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//===- llvm/Analysis/AliasSetTracker.h - Build Alias Sets -------*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// This file defines two classes: AliasSetTracker and AliasSet. These interfaces

// are used to classify a collection of pointer references into a maximal number

// of disjoint sets. Each AliasSet object constructed by the AliasSetTracker

// object refers to memory disjoint from the other sets.

//

// An AliasSetTracker can only be used on immutable IR.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_ANALYSIS_ALIASSETTRACKER_H

#define LLVM_ANALYSIS_ALIASSETTRACKER_H

#include "llvm/ADT/DenseMap.h"

#include "llvm/ADT/DenseMapInfo.h"

#include "llvm/ADT/ilist.h"

#include "llvm/ADT/ilist_node.h"

#include "llvm/Analysis/MemoryLocation.h"

#include "llvm/IR/Instruction.h"

#include "llvm/IR/PassManager.h"

#include "llvm/IR/ValueHandle.h"

#include <cassert>

#include <cstddef>

#include <iterator>

#include <vector>

namespace llvm {

class AliasResult;

class AliasSetTracker;

class AnyMemSetInst;

class AnyMemTransferInst;

class BasicBlock;

class BatchAAResults;

class LoadInst;

enum class ModRefInfo : uint8_t;

class raw_ostream;

class StoreInst;

class VAArgInst;

class Value;

class AliasSet : public ilist_node<AliasSet> {

  friend class AliasSetTracker;

  class PointerRec {

    Value *Val;  // The pointer this record corresponds to.

    PointerRec **PrevInList = nullptr;

    PointerRec *NextInList = nullptr;

    AliasSet *AS = nullptr;

    LocationSize Size = LocationSize::mapEmpty();

    AAMDNodes AAInfo;

    // Whether the size for this record has been set at all. This makes no

    // guarantees about the size being known.

    bool isSizeSet() const { return Size != LocationSize::mapEmpty(); }

  public:

    PointerRec(Value *V)

      : Val(V), AAInfo(DenseMapInfo<AAMDNodes>::getEmptyKey()) {}

    Value *getValue() const { return Val; }

    PointerRec *getNext() const { return NextInList; }

    bool hasAliasSet() const { return AS != nullptr; }

    PointerRec** setPrevInList(PointerRec **PIL) {

      PrevInList = PIL;

      return &NextInList;

    }

    bool updateSizeAndAAInfo(LocationSize NewSize, const AAMDNodes &NewAAInfo) {

      bool SizeChanged = false;

      if (NewSize != Size) {

        LocationSize OldSize = Size;

        Size = isSizeSet() ? Size.unionWith(NewSize) : NewSize;

        SizeChanged = OldSize != Size;

      }

      if (AAInfo == DenseMapInfo<AAMDNodes>::getEmptyKey())

        // We don't have a AAInfo yet. Set it to NewAAInfo.

        AAInfo = NewAAInfo;

      else {

        AAMDNodes Intersection(AAInfo.intersect(NewAAInfo));

        SizeChanged |= Intersection != AAInfo;

        AAInfo = Intersection;

      }

      return SizeChanged;

    }

    LocationSize getSize() const {

      assert(isSizeSet() && "Getting an unset size!");

      return Size;

    }

    /// Return the AAInfo, or null if there is no information or conflicting

    /// information.

    AAMDNodes getAAInfo() const {

      // If we have missing or conflicting AAInfo, return null.

      if (AAInfo == DenseMapInfo<AAMDNodes>::getEmptyKey() ||

          AAInfo == DenseMapInfo<AAMDNodes>::getTombstoneKey())

        return AAMDNodes();

      return AAInfo;

    }

    AliasSet *getAliasSet(AliasSetTracker &AST) {

      assert(AS && "No AliasSet yet!");

      if (AS->Forward) {

        AliasSet *OldAS = AS;

        AS = OldAS->getForwardedTarget(AST);

        AS->addRef();

        OldAS->dropRef(AST);

      }

      return AS;

    }

    void setAliasSet(AliasSet *as) {

      assert(!AS && "Already have an alias set!");

      AS = as;

    }

    void eraseFromList() {

      if (NextInList) NextInList->PrevInList = PrevInList;

      *PrevInList = NextInList;

      if (AS->PtrListEnd == &NextInList) {

        AS->PtrListEnd = PrevInList;

        assert(*AS->PtrListEnd == nullptr && "List not terminated right!");

      }

      delete this;

    }

  };

  // Doubly linked list of nodes.

  PointerRec *PtrList = nullptr;

  PointerRec **PtrListEnd;

  // Forwarding pointer.

  AliasSet *Forward = nullptr;

  /// All instructions without a specific address in this alias set.

  std::vector<AssertingVH<Instruction>> UnknownInsts;

  /// Number of nodes pointing to this AliasSet plus the number of AliasSets

  /// forwarding to it.

  unsigned RefCount : 27;

  // Signifies that this set should be considered to alias any pointer.

