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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/Instruction.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 LoadInst;
enum class ModRefInfo : uint8_t;
class raw_ostream;
class StoreInst;
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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