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//===- llvm/Analysis/AliasSetTracker.h - Build Alias Sets -------*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This file defines two classes: AliasSetTracker and AliasSet. These interface
// 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.
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/ilist.h"
#include "llvm/ADT/ilist_node.h"
#include "llvm/IR/ValueHandle.h"
#include <vector>
namespace llvm {
class AliasAnalysis;
class LoadInst;
class StoreInst;
class VAArgInst;
class AliasSetTracker;
class AliasSet;
class AliasSet : public ilist_node<AliasSet> {
friend class AliasSetTracker;
class PointerRec {
Value *Val; // The pointer this record corresponds to.
PointerRec **PrevInList, *NextInList;
AliasSet *AS;
uint64_t Size;
const MDNode *TBAAInfo;
PointerRec(Value *V)
: Val(V), PrevInList(nullptr), NextInList(nullptr), AS(nullptr), Size(0),
TBAAInfo(DenseMapInfo<const MDNode *>::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;
void updateSizeAndTBAAInfo(uint64_t NewSize, const MDNode *NewTBAAInfo) {
if (NewSize > Size) Size = NewSize;
if (TBAAInfo == DenseMapInfo<const MDNode *>::getEmptyKey())
// We don't have a TBAAInfo yet. Set it to NewTBAAInfo.
TBAAInfo = NewTBAAInfo;
else if (TBAAInfo != NewTBAAInfo)
// NewTBAAInfo conflicts with TBAAInfo.
TBAAInfo = DenseMapInfo<const MDNode *>::getTombstoneKey();
uint64_t getSize() const { return Size; }
/// getTBAAInfo - Return the TBAAInfo, or null if there is no
/// information or conflicting information.
const MDNode *getTBAAInfo() const {
// If we have missing or conflicting TBAAInfo, return null.
if (TBAAInfo == DenseMapInfo<const MDNode *>::getEmptyKey() ||
TBAAInfo == DenseMapInfo<const MDNode *>::getTombstoneKey())
return nullptr;
return TBAAInfo;
AliasSet *getAliasSet(AliasSetTracker &AST) {
assert(AS && "No AliasSet yet!");
if (AS->Forward) {
AliasSet *OldAS = AS;
AS = OldAS->getForwardedTarget(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;
PointerRec *PtrList, **PtrListEnd; // Doubly linked list of nodes.
AliasSet *Forward; // Forwarding pointer.
// All instructions without a specific address in this alias set.
std::vector<AssertingVH<Instruction> > UnknownInsts;
// RefCount - Number of nodes pointing to this AliasSet plus the number of
// AliasSets forwarding to it.
unsigned RefCount : 28;
/// AccessType - Keep track of whether this alias set merely refers to the
/// locations of memory, whether it modifies the memory, or whether it does
/// both. The lattice goes from "NoModRef" to either Refs or Mods, then to
/// ModRef as necessary.
enum AccessType {
NoModRef = 0, Refs = 1, // Ref = bit 1
Mods = 2, ModRef = 3 // Mod = bit 2
unsigned AccessTy : 2;
/// AliasType - Keep track the relationships between the pointers in the set.
/// Lattice goes from MustAlias to MayAlias.
enum AliasType {
MustAlias = 0, MayAlias = 1
unsigned AliasTy : 1;
// Volatile - True if this alias set contains volatile loads or stores.
bool Volatile : 1;
void addRef() { ++RefCount; }
void dropRef(AliasSetTracker &AST) {
assert(RefCount >= 1 && "Invalid reference count detected!");
if (--RefCount == 0)
Instruction *getUnknownInst(unsigned i) const {
assert(i < UnknownInsts.size());
return UnknownInsts[i];
/// Accessors...
bool isRef() const { return AccessTy & Refs; }
bool isMod() const { return AccessTy & Mods; }
bool isMustAlias() const { return AliasTy == MustAlias; }
bool isMayAlias() const { return AliasTy == MayAlias; }
// isVolatile - Return true if this alias set contains volatile loads or
// stores.
