1 //===- BasicAliasAnalysis.h - Stateless, local Alias Analysis ---*- C++ -*-===// 2 // 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 6 // 7 //===----------------------------------------------------------------------===// 8 /// \file 9 /// This is the interface for LLVM's primary stateless and local alias analysis. 10 /// 11 //===----------------------------------------------------------------------===// 12 13 #ifndef LLVM_ANALYSIS_BASICALIASANALYSIS_H 14 #define LLVM_ANALYSIS_BASICALIASANALYSIS_H 15 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" 26 #include <algorithm> 27 #include <cstdint> 28 #include <memory> 29 #include <utility> 30 31 namespace llvm { 32 33 struct AAMDNodes; 34 class APInt; 35 class AssumptionCache; 36 class BasicBlock; 37 class DataLayout; 38 class DominatorTree; 39 class Function; 40 class GEPOperator; 41 class LoopInfo; 42 class PHINode; 43 class SelectInst; 44 class TargetLibraryInfo; 45 class PhiValues; 46 class Value; 47 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>; 56 57 const DataLayout &DL; 58 const Function &F; 59 const TargetLibraryInfo &TLI; 60 AssumptionCache &AC; 61 DominatorTree *DT; 62 LoopInfo *LI; 63 PhiValues *PV; 64 65 public: 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) 71 {} 72 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) {} 79 80 /// Handle invalidation events in the new pass manager. 81 bool invalidate(Function &Fn, const PreservedAnalyses &PA, 82 FunctionAnalysisManager::Invalidator &Inv); 83 84 AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB, 85 AAQueryInfo &AAQI); 86 87 ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc, 88 AAQueryInfo &AAQI); 89 90 ModRefInfo getModRefInfo(const CallBase *Call1, const CallBase *Call2, 91 AAQueryInfo &AAQI); 92 93 /// Chases pointers until we find a (constant global) or not. 94 bool pointsToConstantMemory(const MemoryLocation &Loc, AAQueryInfo &AAQI, 95 bool OrLocal); 96 97 /// Get the location associated with a pointer argument of a callsite. 98 ModRefInfo getArgModRefInfo(const CallBase *Call, unsigned ArgIdx); 99 100 /// Returns the behavior when calling the given call site. 101 FunctionModRefBehavior getModRefBehavior(const CallBase *Call); 102 103 /// Returns the behavior when calling the given function. For use when the 104 /// call site is not known. 105 FunctionModRefBehavior getModRefBehavior(const Function *Fn); 106 107 private: 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. 112 const Value *V; 113 114 // 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 116 // expression; 117 // e.g.: if V == -1, then sext(x) != zext(x). 118 unsigned ZExtBits; 119 unsigned SExtBits; 120 121 APInt Scale; 122 123 bool operator==(const VariableGEPIndex &Other) const { 124 return V == Other.V && ZExtBits == Other.ZExtBits && 125 SExtBits == Other.SExtBits && Scale == Other.Scale; 126 } 127 128 bool operator!=(const VariableGEPIndex &Other) const { 129 return !operator==(Other); 130 } 131 }; 132 133 // 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 137 const Value *Base; 138 // Total constant offset w.r.t the base from indexing into structs 139 APInt StructOffset; 140 // Total constant offset w.r.t the base from indexing through 141 // pointers/arrays/vectors 142 APInt OtherOffset; 143 // Scaled variable (non-constant) indices. 144 SmallVector<VariableGEPIndex, 4> VarIndices; 145 }; 146 147 /// Tracks phi nodes we have visited. 148 /// 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. 153 /// 154 /// The following example shows the problem: 155 /// %p = phi(%alloca1, %addr2) 156 /// %l = load %ptr 157 /// %addr1 = gep, %alloca2, 0, %l 158 /// %addr2 = gep %alloca2, 0, (%l + 1) 159 /// alias(%p, %addr1) -> MayAlias ! 160 /// store %l, ... 161 SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs; 162 163 /// Tracks instructions visited by pointsToConstantMemory. 164 SmallPtrSet<const Value *, 16> Visited; 165 166 static const Value * 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); 171 172 static bool DecomposeGEPExpression(const Value *V, DecomposedGEP &Decomposed, 173 const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT); 174 175 static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp, 176 const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject, 177 LocationSize ObjectAccessSize); 178 179 /// A Heuristic for aliasGEP that searches for a constant offset 180 /// between the variables. 181 /// 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. 187 bool 188 constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices, 189 LocationSize V1Size, LocationSize V2Size, 190 APInt BaseOffset, AssumptionCache *AC, 191 DominatorTree *DT); 192 193 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2); 194 195 void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest, 196 const SmallVectorImpl<VariableGEPIndex> &Src); 197 198 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, 202 AAQueryInfo &AAQI); 203 204 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); 208 209 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); 213 214 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); 219 }; 220 221 /// Analysis pass providing a never-invalidated alias analysis result. 222 class BasicAA : public AnalysisInfoMixin<BasicAA> { 223 friend AnalysisInfoMixin<BasicAA>; 224 225 static AnalysisKey Key; 226 227 public: 228 using Result = BasicAAResult; 229 230 BasicAAResult run(Function &F, FunctionAnalysisManager &AM); 231 }; 232 233 /// Legacy wrapper pass to provide the BasicAAResult object. 234 class BasicAAWrapperPass : public FunctionPass { 235 std::unique_ptr<BasicAAResult> Result; 236 237 virtual void anchor(); 238 239 public: 240 static char ID; 241 242 BasicAAWrapperPass(); 243 244 BasicAAResult &getResult() { return *Result; } 245 const BasicAAResult &getResult() const { return *Result; } 246 247 bool runOnFunction(Function &F) override; 248 void getAnalysisUsage(AnalysisUsage &AU) const override; 249 }; 250 251 FunctionPass *createBasicAAWrapperPass(); 252 253 /// 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); 257 258 /// 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 { 262 Pass &P; 263 Optional<BasicAAResult> BAR; 264 Optional<AAResults> AAR; 265 266 public: 267 LegacyAARGetter(Pass &P) : P(P) {} 268 AAResults &operator()(Function &F) { 269 BAR.emplace(createLegacyPMBasicAAResult(P, F)); 270 AAR.emplace(createLegacyPMAAResults(P, F, *BAR)); 271 return *AAR; 272 } 273 }; 274 275 } // end namespace llvm 276 277 #endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H 278