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 AssumptionCache &AC; 44 DominatorTree *DT; 45 LoopInfo *LI; 46 47 public: 48 BasicAAResult(const DataLayout &DL, const TargetLibraryInfo &TLI, 49 AssumptionCache &AC, DominatorTree *DT = nullptr, 50 LoopInfo *LI = nullptr) AAResultBase(TLI)51 : AAResultBase(TLI), DL(DL), AC(AC), DT(DT), LI(LI) {} 52 BasicAAResult(const BasicAAResult & Arg)53 BasicAAResult(const BasicAAResult &Arg) 54 : AAResultBase(Arg), DL(Arg.DL), AC(Arg.AC), DT(Arg.DT), LI(Arg.LI) {} BasicAAResult(BasicAAResult && Arg)55 BasicAAResult(BasicAAResult &&Arg) 56 : AAResultBase(std::move(Arg)), DL(Arg.DL), AC(Arg.AC), DT(Arg.DT), 57 LI(Arg.LI) {} 58 59 /// Handle invalidation events from the new pass manager. 60 /// 61 /// By definition, this result is stateless and so remains valid. invalidate(Function &,const PreservedAnalyses &)62 bool invalidate(Function &, const PreservedAnalyses &) { return false; } 63 64 AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB); 65 66 ModRefInfo getModRefInfo(ImmutableCallSite CS, const MemoryLocation &Loc); 67 68 ModRefInfo getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2); 69 70 /// Chases pointers until we find a (constant global) or not. 71 bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal); 72 73 /// Get the location associated with a pointer argument of a callsite. 74 ModRefInfo getArgModRefInfo(ImmutableCallSite CS, unsigned ArgIdx); 75 76 /// Returns the behavior when calling the given call site. 77 FunctionModRefBehavior getModRefBehavior(ImmutableCallSite CS); 78 79 /// Returns the behavior when calling the given function. For use when the 80 /// call site is not known. 81 FunctionModRefBehavior getModRefBehavior(const Function *F); 82 83 private: 84 // A linear transformation of a Value; this class represents ZExt(SExt(V, 85 // SExtBits), ZExtBits) * Scale + Offset. 86 struct VariableGEPIndex { 87 88 // An opaque Value - we can't decompose this further. 89 const Value *V; 90 91 // We need to track what extensions we've done as we consider the same Value 92 // with different extensions as different variables in a GEP's linear 93 // expression; 94 // e.g.: if V == -1, then sext(x) != zext(x). 95 unsigned ZExtBits; 96 unsigned SExtBits; 97 98 int64_t Scale; 99 100 bool operator==(const VariableGEPIndex &Other) const { 101 return V == Other.V && ZExtBits == Other.ZExtBits && 102 SExtBits == Other.SExtBits && Scale == Other.Scale; 103 } 104 105 bool operator!=(const VariableGEPIndex &Other) const { 106 return !operator==(Other); 107 } 108 }; 109 110 /// Track alias queries to guard against recursion. 111 typedef std::pair<MemoryLocation, MemoryLocation> LocPair; 112 typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy; 113 AliasCacheTy AliasCache; 114 115 /// Tracks phi nodes we have visited. 116 /// 117 /// When interpret "Value" pointer equality as value equality we need to make 118 /// sure that the "Value" is not part of a cycle. Otherwise, two uses could 119 /// come from different "iterations" of a cycle and see different values for 120 /// the same "Value" pointer. 121 /// 122 /// The following example shows the problem: 123 /// %p = phi(%alloca1, %addr2) 124 /// %l = load %ptr 125 /// %addr1 = gep, %alloca2, 0, %l 126 /// %addr2 = gep %alloca2, 0, (%l + 1) 127 /// alias(%p, %addr1) -> MayAlias ! 128 /// store %l, ... 129 SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs; 130 131 /// Tracks instructions visited by pointsToConstantMemory. 132 SmallPtrSet<const Value *, 16> Visited; 133 134 static const Value * 135 GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset, 136 unsigned &ZExtBits, unsigned &SExtBits, 137 const DataLayout &DL, unsigned Depth, AssumptionCache *AC, 138 DominatorTree *DT, bool &NSW, bool &NUW); 139 140 static const Value * 141 DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, 142 SmallVectorImpl<VariableGEPIndex> &VarIndices, 143 bool &MaxLookupReached, const DataLayout &DL, 144 AssumptionCache *AC, DominatorTree *DT); 145 /// \brief A Heuristic for aliasGEP that searches for a constant offset 146 /// between the variables. 147 /// 148 /// GetLinearExpression has some limitations, as generally zext(%x + 1) 149 /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression 150 /// will therefore conservatively refuse to decompose these expressions. 151 /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if 152 /// the addition overflows. 153 bool 154 constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices, 155 uint64_t V1Size, uint64_t V2Size, int64_t BaseOffset, 156 AssumptionCache *AC, DominatorTree *DT); 157 158 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2); 159 160 void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest, 161 const SmallVectorImpl<VariableGEPIndex> &Src); 162 163 AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size, 164 const AAMDNodes &V1AAInfo, const Value *V2, 165 uint64_t V2Size, const AAMDNodes &V2AAInfo, 166 const Value *UnderlyingV1, const Value *UnderlyingV2); 167 168 AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize, 169 const AAMDNodes &PNAAInfo, const Value *V2, 170 uint64_t V2Size, const AAMDNodes &V2AAInfo); 171 172 AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize, 173 const AAMDNodes &SIAAInfo, const Value *V2, 174 uint64_t V2Size, const AAMDNodes &V2AAInfo); 175 176 AliasResult aliasCheck(const Value *V1, uint64_t V1Size, AAMDNodes V1AATag, 177 const Value *V2, uint64_t V2Size, AAMDNodes V2AATag); 178 }; 179 180 /// Analysis pass providing a never-invalidated alias analysis result. 181 class BasicAA { 182 public: 183 typedef BasicAAResult Result; 184 185 /// \brief Opaque, unique identifier for this analysis pass. ID()186 static void *ID() { return (void *)&PassID; } 187 188 BasicAAResult run(Function &F, AnalysisManager<Function> *AM); 189 190 /// \brief Provide access to a name for this pass for debugging purposes. name()191 static StringRef name() { return "BasicAliasAnalysis"; } 192 193 private: 194 static char PassID; 195 }; 196 197 /// Legacy wrapper pass to provide the BasicAAResult object. 198 class BasicAAWrapperPass : public FunctionPass { 199 std::unique_ptr<BasicAAResult> Result; 200 201 virtual void anchor(); 202 203 public: 204 static char ID; 205 206 BasicAAWrapperPass(); 207 getResult()208 BasicAAResult &getResult() { return *Result; } getResult()209 const BasicAAResult &getResult() const { return *Result; } 210 211 bool runOnFunction(Function &F) override; 212 void getAnalysisUsage(AnalysisUsage &AU) const override; 213 }; 214 215 FunctionPass *createBasicAAWrapperPass(); 216 217 /// A helper for the legacy pass manager to create a \c BasicAAResult object 218 /// populated to the best of our ability for a particular function when inside 219 /// of a \c ModulePass or a \c CallGraphSCCPass. 220 BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F); 221 } 222 223 #endif 224