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;
145 // Is GEP index scale compile-time constant.
146 bool HasCompileTimeConstantScale;
149 /// Tracks phi nodes we have visited.
151 /// When interpret "Value" pointer equality as value equality we need to make
152 /// sure that the "Value" is not part of a cycle. Otherwise, two uses could
153 /// come from different "iterations" of a cycle and see different values for
154 /// the same "Value" pointer.
156 /// The following example shows the problem:
157 /// %p = phi(%alloca1, %addr2)
159 /// %addr1 = gep, %alloca2, 0, %l
160 /// %addr2 = gep %alloca2, 0, (%l + 1)
161 /// alias(%p, %addr1) -> MayAlias !
163 SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs;
165 /// Tracks instructions visited by pointsToConstantMemory.
166 SmallPtrSet<const Value *, 16> Visited;
169 GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset,
170 unsigned &ZExtBits, unsigned &SExtBits,
171 const DataLayout &DL, unsigned Depth, AssumptionCache *AC,
172 DominatorTree *DT, bool &NSW, bool &NUW);
174 static bool DecomposeGEPExpression(const Value *V, DecomposedGEP &Decomposed,
175 const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT);
177 static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp,
178 const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject,
179 LocationSize ObjectAccessSize);
181 /// A Heuristic for aliasGEP that searches for a constant offset
182 /// between the variables.
184 /// GetLinearExpression has some limitations, as generally zext(%x + 1)
185 /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression
186 /// will therefore conservatively refuse to decompose these expressions.
187 /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if
188 /// the addition overflows.
190 constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices,
191 LocationSize V1Size, LocationSize V2Size,
192 const APInt &BaseOffset, AssumptionCache *AC,
195 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
197 void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
198 const SmallVectorImpl<VariableGEPIndex> &Src);
200 AliasResult aliasGEP(const GEPOperator *V1, LocationSize V1Size,
201 const AAMDNodes &V1AAInfo, const Value *V2,
202 LocationSize V2Size, const AAMDNodes &V2AAInfo,
203 const Value *UnderlyingV1, const Value *UnderlyingV2,
206 AliasResult aliasPHI(const PHINode *PN, LocationSize PNSize,
207 const AAMDNodes &PNAAInfo, const Value *V2,
208 LocationSize V2Size, const AAMDNodes &V2AAInfo,
209 const Value *UnderV2, AAQueryInfo &AAQI);
211 AliasResult aliasSelect(const SelectInst *SI, LocationSize SISize,
212 const AAMDNodes &SIAAInfo, const Value *V2,
213 LocationSize V2Size, const AAMDNodes &V2AAInfo,
214 const Value *UnderV2, AAQueryInfo &AAQI);
216 AliasResult aliasCheck(const Value *V1, LocationSize V1Size,
217 AAMDNodes V1AATag, const Value *V2,
218 LocationSize V2Size, AAMDNodes V2AATag,
219 AAQueryInfo &AAQI, const Value *O1 = nullptr,
220 const Value *O2 = nullptr);
223 /// Analysis pass providing a never-invalidated alias analysis result.
224 class BasicAA : public AnalysisInfoMixin<BasicAA> {
225 friend AnalysisInfoMixin<BasicAA>;
227 static AnalysisKey Key;
230 using Result = BasicAAResult;
232 BasicAAResult run(Function &F, FunctionAnalysisManager &AM);
235 /// Legacy wrapper pass to provide the BasicAAResult object.
236 class BasicAAWrapperPass : public FunctionPass {
237 std::unique_ptr<BasicAAResult> Result;
239 virtual void anchor();
244 BasicAAWrapperPass();
246 BasicAAResult &getResult() { return *Result; }
247 const BasicAAResult &getResult() const { return *Result; }
249 bool runOnFunction(Function &F) override;
250 void getAnalysisUsage(AnalysisUsage &AU) const override;
253 FunctionPass *createBasicAAWrapperPass();
255 /// A helper for the legacy pass manager to create a \c BasicAAResult object
256 /// populated to the best of our ability for a particular function when inside
257 /// of a \c ModulePass or a \c CallGraphSCCPass.
258 BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F);
260 /// This class is a functor to be used in legacy module or SCC passes for
261 /// computing AA results for a function. We store the results in fields so that
262 /// they live long enough to be queried, but we re-use them each time.
263 class LegacyAARGetter {
265 Optional<BasicAAResult> BAR;
266 Optional<AAResults> AAR;
269 LegacyAARGetter(Pass &P) : P(P) {}
270 AAResults &operator()(Function &F) {
271 BAR.emplace(createLegacyPMBasicAAResult(P, F));
272 AAR.emplace(createLegacyPMAAResults(P, F, *BAR));
277 } // end namespace llvm
279 #endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H