  // Use when the tracker holding this set is saturated.

  unsigned AliasAny : 1;

  /// The kinds of access this alias set models.

  ///

  /// We keep track of whether this alias set merely refers to the locations of

  /// memory (and not any particular access), whether it modifies or references

  /// the memory, or whether it does both. The lattice goes from "NoAccess" to

  /// either RefAccess or ModAccess, then to ModRefAccess as necessary.

  enum AccessLattice {

    NoAccess = 0,

    RefAccess = 1,

    ModAccess = 2,

    ModRefAccess = RefAccess | ModAccess

  };

  unsigned Access : 2;

  /// The kind of alias relationship between pointers of the set.

  ///

  /// These represent conservatively correct alias results between any members

  /// of the set. We represent these independently of the values of alias

  /// results in order to pack it into a single bit. Lattice goes from

  /// MustAlias to MayAlias.

  enum AliasLattice {

    SetMustAlias = 0, SetMayAlias = 1

  };

  unsigned Alias : 1;

  unsigned SetSize = 0;

  void addRef() { ++RefCount; }

  void dropRef(AliasSetTracker &AST) {

    assert(RefCount >= 1 && "Invalid reference count detected!");

    if (--RefCount == 0)

      removeFromTracker(AST);

  }

public:

  AliasSet(const AliasSet &) = delete;

  AliasSet &operator=(const AliasSet &) = delete;

  /// Accessors...

  bool isRef() const { return Access & RefAccess; }

  bool isMod() const { return Access & ModAccess; }

  bool isMustAlias() const { return Alias == SetMustAlias; }

  bool isMayAlias()  const { return Alias == SetMayAlias; }

  /// Return true if this alias set should be ignored as part of the

  /// AliasSetTracker object.

  bool isForwardingAliasSet() const { return Forward; }

  /// Merge the specified alias set into this alias set.

  void mergeSetIn(AliasSet &AS, AliasSetTracker &AST, BatchAAResults &BatchAA);

  // Alias Set iteration - Allow access to all of the pointers which are part of

  // this alias set.

  class iterator;

  iterator begin() const { return iterator(PtrList); }

  iterator end()   const { return iterator(); }

  bool empty() const { return PtrList == nullptr; }

  // Unfortunately, ilist::size() is linear, so we have to add code to keep

  // track of the list's exact size.

  unsigned size() { return SetSize; }

  void print(raw_ostream &OS) const;

  void dump() const;

  /// Define an iterator for alias sets... this is just a forward iterator.

  class iterator {

    PointerRec *CurNode;

  public:

    using iterator_category = std::forward_iterator_tag;

    using value_type = PointerRec;

    using difference_type = std::ptrdiff_t;

    using pointer = value_type *;

    using reference = value_type &;

    explicit iterator(PointerRec *CN = nullptr) : CurNode(CN) {}

    bool operator==(const iterator& x) const {

      return CurNode == x.CurNode;

    }

    bool operator!=(const iterator& x) const { return !operator==(x); }

    value_type &operator*() const {

      assert(CurNode && "Dereferencing AliasSet.end()!");

      return *CurNode;

    }

    value_type *operator->() const { return &operator*(); }

    Value *getPointer() const { return CurNode->getValue(); }

    LocationSize getSize() const { return CurNode->getSize(); }

    AAMDNodes getAAInfo() const { return CurNode->getAAInfo(); }

    iterator& operator++() {                // Preincrement

      assert(CurNode && "Advancing past AliasSet.end()!");

      CurNode = CurNode->getNext();

      return *this;

    }

    iterator operator++(int) { // Postincrement

      iterator tmp = *this; ++*this; return tmp;

    }

  };

private:

  // Can only be created by AliasSetTracker.

  AliasSet()

      : PtrListEnd(&PtrList), RefCount(0),  AliasAny(false), Access(NoAccess),

        Alias(SetMustAlias) {}

  PointerRec *getSomePointer() const {

    return PtrList;

  }

  /// Return the real alias set this represents. If this has been merged with

  /// another set and is forwarding, return the ultimate destination set. This

  /// also implements the union-find collapsing as well.

  AliasSet *getForwardedTarget(AliasSetTracker &AST) {

    if (!Forward) return this;

    AliasSet *Dest = Forward->getForwardedTarget(AST);

    if (Dest != Forward) {

      Dest->addRef();

      Forward->dropRef(AST);

      Forward = Dest;

    }

    return Dest;

  }

  void removeFromTracker(AliasSetTracker &AST);

  void addPointer(AliasSetTracker &AST, PointerRec &Entry, LocationSize Size,

                  const AAMDNodes &AAInfo, bool KnownMustAlias = false,

                  bool SkipSizeUpdate = false);

  void addUnknownInst(Instruction *I, BatchAAResults &AA);

public:

  /// If the specified pointer "may" (or must) alias one of the members in the

  /// set return the appropriate AliasResult. Otherwise return NoAlias.

