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/Optional.h" 17 #include "llvm/ADT/SmallPtrSet.h" 18 #include "llvm/Analysis/AliasAnalysis.h" 19 #include "llvm/IR/PassManager.h" 20 #include "llvm/Pass.h" 21 #include <algorithm> 22 #include <cstdint> 23 #include <memory> 24 #include <utility> 25 26 namespace llvm { 27 28 class AssumptionCache; 29 class BasicBlock; 30 class DataLayout; 31 class DominatorTree; 32 class Function; 33 class GEPOperator; 34 class PHINode; 35 class SelectInst; 36 class TargetLibraryInfo; 37 class PhiValues; 38 class Value; 39 40 /// This is the AA result object for the basic, local, and stateless alias 41 /// analysis. It implements the AA query interface in an entirely stateless 42 /// manner. As one consequence, it is never invalidated due to IR changes. 43 /// While it does retain some storage, that is used as an optimization and not 44 /// to preserve information from query to query. However it does retain handles 45 /// to various other analyses and must be recomputed when those analyses are. 46 class BasicAAResult : public AAResultBase<BasicAAResult> { 47 friend AAResultBase<BasicAAResult>; 48 49 const DataLayout &DL; 50 const Function &F; 51 const TargetLibraryInfo &TLI; 52 AssumptionCache &AC; 53 DominatorTree *DT; 54 PhiValues *PV; 55 56 public: 57 BasicAAResult(const DataLayout &DL, const Function &F, 58 const TargetLibraryInfo &TLI, AssumptionCache &AC, 59 DominatorTree *DT = nullptr, PhiValues *PV = nullptr) 60 : DL(DL), F(F), TLI(TLI), AC(AC), DT(DT), PV(PV) {} 61 62 BasicAAResult(const BasicAAResult &Arg) 63 : AAResultBase(Arg), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), AC(Arg.AC), 64 DT(Arg.DT), PV(Arg.PV) {} 65 BasicAAResult(BasicAAResult &&Arg) 66 : AAResultBase(std::move(Arg)), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), 67 AC(Arg.AC), DT(Arg.DT), PV(Arg.PV) {} 68 69 /// Handle invalidation events in the new pass manager. 70 bool invalidate(Function &Fn, const PreservedAnalyses &PA, 71 FunctionAnalysisManager::Invalidator &Inv); 72 73 AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB, 74 AAQueryInfo &AAQI); 75 76 ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc, 77 AAQueryInfo &AAQI); 78 79 ModRefInfo getModRefInfo(const CallBase *Call1, const CallBase *Call2, 80 AAQueryInfo &AAQI); 81 82 /// Chases pointers until we find a (constant global) or not. 83 bool pointsToConstantMemory(const MemoryLocation &Loc, AAQueryInfo &AAQI, 84 bool OrLocal); 85 86 /// Get the location associated with a pointer argument of a callsite. 87 ModRefInfo getArgModRefInfo(const CallBase *Call, unsigned ArgIdx); 88 89 /// Returns the behavior when calling the given call site. 90 FunctionModRefBehavior getModRefBehavior(const CallBase *Call); 91 92 /// Returns the behavior when calling the given function. For use when the 93 /// call site is not known. 94 FunctionModRefBehavior getModRefBehavior(const Function *Fn); 95 96 private: 97 struct DecomposedGEP; 98 99 /// Tracks phi nodes we have visited. 100 /// 101 /// When interpret "Value" pointer equality as value equality we need to make 102 /// sure that the "Value" is not part of a cycle. Otherwise, two uses could 103 /// come from different "iterations" of a cycle and see different values for 104 /// the same "Value" pointer. 105 /// 106 /// The following example shows the problem: 107 /// %p = phi(%alloca1, %addr2) 108 /// %l = load %ptr 109 /// %addr1 = gep, %alloca2, 0, %l 110 /// %addr2 = gep %alloca2, 0, (%l + 1) 111 /// alias(%p, %addr1) -> MayAlias ! 112 /// store %l, ... 