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/IR/PassManager.h" 22 #include "llvm/Pass.h" 23 #include <algorithm> 24 #include <cstdint> 25 #include <memory> 26 #include <utility> 27 28 namespace llvm { 29 30 struct AAMDNodes; 31 class APInt; 32 class AssumptionCache; 33 class BasicBlock; 34 class DataLayout; 35 class DominatorTree; 36 class Function; 37 class GEPOperator; 38 class LoopInfo; 39 class PHINode; 40 class SelectInst; 41 class TargetLibraryInfo; 42 class PhiValues; 43 class Value; 44 45 /// This is the AA result object for the basic, local, and stateless alias 46 /// analysis. It implements the AA query interface in an entirely stateless 47 /// manner. As one consequence, it is never invalidated due to IR changes. 48 /// While it does retain some storage, that is used as an optimization and not 49 /// to preserve information from query to query. However it does retain handles 50 /// to various other analyses and must be recomputed when those analyses are. 51 class BasicAAResult : public AAResultBase<BasicAAResult> { 52 friend AAResultBase<BasicAAResult>; 53 54 const DataLayout &DL; 55 const Function &F; 56 const TargetLibraryInfo &TLI; 57 AssumptionCache &AC; 58 DominatorTree *DT; 59 LoopInfo *LI; 60 PhiValues *PV; 61 62 public: 63 BasicAAResult(const DataLayout &DL, const Function &F, 64 const TargetLibraryInfo &TLI, AssumptionCache &AC, 65 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr, 66 PhiValues *PV = nullptr) 67 : AAResultBase(), DL(DL), F(F), TLI(TLI), AC(AC), DT(DT), LI(LI), PV(PV) 68 {} 69 70 BasicAAResult(const BasicAAResult &Arg) 71 : AAResultBase(Arg), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), AC(Arg.AC), 72 DT(Arg.DT), LI(Arg.LI), PV(Arg.PV) {} 73 BasicAAResult(BasicAAResult &&Arg) 74 : AAResultBase(std::move(Arg)), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), 75 AC(Arg.AC), DT(Arg.DT), LI(Arg.LI), PV(Arg.PV) {} 76 77 /// Handle invalidation events in the new pass manager. 78 bool invalidate(Function &Fn, const PreservedAnalyses &PA, 79 FunctionAnalysisManager::Invalidator &Inv); 80 81 AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB, 82 AAQueryInfo &AAQI); 83 84 ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc, 85 AAQueryInfo &AAQI); 86 87 ModRefInfo getModRefInfo(const CallBase *Call1, const CallBase *Call2, 88 AAQueryInfo &AAQI); 89 90 /// Chases pointers until we find a (constant global) or not. 91 bool pointsToConstantMemory(const MemoryLocation &Loc, AAQueryInfo &AAQI, 92 bool OrLocal); 93 94 /// Get the location associated with a pointer argument of a callsite. 95 ModRefInfo getArgModRefInfo(const CallBase *Call, unsigned ArgIdx); 96 97 /// Returns the behavior when calling the given call site. 98 FunctionModRefBehavior getModRefBehavior(const CallBase *Call); 99 100 /// Returns the behavior when calling the given function. For use when the 101 /// call site is not known. 102 FunctionModRefBehavior getModRefBehavior(const Function *Fn); 103 104 private: 105 // A linear transformation of a Value; this class represents ZExt(SExt(V, 106 // SExtBits), ZExtBits) * Scale + Offset. 107 struct VariableGEPIndex { 108 // An opaque Value - we can't decompose this further. 109 const Value *V; 110 111 // We need to track what extensions we've done as we consider the same Value 112 // with different extensions as different variables in a GEP's linear 113 // expression; 114 // e.g.: if V == -1, then sext(x) != zext(x). 115 unsigned ZExtBits; 116 unsigned SExtBits; 117 118 APInt Scale; 119 120 // Context instruction to use when querying information about this index. 121 const Instruction *CxtI; 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 void dump() const { 133 print(dbgs()); 134 dbgs() << "\n"; 135 } 136 void print(raw_ostream &OS) const { 137 OS << "(V=" << V->getName() 138 << ", zextbits=" << ZExtBits 139 << ", sextbits=" << SExtBits 140 << ", scale=" << Scale << ")"; 141 } 142 }; 143 144 // Represents the internal structure of a GEP, decomposed into a base pointer, 145 // constant offsets, and variable scaled indices. 146 struct DecomposedGEP { 147 // Base pointer of the GEP 148 const Value *Base; 149 // Total constant offset from base. 150 APInt Offset; 151 // Scaled variable (non-constant) indices. 152 SmallVector<VariableGEPIndex, 4> VarIndices; 153 // Is GEP index scale compile-time constant. 154 bool HasCompileTimeConstantScale; 155 156 void dump() const { 157 print(dbgs()); 158 dbgs() << "\n"; 159 } 160 void print(raw_ostream &OS) const { 161 OS << "(DecomposedGEP Base=" << Base->getName() 162 << ", Offset=" << Offset 163 << ", VarIndices=["; 164 for (size_t i = 0; i < VarIndices.size(); i++) { 165 if (i != 0) 166 OS << ", "; 167 VarIndices[i].print(OS); 168 } 169 OS << "], HasCompileTimeConstantScale=" << HasCompileTimeConstantScale 170 << ")"; 171 } 172 }; 173 174 /// Tracks phi nodes we have visited. 