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//===- BasicAliasAnalysis.h - Stateless, local Alias Analysis ---*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
/// \file
/// This is the interface for LLVM's primary stateless and local alias analysis.
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Pass.h"
#include <algorithm>
#include <cstdint>
#include <memory>
#include <utility>
namespace llvm {
struct AAMDNodes;
class APInt;
class AssumptionCache;
class BasicBlock;
class DataLayout;
class DominatorTree;
class Function;
class GEPOperator;
class LoopInfo;
class PHINode;
class SelectInst;
class TargetLibraryInfo;
class PhiValues;
class Value;
/// This is the AA result object for the basic, local, and stateless alias
/// analysis. It implements the AA query interface in an entirely stateless
/// manner. As one consequence, it is never invalidated due to IR changes.
/// While it does retain some storage, that is used as an optimization and not
/// to preserve information from query to query. However it does retain handles
/// to various other analyses and must be recomputed when those analyses are.
class BasicAAResult : public AAResultBase<BasicAAResult> {
friend AAResultBase<BasicAAResult>;
const DataLayout &DL;
const Function &F;
const TargetLibraryInfo &TLI;
AssumptionCache &AC;
DominatorTree *DT;
LoopInfo *LI;
PhiValues *PV;
BasicAAResult(const DataLayout &DL, const Function &F,
const TargetLibraryInfo &TLI, AssumptionCache &AC,
DominatorTree *DT = nullptr, LoopInfo *LI = nullptr,
PhiValues *PV = nullptr)
: AAResultBase(), DL(DL), F(F), TLI(TLI), AC(AC), DT(DT), LI(LI), PV(PV)
BasicAAResult(const BasicAAResult &Arg)
: AAResultBase(Arg), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), AC(Arg.AC),
DT(Arg.DT), LI(Arg.LI), PV(Arg.PV) {}
BasicAAResult(BasicAAResult &&Arg)
: AAResultBase(std::move(Arg)), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI),
AC(Arg.AC), DT(Arg.DT), LI(Arg.LI), PV(Arg.PV) {}
/// Handle invalidation events in the new pass manager.
bool invalidate(Function &Fn, const PreservedAnalyses &PA,
FunctionAnalysisManager::Invalidator &Inv);
AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB);
ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc);
ModRefInfo getModRefInfo(const CallBase *Call1, const CallBase *Call2);
/// Chases pointers until we find a (constant global) or not.
bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal);
/// Get the location associated with a pointer argument of a callsite.
ModRefInfo getArgModRefInfo(const CallBase *Call, unsigned ArgIdx);
/// Returns the behavior when calling the given call site.
FunctionModRefBehavior getModRefBehavior(const CallBase *Call);
/// Returns the behavior when calling the given function. For use when the
/// call site is not known.
FunctionModRefBehavior getModRefBehavior(const Function *Fn);
// A linear transformation of a Value; this class represents ZExt(SExt(V,
// SExtBits), ZExtBits) * Scale + Offset.
struct VariableGEPIndex {
// An opaque Value - we can't decompose this further.
const Value *V;
// We need to track what extensions we've done as we consider the same Value
// with different extensions as different variables in a GEP's linear
// expression;
// e.g.: if V == -1, then sext(x) != zext(x).
unsigned ZExtBits;
unsigned SExtBits;
APInt Scale;
bool operator==(const VariableGEPIndex &Other) const {
return V == Other.V && ZExtBits == Other.ZExtBits &&
SExtBits == Other.SExtBits && Scale == Other.Scale;
bool operator!=(const VariableGEPIndex &Other) const {
return !operator==(Other);
// Represents the internal structure of a GEP, decomposed into a base pointer,
// constant offsets, and variable scaled indices.
struct DecomposedGEP {
// Base pointer of the GEP
const Value *Base;
// Total constant offset w.r.t the base from indexing into structs
APInt StructOffset;
// Total constant offset w.r.t the base from indexing through
// pointers/arrays/vectors
APInt OtherOffset;
// Scaled variable (non-constant) indices.
SmallVector<VariableGEPIndex, 4> VarIndices;
/// Track alias queries to guard against recursion.
using LocPair = std::pair<MemoryLocation, MemoryLocation>;
using AliasCacheTy = SmallDenseMap<LocPair, AliasResult, 8>;
AliasCacheTy AliasCache;
using IsCapturedCacheTy = SmallDenseMap<const Value *, bool, 8>;
IsCapturedCacheTy IsCapturedCache;
/// Tracks phi nodes we have visited.
