the traditional transitive closure
  21 // algorithm to perform CFL matching along the way: instead of recording
  22 // "whether X is reachable from Y", we keep track of "whether X is reachable
  23 // from Y at state Z", where the "state" field indicates where we are in the CFL
  24 // matching process. To understand the matching better, it is advisable to have
  25 // the state machine shown in Figure 3 of the paper available when reading the
  26 // codes: all we do here is to selectively expand the transitive closure by
  27 // discarding edges that are not recognized by the state machine.
  28 //
  29 // There are two differences between our current implementation and the one
  30 // described in the paper:
  31 // - Our algorithm eagerly computes all alias pairs after the CFLGraph is built,
  32 // while in the paper the authors did the computation in a demand-driven
  33 // fashion. We did not implement the demand-driven algorithm due to the
  34 // additional coding complexity and higher memory profile, but if we found it
  35 // necessary we may switch to it eventually.
  36 // - In the paper the authors use a state machine that does not distinguish
  37 // value reads from value writes. For example, if Y is reachable from X at state
  38 // S3, it may be the case that X is written into Y, or it may be the case that
  39 // there's a third value Z that writes into both X and Y. To make that
  40 // distinction (which is crucial in building function summary as well as
  41 // retrieving mod-ref info), we choose to duplicate some of the states in the
  42 // paper's proposed state machine. The duplication does not change the set the
  43 // machine accepts. Given a pair of reachable values, it only provides more
  44 // detailed information on which value is being written into and which is being
  45 // read from.
  46 //
  47 //===----------------------------------------------------------------------===//
  48
  49 // N.B. AliasAnalysis as a whole is phrased as a FunctionPass at the moment, and
  50 // CFLAndersAA is interprocedural. This is *technically* A Bad Thing, because
  51 // FunctionPasses are only allowed to inspect the Function that they're being
  52 // run on. Realistically, this likely isn't a problem until we allow
  53 // FunctionPasses to run concurrently.
  54
  55 #include "llvm/Analysis/CFLAndersAliasAnalysis.h"
  56 #include "AliasAnalysisSummary.h"
  57 #include "CFLGraph.h"
  58 #include "llvm/ADT/DenseMap.h"
  59 #include "llvm/ADT/DenseMapInfo.h"
  60 #include "llvm/ADT/DenseSet.h"
  61 #include "llvm/ADT/None.h"
  62 #include "llvm/ADT/Optional.h"
  63 #include "llvm/ADT/STLExtras.h"
  64 #include "llvm/ADT/SmallVector.h"
  65 #include "llvm/ADT/iterator_range.h"
  66 #include "llvm/Analysis/AliasAnalysis.h"
  67 #include "llvm/Analysis/MemoryLocation.h"
  68 #include "llvm/IR/Argument.h"
  69 #include "llvm/IR/Function.h"
  70 #include "llvm/IR/PassManager.h"
  71 #include "llvm/IR/Type.h"
  72 #include "llvm/Pass.h"
  73 #include "llvm/Support/Casting.h"
  74 #include "llvm/Support/Compiler.h"
  75 #include "llvm/Support/Debug.h"
  76 #include "llvm/Support/raw_ostream.h"
  77 #include <algorithm>
  78 #include <bitset>
  79 #include <cassert>
  80 #include <cstddef>
  81 #include <cstdint>
  82 #include <functional>
  83 #include <utility>
  84 #include <vector>
  85
  86 using namespace llvm;
  87 using namespace llvm::cflaa;
  88
  89 #define DEBUG_TYPE "cfl-anders-aa"
  90
  91 CFLAndersAAResult::CFLAndersAAResult(const TargetLibraryInfo &TLI) : TLI(TLI) {}
  92 CFLAndersAAResult::CFLAndersAAResult(CFLAndersAAResult &&RHS)
  93     : AAResultBase(std::move(RHS)), TLI(RHS.TLI) {}
  94 CFLAndersAAResult::~CFLAndersAAResult() = default;
  95
  96 namespace {
  97
  98 enum class MatchState : uint8_t {
  99   // The following state represents S1 in the paper.
 100   FlowFromReadOnly = 0,
 101   // The following two states together represent S2 in the paper.
 102   // The 'NoReadWrite' suffix indicates that there exists an alias path that
 103   // does not contain assignment and reverse assignment edges.
 104   // The 'ReadOnly' suffix indicates that there exists an alias path that
 105   // contains reverse assignment edges only.
 106   FlowFromMemAliasNoReadWrite,
 107   FlowFromMemAliasReadOnly,
 108   // The following two states together represent S3 in the paper.
 109   // The 'WriteOnly' suffix indicates that there exists an alias path that
 110   // contains assignment edges only.
 111   // The 'ReadWrite' suffix indicates that there exists an alias path that
 112   // contains both assignment and reverse assignment edges. Note that if X and Y
 113   // are reachable at 'ReadWrite' state, it does NOT mean X is both read from
 114   // and written to Y. Instead, it means that a third value Z is written to both
 115   // X and Y.
 116   FlowToWriteOnly,
 117   FlowToReadWrite,
 118   // The following two states together represent S4 in the paper.
