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      1 //===- llvm/Analysis/AliasSetTracker.h - Build Alias Sets -------*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file defines two classes: AliasSetTracker and AliasSet. These interfaces
     11 // are used to classify a collection of pointer references into a maximal number
     12 // of disjoint sets. Each AliasSet object constructed by the AliasSetTracker
     13 // object refers to memory disjoint from the other sets.
     14 //
     15 //===----------------------------------------------------------------------===//
     16 
     17 #ifndef LLVM_ANALYSIS_ALIASSETTRACKER_H
     18 #define LLVM_ANALYSIS_ALIASSETTRACKER_H
     19 
     20 #include "llvm/ADT/DenseMap.h"
     21 #include "llvm/ADT/ilist.h"
     22 #include "llvm/ADT/ilist_node.h"
     23 #include "llvm/Analysis/AliasAnalysis.h"
     24 #include "llvm/IR/Metadata.h"
     25 #include "llvm/IR/ValueHandle.h"
     26 #include <vector>
     27 
     28 namespace llvm {
     29 
     30 class LoadInst;
     31 class StoreInst;
     32 class VAArgInst;
     33 class MemSetInst;
     34 class AliasSetTracker;
     35 class AliasSet;
     36 
     37 class AliasSet : public ilist_node<AliasSet> {
     38   friend class AliasSetTracker;
     39 
     40   class PointerRec {
     41     Value *Val;  // The pointer this record corresponds to.
     42     PointerRec **PrevInList, *NextInList;
     43     AliasSet *AS;
     44     uint64_t Size;
     45     AAMDNodes AAInfo;
     46 
     47   public:
     48     PointerRec(Value *V)
     49       : Val(V), PrevInList(nullptr), NextInList(nullptr), AS(nullptr), Size(0),
     50         AAInfo(DenseMapInfo<AAMDNodes>::getEmptyKey()) {}
     51 
     52     Value *getValue() const { return Val; }
     53 
     54     PointerRec *getNext() const { return NextInList; }
     55     bool hasAliasSet() const { return AS != nullptr; }
     56 
     57     PointerRec** setPrevInList(PointerRec **PIL) {
     58       PrevInList = PIL;
     59       return &NextInList;
     60     }
     61 
     62     bool updateSizeAndAAInfo(uint64_t NewSize, const AAMDNodes &NewAAInfo) {
     63       bool SizeChanged = false;
     64       if (NewSize > Size) {
     65         Size = NewSize;
     66         SizeChanged = true;
     67       }
     68 
     69       if (AAInfo == DenseMapInfo<AAMDNodes>::getEmptyKey())
     70         // We don't have a AAInfo yet. Set it to NewAAInfo.
     71         AAInfo = NewAAInfo;
     72       else if (AAInfo != NewAAInfo)
     73         // NewAAInfo conflicts with AAInfo.
     74         AAInfo = DenseMapInfo<AAMDNodes>::getTombstoneKey();
     75 
     76       return SizeChanged;
     77     }
     78 
     79     uint64_t getSize() const { return Size; }
     80 
     81     /// Return the AAInfo, or null if there is no information or conflicting
     82     /// information.
     83     AAMDNodes getAAInfo() const {
     84       // If we have missing or conflicting AAInfo, return null.
     85       if (AAInfo == DenseMapInfo<AAMDNodes>::getEmptyKey() ||
     86           AAInfo == DenseMapInfo<AAMDNodes>::getTombstoneKey())
     87         return AAMDNodes();
     88       return AAInfo;
     89     }
     90 
     91     AliasSet *getAliasSet(AliasSetTracker &AST) {
     92       assert(AS && "No AliasSet yet!");
     93       if (AS->Forward) {
     94         AliasSet *OldAS = AS;
     95         AS = OldAS->getForwardedTarget(AST);
     96         AS->addRef();
     97         OldAS->dropRef(AST);
     98       }
     99       return AS;
    100     }
    101 
    102     void setAliasSet(AliasSet *as) {
    103       assert(!AS && "Already have an alias set!");
    104       AS = as;
    105     }
    106 
    107     void eraseFromList() {
    108       if (NextInList) NextInList->PrevInList = PrevInList;
    109       *PrevInList = NextInList;
    110       if (AS->PtrListEnd == &NextInList) {
    111         AS->PtrListEnd = PrevInList;
    112         assert(*AS->PtrListEnd == nullptr && "List not terminated right!");
    113       }
    114       delete this;
    115     }
    116   };
    117 
    118   PointerRec *PtrList, **PtrListEnd;  // Doubly linked list of nodes.
    119   AliasSet *Forward;             // Forwarding pointer.
    120 
    121   /// All instructions without a specific address in this alias set.
