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/SmallPtrSet.h" 17 #include "llvm/Analysis/AliasAnalysis.h" 18 #include "llvm/IR/PassManager.h" 19 #include "llvm/Pass.h" 20 #include <memory> 21 #include <utility> 22 23 namespace llvm { 24 25 class AssumptionCache; 26 class DataLayout; 27 class DominatorTree; 28 class Function; 29 class GEPOperator; 30 class PHINode; 31 class SelectInst; 32 class TargetLibraryInfo; 33 class Value; 34 35 /// This is the AA result object for the basic, local, and stateless alias 36 /// analysis. It implements the AA query interface in an entirely stateless 37 /// manner. As one consequence, it is never invalidated due to IR changes. 38 /// While it does retain some storage, that is used as an optimization and not 39 /// to preserve information from query to query. However it does retain handles 40 /// to various other analyses and must be recomputed when those analyses are. 41 class BasicAAResult : public AAResultBase { 42 const DataLayout &DL; 43 const Function &F; 44 const TargetLibraryInfo &TLI; 45 AssumptionCache &AC; 46 /// Use getDT() instead of accessing this member directly, in order to 47 /// respect the AAQI.UseDominatorTree option. 48 DominatorTree *DT_; 49 50 DominatorTree *getDT(const AAQueryInfo &AAQI) const { 51 return AAQI.UseDominatorTree ? DT_ : nullptr; 52 } 53 54 public: 55 BasicAAResult(const DataLayout &DL, const Function &F, 56 const TargetLibraryInfo &TLI, AssumptionCache &AC, 57 DominatorTree *DT = nullptr) 58 : DL(DL), F(F), TLI(TLI), AC(AC), DT_(DT) {} 59 60 BasicAAResult(const BasicAAResult &Arg) 61 : AAResultBase(Arg), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), AC(Arg.AC), 62 DT_(Arg.DT_) {} 63 BasicAAResult(BasicAAResult &&Arg) 64 : AAResultBase(std::move(Arg)), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), 65 AC(Arg.AC), DT_(Arg.DT_) {} 66 67 /// Handle invalidation events in the new pass manager. 68 bool invalidate(Function &Fn, const PreservedAnalyses &PA, 69 FunctionAnalysisManager::Invalidator &Inv); 70 71 AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB, 72 AAQueryInfo &AAQI, const Instruction *CtxI); 73 74 ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc, 75 AAQueryInfo &AAQI); 76 77 ModRefInfo getModRefInfo(const CallBase *Call1, const CallBase *Call2, 78 AAQueryInfo &AAQI); 79 80 /// Returns a bitmask that should be unconditionally applied to the ModRef 81 /// info of a memory location. This allows us to eliminate Mod and/or Ref 82 /// from the ModRef info based on the knowledge that the memory location 83 /// points to constant and/or locally-invariant memory. 84 /// 85 /// If IgnoreLocals is true, then this method returns NoModRef for memory 86 /// that points to a local alloca. 87 ModRefInfo getModRefInfoMask(const MemoryLocation &Loc, AAQueryInfo &AAQI, 88 bool IgnoreLocals = false); 89 90 /// Get the location associated with a pointer argument of a callsite. 91 ModRefInfo getArgModRefInfo(const CallBase *Call, unsigned ArgIdx); 92 93 /// Returns the behavior when calling the given call site. 94 MemoryEffects getMemoryEffects(const CallBase *Call, AAQueryInfo &AAQI); 95 96 /// Returns the behavior when calling the given function. For use when the 97 /// call site is not known. 98 MemoryEffects getMemoryEffects(const Function *Fn); 99 100 private: 101 struct DecomposedGEP; 102 103 /// Tracks instructions visited by pointsToConstantMemory. 104 SmallPtrSet<const Value *, 16> Visited; 105 106 static DecomposedGEP 107 DecomposeGEPExpression(const Value *V, const DataLayout &DL, 108 AssumptionCache *AC, DominatorTree *DT); 109 110 /// A Heuristic for aliasGEP that searches for a constant offset 111 /// between the variables. 112 /// 113 /// GetLinearExpression has some limitations, as generally zext(%x + 1) 114 /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression 115 /// will therefore conservatively refuse to decompose these expressions. 116 /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if 117 /// the addition overflows. 118 bool constantOffsetHeuristic(const DecomposedGEP &GEP, LocationSize V1Size, 119 LocationSize V2Size, AssumptionCache *AC, 120 DominatorTree *DT, const AAQueryInfo &AAQI); 121 122 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2, 123 const AAQueryInfo &AAQI); 124 125 void subtractDecomposedGEPs(DecomposedGEP &DestGEP, 126 const DecomposedGEP &SrcGEP, 127 const AAQueryInfo &AAQI); 128 129 AliasResult aliasGEP(const GEPOperator *V1, LocationSize V1Size, 130 const Value *V2, LocationSize V2Size, 131 const Value *UnderlyingV1, const Value *UnderlyingV2, 132 AAQueryInfo &AAQI); 133 134 AliasResult aliasPHI(const PHINode *PN, LocationSize PNSize, 135 const Value *V2, LocationSize V2Size, AAQueryInfo &AAQI); 136 137 AliasResult aliasSelect(const SelectInst *SI, LocationSize SISize, 138 const Value *V2, LocationSize V2Size, 139 AAQueryInfo &AAQI); 140 141 AliasResult aliasCheck(const Value *V1, LocationSize V1Size, const Value *V2, 142 LocationSize V2Size, AAQueryInfo &AAQI, 143 const Instruction *CtxI); 144 145 AliasResult aliasCheckRecursive(const Value *V1, LocationSize V1Size, 146 const Value *V2, LocationSize V2Size, 147 AAQueryInfo &AAQI, const Value *O1, 148 const Value *O2); 149 }; 150 151 /// Analysis pass providing a never-invalidated alias analysis result. 152 class BasicAA : public AnalysisInfoMixin<BasicAA> { 153 friend AnalysisInfoMixin<BasicAA>; 154 155 static AnalysisKey Key; 156 157 public: 158 using Result = BasicAAResult; 159 160 BasicAAResult run(Function &F, FunctionAnalysisManager &AM); 161 }; 162 163 /// Legacy wrapper pass to provide the BasicAAResult object. 164 class BasicAAWrapperPass : public FunctionPass { 165 std::unique_ptr<BasicAAResult> Result; 166 167 virtual void anchor(); 168 169 public: 170 static char ID; 171 172 BasicAAWrapperPass(); 173 174 BasicAAResult &getResult() { return *Result; } 175 const BasicAAResult &getResult() const { return *Result; } 176 177 bool runOnFunction(Function &F) override; 178 void getAnalysisUsage(AnalysisUsage &AU) const override; 179 }; 180 181 FunctionPass *createBasicAAWrapperPass(); 182 183 } // end namespace llvm 184 185 #endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H 186