 119   FlowToMemAliasWriteOnly,
 120   FlowToMemAliasReadWrite,
 121 };
 122
 123 using StateSet = std::bitset<7>;
 124
 125 const unsigned ReadOnlyStateMask =
 126     (1U << static_cast<uint8_t>(MatchState::FlowFromReadOnly)) |
 127     (1U << static_cast<uint8_t>(MatchState::FlowFromMemAliasReadOnly));
 128 const unsigned WriteOnlyStateMask =
 129     (1U << static_cast<uint8_t>(MatchState::FlowToWriteOnly)) |
 130     (1U << static_cast<uint8_t>(MatchState::FlowToMemAliasWriteOnly));
 131
 132 // A pair that consists of a value and an offset
 133 struct OffsetValue {
 134   const Value *Val;
 135   int64_t Offset;
 136 };
 137
 138 bool operator==(OffsetValue LHS, OffsetValue RHS) {
 139   return LHS.Val == RHS.Val && LHS.Offset == RHS.Offset;
 140 }
 141 bool operator<(OffsetValue LHS, OffsetValue RHS) {
 142   return std::less<const Value *>()(LHS.Val, RHS.Val) ||
 143          (LHS.Val == RHS.Val && LHS.Offset < RHS.Offset);
 144 }
 145
 146 // A pair that consists of an InstantiatedValue and an offset
 147 struct OffsetInstantiatedValue {
 148   InstantiatedValue IVal;
 149   int64_t Offset;
 150 };
 151
 152 bool operator==(OffsetInstantiatedValue LHS, OffsetInstantiatedValue RHS) {
 153   return LHS.IVal == RHS.IVal && LHS.Offset == RHS.Offset;
 154 }
 155
 156 // We use ReachabilitySet to keep track of value aliases (The nonterminal "V" in
 157 // the paper) during the analysis.
 158 class ReachabilitySet {
 159   using ValueStateMap = DenseMap<InstantiatedValue, StateSet>;
 160   using ValueReachMap = DenseMap<InstantiatedValue, ValueStateMap>;
 161
 162   ValueReachMap ReachMap;
 163
 164 public:
 165   using const_valuestate_iterator = ValueStateMap::const_iterator;
 166   using const_value_iterator = ValueReachMap::const_iterator;
 167
 168   // Insert edge 'From->To' at state 'State'
 169   bool insert(InstantiatedValue From, InstantiatedValue To, MatchState State) {
 170     assert(From != To);
 171     auto &States = ReachMap[To][From];
 172     auto Idx = static_cast<size_t>(State);
 173     if (!States.test(Idx)) {
 174       States.set(Idx);
 175       return true;
 176     }
 177     return false;
 178   }
 179
 180   // Return the set of all ('From', 'State') pair for a given node 'To'
 181   iterator_range<const_valuestate_iterator>
 182   reachableValueAliases(InstantiatedValue V) const {
 183     auto Itr = ReachMap.find(V);
 184     if (Itr == ReachMap.end())
 185       return make_range<const_valuestate_iterator>(const_valuestate_iterator(),
 186                                                    const_valuestate_iterator());
 187     return make_range<const_valuestate_iterator>(Itr->second.begin(),
 188                                                  Itr->second.end());
 189   }
 190
 191   iterator_range<const_value_iterator> value_mappings() const {
 192     return make_range<const_value_iterator>(ReachMap.begin(), ReachMap.end());
 193   }
 194 };
 195
 196 // We use AliasMemSet to keep track of all memory aliases (the nonterminal "M"
 197 // in the paper) during the analysis.
 198 class AliasMemSet {
 199   using MemSet = DenseSet<InstantiatedValue>;
 200   using MemMapType = DenseMap<InstantiatedValue, MemSet>;
 201
 202   MemMapType MemMap;
 203
 204 public:
 205   using const_mem_iterator = MemSet::const_iterator;
 206
 207   bool insert(InstantiatedValue LHS, InstantiatedValue RHS) {
 208     // Top-level values can never be memory aliases because one cannot take the
 209     // addresses of them
 210     assert(LHS.DerefLevel > 0 && RHS.DerefLevel > 0);
 211     return MemMap[LHS].insert(RHS).second;
 212   }
 213
 214   const MemSet *getMemoryAliases(InstantiatedValue V) const {
 215     auto Itr = MemMap.find(V);
 216     if (Itr == MemMap.end())
 217       return nullptr;
 218     return &Itr->second;
 219   }
 220 };
 221
 222 // We use AliasAttrMap to keep track of the AliasAttr of each node.
 223 class AliasAttrMap {
 224   using MapType = DenseMap<InstantiatedValue, AliasAttrs>;
 225
 226   MapType AttrMap;
 227
 228 public:
 229   using const_iterator = MapType::const_iterator;
 230
 231   bool add(InstantiatedValue V, AliasAttrs Attr) {
 232     auto &OldAttr = AttrMap[V];
 233     auto NewAttr = OldAttr | Attr;
 234     if (OldAttr == NewAttr)
 235       return false;
 236     OldAttr = NewAttr;
 237     return true;
 238   }
 239
 240   AliasAttrs getAttrs(InstantiatedValue V) const {
 241     AliasAttrs Attr;
 242     auto Itr = AttrMap.find(V);
 243     if (Itr != AttrMap.end())
 244       Attr = Itr->second;
 245     return Attr;
 246   }
 247
 248   iterator_range<const_iterator> mappings() const {
 249     return make_range<const_iterator>(AttrMap.begin(), AttrMap.end());
 250   }
 251 };
 252
 253 struct WorkListItem {
 254   InstantiatedValue From;
 255   InstantiatedValue To;
 256   MatchState State;
 257 };
 258
 259 struct ValueSummary {
 260   struct Record {
 261     InterfaceValue IValue;
 262     unsigned DerefLevel;
 263   };
 264   SmallVector<Record, 4> FromRecords, ToRecords;
 265 };
 266
 267 } // end anonymous namespace
 268
 269 namespace llvm {
 270
 271 // Specialize DenseMapInfo for OffsetValue.
