include/llvm/Analysis/BasicAliasAnalysis.h

   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/DenseMap.h"
  17 #include "llvm/ADT/Optional.h"
  18 #include "llvm/ADT/SmallPtrSet.h"
  19 #include "llvm/ADT/SmallVector.h"
  20 #include "llvm/Analysis/AliasAnalysis.h"
  21 #include "llvm/Analysis/AssumptionCache.h"
  22 #include "llvm/Analysis/MemoryLocation.h"
  23 #include "llvm/IR/InstrTypes.h"
  24 #include "llvm/IR/PassManager.h"
  25 #include "llvm/Pass.h"
  26 #include <algorithm>
  27 #include <cstdint>
  28 #include <memory>
  29 #include <utility>
  30
  31 namespace llvm {
  32
  33 struct AAMDNodes;
  34 class APInt;
  35 class AssumptionCache;
  36 class BasicBlock;
  37 class DataLayout;
  38 class DominatorTree;
  39 class Function;
  40 class GEPOperator;
  41 class LoopInfo;
  42 class PHINode;
  43 class SelectInst;
  44 class TargetLibraryInfo;
  45 class PhiValues;
  46 class 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.
  54 class BasicAAResult : public AAResultBase<BasicAAResult> {
  55   friend AAResultBase<BasicAAResult>;
  56
  57   const DataLayout &DL;
  58   const Function &F;
  59   const TargetLibraryInfo &TLI;
  60   AssumptionCache &AC;
  61   DominatorTree *DT;
  62   LoopInfo *LI;
  63   PhiValues *PV;
  64
  65 public:
  66   BasicAAResult(const DataLayout &DL, const Function &F,
  67                 const TargetLibraryInfo &TLI, AssumptionCache &AC,
  68                 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr,
  69                 PhiValues *PV = nullptr)
  70       : AAResultBase(), DL(DL), F(F), TLI(TLI), AC(AC), DT(DT), LI(LI), PV(PV)
  71         {}
  72
  73   BasicAAResult(const BasicAAResult &Arg)
  74       : AAResultBase(Arg), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), AC(Arg.AC),
  75         DT(Arg.DT),  LI(Arg.LI), PV(Arg.PV) {}
  76   BasicAAResult(BasicAAResult &&Arg)
  77       : AAResultBase(std::move(Arg)), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI),
  78         AC(Arg.AC), DT(Arg.DT), LI(Arg.LI), PV(Arg.PV) {}
  79
  80   /// Handle invalidation events in the new pass manager.
  81   bool invalidate(Function &Fn, const PreservedAnalyses &PA,
  82                   FunctionAnalysisManager::Invalidator &Inv);
  83
  84   AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB);
  85
  86   ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc);
  87
  88   ModRefInfo getModRefInfo(const CallBase *Call1, const CallBase *Call2);
  89
  90   /// Chases pointers until we find a (constant global) or not.
  91   bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal);
  92
  93   /// Get the location associated with a pointer argument of a callsite.
  94   ModRefInfo getArgModRefInfo(const CallBase *Call, unsigned ArgIdx);
  95
  96   /// Returns the behavior when calling the given call site.
  97   FunctionModRefBehavior getModRefBehavior(const CallBase *Call);
  98
  99   /// Returns the behavior when calling the given function. For use when the
 100   /// call site is not known.
 101   FunctionModRefBehavior getModRefBehavior(const Function *Fn);
 102
 103 private:
 104   // A linear transformation of a Value; this class represents ZExt(SExt(V,
 105   // SExtBits), ZExtBits) * Scale + Offset.
 106   struct VariableGEPIndex {
 107     // An opaque Value - we can't decompose this further.
 108     const Value *V;
 109
 110     // We need to track what extensions we've done as we consider the same Value
 111     // with different extensions as different variables in a GEP's linear
 112     // expression;
 113     // e.g.: if V == -1, then sext(x) != zext(x).
 114     unsigned ZExtBits;
 115     unsigned SExtBits;
 116
 117     APInt Scale;
 118
 119     bool operator==(const VariableGEPIndex &Other) const {
 120       return V == Other.V && ZExtBits == Other.ZExtBits &&
 121              SExtBits == Other.SExtBits && Scale == Other.Scale;
 122     }
 123
 124     bool operator!=(const VariableGEPIndex &Other) const {
 125       return !operator==(Other);
 126     }
 127   };
 128
 129   // Represents the internal structure of a GEP, decomposed into a base pointer,
 130   // constant offsets, and variable scaled indices.
 131   struct DecomposedGEP {
 132     // Base pointer of the GEP
 133     const Value *Base;
 134     // Total constant offset w.r.t the base from indexing into structs
 135     APInt StructOffset;
 136     // Total constant offset w.r.t the base from indexing through
 137     // pointers/arrays/vectors
 138     APInt OtherOffset;
 139     // Scaled variable (non-constant) indices.
 140     SmallVector<VariableGEPIndex, 4> VarIndices;
 141   };
 142
 143   /// Track alias queries to guard against recursion.
 144   using LocPair = std::pair<MemoryLocation, MemoryLocation>;
 145   using AliasCacheTy = SmallDenseMap<LocPair, AliasResult, 8>;
 146   AliasCacheTy AliasCache;
 147   using IsCapturedCacheTy = SmallDenseMap<const Value *, bool, 8>;
 148   IsCapturedCacheTy IsCapturedCache;
 149
 150   /// Tracks phi nodes we have visited.
