1 //===- BasicAliasAnalysis.h - Stateless, local Alias Analysis ---*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 /// \file 10 /// This is the interface for LLVM's primary stateless and local alias analysis. 11 /// 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_ANALYSIS_BASICALIASANALYSIS_H 15 #define LLVM_ANALYSIS_BASICALIASANALYSIS_H 16 17 #include "llvm/ADT/SmallPtrSet.h" 18 #include "llvm/Analysis/AliasAnalysis.h" 19 #include "llvm/Analysis/AssumptionCache.h" 20 #include "llvm/Analysis/TargetLibraryInfo.h" 21 #include "llvm/IR/Function.h" 22 #include "llvm/IR/GetElementPtrTypeIterator.h" 23 #include "llvm/IR/Instruction.h" 24 #include "llvm/IR/LLVMContext.h" 25 #include "llvm/IR/Module.h" 26 #include "llvm/IR/PassManager.h" 27 #include "llvm/Support/ErrorHandling.h" 28 29 namespace llvm { 30 class AssumptionCache; 31 class DominatorTree; 32 class LoopInfo; 33 34 /// This is the AA result object for the basic, local, and stateless alias 35 /// analysis. It implements the AA query interface in an entirely stateless 36 /// manner. As one consequence, it is never invalidated. While it does retain 37 /// some storage, that is used as an optimization and not to preserve 38 /// information from query to query. 39 class BasicAAResult : public AAResultBase<BasicAAResult> { 40 friend AAResultBase<BasicAAResult>; 41 42 const DataLayout &DL; 43 const TargetLibraryInfo &TLI; 44 AssumptionCache &AC; 45 DominatorTree *DT; 46 LoopInfo *LI; 47 48 public: 49 BasicAAResult(const DataLayout &DL, const TargetLibraryInfo &TLI, 50 AssumptionCache &AC, DominatorTree *DT = nullptr, 51 LoopInfo *LI = nullptr) AAResultBase()52 : AAResultBase(), DL(DL), TLI(TLI), AC(AC), DT(DT), LI(LI) {} 53 BasicAAResult(const BasicAAResult & Arg)54 BasicAAResult(const BasicAAResult &Arg) 55 : AAResultBase(Arg), DL(Arg.DL), TLI(Arg.TLI), AC(Arg.AC), DT(Arg.DT), 56 LI(Arg.LI) {} BasicAAResult(BasicAAResult && Arg)57 BasicAAResult(BasicAAResult &&Arg) 58 : AAResultBase(std::move(Arg)), DL(Arg.DL), TLI(Arg.TLI), AC(Arg.AC), 59 DT(Arg.DT), LI(Arg.LI) {} 60 61 /// Handle invalidation events from the new pass manager. 62 /// 63 /// By definition, this result is stateless and so remains valid. invalidate(Function &,const PreservedAnalyses &)64 bool invalidate(Function &, const PreservedAnalyses &) { return false; } 65 66 AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB); 67 68 ModRefInfo getModRefInfo(ImmutableCallSite CS, const MemoryLocation &Loc); 69 70 ModRefInfo getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2); 71 72 /// Chases pointers until we find a (constant global) or not. 73 bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal); 74 75 /// Get the location associated with a pointer argument of a callsite. 76 ModRefInfo getArgModRefInfo(ImmutableCallSite CS, unsigned ArgIdx); 77 78 /// Returns the behavior when calling the given call site. 79 FunctionModRefBehavior getModRefBehavior(ImmutableCallSite CS); 80 81 /// Returns the behavior when calling the given function. For use when the 82 /// call site is not known. 83 FunctionModRefBehavior getModRefBehavior(const Function *F); 84 85 private: 86 // A linear transformation of a Value; this class represents ZExt(SExt(V, 87 // SExtBits), ZExtBits) * Scale + Offset. 88 struct VariableGEPIndex { 89 90 // An opaque Value - we can't decompose this further. 91 const Value *V; 92 93 // We need to track what extensions we've done as we consider the same Value 94 // with different extensions as different variables in a GEP's linear 95 // expression; 96 // e.g.: if V == -1, then sext(x) != zext(x). 97 unsigned ZExtBits; 98 unsigned SExtBits; 99 100 int64_t Scale; 101 102 bool operator==(const VariableGEPIndex &Other) const { 103 return V == Other.V && ZExtBits == Other.ZExtBits && 104 SExtBits == Other.SExtBits && Scale == Other.Scale; 105 } 106 107 bool operator!=(const VariableGEPIndex &Other) const { 108 return !operator==(Other); 109 } 110 }; 111 112 // Represents the internal structure of a GEP, decomposed into a base pointer, 113 // constant offsets, and variable scaled indices. 114 struct DecomposedGEP { 115 // Base pointer of the GEP 116 const Value *Base; 117 // Total constant offset w.r.t the base from indexing into structs 118 int64_t StructOffset; 119 // Total constant offset w.r.t the base from indexing through 120 // pointers/arrays/vectors 121 int64_t OtherOffset; 122 // Scaled variable (non-constant) indices. 