    122   std::vector<AssertingVH<Instruction> > UnknownInsts;
    123 
    124   /// Number of nodes pointing to this AliasSet plus the number of AliasSets
    125   /// forwarding to it.
    126   unsigned RefCount : 28;
    127 
    128   /// The kinds of access this alias set models.
    129   ///
    130   /// We keep track of whether this alias set merely refers to the locations of
    131   /// memory (and not any particular access), whether it modifies or references
    132   /// the memory, or whether it does both. The lattice goes from "NoAccess" to
    133   /// either RefAccess or ModAccess, then to ModRefAccess as necessary.
    134   enum AccessLattice {
    135     NoAccess = 0,
    136     RefAccess = 1,
    137     ModAccess = 2,
    138     ModRefAccess = RefAccess | ModAccess
    139   };
    140   unsigned Access : 2;
    141 
    142   /// The kind of alias relationship between pointers of the set.
    143   ///
    144   /// These represent conservatively correct alias results between any members
    145   /// of the set. We represent these independently of the values of alias
    146   /// results in order to pack it into a single bit. Lattice goes from
    147   /// MustAlias to MayAlias.
    148   enum AliasLattice {
    149     SetMustAlias = 0, SetMayAlias = 1
    150   };
    151   unsigned Alias : 1;
    152 
    153   /// True if this alias set contains volatile loads or stores.
    154   unsigned Volatile : 1;
    155 
    156   void addRef() { ++RefCount; }
    157   void dropRef(AliasSetTracker &AST) {
    158     assert(RefCount >= 1 && "Invalid reference count detected!");
    159     if (--RefCount == 0)
    160       removeFromTracker(AST);
    161   }
    162 
    163   Instruction *getUnknownInst(unsigned i) const {
    164     assert(i < UnknownInsts.size());
    165     return UnknownInsts[i];
    166   }
    167 
    168 public:
    169   /// Accessors...
    170   bool isRef() const { return Access & RefAccess; }
    171   bool isMod() const { return Access & ModAccess; }
    172   bool isMustAlias() const { return Alias == SetMustAlias; }
    173   bool isMayAlias()  const { return Alias == SetMayAlias; }
    174 
    175   /// Return true if this alias set contains volatile loads or stores.
    176   bool isVolatile() const { return Volatile; }
    177 
    178   /// Return true if this alias set should be ignored as part of the
    179   /// AliasSetTracker object.
    180   bool isForwardingAliasSet() const { return Forward; }
    181 
    182   /// Merge the specified alias set into this alias set.
    183   void mergeSetIn(AliasSet &AS, AliasSetTracker &AST);
    184 
    185   // Alias Set iteration - Allow access to all of the pointers which are part of
    186   // this alias set.
    187   class iterator;
    188   iterator begin() const { return iterator(PtrList); }
    189   iterator end()   const { return iterator(); }
    190   bool empty() const { return PtrList == nullptr; }
    191 
    192   void print(raw_ostream &OS) const;
    193   void dump() const;
    194 
    195   /// Define an iterator for alias sets... this is just a forward iterator.
    196   class iterator : public std::iterator<std::forward_iterator_tag,
    197                                         PointerRec, ptrdiff_t> {
    198     PointerRec *CurNode;
    199 
    200   public:
    201     explicit iterator(PointerRec *CN = nullptr) : CurNode(CN) {}
    202 
    203     bool operator==(const iterator& x) const {
    204       return CurNode == x.CurNode;
    205     }
    206     bool operator!=(const iterator& x) const { return !operator==(x); }
    207 
    208     value_type &operator*() const {
    209       assert(CurNode && "Dereferencing AliasSet.end()!");
    210       return *CurNode;
    211     }
    212     value_type *operator->() const { return &operator*(); }
    213 
    214     Value *getPointer() const { return CurNode->getValue(); }
    215     uint64_t getSize() const { return CurNode->getSize(); }
    216     AAMDNodes getAAInfo() const { return CurNode->getAAInfo(); }
    217 
    218     iterator& operator++() {                // Preincrement
    219       assert(CurNode && "Advancing past AliasSet.end()!");
    220       CurNode = CurNode->getNext();
    221       return *this;
    222     }
    223     iterator operator++(int) { // Postincrement
    224       iterator tmp = *this; ++*this; return tmp;
    225     }
    226   };
    227 
    228 private:
    229   // Can only be created by AliasSetTracker. Also, ilist creates one
    230   // to serve as a sentinel.
    231   friend struct ilist_sentinel_traits<AliasSet>;
    232   AliasSet()
    233     : PtrList(nullptr), PtrListEnd(&PtrList), Forward(nullptr), RefCount(0),
    234       Access(NoAccess), Alias(SetMustAlias), Volatile(false) {
    235   }
    236 
    237   AliasSet(const AliasSet &AS) = delete;
    238   void operator=(const AliasSet &AS) = delete;
    239 
    240   PointerRec *getSomePointer() const {
    241     return PtrList;
    242   }
    243 
    244   /// Return the real alias set this represents. If this has been merged with
    245   /// another set and is forwarding, return the ultimate destination set. This
    246   /// also implements the union-find collapsing as well.