113 SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs; 114 115 /// Tracks instructions visited by pointsToConstantMemory. 116 SmallPtrSet<const Value *, 16> Visited; 117 118 static DecomposedGEP 119 DecomposeGEPExpression(const Value *V, const DataLayout &DL, 120 AssumptionCache *AC, DominatorTree *DT); 121 122 /// A Heuristic for aliasGEP that searches for a constant offset 123 /// between the variables. 124 /// 125 /// GetLinearExpression has some limitations, as generally zext(%x + 1) 126 /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression 127 /// will therefore conservatively refuse to decompose these expressions. 128 /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if 129 /// the addition overflows. 130 bool 131 constantOffsetHeuristic(const DecomposedGEP &GEP, LocationSize V1Size, 132 LocationSize V2Size, AssumptionCache *AC, 133 DominatorTree *DT); 134 135 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2); 136 137 void subtractDecomposedGEPs(DecomposedGEP &DestGEP, 138 const DecomposedGEP &SrcGEP); 139 140 AliasResult aliasGEP(const GEPOperator *V1, LocationSize V1Size, 141 const Value *V2, LocationSize V2Size, 142 const Value *UnderlyingV1, const Value *UnderlyingV2, 143 AAQueryInfo &AAQI); 144 145 AliasResult aliasPHI(const PHINode *PN, LocationSize PNSize, 146 const Value *V2, LocationSize V2Size, AAQueryInfo &AAQI); 147 148 AliasResult aliasSelect(const SelectInst *SI, LocationSize SISize, 149 const Value *V2, LocationSize V2Size, 150 AAQueryInfo &AAQI); 151 152 AliasResult aliasCheck(const Value *V1, LocationSize V1Size, 153 const Value *V2, LocationSize V2Size, 154 AAQueryInfo &AAQI); 155 156 AliasResult aliasCheckRecursive(const Value *V1, LocationSize V1Size, 157 const Value *V2, LocationSize V2Size, 158 AAQueryInfo &AAQI, const Value *O1, 159 const Value *O2); 160 }; 161 162 /// Analysis pass providing a never-invalidated alias analysis result. 163 class BasicAA : public AnalysisInfoMixin<BasicAA> { 164 friend AnalysisInfoMixin<BasicAA>; 165 166 static AnalysisKey Key; 167 168 public: 169 using Result = BasicAAResult; 170 171 BasicAAResult run(Function &F, FunctionAnalysisManager &AM); 172 }; 173 174 /// Legacy wrapper pass to provide the BasicAAResult object. 175 class BasicAAWrapperPass : public FunctionPass { 176 std::unique_ptr<BasicAAResult> Result; 177 178 virtual void anchor(); 179 180 public: 181 static char ID; 182 183 BasicAAWrapperPass(); 184 185 BasicAAResult &getResult() { return *Result; } 186 const BasicAAResult &getResult() const { return *Result; } 187 188 bool runOnFunction(Function &F) override; 189 void getAnalysisUsage(AnalysisUsage &AU) const override; 190 }; 191 192 FunctionPass *createBasicAAWrapperPass(); 193 194 /// A helper for the legacy pass manager to create a \c BasicAAResult object 195 /// populated to the best of our ability for a particular function when inside 196 /// of a \c ModulePass or a \c CallGraphSCCPass. 197 BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F); 198 199 /// This class is a functor to be used in legacy module or SCC passes for 200 /// computing AA results for a function. We store the results in fields so that 201 /// they live long enough to be queried, but we re-use them each time. 202 class LegacyAARGetter { 203 Pass &P; 204 Optional<BasicAAResult> BAR; 205 Optional<AAResults> AAR; 206 207 public: 208 LegacyAARGetter(Pass &P) : P(P) {} 209 AAResults &operator()(Function &F) { 210 BAR.emplace(createLegacyPMBasicAAResult(P, F)); 211 AAR.emplace(createLegacyPMAAResults(P, F, *BAR)); 212 return *AAR; 213 } 214 }; 215 216 } // end namespace llvm 217 218 #endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H 219