 272 template <> struct DenseMapInfo<OffsetValue> {
 273   static OffsetValue getEmptyKey() {
 274     return OffsetValue{DenseMapInfo<const Value *>::getEmptyKey(),
 275                        DenseMapInfo<int64_t>::getEmptyKey()};
 276   }
 277
 278   static OffsetValue getTombstoneKey() {
 279     return OffsetValue{DenseMapInfo<const Value *>::getTombstoneKey(),
 280                        DenseMapInfo<int64_t>::getEmptyKey()};
 281   }
 282
 283   static unsigned getHashValue(const OffsetValue &OVal) {
 284     return DenseMapInfo<std::pair<const Value *, int64_t>>::getHashValue(
 285         std::make_pair(OVal.Val, OVal.Offset));
 286   }
 287
 288   static bool isEqual(const OffsetValue &LHS, const OffsetValue &RHS) {
 289     return LHS == RHS;
 290   }
 291 };
 292
 293 // Specialize DenseMapInfo for OffsetInstantiatedValue.
 294 template <> struct DenseMapInfo<OffsetInstantiatedValue> {
 295   static OffsetInstantiatedValue getEmptyKey() {
 296     return OffsetInstantiatedValue{
 297         DenseMapInfo<InstantiatedValue>::getEmptyKey(),
 298         DenseMapInfo<int64_t>::getEmptyKey()};
 299   }
 300
 301   static OffsetInstantiatedValue getTombstoneKey() {
 302     return OffsetInstantiatedValue{
 303         DenseMapInfo<InstantiatedValue>::getTombstoneKey(),
 304         DenseMapInfo<int64_t>::getEmptyKey()};
 305   }
 306
 307   static unsigned getHashValue(const OffsetInstantiatedValue &OVal) {
 308     return DenseMapInfo<std::pair<InstantiatedValue, int64_t>>::getHashValue(
 309         std::make_pair(OVal.IVal, OVal.Offset));
 310   }
 311
 312   static bool isEqual(const OffsetInstantiatedValue &LHS,
 313                       const OffsetInstantiatedValue &RHS) {
 314     return LHS == RHS;
 315   }
 316 };
 317
 318 } // end namespace llvm
 319
 320 class CFLAndersAAResult::FunctionInfo {
 321   /// Map a value to other values that may alias it
 322   /// Since the alias relation is symmetric, to save some space we assume values
 323   /// are properly ordered: if a and b alias each other, and a < b, then b is in
 324   /// AliasMap[a] but not vice versa.
 325   DenseMap<const Value *, std::vector<OffsetValue>> AliasMap;
 326
 327   /// Map a value to its corresponding AliasAttrs
 328   DenseMap<const Value *, AliasAttrs> AttrMap;
 329
 330   /// Summary of externally visible effects.
 331   AliasSummary Summary;
 332
 333   Optional<AliasAttrs> getAttrs(const Value *) const;
 334
 335 public:
 336   FunctionInfo(const Function &, const SmallVectorImpl<Value *> &,
 337                const ReachabilitySet &, const AliasAttrMap &);
 338
 339   bool mayAlias(const Value *, LocationSize, const Value *, LocationSize) const;
 340   const AliasSummary &getAliasSummary() const { return Summary; }
 341 };
 342
 343 static bool hasReadOnlyState(StateSet Set) {
 344   return (Set & StateSet(ReadOnlyStateMask)).any();
 345 }
 346
 347 static bool hasWriteOnlyState(StateSet Set) {
 348   return (Set & StateSet(WriteOnlyStateMask)).any();
 349 }
 350
 351 static Optional<InterfaceValue>
 352 getInterfaceValue(InstantiatedValue IValue,
 353                   const SmallVectorImpl<Value *> &RetVals) {
 354   auto Val = IValue.Val;
 355
 356   Optional<unsigned> Index;
 357   if (auto Arg = dyn_cast<Argument>(Val))
 358     Index = Arg->getArgNo() + 1;
 359   else if (is_contained(RetVals, Val))
 360     Index = 0;
 361
 362   if (Index)
 363     return InterfaceValue{*Index, IValue.DerefLevel};
 364   return None;
 365 }
 366
 367 static void populateAttrMap(DenseMap<const Value *, AliasAttrs> &AttrMap,
 368                             const AliasAttrMap &AMap) {
 369   for (const auto &Mapping : AMap.mappings()) {
 370     auto IVal = Mapping.first;
 371
 372     // Insert IVal into the map
 373     auto &Attr = AttrMap[IVal.Val];
 374     // AttrMap only cares about top-level values
 375     if (IVal.DerefLevel == 0)
 376       Attr |= Mapping.second;
 377   }
 378 }
 379
 380 static void
 381 populateAliasMap(DenseMap<const Value *, std::vector<OffsetValue>> &AliasMap,
 382                  const ReachabilitySet &ReachSet) {
 383   for (const auto &OuterMapping : ReachSet.value_mappings()) {
 384     // AliasMap only cares about top-level values
 385     if (OuterMapping.first.DerefLevel > 0)
 386       continue;
 387
 388     auto Val = OuterMapping.first.Val;
 389     auto &AliasList = AliasMap[Val];
 390     for (const auto &InnerMapping : OuterMapping.second) {
 391       // Again, AliasMap only cares about top-level values
 392       if (InnerMapping.first.DerefLevel == 0)
 393         AliasList.push_back(OffsetValue{InnerMapping.first.Val, UnknownOffset});
 394     }
 395
 396     // Sort AliasList for faster lookup
 397     llvm::sort(AliasList);
 398   }
 399 }
 400
 401 static void populateExternalRelations(
 402     SmallVectorImpl<ExternalRelation> &ExtRelations, const Function &Fn,
 403     const SmallVectorImpl<Value *> &RetVals, const ReachabilitySet &ReachSet) {
 404   // If a function only returns one of its argument X, then X will be both an
 405   // argument and a return value at the same time. This is an edge case that
 406   // needs special handling here.