 151   ///
 152   /// When interpret "Value" pointer equality as value equality we need to make
 153   /// sure that the "Value" is not part of a cycle. Otherwise, two uses could
 154   /// come from different "iterations" of a cycle and see different values for
 155   /// the same "Value" pointer.
 156   ///
 157   /// The following example shows the problem:
 158   ///   %p = phi(%alloca1, %addr2)
 159   ///   %l = load %ptr
 160   ///   %addr1 = gep, %alloca2, 0, %l
 161   ///   %addr2 = gep  %alloca2, 0, (%l + 1)
 162   ///      alias(%p, %addr1) -> MayAlias !
 163   ///   store %l, ...
 164   SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs;
 165
 166   /// Tracks instructions visited by pointsToConstantMemory.
 167   SmallPtrSet<const Value *, 16> Visited;
 168
 169   static const Value *
 170   GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset,
 171                       unsigned &ZExtBits, unsigned &SExtBits,
 172                       const DataLayout &DL, unsigned Depth, AssumptionCache *AC,
 173                       DominatorTree *DT, bool &NSW, bool &NUW);
 174
 175   static bool DecomposeGEPExpression(const Value *V, DecomposedGEP &Decomposed,
 176       const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT);
 177
 178   static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp,
 179       const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject,
 180       LocationSize ObjectAccessSize);
 181
 182   /// A Heuristic for aliasGEP that searches for a constant offset
 183   /// between the variables.
 184   ///
 185   /// GetLinearExpression has some limitations, as generally zext(%x + 1)
 186   /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression
 187   /// will therefore conservatively refuse to decompose these expressions.
 188   /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if
 189   /// the addition overflows.
 190   bool
 191   constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices,
 192                           LocationSize V1Size, LocationSize V2Size,
 193                           APInt BaseOffset, AssumptionCache *AC,
 194                           DominatorTree *DT);
 195
 196   bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
 197
 198   void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
 199                           const SmallVectorImpl<VariableGEPIndex> &Src);
 200
 201   AliasResult aliasGEP(const GEPOperator *V1, LocationSize V1Size,
 202                        const AAMDNodes &V1AAInfo, const Value *V2,
 203                        LocationSize V2Size, const AAMDNodes &V2AAInfo,
 204                        const Value *UnderlyingV1, const Value *UnderlyingV2);
 205
 206   AliasResult aliasPHI(const PHINode *PN, LocationSize PNSize,
 207                        const AAMDNodes &PNAAInfo, const Value *V2,
 208                        LocationSize V2Size, const AAMDNodes &V2AAInfo,
 209                        const Value *UnderV2);
 210
 211   AliasResult aliasSelect(const SelectInst *SI, LocationSize SISize,
 212                           const AAMDNodes &SIAAInfo, const Value *V2,
 213                           LocationSize V2Size, const AAMDNodes &V2AAInfo,
 214                           const Value *UnderV2);
 215
 216   AliasResult aliasCheck(const Value *V1, LocationSize V1Size,
 217                          AAMDNodes V1AATag, const Value *V2,
 218                          LocationSize V2Size, AAMDNodes V2AATag,
 219                          const Value *O1 = nullptr, const Value *O2 = nullptr);
 220 };
 221
 222 /// Analysis pass providing a never-invalidated alias analysis result.
 223 class BasicAA : public AnalysisInfoMixin<BasicAA> {
 224   friend AnalysisInfoMixin<BasicAA>;
 225
 226   static AnalysisKey Key;
 227
 228 public:
 229   using Result = BasicAAResult;
 230
 231   BasicAAResult run(Function &F, FunctionAnalysisManager &AM);
 232 };
 233
 234 /// Legacy wrapper pass to provide the BasicAAResult object.
 235 class BasicAAWrapperPass : public FunctionPass {
 236   std::unique_ptr<BasicAAResult> Result;
 237
 238   virtual void anchor();
 239
 240 public:
 241   static char ID;
 242
 243   BasicAAWrapperPass();
 244
 245   BasicAAResult &getResult() { return *Result; }
 246   const BasicAAResult &getResult() const { return *Result; }
 247
 248   bool runOnFunction(Function &F) override;
 249   void getAnalysisUsage(AnalysisUsage &AU) const override;
 250 };
 251
 252 FunctionPass *createBasicAAWrapperPass();
 253
 254 /// A helper for the legacy pass manager to create a \c BasicAAResult object
 255 /// populated to the best of our ability for a particular function when inside
 256 /// of a \c ModulePass or a \c CallGraphSCCPass.
 257 BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F);
 258
 259 /// This class is a functor to be used in legacy module or SCC passes for
 260 /// computing AA results for a function. We store the results in fields so that
 261 /// they live long enough to be queried, but we re-use them each time.
 262 class LegacyAARGetter {
 263   Pass &P;
 264   Optional<BasicAAResult> BAR;
 265   Optional<AAResults> AAR;
 266
 267 public:
 268   LegacyAARGetter(Pass &P) : P(P) {}
 269   AAResults &operator()(Function &F) {
 270     BAR.emplace(createLegacyPMBasicAAResult(P, F));
 271     AAR.emplace(createLegacyPMAAResults(P, F, *BAR));
 272     return *AAR;
 273   }
 274 };
 275
 276 } // end namespace llvm
 277
 278 #endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H