bool isVolatile() const { return Volatile; }
/// isForwardingAliasSet - Return true if this alias set should be ignored as
/// part of the AliasSetTracker object.
bool isForwardingAliasSet() const { return Forward; }
/// mergeSetIn - Merge the specified alias set into this alias set...
void mergeSetIn(AliasSet &AS, AliasSetTracker &AST);
// Alias Set iteration - Allow access to all of the pointer 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; }
void print(raw_ostream &OS) const;
void dump() const;
/// Define an iterator for alias sets... this is just a forward iterator.
class iterator : public std::iterator<std::forward_iterator_tag,
PointerRec, ptrdiff_t> {
PointerRec *CurNode;
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); }
const iterator &operator=(const iterator &I) {
CurNode = I.CurNode;
return *this;
value_type &operator*() const {
assert(CurNode && "Dereferencing AliasSet.end()!");
return *CurNode;
value_type *operator->() const { return &operator*(); }
Value *getPointer() const { return CurNode->getValue(); }
uint64_t getSize() const { return CurNode->getSize(); }
const MDNode *getTBAAInfo() const { return CurNode->getTBAAInfo(); }
iterator& operator++() { // Preincrement
assert(CurNode && "Advancing past AliasSet.end()!");
CurNode = CurNode->getNext();
return *this;
iterator operator++(int) { // Postincrement
iterator tmp = *this; ++*this; return tmp;
// Can only be created by AliasSetTracker. Also, ilist creates one
// to serve as a sentinel.
friend struct ilist_sentinel_traits<AliasSet>;
: PtrList(nullptr), PtrListEnd(&PtrList), Forward(nullptr), RefCount(0),
AccessTy(NoModRef), AliasTy(MustAlias), Volatile(false) {
AliasSet(const AliasSet &AS) LLVM_DELETED_FUNCTION;
void operator=(const AliasSet &AS) LLVM_DELETED_FUNCTION;
PointerRec *getSomePointer() const {
return PtrList;
/// getForwardedTarget - 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) {
Forward = Dest;
return Dest;
void removeFromTracker(AliasSetTracker &AST);
void addPointer(AliasSetTracker &AST, PointerRec &Entry, uint64_t Size,
const MDNode *TBAAInfo,
bool KnownMustAlias = false);
void addUnknownInst(Instruction *I, AliasAnalysis &AA);
void removeUnknownInst(AliasSetTracker &AST, Instruction *I) {
bool WasEmpty = UnknownInsts.empty();
for (size_t i = 0, e = UnknownInsts.size(); i != e; ++i)
if (UnknownInsts[i] == I) {
UnknownInsts[i] = UnknownInsts.back();
--i; --e; // Revisit the moved entry.
if (!WasEmpty && UnknownInsts.empty())
void setVolatile() { Volatile = true; }
/// aliasesPointer - Return true if the specified pointer "may" (or must)
/// alias one of the members in the set.
bool aliasesPointer(const Value *Ptr, uint64_t Size, const MDNode *TBAAInfo,
AliasAnalysis &AA) const;
bool aliasesUnknownInst(Instruction *Inst, AliasAnalysis &AA) const;
inline raw_ostream& operator<<(raw_ostream &OS, const AliasSet &AS) {
return OS;
class AliasSetTracker {
/// CallbackVH - A CallbackVH to arrange for AliasSetTracker to be
/// notified whenever a Value is deleted.
class ASTCallbackVH : public CallbackVH {
AliasSetTracker *AST;
void deleted() override;
void allUsesReplacedWith(Value *) override;
ASTCallbackVH(Value *V, AliasSetTracker *AST = nullptr);
ASTCallbackVH &operator=(Value *V);
/// ASTCallbackVHDenseMapInfo - Traits to tell DenseMap that tell us how to
/// compare and hash the value handle.
