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