1 //===- BasicAliasAnalysis.h - Stateless, local Alias Analysis ---*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 /// This is the interface for LLVM's primary stateless and local alias analysis.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_ANALYSIS_BASICALIASANALYSIS_H
15 #define LLVM_ANALYSIS_BASICALIASANALYSIS_H
17 #include "llvm/ADT/DenseMap.h"
18 #include "llvm/ADT/Optional.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/ADT/SmallVector.h"
21 #include "llvm/Analysis/AliasAnalysis.h"
22 #include "llvm/Analysis/AssumptionCache.h"
23 #include "llvm/Analysis/MemoryLocation.h"
24 #include "llvm/IR/CallSite.h"
25 #include "llvm/IR/PassManager.h"
26 #include "llvm/Pass.h"
36 class AssumptionCache;
45 class TargetLibraryInfo;
48 /// This is the AA result object for the basic, local, and stateless alias
49 /// analysis. It implements the AA query interface in an entirely stateless
50 /// manner. As one consequence, it is never invalidated due to IR changes.
51 /// While it does retain some storage, that is used as an optimization and not
52 /// to preserve information from query to query. However it does retain handles
53 /// to various other analyses and must be recomputed when those analyses are.
54 class BasicAAResult : public AAResultBase<BasicAAResult> {
55 friend AAResultBase<BasicAAResult>;
58 const TargetLibraryInfo &TLI;
64 BasicAAResult(const DataLayout &DL, const TargetLibraryInfo &TLI,
65 AssumptionCache &AC, DominatorTree *DT = nullptr,
66 LoopInfo *LI = nullptr)
67 : AAResultBase(), DL(DL), TLI(TLI), AC(AC), DT(DT), LI(LI) {}
69 BasicAAResult(const BasicAAResult &Arg)
70 : AAResultBase(Arg), DL(Arg.DL), TLI(Arg.TLI), AC(Arg.AC), DT(Arg.DT),
72 BasicAAResult(BasicAAResult &&Arg)
73 : AAResultBase(std::move(Arg)), DL(Arg.DL), TLI(Arg.TLI), AC(Arg.AC),
74 DT(Arg.DT), LI(Arg.LI) {}
76 /// Handle invalidation events in the new pass manager.
77 bool invalidate(Function &F, const PreservedAnalyses &PA,
78 FunctionAnalysisManager::Invalidator &Inv);
80 AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB);
82 ModRefInfo getModRefInfo(ImmutableCallSite CS, const MemoryLocation &Loc);
84 ModRefInfo getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2);
86 /// Chases pointers until we find a (constant global) or not.
87 bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal);
89 /// Get the location associated with a pointer argument of a callsite.
90 ModRefInfo getArgModRefInfo(ImmutableCallSite CS, unsigned ArgIdx);
92 /// Returns the behavior when calling the given call site.
93 FunctionModRefBehavior getModRefBehavior(ImmutableCallSite CS);
95 /// Returns the behavior when calling the given function. For use when the
96 /// call site is not known.
97 FunctionModRefBehavior getModRefBehavior(const Function *F);
100 // A linear transformation of a Value; this class represents ZExt(SExt(V,
101 // SExtBits), ZExtBits) * Scale + Offset.
102 struct VariableGEPIndex {
103 // An opaque Value - we can't decompose this further.
106 // We need to track what extensions we've done as we consider the same Value
107 // with different extensions as different variables in a GEP's linear
109 // e.g.: if V == -1, then sext(x) != zext(x).
115 bool operator==(const VariableGEPIndex &Other) const {
116 return V == Other.V && ZExtBits == Other.ZExtBits &&
117 SExtBits == Other.SExtBits && Scale == Other.Scale;
120 bool operator!=(const VariableGEPIndex &Other) const {
121 return !operator==(Other);
125 // Represents the internal structure of a GEP, decomposed into a base pointer,
126 // constant offsets, and variable scaled indices.
127 struct DecomposedGEP {
128 // Base pointer of the GEP
130 // Total constant offset w.r.t the base from indexing into structs
131 int64_t StructOffset;
132 // Total constant offset w.r.t the base from indexing through
133 // pointers/arrays/vectors
135 // Scaled variable (non-constant) indices.
136 SmallVector<VariableGEPIndex, 4> VarIndices;
139 /// Track alias queries to guard against recursion.