struct ASTCallbackVHDenseMapInfo : public DenseMapInfo<Value *> {};
AliasAnalysis &AA;
ilist<AliasSet> AliasSets;
typedef DenseMap<ASTCallbackVH, AliasSet::PointerRec*,
// Map from pointers to their node
PointerMapType PointerMap;
/// AliasSetTracker ctor - Create an empty collection of AliasSets, and use
/// the specified alias analysis object to disambiguate load and store
/// addresses.
explicit AliasSetTracker(AliasAnalysis &aa) : AA(aa) {}
~AliasSetTracker() { clear(); }
/// add methods - 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).
bool add(Value *Ptr, uint64_t Size, const MDNode *TBAAInfo); // Add a location
bool add(LoadInst *LI);
bool add(StoreInst *SI);
bool add(VAArgInst *VAAI);
bool 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
bool addUnknown(Instruction *I);
/// remove methods - These methods are used to remove all entries that might
/// be aliased by the specified instruction. These methods return true if any
/// alias sets were eliminated.
// Remove a location
bool remove(Value *Ptr, uint64_t Size, const MDNode *TBAAInfo);
bool remove(LoadInst *LI);
bool remove(StoreInst *SI);
bool remove(VAArgInst *VAAI);
bool remove(Instruction *I);
void remove(AliasSet &AS);
bool removeUnknown(Instruction *I);
void clear();
/// getAliasSets - Return the alias sets that are active.
const ilist<AliasSet> &getAliasSets() const { return AliasSets; }
/// getAliasSetForPointer - Return the alias set that the specified pointer
/// lives in. If the New argument is non-null, this method sets the value to
/// true if a new alias set is created to contain the pointer (because the
/// pointer didn't alias anything).
AliasSet &getAliasSetForPointer(Value *P, uint64_t Size,
const MDNode *TBAAInfo,
bool *New = nullptr);
/// getAliasSetForPointerIfExists - Return the alias set containing the
/// location specified if one exists, otherwise return null.
AliasSet *getAliasSetForPointerIfExists(Value *P, uint64_t Size,
const MDNode *TBAAInfo) {
return findAliasSetForPointer(P, Size, TBAAInfo);
/// containsPointer - Return true if the specified location is represented by
/// this alias set, false otherwise. This does not modify the AST object or
/// alias sets.
bool containsPointer(Value *P, uint64_t Size, const MDNode *TBAAInfo) const;
/// getAliasAnalysis - Return the underlying alias analysis object used by
/// this tracker.
AliasAnalysis &getAliasAnalysis() const { return AA; }
/// deleteValue method - This method is used to remove a pointer value from
/// the AliasSetTracker entirely. It should be used when an instruction is
/// deleted from the program to update the AST. If you don't use this, you
/// would have dangling pointers to deleted instructions.
void deleteValue(Value *PtrVal);
/// copyValue - This method should be used whenever a preexisting value in the
/// program is copied or cloned, introducing a new value. Note that it is ok
/// for clients that use this method to introduce the same value multiple
/// times: if the tracker already knows about a value, it will ignore the
/// request.
void copyValue(Value *From, Value *To);
typedef ilist<AliasSet>::iterator iterator;
typedef ilist<AliasSet>::const_iterator 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;
friend class AliasSet;
void removeAliasSet(AliasSet *AS);
// getEntryFor - 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[ASTCallbackVH(V, this)];
if (!Entry)
Entry = new AliasSet::PointerRec(V);
return *Entry;
AliasSet &addPointer(Value *P, uint64_t Size, const MDNode *TBAAInfo,
AliasSet::AccessType E,
bool &NewSet) {
NewSet = false;
AliasSet &AS = getAliasSetForPointer(P, Size, TBAAInfo, &NewSet);
AS.AccessTy |= E;
return AS;
AliasSet *findAliasSetForPointer(const Value *Ptr, uint64_t Size,
const MDNode *TBAAInfo);
AliasSet *findAliasSetForUnknownInst(Instruction *Inst);
inline raw_ostream& operator<<(raw_ostream &OS, const AliasSetTracker &AST) {
return OS;
} // End llvm namespace