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/DenseMap.h" 18#include "llvm/ADT/Optional.h" 19#include "llvm/ADT/SmallPtrSet.h" 20#include "llvm/ADT/SmallVector.h" 21#include "llvm/Analysis/AliasAnalysis.h" 22#include "llvm/Analysis/AssumptionCache.h" 23#include "llvm/Analysis/MemoryLocation.h" 24#include "llvm/IR/CallSite.h" 25#include "llvm/IR/PassManager.h" 26#include "llvm/Pass.h" 27#include <algorithm> 28#include <cstdint> 29#include <memory> 30#include <utility> 31 32namespace llvm { 33 34struct AAMDNodes; 35class APInt; 36class AssumptionCache; 37class BasicBlock; 38class DataLayout; 39class DominatorTree; 40class Function; 41class GEPOperator; 42class LoopInfo; 43class PHINode; 44class SelectInst; 45class TargetLibraryInfo; 46class Value; 47 48/// This is the AA result object for the basic, local, and stateless alias 49/// analysis. It implements the AA query interface in an entirely stateless 50/// manner. As one consequence, it is never invalidated due to IR changes. 51/// While it does retain some storage, that is used as an optimization and not 52/// to preserve information from query to query. However it does retain handles 53/// to various other analyses and must be recomputed when those analyses are. 54class BasicAAResult : public AAResultBase<BasicAAResult> { 55 friend AAResultBase<BasicAAResult>; 56 57 const DataLayout &DL; 58 const TargetLibraryInfo &TLI; 59 AssumptionCache &AC; 60 DominatorTree *DT; 61 LoopInfo *LI; 62 63public: 64 BasicAAResult(const DataLayout &DL, const TargetLibraryInfo &TLI, 65 AssumptionCache &AC, DominatorTree *DT = nullptr, 66 LoopInfo *LI = nullptr) 67 : AAResultBase(), DL(DL), TLI(TLI), AC(AC), DT(DT), LI(LI) {} 68 69 BasicAAResult(const BasicAAResult &Arg) 70 : AAResultBase(Arg), DL(Arg.DL), TLI(Arg.TLI), AC(Arg.AC), DT(Arg.DT), 71 LI(Arg.LI) {} 72 BasicAAResult(BasicAAResult &&Arg) 73 : AAResultBase(std::move(Arg)), DL(Arg.DL), TLI(Arg.TLI), AC(Arg.AC), 74 DT(Arg.DT), LI(Arg.LI) {} 75 76 /// Handle invalidation events in the new pass manager. 77 bool invalidate(Function &F, const PreservedAnalyses &PA, 78 FunctionAnalysisManager::Invalidator &Inv); 79 80 AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB); 81 82 ModRefInfo getModRefInfo(ImmutableCallSite CS, const MemoryLocation &Loc); 83 84 ModRefInfo getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2); 85 86 /// Chases pointers until we find a (constant global) or not. 87 bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal); 88 89 /// Get the location associated with a pointer argument of a callsite. 90 ModRefInfo getArgModRefInfo(ImmutableCallSite CS, unsigned ArgIdx); 91 92 /// Returns the behavior when calling the given call site. 93 FunctionModRefBehavior getModRefBehavior(ImmutableCallSite CS); 94 95 /// Returns the behavior when calling the given function. For use when the 96 /// call site is not known. 97 FunctionModRefBehavior getModRefBehavior(const Function *F); 98 99private: 100 // A linear transformation of a Value; this class represents ZExt(SExt(V, 101 // SExtBits), ZExtBits) * Scale + Offset. 102 struct VariableGEPIndex { 103 // An opaque Value - we can't decompose this further. 104 const Value *V; 105 106 // We need to track what extensions we've done as we consider the same Value 107 // with different extensions as different variables in a GEP's linear 108 // expression; 109 // e.g.: if V == -1, then sext(x) != zext(x). 110 unsigned ZExtBits; 111 unsigned SExtBits; 112 113 int64_t Scale; 114 115 bool operator==(const VariableGEPIndex &Other) const { 116 return V == Other.V && ZExtBits == Other.ZExtBits && 117 SExtBits == Other.SExtBits && Scale == Other.Scale; 118 } 119 120 bool operator!=(const VariableGEPIndex &Other) const { 121 return !operator==(Other); 122 } 123 }; 124 125 // Represents the internal structure of a GEP, decomposed into a base pointer, 126 // constant offsets, and variable scaled indices. 127 struct DecomposedGEP { 128 // Base pointer of the GEP 129 const Value *Base; 130 // Total constant offset w.r.t the base from indexing into structs 131 int64_t StructOffset; 132 // Total constant offset w.r.t the base from indexing through 133 // pointers/arrays/vectors 134 int64_t OtherOffset; 135 // Scaled variable (non-constant) indices. 136 SmallVector<VariableGEPIndex, 4> VarIndices; 137 }; 138 139 /// Track alias queries to guard against recursion. 140 using LocPair = std::pair<MemoryLocation, MemoryLocation>; 141 using AliasCacheTy = SmallDenseMap<LocPair, AliasResult, 8>; 142 AliasCacheTy AliasCache; 143 144 /// Tracks phi nodes we have visited. 