    247   AliasSet *getForwardedTarget(AliasSetTracker &AST) {
    248     if (!Forward) return this;
    249 
    250     AliasSet *Dest = Forward->getForwardedTarget(AST);
    251     if (Dest != Forward) {
    252       Dest->addRef();
    253       Forward->dropRef(AST);
    254       Forward = Dest;
    255     }
    256     return Dest;
    257   }
    258 
    259   void removeFromTracker(AliasSetTracker &AST);
    260 
    261   void addPointer(AliasSetTracker &AST, PointerRec &Entry, uint64_t Size,
    262                   const AAMDNodes &AAInfo,
    263                   bool KnownMustAlias = false);
    264   void addUnknownInst(Instruction *I, AliasAnalysis &AA);
    265   void removeUnknownInst(AliasSetTracker &AST, Instruction *I) {
    266     bool WasEmpty = UnknownInsts.empty();
    267     for (size_t i = 0, e = UnknownInsts.size(); i != e; ++i)
    268       if (UnknownInsts[i] == I) {
    269         UnknownInsts[i] = UnknownInsts.back();
    270         UnknownInsts.pop_back();
    271         --i; --e;  // Revisit the moved entry.
    272       }
    273     if (!WasEmpty && UnknownInsts.empty())
    274       dropRef(AST);
    275   }
    276   void setVolatile() { Volatile = true; }
    277 
    278 public:
    279   /// Return true if the specified pointer "may" (or must) alias one of the
    280   /// members in the set.
    281   bool aliasesPointer(const Value *Ptr, uint64_t Size, const AAMDNodes &AAInfo,
    282                       AliasAnalysis &AA) const;
    283   bool aliasesUnknownInst(const Instruction *Inst, AliasAnalysis &AA) const;
    284 };
    285 
    286 inline raw_ostream& operator<<(raw_ostream &OS, const AliasSet &AS) {
    287   AS.print(OS);
    288   return OS;
    289 }
    290 
    291 class AliasSetTracker {
    292   /// A CallbackVH to arrange for AliasSetTracker to be notified whenever a
    293   /// Value is deleted.
    294   class ASTCallbackVH final : public CallbackVH {
    295     AliasSetTracker *AST;
    296     void deleted() override;
    297     void allUsesReplacedWith(Value *) override;
    298 
    299   public:
    300     ASTCallbackVH(Value *V, AliasSetTracker *AST = nullptr);
    301     ASTCallbackVH &operator=(Value *V);
    302   };
    303   /// Traits to tell DenseMap that tell us how to compare and hash the value
    304   /// handle.
    305   struct ASTCallbackVHDenseMapInfo : public DenseMapInfo<Value *> {};
    306 
    307   AliasAnalysis &AA;
    308   ilist<AliasSet> AliasSets;
    309 
    310   typedef DenseMap<ASTCallbackVH, AliasSet::PointerRec*,
    311                    ASTCallbackVHDenseMapInfo>
    312     PointerMapType;
    313 
    314   // Map from pointers to their node
    315   PointerMapType PointerMap;
    316 
    317 public:
    318   /// Create an empty collection of AliasSets, and use the specified alias
    319   /// analysis object to disambiguate load and store addresses.
    320   explicit AliasSetTracker(AliasAnalysis &aa) : AA(aa) {}
    321   ~AliasSetTracker() { clear(); }
    322 
    323   /// These methods are used to add different types of instructions to the alias
    324   /// sets. Adding a new instruction can result in one of three actions
    325   /// happening:
    326   ///
    327   ///   1. If the instruction doesn't alias any other sets, create a new set.
    328   ///   2. If the instruction aliases exactly one set, add it to the set
    329   ///   3. If the instruction aliases multiple sets, merge the sets, and add
    330   ///      the instruction to the result.
    331   ///
    332   /// These methods return true if inserting the instruction resulted in the
    333   /// addition of a new alias set (i.e., the pointer did not alias anything).
    334   ///
    335   bool add(Value *Ptr, uint64_t Size, const AAMDNodes &AAInfo); // Add a loc.
    336   bool add(LoadInst *LI);
    337   bool add(StoreInst *SI);
    338   bool add(VAArgInst *VAAI);
    339   bool add(MemSetInst *MSI);
    340   bool add(Instruction *I);       // Dispatch to one of the other add methods...