 407   for (const auto &Arg : Fn.args()) {
 408     if (is_contained(RetVals, &Arg)) {
 409       auto ArgVal = InterfaceValue{Arg.getArgNo() + 1, 0};
 410       auto RetVal = InterfaceValue{0, 0};
 411       ExtRelations.push_back(ExternalRelation{ArgVal, RetVal, 0});
 412     }
 413   }
 414
 415   // Below is the core summary construction logic.
 416   // A naive solution of adding only the value aliases that are parameters or
 417   // return values in ReachSet to the summary won't work: It is possible that a
 418   // parameter P is written into an intermediate value I, and the function
 419   // subsequently returns *I. In that case, *I is does not value alias anything
 420   // in ReachSet, and the naive solution will miss a summary edge from (P, 1) to
 421   // (I, 1).
 422   // To account for the aforementioned case, we need to check each non-parameter
 423   // and non-return value for the possibility of acting as an intermediate.
 424   // 'ValueMap' here records, for each value, which InterfaceValues read from or
 425   // write into it. If both the read list and the write list of a given value
 426   // are non-empty, we know that a particular value is an intermidate and we
 427   // need to add summary edges from the writes to the reads.
 428   DenseMap<Value *, ValueSummary> ValueMap;
 429   for (const auto &OuterMapping : ReachSet.value_mappings()) {
 430     if (auto Dst = getInterfaceValue(OuterMapping.first, RetVals)) {
 431       for (const auto &InnerMapping : OuterMapping.second) {
 432         // If Src is a param/return value, we get a same-level assignment.
 433         if (auto Src = getInterfaceValue(InnerMapping.first, RetVals)) {
 434           // This may happen if both Dst and Src are return values
 435           if (*Dst == *Src)
 436             continue;
 437
 438           if (hasReadOnlyState(InnerMapping.second))
 439             ExtRelations.push_back(ExternalRelation{*Dst, *Src, UnknownOffset});
 440           // No need to check for WriteOnly state, since ReachSet is symmetric
 441         } else {
 442           // If Src is not a param/return, add it to ValueMap
 443           auto SrcIVal = InnerMapping.first;
 444           if (hasReadOnlyState(InnerMapping.second))
 445             ValueMap[SrcIVal.Val].FromRecords.push_back(
 446                 ValueSummary::Record{*Dst, SrcIVal.DerefLevel});
 447           if (hasWriteOnlyState(InnerMapping.second))
 448             ValueMap[SrcIVal.Val].ToRecords.push_back(
 449                 ValueSummary::Record{*Dst, SrcIVal.DerefLevel});
 450         }
 451       }
 452     }
 453   }
 454
 455   for (const auto &Mapping : ValueMap) {
 456     for (const auto &FromRecord : Mapping.second.FromRecords) {
 457       for (const auto &ToRecord : Mapping.second.ToRecords) {
 458         auto ToLevel = ToRecord.DerefLevel;
 459         auto FromLevel = FromRecord.DerefLevel;
 460         // Same-level assignments should have already been processed by now
 461         if (ToLevel == FromLevel)
 462           continue;
 463
 464         auto SrcIndex = FromRecord.IValue.Index;
 465         auto SrcLevel = FromRecord.IValue.DerefLevel;
 466         auto DstIndex = ToRecord.IValue.Index;
 467         auto DstLevel = ToRecord.IValue.DerefLevel;
 468         if (ToLevel > FromLevel)
 469           SrcLevel += ToLevel - FromLevel;
 470         else
 471           DstLevel += FromLevel - ToLevel;
 472
 473         ExtRelations.push_back(ExternalRelation{
 474             InterfaceValue{SrcIndex, SrcLevel},
 475             InterfaceValue{DstIndex, DstLevel}, UnknownOffset});
 476       }
 477     }
 478   }
 479
 480   // Remove duplicates in ExtRelations
 481   llvm::sort(ExtRelations);
 482   ExtRelations.erase(std::unique(ExtRelations.begin(), ExtRelations.end()),
 483                      ExtRelations.end());
 484 }
 485
 486 static void populateExternalAttributes(