145 /// 146 /// When interpret "Value" pointer equality as value equality we need to make 147 /// sure that the "Value" is not part of a cycle. Otherwise, two uses could 148 /// come from different "iterations" of a cycle and see different values for 149 /// the same "Value" pointer. 150 /// 151 /// The following example shows the problem: 152 /// %p = phi(%alloca1, %addr2) 153 /// %l = load %ptr 154 /// %addr1 = gep, %alloca2, 0, %l 155 /// %addr2 = gep %alloca2, 0, (%l + 1) 156 /// alias(%p, %addr1) -> MayAlias ! 157 /// store %l, ... 158 SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs; 159 160 /// Tracks instructions visited by pointsToConstantMemory. 161 SmallPtrSet<const Value *, 16> Visited; 162 163 static const Value * 164 GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset, 165 unsigned &ZExtBits, unsigned &SExtBits, 166 const DataLayout &DL, unsigned Depth, AssumptionCache *AC, 167 DominatorTree *DT, bool &NSW, bool &NUW); 168 169 static bool DecomposeGEPExpression(const Value *V, DecomposedGEP &Decomposed, 170 const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT); 171 172 static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp, 173 const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject, 174 uint64_t ObjectAccessSize); 175 176 /// \brief A Heuristic for aliasGEP that searches for a constant offset 177 /// between the variables. 178 /// 179 /// GetLinearExpression has some limitations, as generally zext(%x + 1) 180 /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression 181 /// will therefore conservatively refuse to decompose these expressions. 182 /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if 183 /// the addition overflows. 184 bool 185 constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices, 186 uint64_t V1Size, uint64_t V2Size, int64_t BaseOffset, 187 AssumptionCache *AC, DominatorTree *DT); 188 189 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2); 190 191 void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest, 192 const SmallVectorImpl<VariableGEPIndex> &Src); 193 194 AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size, 195 const AAMDNodes &V1AAInfo, const Value *V2, 196 uint64_t V2Size, const AAMDNodes &V2AAInfo, 197 const Value *UnderlyingV1, const Value *UnderlyingV2); 198 199 AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize, 200 const AAMDNodes &PNAAInfo, const Value *V2, 201 uint64_t V2Size, const AAMDNodes &V2AAInfo, 202 const Value *UnderV2); 203 204 AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize, 205 const AAMDNodes &SIAAInfo, const Value *V2, 206 uint64_t V2Size, const AAMDNodes &V2AAInfo, 207 const Value *UnderV2); 208 209 AliasResult aliasCheck(const Value *V1, uint64_t V1Size, AAMDNodes V1AATag, 210 const Value *V2, uint64_t V2Size, AAMDNodes V2AATag, 211 const Value *O1 = nullptr, const Value *O2 = nullptr); 212}; 213 214/// Analysis pass providing a never-invalidated alias analysis result. 215class BasicAA : public AnalysisInfoMixin<BasicAA> { 216 friend AnalysisInfoMixin<BasicAA>; 217 218 static AnalysisKey Key; 219 220public: 221 using Result = BasicAAResult; 222 223 BasicAAResult run(Function &F, FunctionAnalysisManager &AM); 224}; 225 226/// Legacy wrapper pass to provide the BasicAAResult object. 227class BasicAAWrapperPass : public FunctionPass { 228 std::unique_ptr<BasicAAResult> Result; 229 230 virtual void anchor(); 231 232public: 233 static char ID; 234 235 BasicAAWrapperPass(); 236 237 BasicAAResult &getResult() { return *Result; } 238 const BasicAAResult &getResult() const { return *Result; } 239 240 bool runOnFunction(Function &F) override; 241 void getAnalysisUsage(AnalysisUsage &AU) const override; 242}; 243 244FunctionPass *createBasicAAWrapperPass(); 245 246/// A helper for the legacy pass manager to create a \c BasicAAResult object 247/// populated to the best of our ability for a particular function when inside 248/// of a \c ModulePass or a \c CallGraphSCCPass. 249BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F); 250 251/// This class is a functor to be used in legacy module or SCC passes for 252/// computing AA results for a function. We store the results in fields so that 253/// they live long enough to be queried, but we re-use them each time. 254class LegacyAARGetter { 255 Pass &P; 256 Optional<BasicAAResult> BAR; 257 Optional<AAResults> AAR; 258 259public: 260 LegacyAARGetter(Pass &P) : P(P) {} 261 AAResults &operator()(Function &F) { 262 BAR.emplace(createLegacyPMBasicAAResult(P, F)); 263 AAR.emplace(createLegacyPMAAResults(P, F, *BAR)); 264 return *AAR; 265 } 266}; 267 268} // end namespace llvm 269 270#endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H 271