    341   void add(BasicBlock &BB);       // Add all instructions in basic block
    342   void add(const AliasSetTracker &AST); // Add alias relations from another AST
    343   bool addUnknown(Instruction *I);
    344 
    345   /// These methods are used to remove all entries that might be aliased by the
    346   /// specified instruction. These methods return true if any alias sets were
    347   /// eliminated.
    348   bool remove(Value *Ptr, uint64_t Size, const AAMDNodes &AAInfo);
    349   bool remove(LoadInst *LI);
    350   bool remove(StoreInst *SI);
    351   bool remove(VAArgInst *VAAI);
    352   bool remove(MemSetInst *MSI);
    353   bool remove(Instruction *I);
    354   void remove(AliasSet &AS);
    355   bool removeUnknown(Instruction *I);
    356 
    357   void clear();
    358 
    359   /// Return the alias sets that are active.
    360   const ilist<AliasSet> &getAliasSets() const { return AliasSets; }
    361 
    362   /// Return the alias set that the specified pointer lives in. If the New
    363   /// argument is non-null, this method sets the value to true if a new alias
    364   /// set is created to contain the pointer (because the pointer didn't alias
    365   /// anything).
    366   AliasSet &getAliasSetForPointer(Value *P, uint64_t Size,
    367                                   const AAMDNodes &AAInfo,
    368                                   bool *New = nullptr);
    369 
    370   /// Return the alias set containing the location specified if one exists,
    371   /// otherwise return null.
    372   AliasSet *getAliasSetForPointerIfExists(const Value *P, uint64_t Size,
    373                                           const AAMDNodes &AAInfo) {
    374     return mergeAliasSetsForPointer(P, Size, AAInfo);
    375   }
    376 
    377   /// Return true if the specified location is represented by this alias set,
    378   /// false otherwise. This does not modify the AST object or alias sets.
    379   bool containsPointer(const Value *P, uint64_t Size,
    380                        const AAMDNodes &AAInfo) const;
    381 
    382   /// Return true if the specified instruction "may" (or must) alias one of the
    383   /// members in any of the sets.
    384   bool containsUnknown(const Instruction *I) const;
    385 
    386   /// Return the underlying alias analysis object used by this tracker.
    387   AliasAnalysis &getAliasAnalysis() const { return AA; }
    388 
    389   /// This method is used to remove a pointer value from the AliasSetTracker
    390   /// entirely. It should be used when an instruction is deleted from the
    391   /// program to update the AST. If you don't use this, you would have dangling
    392   /// pointers to deleted instructions.
    393   void deleteValue(Value *PtrVal);
    394 
    395   /// This method should be used whenever a preexisting value in the program is
    396   /// copied or cloned, introducing a new value.  Note that it is ok for clients
    397   /// that use this method to introduce the same value multiple times: if the
    398   /// tracker already knows about a value, it will ignore the request.
    399   void copyValue(Value *From, Value *To);
    400 
    401   typedef ilist<AliasSet>::iterator iterator;
    402   typedef ilist<AliasSet>::const_iterator const_iterator;
    403 
    404   const_iterator begin() const { return AliasSets.begin(); }
    405   const_iterator end()   const { return AliasSets.end(); }
    406 
    407   iterator begin() { return AliasSets.begin(); }
    408   iterator end()   { return AliasSets.end(); }
    409 
    410   void print(raw_ostream &OS) const;
    411   void dump() const;
    412 
    413 private:
    414   friend class AliasSet;
    415   void removeAliasSet(AliasSet *AS);
    416 
    417   /// Just like operator[] on the map, except that it creates an entry for the
    418   /// pointer if it doesn't already exist.
    419   AliasSet::PointerRec &getEntryFor(Value *V) {
    420     AliasSet::PointerRec *&Entry = PointerMap[ASTCallbackVH(V, this)];
    421     if (!Entry)
    422       Entry = new AliasSet::PointerRec(V);
    423     return *Entry;
    424   }
    425 
    426   AliasSet &addPointer(Value *P, uint64_t Size, const AAMDNodes &AAInfo,
    427                        AliasSet::AccessLattice E,
    428                        bool &NewSet) {
    429     NewSet = false;
    430     AliasSet &AS = getAliasSetForPointer(P, Size, AAInfo, &NewSet);
    431     AS.Access |= E;
    432     return AS;
    433   }
    434   AliasSet *mergeAliasSetsForPointer(const Value *Ptr, uint64_t Size,
    435                                      const AAMDNodes &AAInfo);
    436 
    437   AliasSet *findAliasSetForUnknownInst(Instruction *Inst);
    438 };
    439 
    440 inline raw_ostream& operator<<(raw_ostream &OS, const AliasSetTracker &AST) {
    441   AST.print(OS);
    442   return OS;
    443 }
    444 
    445 } // End llvm namespace
    446 
    447 #endif
    448