 487     SmallVectorImpl<ExternalAttribute> &ExtAttributes, const Function &Fn,
 488     const SmallVectorImpl<Value *> &RetVals, const AliasAttrMap &AMap) {
 489   for (const auto &Mapping : AMap.mappings()) {
 490     if (auto IVal = getInterfaceValue(Mapping.first, RetVals)) {
 491       auto Attr = getExternallyVisibleAttrs(Mapping.second);
 492       if (Attr.any())
 493         ExtAttributes.push_back(ExternalAttribute{*IVal, Attr});
 494     }
 495   }
 496 }
 497
 498 CFLAndersAAResult::FunctionInfo::FunctionInfo(
 499     const Function &Fn, const SmallVectorImpl<Value *> &RetVals,
 500     const ReachabilitySet &ReachSet, const AliasAttrMap &AMap) {
 501   populateAttrMap(AttrMap, AMap);
 502   populateExternalAttributes(Summary.RetParamAttributes, Fn, RetVals, AMap);
 503   populateAliasMap(AliasMap, ReachSet);
 504   populateExternalRelations(Summary.RetParamRelations, Fn, RetVals, ReachSet);
 505 }
 506
 507 Optional<AliasAttrs>
 508 CFLAndersAAResult::FunctionInfo::getAttrs(const Value *V) const {
 509   assert(V != nullptr);
 510
 511   auto Itr = AttrMap.find(V);
 512   if (Itr != AttrMap.end())
 513     return Itr->second;
 514   return None;
 515 }
 516
 517 bool CFLAndersAAResult::FunctionInfo::mayAlias(
 518     const Value *LHS, LocationSize MaybeLHSSize, const Value *RHS,
 519     LocationSize MaybeRHSSize) const {
 520   assert(LHS && RHS);
 521
 522   // Check if we've seen LHS and RHS before. Sometimes LHS or RHS can be created
 523   // after the analysis gets executed, and we want to be conservative in those
 524   // cases.
 525   auto MaybeAttrsA = getAttrs(LHS);
 526   auto MaybeAttrsB = getAttrs(RHS);
 527   if (!MaybeAttrsA || !MaybeAttrsB)
 528     return true;
 529
 530   // Check AliasAttrs before AliasMap lookup since it's cheaper
 531   auto AttrsA = *MaybeAttrsA;
 532   auto AttrsB = *MaybeAttrsB;
 533   if (hasUnknownOrCallerAttr(AttrsA))
 534     return AttrsB.any();
 535   if (hasUnknownOrCallerAttr(AttrsB))
 536     return AttrsA.any();
 537   if (isGlobalOrArgAttr(AttrsA))
 538     return isGlobalOrArgAttr(AttrsB);
 539   if (isGlobalOrArgAttr(AttrsB))
 540     return isGlobalOrArgAttr(AttrsA);
 541
 542   // At this point both LHS and RHS should point to locally allocated objects
 543
 544   auto Itr = AliasMap.find(LHS);
 545   if (Itr != AliasMap.end()) {
 546
 547     // Find out all (X, Offset) where X == RHS
 548     auto Comparator = [](OffsetValue LHS, OffsetValue RHS) {
 549       return std::less<const Value *>()(LHS.Val, RHS.Val);
 550     };
 551 #ifdef EXPENSIVE_CHECKS
 552     assert(std::is_sorted(Itr->second.begin(), Itr->second.end(), Comparator));
 553 #endif
 554     auto RangePair = std::equal_range(Itr->second.begin(), Itr->second.end(),
 555                                       OffsetValue{RHS, 0}, Comparator);
 556
 557     if (RangePair.first != RangePair.second) {
 558       // Be conservative about unknown sizes
 559       if (MaybeLHSSize == LocationSize::unknown() ||
 560           MaybeRHSSize == LocationSize::unknown())
 561         return true;
 562
 563       const uint64_t LHSSize = MaybeLHSSize.getValue();
 564       const uint64_t RHSSize = MaybeRHSSize.getValue();
 565
 566       for (const auto &OVal : make_range(RangePair)) {
 567         // Be conservative about UnknownOffset
 568         if (OVal.Offset == UnknownOffset)
 569           return true;
 570
 571         // We know that LHS aliases (RHS + OVal.Offset) if the control flow
 572         // reaches here. The may-alias query essentially becomes integer
 573         // range-overlap queries over two ranges [OVal.Offset, OVal.Offset +
 574         // LHSSize) and [0, RHSSize).
 575
 576         // Try to be conservative on super large offsets
 577         if (LLVM_UNLIKELY(LHSSize > INT64_MAX || RHSSize > INT64_MAX))
 578           return true;
 579
 580         auto LHSStart = OVal.Offset;
 581         // FIXME: Do we need to guard against integer overflow?
