1 //===- BasicAliasAnalysis.h - Stateless, local Alias Analysis ---*- C++ -*-===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 /// This is the interface for LLVM's primary stateless and local alias analysis.
11 //===----------------------------------------------------------------------===//
13 #ifndef LLVM_ANALYSIS_BASICALIASANALYSIS_H
14 #define LLVM_ANALYSIS_BASICALIASANALYSIS_H
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/ADT/Optional.h"
18 #include "llvm/ADT/SmallPtrSet.h"
19 #include "llvm/ADT/SmallVector.h"
20 #include "llvm/Analysis/AliasAnalysis.h"
21 #include "llvm/Analysis/AssumptionCache.h"
22 #include "llvm/Analysis/MemoryLocation.h"
23 #include "llvm/IR/InstrTypes.h"
24 #include "llvm/IR/PassManager.h"
25 #include "llvm/Pass.h"
35 class AssumptionCache;
44 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>;
59 const TargetLibraryInfo &TLI;
66 BasicAAResult(const DataLayout &DL, const Function &F,
67 const TargetLibraryInfo &TLI, AssumptionCache &AC,
68 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr,
69 PhiValues *PV = nullptr)
70 : AAResultBase(), DL(DL), F(F), TLI(TLI), AC(AC), DT(DT), LI(LI), PV(PV)
73 BasicAAResult(const BasicAAResult &Arg)
74 : AAResultBase(Arg), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), AC(Arg.AC),
75 DT(Arg.DT), LI(Arg.LI), PV(Arg.PV) {}
76 BasicAAResult(BasicAAResult &&Arg)
77 : AAResultBase(std::move(Arg)), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI),
78 AC(Arg.AC), DT(Arg.DT), LI(Arg.LI), PV(Arg.PV) {}
80 /// Handle invalidation events in the new pass manager.
81 bool invalidate(Function &Fn, const PreservedAnalyses &PA,
82 FunctionAnalysisManager::Invalidator &Inv);
84 AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB,
87 ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc,
90 ModRefInfo getModRefInfo(const CallBase *Call1, const CallBase *Call2,
93 /// Chases pointers until we find a (constant global) or not.
94 bool pointsToConstantMemory(const MemoryLocation &Loc, AAQueryInfo &AAQI,
97 /// Get the location associated with a pointer argument of a callsite.
98 ModRefInfo getArgModRefInfo(const CallBase *Call, unsigned ArgIdx);
100 /// Returns the behavior when calling the given call site.
101 FunctionModRefBehavior getModRefBehavior(const CallBase *Call);
103 /// Returns the behavior when calling the given function. For use when the
104 /// call site is not known.
105 FunctionModRefBehavior getModRefBehavior(const Function *Fn);
108 // A linear transformation of a Value; this class represents ZExt(SExt(V,
109 // SExtBits), ZExtBits) * Scale + Offset.
110 struct VariableGEPIndex {
111 // An opaque Value - we can't decompose this further.
114 // We need to track what extensions we've done as we consider the same Value
115 // with different extensions as different variables in a GEP's linear
117 // e.g.: if V == -1, then sext(x) != zext(x).
123 bool operator==(const VariableGEPIndex &Other) const {
124 return V == Other.V && ZExtBits == Other.ZExtBits &&
125 SExtBits == Other.SExtBits && Scale == Other.Scale;
128 bool operator!=(const VariableGEPIndex &Other) const {
129 return !operator==(Other);
133 // Represents the internal structure of a GEP, decomposed into a base pointer,
134 // constant offsets, and variable scaled indices.
135 struct DecomposedGEP {
136 // Base pointer of the GEP
138 // Total constant offset w.r.t the base from indexing into structs
140 // Total constant offset w.r.t the base from indexing through
141 // pointers/arrays/vectors
143 // Scaled variable (non-constant) indices.
144 SmallVector<VariableGEPIndex, 4> VarIndices;
147 /// Tracks phi nodes we have visited.
149 /// When interpret "Value" pointer equality as value equality we need to make
150 /// sure that the "Value" is not part of a cycle. Otherwise, two uses could
151 /// come from different "iterations" of a cycle and see different values for
152 /// the same "Value" pointer.
