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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 memory locations 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/SmallVector.h"
 #include "llvm/ADT/ilist.h"
 #include "llvm/ADT/ilist_node.h"
 #include "llvm/Analysis/MemoryLocation.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/ValueHandle.h"
 #include <cassert>
 #include <vector>
 
 namespace llvm {
 
 class AliasResult;
 class AliasSetTracker;
 class AnyMemSetInst;
 class AnyMemTransferInst;
 class BasicBlock;
 class BatchAAResults;
 class Function;
 class Instruction;
 class StoreInst;
 class LoadInst;
 enum class ModRefInfo : uint8_t;
 class raw_ostream;
 class VAArgInst;
 class Value;
 
 class AliasSet : public ilist_node<AliasSet> {
   friend class AliasSetTracker;
 
   // Forwarding pointer.
   AliasSet *Forward = nullptr;
 
   /// Memory locations in this alias set.
   SmallVector<MemoryLocation, 0> MemoryLocs;
 
   /// 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;
 
   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 memory locations which are
   // part of this alias set.
   using iterator = SmallVectorImpl<MemoryLocation>::const_iterator;
   iterator begin() const { return MemoryLocs.begin(); }
   iterator end() const { return MemoryLocs.end(); }
 
   unsigned size() const { return MemoryLocs.size(); }
 
   /// Retrieve the pointer values for the memory locations in this alias set.
   /// The order matches that of the memory locations, but duplicate pointer
   /// values are omitted.
   using PointerVector = SmallVector<const Value *, 8>;
   PointerVector getPointers() const;
 
   void print(raw_ostream &OS) const;
   void dump() const;
 
 private:
   // Can only be created by AliasSetTracker.
   AliasSet()
       : RefCount(0), AliasAny(false), Access(NoAccess), Alias(SetMustAlias) {}
 
   void removeFromTracker(AliasSetTracker &AST);
 
   void addMemoryLocation(AliasSetTracker &AST, const MemoryLocation &MemLoc,
                          bool KnownMustAlias = false);
   void addUnknownInst(Instruction *I, BatchAAResults &AA);
 
 public:
   /// If the specified memory location "may" (or must) alias one of the members
   /// in the set return the appropriate AliasResult. Otherwise return NoAlias.
   AliasResult aliasesMemoryLocation(const MemoryLocation &MemLoc,
                                     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<const Value>, AliasSet *>;
 
   // Map from pointer values to the alias set holding one or more memory
   // locations with that pointer value.
   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.
   ///
   void add(const MemoryLocation &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 memory locations contained in all alias sets.
   unsigned TotalAliasSetSize = 0;
 
   // A non-null value signifies this AST is saturated. A saturated AST lumps
   // all elements into a single "May" set.
   AliasSet *AliasAnyAS = nullptr;
 
   void removeAliasSet(AliasSet *AS);
 
   // Update an alias set field to point to its real destination. If the field is
   // pointing to a set that has been merged with another set and is forwarding,
   // the field is updated to point to the set obtained by following the
   // forwarding links. The Forward fields of intermediate alias sets are
   // collapsed as well, and alias set reference counts are updated to reflect
   // the new situation.
   void collapseForwardingIn(AliasSet *&AS) {
     if (AS->Forward) {
       collapseForwardingIn(AS->Forward);
       // Swap out AS for AS->Forward, while updating reference counts.
       AliasSet *NewAS = AS->Forward;
       NewAS->addRef();
       AS->dropRef(*this);
       AS = NewAS;
     }
   }
 
   AliasSet &addMemoryLocation(MemoryLocation Loc, AliasSet::AccessLattice E);
   AliasSet *mergeAliasSetsForMemoryLocation(const MemoryLocation &MemLoc,
                                             AliasSet *PtrAS,
                                             bool &MustAliasAll);
 
   /// Merge all alias sets into a single set that is considered to alias
   /// any memory location or instruction.
   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);
   static bool isRequired() { return true; }
 };
 
 } // end namespace llvm
 
 #endif // LLVM_ANALYSIS_ALIASSETTRACKER_H

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