 582         auto LHSEnd = OVal.Offset + static_cast<int64_t>(LHSSize);
 583         auto RHSStart = 0;
 584         auto RHSEnd = static_cast<int64_t>(RHSSize);
 585         if (LHSEnd > RHSStart && LHSStart < RHSEnd)
 586           return true;
 587       }
 588     }
 589   }
 590
 591   return false;
 592 }
 593
 594 static void propagate(InstantiatedValue From, InstantiatedValue To,
 595                       MatchState State, ReachabilitySet &ReachSet,
 596                       std::vector<WorkListItem> &WorkList) {
 597   if (From == To)
 598     return;
 599   if (ReachSet.insert(From, To, State))
 600     WorkList.push_back(WorkListItem{From, To, State});
 601 }
 602
 603 static void initializeWorkList(std::vector<WorkListItem> &WorkList,
 604                                ReachabilitySet &ReachSet,
 605                                const CFLGraph &Graph) {
 606   for (const auto &Mapping : Graph.value_mappings()) {
 607     auto Val = Mapping.first;
 608     auto &ValueInfo = Mapping.second;
 609     assert(ValueInfo.getNumLevels() > 0);
 610
 611     // Insert all immediate assignment neighbors to the worklist
 612     for (unsigned I = 0, E = ValueInfo.getNumLevels(); I < E; ++I) {
 613       auto Src = InstantiatedValue{Val, I};
 614       // If there's an assignment edge from X to Y, it means Y is reachable from
 615       // X at S3 and X is reachable from Y at S1
 616       for (auto &Edge : ValueInfo.getNodeInfoAtLevel(I).Edges) {
 617         propagate(Edge.Other, Src, MatchState::FlowFromReadOnly, ReachSet,
 618                   WorkList);
 619         propagate(Src, Edge.Other, MatchState::FlowToWriteOnly, ReachSet,
 620                   WorkList);
 621       }
 622     }
 623   }
 624 }
 625
 626 static Optional<InstantiatedValue> getNodeBelow(const CFLGraph &Graph,
 627                                                 InstantiatedValue V) {
 628   auto NodeBelow = InstantiatedValue{V.Val, V.DerefLevel + 1};
 629   if (Graph.getNode(NodeBelow))
 630     return NodeBelow;
 631   return None;
 632 }
 633
 634 static void processWorkListItem(const WorkListItem &Item, const CFLGraph &Graph,
 635                                 ReachabilitySet &ReachSet, AliasMemSet &MemSet,
 636                                 std::vector<WorkListItem> &WorkList) {
 637   auto FromNode = Item.From;
 638   auto ToNode = Item.To;
 639
 640   auto NodeInfo = Graph.getNode(ToNode);
 641   assert(NodeInfo != nullptr);
 642
 643   // TODO: propagate field offsets
 644
 645   // FIXME: Here is a neat trick we can do: since both ReachSet and MemSet holds
 646   // relations that are symmetric, we could actually cut the storage by half by
 647   // sorting FromNode and ToNode before insertion happens.
 648
 649   // The newly added value alias pair may potentially generate more memory
 650   // alias pairs. Check for them here.
 651   auto FromNodeBelow = getNodeBelow(Graph, FromNode);
 652   auto ToNodeBelow = getNodeBelow(Graph, ToNode);
 653   if (FromNodeBelow && ToNodeBelow &&
 654       MemSet.insert(*FromNodeBelow, *ToNodeBelow)) {
 655     propagate(*FromNodeBelow, *ToNodeBelow,
 656               MatchState::FlowFromMemAliasNoReadWrite, ReachSet, WorkList);
 657     for (const auto &Mapping : ReachSet.reachableValueAliases(*FromNodeBelow)) {
 658       auto Src = Mapping.first;
 659       auto MemAliasPropagate = [&](MatchState FromState, MatchState ToState) {
 660         if (Mapping.second.test(static_cast<size_t>(FromState)))
 661           propagate(Src, *ToNodeBelow, ToState, ReachSet, WorkList);
 662       };
 663
 664       MemAliasPropagate(MatchState::FlowFromReadOnly,
 665                         MatchState::FlowFromMemAliasReadOnly);
 666       MemAliasPropagate(MatchState::FlowToWriteOnly,
 667                         MatchState::FlowToMemAliasWriteOnly);
 668       MemAliasPropagate(MatchState::FlowToReadWrite,
 669                         MatchState::FlowToMemAliasReadWrite);
 670     }
 671   }
 672
 673   // This is the core of the state machine walking algorithm. We expand ReachSet
 674   // based on which state we are at (which in turn dictates what edges we
 675   // should examine)
 676   // From a high-level point of view, the state machine here guarantees two
 677   // properties:
 678   // - If *X and *Y are memory aliases, then X and Y are value aliases
 679   // - If Y is an alias of X, then reverse assignment edges (if there is any)
 680   // should precede any assignment edges on the path from X to Y.
