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