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 "llvm/Support/Compiler.h" 21 #include <memory> 22 #include <utility> 23 24 namespace llvm { 25 26 class AssumptionCache; 27 class DataLayout; 28 class DominatorTree; 29 class Function; 30 class GEPOperator; 31 class PHINode; 32 class SelectInst; 33 class TargetLibraryInfo; 34 class Value; 35 36 /// This is the AA result object for the basic, local, and stateless alias 37 /// analysis. It implements the AA query interface in an entirely stateless 38 /// manner. As one consequence, it is never invalidated due to IR changes. 39 /// While it does retain some storage, that is used as an optimization and not 40 /// to preserve information from query to query. However it does retain handles 41 /// to various other analyses and must be recomputed when those analyses are. 42 class BasicAAResult : public AAResultBase { 43 const DataLayout &DL; 44 const Function &F; 45 const TargetLibraryInfo &TLI; 46 AssumptionCache &AC; 47 /// Use getDT() instead of accessing this member directly, in order to 48 /// respect the AAQI.UseDominatorTree option. 49 DominatorTree *DT_; 50 51 DominatorTree *getDT(const AAQueryInfo &AAQI) const { 52 return AAQI.UseDominatorTree ? DT_ : nullptr; 53 } 54 55 public: 56 BasicAAResult(const DataLayout &DL, const Function &F, 57 const TargetLibraryInfo &TLI, AssumptionCache &AC, 58 DominatorTree *DT = nullptr) 59 : DL(DL), F(F), TLI(TLI), AC(AC), DT_(DT) {} 60 61 BasicAAResult(const BasicAAResult &Arg) 62 : AAResultBase(Arg), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), AC(Arg.AC), 63 DT_(Arg.DT_) {} 64 BasicAAResult(BasicAAResult &&Arg) 65 : AAResultBase(std::move(Arg)), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), 66 AC(Arg.AC), DT_(Arg.DT_) {} 67 68 /// Handle invalidation events in the new pass manager. 69 LLVM_ABI bool invalidate(Function &Fn, const PreservedAnalyses &PA, 70 FunctionAnalysisManager::Invalidator &Inv); 71 72 LLVM_ABI AliasResult alias(const MemoryLocation &LocA, 73 const MemoryLocation &LocB, AAQueryInfo &AAQI, 74 const Instruction *CtxI); 75 76 LLVM_ABI ModRefInfo getModRefInfo(const CallBase *Call, 77 const MemoryLocation &Loc, 78 AAQueryInfo &AAQI); 79 80 LLVM_ABI ModRefInfo getModRefInfo(const CallBase *Call1, 81 const CallBase *Call2, AAQueryInfo &AAQI); 82 83 /// Returns a bitmask that should be unconditionally applied to the ModRef 84 /// info of a memory location. This allows us to eliminate Mod and/or Ref 85 /// from the ModRef info based on the knowledge that the memory location 86 /// points to constant and/or locally-invariant memory. 87 /// 88 /// If IgnoreLocals is true, then this method returns NoModRef for memory 89 /// that points to a local alloca. 90 LLVM_ABI ModRefInfo getModRefInfoMask(const MemoryLocation &Loc, 91 AAQueryInfo &AAQI, 92 bool IgnoreLocals = false); 93 94 /// Get the location associated with a pointer argument of a callsite. 95 LLVM_ABI ModRefInfo getArgModRefInfo(const CallBase *Call, unsigned ArgIdx); 96 97 /// Returns the behavior when calling the given call site. 98 LLVM_ABI MemoryEffects getMemoryEffects(const CallBase *Call, 99 AAQueryInfo &AAQI); 100 101 /// Returns the behavior when calling the given function. For use when the 102 /// call site is not known. 103 LLVM_ABI MemoryEffects getMemoryEffects(const Function *Fn); 104 105 private: 106 struct DecomposedGEP; 107 108 /// Tracks instructions visited by pointsToConstantMemory. 109 SmallPtrSet<const Value *, 16> Visited; 110 111 static DecomposedGEP 112 DecomposeGEPExpression(const Value *V, const DataLayout &DL, 113 AssumptionCache *AC, DominatorTree *DT); 114 115 /// A Heuristic for aliasGEP that searches for a constant offset 116 /// between the variables. 117 /// 118 /// GetLinearExpression has some limitations, as generally zext(%x + 1) 119 /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression 120 /// will therefore conservatively refuse to decompose these expressions. 121 /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if 122 /// the addition overflows. 123 bool constantOffsetHeuristic(const DecomposedGEP &GEP, LocationSize V1Size, 124 LocationSize V2Size, AssumptionCache *AC, 125 DominatorTree *DT, const AAQueryInfo &AAQI); 126 127 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2, 128 const AAQueryInfo &AAQI); 129 130 void subtractDecomposedGEPs(DecomposedGEP &DestGEP, 131 const DecomposedGEP &SrcGEP, 132 const AAQueryInfo &AAQI); 133 134 AliasResult aliasGEP(const GEPOperator *V1, LocationSize V1Size, 135 const Value *V2, LocationSize V2Size, 136 const Value *UnderlyingV1, const Value *UnderlyingV2, 137 AAQueryInfo &AAQI); 138 139 AliasResult aliasPHI(const PHINode *PN, LocationSize PNSize, 140 const Value *V2, LocationSize V2Size, AAQueryInfo &AAQI); 141 142 AliasResult aliasSelect(const SelectInst *SI, LocationSize SISize, 143 const Value *V2, LocationSize V2Size, 144 AAQueryInfo &AAQI); 145 146 AliasResult aliasCheck(const Value *V1, LocationSize V1Size, const Value *V2, 147 LocationSize V2Size, AAQueryInfo &AAQI, 148 const Instruction *CtxI); 149 150 AliasResult aliasCheckRecursive(const Value *V1, LocationSize V1Size, 151 const Value *V2, LocationSize V2Size, 152 AAQueryInfo &AAQI, const Value *O1, 153 const Value *O2); 154 }; 155 156 /// Analysis pass providing a never-invalidated alias analysis result. 157 class BasicAA : public AnalysisInfoMixin<BasicAA> { 158 friend AnalysisInfoMixin<BasicAA>; 159 160 LLVM_ABI static AnalysisKey Key; 161 162 public: 163 using Result = BasicAAResult; 164 165 LLVM_ABI BasicAAResult run(Function &F, FunctionAnalysisManager &AM); 166 }; 167 168 /// Legacy wrapper pass to provide the BasicAAResult object. 169 class LLVM_ABI BasicAAWrapperPass : public FunctionPass { 170 std::unique_ptr<BasicAAResult> Result; 171 172 virtual void anchor(); 173 174 public: 175 static char ID; 176 177 BasicAAWrapperPass(); 178 179 BasicAAResult &getResult() { return *Result; } 180 const BasicAAResult &getResult() const { return *Result; } 181 182 bool runOnFunction(Function &F) override; 183 void getAnalysisUsage(AnalysisUsage &AU) const override; 184 }; 185 186 LLVM_ABI FunctionPass *createBasicAAWrapperPass(); 187 188 } // end namespace llvm 189 190 #endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H 191