 681   auto NextAssignState = [&](MatchState State) {
 682     for (const auto &AssignEdge : NodeInfo->Edges)
 683       propagate(FromNode, AssignEdge.Other, State, ReachSet, WorkList);
 684   };
 685   auto NextRevAssignState = [&](MatchState State) {
 686     for (const auto &RevAssignEdge : NodeInfo->ReverseEdges)
 687       propagate(FromNode, RevAssignEdge.Other, State, ReachSet, WorkList);
 688   };
 689   auto NextMemState = [&](MatchState State) {
 690     if (auto AliasSet = MemSet.getMemoryAliases(ToNode)) {
 691       for (const auto &MemAlias : *AliasSet)
 692         propagate(FromNode, MemAlias, State, ReachSet, WorkList);
 693     }
 694   };
 695
 696   switch (Item.State) {
 697   case MatchState::FlowFromReadOnly:
 698     NextRevAssignState(MatchState::FlowFromReadOnly);
 699     NextAssignState(MatchState::FlowToReadWrite);
 700     NextMemState(MatchState::FlowFromMemAliasReadOnly);
 701     break;
 702
 703   case MatchState::FlowFromMemAliasNoReadWrite:
 704     NextRevAssignState(MatchState::FlowFromReadOnly);
 705     NextAssignState(MatchState::FlowToWriteOnly);
 706     break;
 707
 708   case MatchState::FlowFromMemAliasReadOnly:
 709     NextRevAssignState(MatchState::FlowFromReadOnly);
 710     NextAssignState(MatchState::FlowToReadWrite);
 711     break;
 712
 713   case MatchState::FlowToWriteOnly:
 714     NextAssignState(MatchState::FlowToWriteOnly);
 715     NextMemState(MatchState::FlowToMemAliasWriteOnly);
 716     break;
 717
 718   case MatchState::FlowToReadWrite:
 719     NextAssignState(MatchState::FlowToReadWrite);
 720     NextMemState(MatchState::FlowToMemAliasReadWrite);
 721     break;
 722
 723   case MatchState::FlowToMemAliasWriteOnly:
 724     NextAssignState(MatchState::FlowToWriteOnly);
 725     break;
 726
 727   case MatchState::FlowToMemAliasReadWrite:
 728     NextAssignState(MatchState::FlowToReadWrite);
 729     break;
 730   }
 731 }
 732
 733 static AliasAttrMap buildAttrMap(const CFLGraph &Graph,
 734                                  const ReachabilitySet &ReachSet) {
 735   AliasAttrMap AttrMap;
 736   std::vector<InstantiatedValue> WorkList, NextList;
 737
 738   // Initialize each node with its original AliasAttrs in CFLGraph
 739   for (const auto &Mapping : Graph.value_mappings()) {
 740     auto Val = Mapping.first;
 741     auto &ValueInfo = Mapping.second;
 742     for (unsigned I = 0, E = ValueInfo.getNumLevels(); I < E; ++I) {
 743       auto Node = InstantiatedValue{Val, I};
 744       AttrMap.add(Node, ValueInfo.getNodeInfoAtLevel(I).Attr);
 745       WorkList.push_back(Node);
 746     }
 747   }
 748
 749   while (!WorkList.empty()) {
 750     for (const auto &Dst : WorkList) {
 751       auto DstAttr = AttrMap.getAttrs(Dst);
 752       if (DstAttr.none())
 753         continue;
 754
 755       // Propagate attr on the same level
 756       for (const auto &Mapping : ReachSet.reachableValueAliases(Dst)) {
 757         auto Src = Mapping.first;
 758         if (AttrMap.add(Src, DstAttr))
 759           NextList.push_back(Src);
 760       }
 761
 762       // Propagate attr to the levels below
 763       auto DstBelow = getNodeBelow(Graph, Dst);
 764       while (DstBelow) {
 765         if (AttrMap.add(*DstBelow, DstAttr)) {
 766           NextList.push_back(*DstBelow);
 767           break;
 768         }
 769         DstBelow = getNodeBelow(Graph, *DstBelow);
 770       }
 771     }
 772     WorkList.swap(NextList);
 773     NextList.clear();
 774   }
 775
 776   return AttrMap;
 777 }
 778
 779 CFLAndersAAResult::FunctionInfo
 780 CFLAndersAAResult::buildInfoFrom(const Function &Fn) {
 781   CFLGraphBuilder<CFLAndersAAResult> GraphBuilder(
 782       *this, TLI,
 783       // Cast away the constness here due to GraphBuilder's API requirement
 784       const_cast<Function &>(Fn));
 785   auto &Graph = GraphBuilder.getCFLGraph();
 786
 787   ReachabilitySet ReachSet;
 788   AliasMemSet MemSet;
 789
 790   std::vector<WorkListItem> WorkList, NextList;
 791   initializeWorkList(WorkList, ReachSet, Graph);
 792   // TODO: make sure we don't stop before the fix point is reached
 793   while (!WorkList.empty()) {
 794     for (const auto &Item : WorkList)
 795       processWorkListItem(Item, Graph, ReachSet, MemSet, NextList);
 796
 797     NextList.swap(WorkList);
 798     NextList.clear();
 799   }
 800
 801   // Now that we have all the reachability info, propagate AliasAttrs according
 802   // to it
 803   auto IValueAttrMap = buildAttrMap(Graph, ReachSet);