123 SmallVector<VariableGEPIndex, 4> VarIndices; 124 }; 125 126 /// Track alias queries to guard against recursion. 127 typedef std::pair<MemoryLocation, MemoryLocation> LocPair; 128 typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy; 129 AliasCacheTy AliasCache; 130 131 /// Tracks phi nodes we have visited. 132 /// 133 /// When interpret "Value" pointer equality as value equality we need to make 134 /// sure that the "Value" is not part of a cycle. Otherwise, two uses could 135 /// come from different "iterations" of a cycle and see different values for 136 /// the same "Value" pointer. 137 /// 138 /// The following example shows the problem: 139 /// %p = phi(%alloca1, %addr2) 140 /// %l = load %ptr 141 /// %addr1 = gep, %alloca2, 0, %l 142 /// %addr2 = gep %alloca2, 0, (%l + 1) 143 /// alias(%p, %addr1) -> MayAlias ! 144 /// store %l, ... 145 SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs; 146 147 /// Tracks instructions visited by pointsToConstantMemory. 148 SmallPtrSet<const Value *, 16> Visited; 149 150 static const Value * 151 GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset, 152 unsigned &ZExtBits, unsigned &SExtBits, 153 const DataLayout &DL, unsigned Depth, AssumptionCache *AC, 154 DominatorTree *DT, bool &NSW, bool &NUW); 155 156 static bool DecomposeGEPExpression(const Value *V, DecomposedGEP &Decomposed, 157 const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT); 158 159 static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp, 160 const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject, 161 uint64_t ObjectAccessSize); 162 163 /// \brief A Heuristic for aliasGEP that searches for a constant offset 164 /// between the variables. 165 /// 166 /// GetLinearExpression has some limitations, as generally zext(%x + 1) 167 /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression 168 /// will therefore conservatively refuse to decompose these expressions. 169 /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if 170 /// the addition overflows. 171 bool 172 constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices, 173 uint64_t V1Size, uint64_t V2Size, int64_t BaseOffset, 174 AssumptionCache *AC, DominatorTree *DT); 175 176 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2); 177 178 void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest, 179 const SmallVectorImpl<VariableGEPIndex> &Src); 180 181 AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size, 182 const AAMDNodes &V1AAInfo, const Value *V2, 183 uint64_t V2Size, const AAMDNodes &V2AAInfo, 184 const Value *UnderlyingV1, const Value *UnderlyingV2); 185 186 AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize, 187 const AAMDNodes &PNAAInfo, const Value *V2, 188 uint64_t V2Size, const AAMDNodes &V2AAInfo); 189 190 AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize, 191 const AAMDNodes &SIAAInfo, const Value *V2, 192 uint64_t V2Size, const AAMDNodes &V2AAInfo); 193 194 AliasResult aliasCheck(const Value *V1, uint64_t V1Size, AAMDNodes V1AATag, 195 const Value *V2, uint64_t V2Size, AAMDNodes V2AATag); 196 }; 197 198 /// Analysis pass providing a never-invalidated alias analysis result. 199 class BasicAA : public AnalysisInfoMixin<BasicAA> { 200 friend AnalysisInfoMixin<BasicAA>; 201 static char PassID; 202 203 public: 204 typedef BasicAAResult Result; 205 206 BasicAAResult run(Function &F, AnalysisManager<Function> &AM); 207 }; 208 209 /// Legacy wrapper pass to provide the BasicAAResult object. 210 class BasicAAWrapperPass : public FunctionPass { 211 std::unique_ptr<BasicAAResult> Result; 212 213 virtual void anchor(); 214 215 public: 216 static char ID; 217 218 BasicAAWrapperPass(); 219 getResult()220 BasicAAResult &getResult() { return *Result; } getResult()221 const BasicAAResult &getResult() const { return *Result; } 222 223 bool runOnFunction(Function &F) override; 224 void getAnalysisUsage(AnalysisUsage &AU) const override; 225 }; 226 227 FunctionPass *createBasicAAWrapperPass(); 228 229 /// A helper for the legacy pass manager to create a \c BasicAAResult object 230 /// populated to the best of our ability for a particular function when inside 231 /// of a \c ModulePass or a \c CallGraphSCCPass. 232 BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F); 233 } 234 235 #endif 236