175 /// 176 /// When interpret "Value" pointer equality as value equality we need to make 177 /// sure that the "Value" is not part of a cycle. Otherwise, two uses could 178 /// come from different "iterations" of a cycle and see different values for 179 /// the same "Value" pointer. 180 /// 181 /// The following example shows the problem: 182 /// %p = phi(%alloca1, %addr2) 183 /// %l = load %ptr 184 /// %addr1 = gep, %alloca2, 0, %l 185 /// %addr2 = gep %alloca2, 0, (%l + 1) 186 /// alias(%p, %addr1) -> MayAlias ! 187 /// store %l, ... 188 SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs; 189 190 /// Tracks instructions visited by pointsToConstantMemory. 191 SmallPtrSet<const Value *, 16> Visited; 192 193 static const Value * 194 GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset, 195 unsigned &ZExtBits, unsigned &SExtBits, 196 const DataLayout &DL, unsigned Depth, AssumptionCache *AC, 197 DominatorTree *DT, bool &NSW, bool &NUW); 198 199 static DecomposedGEP 200 DecomposeGEPExpression(const Value *V, const DataLayout &DL, 201 AssumptionCache *AC, DominatorTree *DT); 202 203 static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp, 204 const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject, 205 LocationSize ObjectAccessSize); 206 207 /// A Heuristic for aliasGEP that searches for a constant offset 208 /// between the variables. 209 /// 210 /// GetLinearExpression has some limitations, as generally zext(%x + 1) 211 /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression 212 /// will therefore conservatively refuse to decompose these expressions. 213 /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if 214 /// the addition overflows. 215 bool 216 constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices, 217 LocationSize V1Size, LocationSize V2Size, 218 const APInt &BaseOffset, AssumptionCache *AC, 219 DominatorTree *DT); 220 221 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2); 222 223 void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest, 224 const SmallVectorImpl<VariableGEPIndex> &Src); 225 226 AliasResult aliasGEP(const GEPOperator *V1, LocationSize V1Size, 227 const AAMDNodes &V1AAInfo, const Value *V2, 228 LocationSize V2Size, const AAMDNodes &V2AAInfo, 229 const Value *UnderlyingV1, const Value *UnderlyingV2, 230 AAQueryInfo &AAQI); 231 232 AliasResult aliasPHI(const PHINode *PN, LocationSize PNSize, 233 const AAMDNodes &PNAAInfo, const Value *V2, 234 LocationSize V2Size, const AAMDNodes &V2AAInfo, 235 AAQueryInfo &AAQI); 236 237 AliasResult aliasSelect(const SelectInst *SI, LocationSize SISize, 238 const AAMDNodes &SIAAInfo, const Value *V2, 239 LocationSize V2Size, const AAMDNodes &V2AAInfo, 240 AAQueryInfo &AAQI); 241 242 AliasResult aliasCheck(const Value *V1, LocationSize V1Size, 243 const AAMDNodes &V1AATag, const Value *V2, 244 LocationSize V2Size, const AAMDNodes &V2AATag, 245 AAQueryInfo &AAQI); 246 247 AliasResult aliasCheckRecursive(const Value *V1, LocationSize V1Size, 248 const AAMDNodes &V1AATag, const Value *V2, 249 LocationSize V2Size, const AAMDNodes &V2AATag, 250 AAQueryInfo &AAQI, const Value *O1, 251 const Value *O2); 252 }; 253 254 /// Analysis pass providing a never-invalidated alias analysis result. 255 class BasicAA : public AnalysisInfoMixin<BasicAA> { 256 friend AnalysisInfoMixin<BasicAA>; 257 258 static AnalysisKey Key; 259 260 public: 261 using Result = BasicAAResult; 262 263 BasicAAResult run(Function &F, FunctionAnalysisManager &AM); 264 }; 265 266 /// Legacy wrapper pass to provide the BasicAAResult object. 267 class BasicAAWrapperPass : public FunctionPass { 268 std::unique_ptr<BasicAAResult> Result; 269 270 virtual void anchor(); 271 272 public: 273 static char ID; 274 275 BasicAAWrapperPass(); 276 277 BasicAAResult &getResult() { return *Result; } 278 const BasicAAResult &getResult() const { return *Result; } 279 280 bool runOnFunction(Function &F) override; 281 void getAnalysisUsage(AnalysisUsage &AU) const override; 282 }; 283 284 FunctionPass *createBasicAAWrapperPass(); 285 286 /// A helper for the legacy pass manager to create a \c BasicAAResult object 287 /// populated to the best of our ability for a particular function when inside 288 /// of a \c ModulePass or a \c CallGraphSCCPass. 289 BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F); 290 291 /// This class is a functor to be used in legacy module or SCC passes for 292 /// computing AA results for a function. We store the results in fields so that 293 /// they live long enough to be queried, but we re-use them each time. 294 class LegacyAARGetter { 295 Pass &P; 296 Optional<BasicAAResult> BAR; 297 Optional<AAResults> AAR; 298 299 public: 300 LegacyAARGetter(Pass &P) : P(P) {} 301 AAResults &operator()(Function &F) { 302 BAR.emplace(createLegacyPMBasicAAResult(P, F)); 303 AAR.emplace(createLegacyPMAAResults(P, F, *BAR)); 304 return *AAR; 305 } 306 }; 307 308 } // end namespace llvm 309 310 #endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H 311