  AliasResult aliasesPointer(const Value *Ptr, LocationSize Size,

                             const AAMDNodes &AAInfo, BatchAAResults &AA) const;

  ModRefInfo aliasesUnknownInst(const Instruction *Inst,

                                BatchAAResults &AA) const;

};

inline raw_ostream& operator<<(raw_ostream &OS, const AliasSet &AS) {

  AS.print(OS);

  return OS;

}

class AliasSetTracker {

  BatchAAResults &AA;

  ilist<AliasSet> AliasSets;

  using PointerMapType = DenseMap<AssertingVH<Value>, AliasSet::PointerRec *>;

  // Map from pointers to their node

  PointerMapType PointerMap;

public:

  /// Create an empty collection of AliasSets, and use the specified alias

  /// analysis object to disambiguate load and store addresses.

  explicit AliasSetTracker(BatchAAResults &AA) : AA(AA) {}

  ~AliasSetTracker() { clear(); }

  /// These methods are used to add different types of instructions to the alias

  /// sets. Adding a new instruction can result in one of three actions

  /// happening:

  ///

  ///   1. If the instruction doesn't alias any other sets, create a new set.

  ///   2. If the instruction aliases exactly one set, add it to the set

  ///   3. If the instruction aliases multiple sets, merge the sets, and add

  ///      the instruction to the result.

  ///

  /// These methods return true if inserting the instruction resulted in the

  /// addition of a new alias set (i.e., the pointer did not alias anything).

  ///

  void add(Value *Ptr, LocationSize Size, const AAMDNodes &AAInfo); // Add a loc

  void add(LoadInst *LI);

  void add(StoreInst *SI);

  void add(VAArgInst *VAAI);

  void add(AnyMemSetInst *MSI);

  void add(AnyMemTransferInst *MTI);

  void add(Instruction *I);       // Dispatch to one of the other add methods...

  void add(BasicBlock &BB);       // Add all instructions in basic block

  void add(const AliasSetTracker &AST); // Add alias relations from another AST

  void addUnknown(Instruction *I);

  void clear();

  /// Return the alias sets that are active.

  const ilist<AliasSet> &getAliasSets() const { return AliasSets; }

  /// Return the alias set which contains the specified memory location.  If

  /// the memory location aliases two or more existing alias sets, will have

  /// the effect of merging those alias sets before the single resulting alias

  /// set is returned.

  AliasSet &getAliasSetFor(const MemoryLocation &MemLoc);

  /// Return the underlying alias analysis object used by this tracker.

  BatchAAResults &getAliasAnalysis() const { return AA; }

  using iterator = ilist<AliasSet>::iterator;

  using const_iterator = ilist<AliasSet>::const_iterator;

  const_iterator begin() const { return AliasSets.begin(); }

  const_iterator end()   const { return AliasSets.end(); }

  iterator begin() { return AliasSets.begin(); }

  iterator end()   { return AliasSets.end(); }

  void print(raw_ostream &OS) const;

  void dump() const;

private:

  friend class AliasSet;

  // The total number of pointers contained in all "may" alias sets.

  unsigned TotalMayAliasSetSize = 0;

  // A non-null value signifies this AST is saturated. A saturated AST lumps

  // all pointers into a single "May" set.

  AliasSet *AliasAnyAS = nullptr;

  void removeAliasSet(AliasSet *AS);

  /// Just like operator[] on the map, except that it creates an entry for the

  /// pointer if it doesn't already exist.

  AliasSet::PointerRec &getEntryFor(Value *V) {

    AliasSet::PointerRec *&Entry = PointerMap[V];

    if (!Entry)

      Entry = new AliasSet::PointerRec(V);

    return *Entry;

  }

  AliasSet &addPointer(MemoryLocation Loc, AliasSet::AccessLattice E);

  AliasSet *mergeAliasSetsForPointer(const Value *Ptr, LocationSize Size,

                                     const AAMDNodes &AAInfo,

                                     bool &MustAliasAll);

  /// Merge all alias sets into a single set that is considered to alias any

  /// pointer.

  AliasSet &mergeAllAliasSets();

  AliasSet *findAliasSetForUnknownInst(Instruction *Inst);

};

inline raw_ostream& operator<<(raw_ostream &OS, const AliasSetTracker &AST) {

  AST.print(OS);

  return OS;

}

class AliasSetsPrinterPass : public PassInfoMixin<AliasSetsPrinterPass> {

  raw_ostream &OS;

public:

  explicit AliasSetsPrinterPass(raw_ostream &OS);

  PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);

};

} // end namespace llvm

#endif // LLVM_ANALYSIS_ALIASSETTRACKER_H