140 using LocPair = std::pair<MemoryLocation, MemoryLocation>;
141 using AliasCacheTy = SmallDenseMap<LocPair, AliasResult, 8>;
142 AliasCacheTy AliasCache;
144 /// Tracks phi nodes we have visited.
146 /// When interpret "Value" pointer equality as value equality we need to make
147 /// sure that the "Value" is not part of a cycle. Otherwise, two uses could
148 /// come from different "iterations" of a cycle and see different values for
149 /// the same "Value" pointer.
151 /// The following example shows the problem:
152 /// %p = phi(%alloca1, %addr2)
154 /// %addr1 = gep, %alloca2, 0, %l
155 /// %addr2 = gep %alloca2, 0, (%l + 1)
156 /// alias(%p, %addr1) -> MayAlias !
158 SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs;
160 /// Tracks instructions visited by pointsToConstantMemory.
161 SmallPtrSet<const Value *, 16> Visited;
164 GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset,
165 unsigned &ZExtBits, unsigned &SExtBits,
166 const DataLayout &DL, unsigned Depth, AssumptionCache *AC,
167 DominatorTree *DT, bool &NSW, bool &NUW);
169 static bool DecomposeGEPExpression(const Value *V, DecomposedGEP &Decomposed,
170 const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT);
172 static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp,
173 const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject,
174 uint64_t ObjectAccessSize);
176 /// \brief A Heuristic for aliasGEP that searches for a constant offset
177 /// between the variables.
179 /// GetLinearExpression has some limitations, as generally zext(%x + 1)
180 /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression
181 /// will therefore conservatively refuse to decompose these expressions.
182 /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if
183 /// the addition overflows.
185 constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices,
186 uint64_t V1Size, uint64_t V2Size, int64_t BaseOffset,
187 AssumptionCache *AC, DominatorTree *DT);
189 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
191 void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
192 const SmallVectorImpl<VariableGEPIndex> &Src);
194 AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
195 const AAMDNodes &V1AAInfo, const Value *V2,
196 uint64_t V2Size, const AAMDNodes &V2AAInfo,
197 const Value *UnderlyingV1, const Value *UnderlyingV2);
199 AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
200 const AAMDNodes &PNAAInfo, const Value *V2,
201 uint64_t V2Size, const AAMDNodes &V2AAInfo,
202 const Value *UnderV2);
204 AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
205 const AAMDNodes &SIAAInfo, const Value *V2,
206 uint64_t V2Size, const AAMDNodes &V2AAInfo,
207 const Value *UnderV2);
209 AliasResult aliasCheck(const Value *V1, uint64_t V1Size, AAMDNodes V1AATag,
210 const Value *V2, uint64_t V2Size, AAMDNodes V2AATag,
211 const Value *O1 = nullptr, const Value *O2 = nullptr);
214 /// Analysis pass providing a never-invalidated alias analysis result.
215 class BasicAA : public AnalysisInfoMixin<BasicAA> {
216 friend AnalysisInfoMixin<BasicAA>;
218 static AnalysisKey Key;
221 using Result = BasicAAResult;
223 BasicAAResult run(Function &F, FunctionAnalysisManager &AM);
226 /// Legacy wrapper pass to provide the BasicAAResult object.
227 class BasicAAWrapperPass : public FunctionPass {
228 std::unique_ptr<BasicAAResult> Result;
230 virtual void anchor();
235 BasicAAWrapperPass();
237 BasicAAResult &getResult() { return *Result; }
238 const BasicAAResult &getResult() const { return *Result; }
240 bool runOnFunction(Function &F) override;
241 void getAnalysisUsage(AnalysisUsage &AU) const override;
244 FunctionPass *createBasicAAWrapperPass();
246 /// A helper for the legacy pass manager to create a \c BasicAAResult object
247 /// populated to the best of our ability for a particular function when inside
248 /// of a \c ModulePass or a \c CallGraphSCCPass.
249 BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F);
251 /// This class is a functor to be used in legacy module or SCC passes for
252 /// computing AA results for a function. We store the results in fields so that
253 /// they live long enough to be queried, but we re-use them each time.
254 class LegacyAARGetter {
256 Optional<BasicAAResult> BAR;
257 Optional<AAResults> AAR;
260 LegacyAARGetter(Pass &P) : P(P) {}
261 AAResults &operator()(Function &F) {
262 BAR.emplace(createLegacyPMBasicAAResult(P, F));
263 AAR.emplace(createLegacyPMAAResults(P, F, *BAR));
268 } // end namespace llvm
270 #endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H