154 /// The following example shows the problem:
155 /// %p = phi(%alloca1, %addr2)
157 /// %addr1 = gep, %alloca2, 0, %l
158 /// %addr2 = gep %alloca2, 0, (%l + 1)
159 /// alias(%p, %addr1) -> MayAlias !
161 SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs;
163 /// Tracks instructions visited by pointsToConstantMemory.
164 SmallPtrSet<const Value *, 16> Visited;
167 GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset,
168 unsigned &ZExtBits, unsigned &SExtBits,
169 const DataLayout &DL, unsigned Depth, AssumptionCache *AC,
170 DominatorTree *DT, bool &NSW, bool &NUW);
172 static bool DecomposeGEPExpression(const Value *V, DecomposedGEP &Decomposed,
173 const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT);
175 static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp,
176 const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject,
177 LocationSize ObjectAccessSize);
179 /// A Heuristic for aliasGEP that searches for a constant offset
180 /// between the variables.
182 /// GetLinearExpression has some limitations, as generally zext(%x + 1)
183 /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression
184 /// will therefore conservatively refuse to decompose these expressions.
185 /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if
186 /// the addition overflows.
188 constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices,
189 LocationSize V1Size, LocationSize V2Size,
190 APInt BaseOffset, AssumptionCache *AC,
193 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
195 void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
196 const SmallVectorImpl<VariableGEPIndex> &Src);
198 AliasResult aliasGEP(const GEPOperator *V1, LocationSize V1Size,
199 const AAMDNodes &V1AAInfo, const Value *V2,
200 LocationSize V2Size, const AAMDNodes &V2AAInfo,
201 const Value *UnderlyingV1, const Value *UnderlyingV2,
204 AliasResult aliasPHI(const PHINode *PN, LocationSize PNSize,
205 const AAMDNodes &PNAAInfo, const Value *V2,
206 LocationSize V2Size, const AAMDNodes &V2AAInfo,
207 const Value *UnderV2, AAQueryInfo &AAQI);
209 AliasResult aliasSelect(const SelectInst *SI, LocationSize SISize,
210 const AAMDNodes &SIAAInfo, const Value *V2,
211 LocationSize V2Size, const AAMDNodes &V2AAInfo,
212 const Value *UnderV2, AAQueryInfo &AAQI);
214 AliasResult aliasCheck(const Value *V1, LocationSize V1Size,
215 AAMDNodes V1AATag, const Value *V2,
216 LocationSize V2Size, AAMDNodes V2AATag,
217 AAQueryInfo &AAQI, const Value *O1 = nullptr,
218 const Value *O2 = nullptr);
221 /// Analysis pass providing a never-invalidated alias analysis result.
222 class BasicAA : public AnalysisInfoMixin<BasicAA> {
223 friend AnalysisInfoMixin<BasicAA>;
225 static AnalysisKey Key;
228 using Result = BasicAAResult;
230 BasicAAResult run(Function &F, FunctionAnalysisManager &AM);
233 /// Legacy wrapper pass to provide the BasicAAResult object.
234 class BasicAAWrapperPass : public FunctionPass {
235 std::unique_ptr<BasicAAResult> Result;
237 virtual void anchor();
242 BasicAAWrapperPass();
244 BasicAAResult &getResult() { return *Result; }
245 const BasicAAResult &getResult() const { return *Result; }
247 bool runOnFunction(Function &F) override;
248 void getAnalysisUsage(AnalysisUsage &AU) const override;
251 FunctionPass *createBasicAAWrapperPass();
253 /// A helper for the legacy pass manager to create a \c BasicAAResult object
254 /// populated to the best of our ability for a particular function when inside
255 /// of a \c ModulePass or a \c CallGraphSCCPass.
256 BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F);
258 /// This class is a functor to be used in legacy module or SCC passes for
259 /// computing AA results for a function. We store the results in fields so that
260 /// they live long enough to be queried, but we re-use them each time.
261 class LegacyAARGetter {
263 Optional<BasicAAResult> BAR;
264 Optional<AAResults> AAR;
267 LegacyAARGetter(Pass &P) : P(P) {}
268 AAResults &operator()(Function &F) {
269 BAR.emplace(createLegacyPMBasicAAResult(P, F));
270 AAR.emplace(createLegacyPMAAResults(P, F, *BAR));
275 } // end namespace llvm
277 #endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H