 804
 805   return FunctionInfo(Fn, GraphBuilder.getReturnValues(), ReachSet,
 806                       std::move(IValueAttrMap));
 807 }
 808
 809 void CFLAndersAAResult::scan(const Function &Fn) {
 810   auto InsertPair = Cache.insert(std::make_pair(&Fn, Optional<FunctionInfo>()));
 811   (void)InsertPair;
 812   assert(InsertPair.second &&
 813          "Trying to scan a function that has already been cached");
 814
 815   // Note that we can't do Cache[Fn] = buildSetsFrom(Fn) here: the function call
 816   // may get evaluated after operator[], potentially triggering a DenseMap
 817   // resize and invalidating the reference returned by operator[]
 818   auto FunInfo = buildInfoFrom(Fn);
 819   Cache[&Fn] = std::move(FunInfo);
 820   Handles.emplace_front(const_cast<Function *>(&Fn), this);
 821 }
 822
 823 void CFLAndersAAResult::evict(const Function *Fn) { Cache.erase(Fn); }
 824
 825 const Optional<CFLAndersAAResult::FunctionInfo> &
 826 CFLAndersAAResult::ensureCached(const Function &Fn) {
 827   auto Iter = Cache.find(&Fn);
 828   if (Iter == Cache.end()) {
 829     scan(Fn);
 830     Iter = Cache.find(&Fn);
 831     assert(Iter != Cache.end());
 832     assert(Iter->second.hasValue());
 833   }
 834   return Iter->second;
 835 }
 836
 837 const AliasSummary *CFLAndersAAResult::getAliasSummary(const Function &Fn) {
 838   auto &FunInfo = ensureCached(Fn);
 839   if (FunInfo.hasValue())
 840     return &FunInfo->getAliasSummary();
 841   else
 842     return nullptr;
 843 }
 844
 845 AliasResult CFLAndersAAResult::query(const MemoryLocation &LocA,
 846                                      const MemoryLocation &LocB) {
 847   auto *ValA = LocA.Ptr;
 848   auto *ValB = LocB.Ptr;
 849
 850   if (!ValA->getType()->isPointerTy() || !ValB->getType()->isPointerTy())
 851     return NoAlias;
 852
 853   auto *Fn = parentFunctionOfValue(ValA);
 854   if (!Fn) {
 855     Fn = parentFunctionOfValue(ValB);
 856     if (!Fn) {
 857       // The only times this is known to happen are when globals + InlineAsm are
 858       // involved
 859       LLVM_DEBUG(
 860           dbgs()
 861           << "CFLAndersAA: could not extract parent function information.\n");
 862       return MayAlias;
 863     }
 864   } else {
 865     assert(!parentFunctionOfValue(ValB) || parentFunctionOfValue(ValB) == Fn);
 866   }
 867
 868   assert(Fn != nullptr);
 869   auto &FunInfo = ensureCached(*Fn);
 870
 871   // AliasMap lookup
 872   if (FunInfo->mayAlias(ValA, LocA.Size, ValB, LocB.Size))
 873     return MayAlias;
 874   return NoAlias;
 875 }
 876
 877 AliasResult CFLAndersAAResult::alias(const MemoryLocation &LocA,
 878                                      const MemoryLocation &LocB,
 879                                      AAQueryInfo &AAQI) {
 880   if (LocA.Ptr == LocB.Ptr)
 881     return MustAlias;
 882
 883   // Comparisons between global variables and other constants should be
 884   // handled by BasicAA.
 885   // CFLAndersAA may report NoAlias when comparing a GlobalValue and
 886   // ConstantExpr, but every query needs to have at least one Value tied to a
 887   // Function, and neither GlobalValues nor ConstantExprs are.
 888   if (isa<Constant>(LocA.Ptr) && isa<Constant>(LocB.Ptr))
 889     return AAResultBase::alias(LocA, LocB, AAQI);
 890
 891   AliasResult QueryResult = query(LocA, LocB);
 892   if (QueryResult == MayAlias)
 893     return AAResultBase::alias(LocA, LocB, AAQI);
 894
 895   return QueryResult;
 896 }
 897
 898 AnalysisKey CFLAndersAA::Key;
 899
 900 CFLAndersAAResult CFLAndersAA::run(Function &F, FunctionAnalysisManager &AM) {
 901   return CFLAndersAAResult(AM.getResult<TargetLibraryAnalysis>(F));
 902 }
 903
 904 char CFLAndersAAWrapperPass::ID = 0;
 905 INITIALIZE_PASS(CFLAndersAAWrapperPass, "cfl-anders-aa",
 906                 "Inclusion-Based CFL Alias Analysis", false, true)
 907
 908 ImmutablePass *llvm::createCFLAndersAAWrapperPass() {
 909   return new CFLAndersAAWrapperPass();
 910 }
 911
 912 CFLAndersAAWrapperPass::CFLAndersAAWrapperPass() : ImmutablePass(ID) {
 913   initializeCFLAndersAAWrapperPassPass(*PassRegistry::getPassRegistry());
 914 }
 915
 916 void CFLAndersAAWrapperPass::initializePass() {
 917   auto &TLIWP = getAnalysis<TargetLibraryInfoWrapperPass>();
 918   Result.reset(new CFLAndersAAResult(TLIWP.getTLI()));
 919 }
 920
 921 void CFLAndersAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
 922   AU.setPreservesAll();
 923   AU.addRequired<TargetLibraryInfoWrapperPass>();
 924 }