/// When interpret "Value" pointer equality as value equality we need to make
/// sure that the "Value" is not part of a cycle. Otherwise, two uses could
/// come from different "iterations" of a cycle and see different values for
/// the same "Value" pointer.
/// The following example shows the problem:
/// %p = phi(%alloca1, %addr2)
/// %l = load %ptr
/// %addr1 = gep, %alloca2, 0, %l
/// %addr2 = gep %alloca2, 0, (%l + 1)
/// alias(%p, %addr1) -> MayAlias !
/// store %l, ...
SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs;
/// Tracks instructions visited by pointsToConstantMemory.
SmallPtrSet<const Value *, 16> Visited;
static const Value *
GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset,
unsigned &ZExtBits, unsigned &SExtBits,
const DataLayout &DL, unsigned Depth, AssumptionCache *AC,
DominatorTree *DT, bool &NSW, bool &NUW);
static bool DecomposeGEPExpression(const Value *V, DecomposedGEP &Decomposed,
const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT);
static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp,
const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject,
LocationSize ObjectAccessSize);
/// A Heuristic for aliasGEP that searches for a constant offset
/// between the variables.
/// GetLinearExpression has some limitations, as generally zext(%x + 1)
/// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression
/// will therefore conservatively refuse to decompose these expressions.
/// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if
/// the addition overflows.
constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices,
LocationSize V1Size, LocationSize V2Size,
APInt BaseOffset, AssumptionCache *AC,
DominatorTree *DT);
bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
const SmallVectorImpl<VariableGEPIndex> &Src);
AliasResult aliasGEP(const GEPOperator *V1, LocationSize V1Size,
const AAMDNodes &V1AAInfo, const Value *V2,
LocationSize V2Size, const AAMDNodes &V2AAInfo,
const Value *UnderlyingV1, const Value *UnderlyingV2);
AliasResult aliasPHI(const PHINode *PN, LocationSize PNSize,
const AAMDNodes &PNAAInfo, const Value *V2,
LocationSize V2Size, const AAMDNodes &V2AAInfo,
const Value *UnderV2);
AliasResult aliasSelect(const SelectInst *SI, LocationSize SISize,
const AAMDNodes &SIAAInfo, const Value *V2,
LocationSize V2Size, const AAMDNodes &V2AAInfo,
const Value *UnderV2);
AliasResult aliasCheck(const Value *V1, LocationSize V1Size,
AAMDNodes V1AATag, const Value *V2,
LocationSize V2Size, AAMDNodes V2AATag,
const Value *O1 = nullptr, const Value *O2 = nullptr);
/// Analysis pass providing a never-invalidated alias analysis result.
class BasicAA : public AnalysisInfoMixin<BasicAA> {
friend AnalysisInfoMixin<BasicAA>;
static AnalysisKey Key;
using Result = BasicAAResult;
BasicAAResult run(Function &F, FunctionAnalysisManager &AM);
/// Legacy wrapper pass to provide the BasicAAResult object.
class BasicAAWrapperPass : public FunctionPass {
std::unique_ptr<BasicAAResult> Result;
virtual void anchor();
static char ID;
BasicAAResult &getResult() { return *Result; }
const BasicAAResult &getResult() const { return *Result; }
bool runOnFunction(Function &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override;
FunctionPass *createBasicAAWrapperPass();
/// A helper for the legacy pass manager to create a \c BasicAAResult object
/// populated to the best of our ability for a particular function when inside
/// of a \c ModulePass or a \c CallGraphSCCPass.
BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F);
/// This class is a functor to be used in legacy module or SCC passes for
/// computing AA results for a function. We store the results in fields so that
/// they live long enough to be queried, but we re-use them each time.
class LegacyAARGetter {
Pass &P;
Optional<BasicAAResult> BAR;
Optional<AAResults> AAR;
LegacyAARGetter(Pass &P) : P(P) {}
AAResults &operator()(Function &F) {
BAR.emplace(createLegacyPMBasicAAResult(P, F));
AAR.emplace(createLegacyPMAAResults(P, F, *BAR));
return *AAR;
} // end namespace llvm