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. While it does retain
37/// some storage, that is used as an optimization and not to preserve
38/// information from query to query.
39class BasicAAResult : public AAResultBase<BasicAAResult> {
40  friend AAResultBase<BasicAAResult>;
41
42  const DataLayout &DL;
43  AssumptionCache &AC;
44  DominatorTree *DT;
45  LoopInfo *LI;
46
47public:
48  BasicAAResult(const DataLayout &DL, const TargetLibraryInfo &TLI,
49                AssumptionCache &AC, DominatorTree *DT = nullptr,
50                LoopInfo *LI = nullptr)
51      : AAResultBase(TLI), DL(DL), AC(AC), DT(DT), LI(LI) {}
52
53  BasicAAResult(const BasicAAResult &Arg)
54      : AAResultBase(Arg), DL(Arg.DL), AC(Arg.AC), DT(Arg.DT), LI(Arg.LI) {}
55  BasicAAResult(BasicAAResult &&Arg)
56      : AAResultBase(std::move(Arg)), DL(Arg.DL), AC(Arg.AC), DT(Arg.DT),
57        LI(Arg.LI) {}
58
59  /// Handle invalidation events from the new pass manager.
60  ///
61  /// By definition, this result is stateless and so remains valid.
62  bool invalidate(Function &, const PreservedAnalyses &) { return false; }
63
64  AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB);
65
66  ModRefInfo getModRefInfo(ImmutableCallSite CS, const MemoryLocation &Loc);
67
68  ModRefInfo getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2);
69
70  /// Chases pointers until we find a (constant global) or not.
71  bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal);
72
73  /// Get the location associated with a pointer argument of a callsite.
74  ModRefInfo getArgModRefInfo(ImmutableCallSite CS, unsigned ArgIdx);
75
76  /// Returns the behavior when calling the given call site.
77  FunctionModRefBehavior getModRefBehavior(ImmutableCallSite CS);
78
79  /// Returns the behavior when calling the given function. For use when the
80  /// call site is not known.
81  FunctionModRefBehavior getModRefBehavior(const Function *F);
82
83private:
84  // A linear transformation of a Value; this class represents ZExt(SExt(V,
85  // SExtBits), ZExtBits) * Scale + Offset.
86  struct VariableGEPIndex {
87
88    // An opaque Value - we can't decompose this further.
89    const Value *V;
90
91    // We need to track what extensions we've done as we consider the same Value
92    // with different extensions as different variables in a GEP's linear
93    // expression;
94    // e.g.: if V == -1, then sext(x) != zext(x).
95    unsigned ZExtBits;
96    unsigned SExtBits;
97
98    int64_t Scale;
99
100    bool operator==(const VariableGEPIndex &Other) const {
101      return V == Other.V && ZExtBits == Other.ZExtBits &&
102             SExtBits == Other.SExtBits && Scale == Other.Scale;
103    }
104
105    bool operator!=(const VariableGEPIndex &Other) const {
106      return !operator==(Other);
107    }
108  };
109
110  /// Track alias queries to guard against recursion.
111  typedef std::pair<MemoryLocation, MemoryLocation> LocPair;
112  typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
113  AliasCacheTy AliasCache;
114
115  /// Tracks phi nodes we have visited.
116  ///
117  /// When interpret "Value" pointer equality as value equality we need to make
118  /// sure that the "Value" is not part of a cycle. Otherwise, two uses could
119  /// come from different "iterations" of a cycle and see different values for
120  /// the same "Value" pointer.
121  ///
122  /// The following example shows the problem:
123  ///   %p = phi(%alloca1, %addr2)
124  ///   %l = load %ptr
125  ///   %addr1 = gep, %alloca2, 0, %l
126  ///   %addr2 = gep  %alloca2, 0, (%l + 1)
127  ///      alias(%p, %addr1) -> MayAlias !
128  ///   store %l, ...
129  SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs;
130
131  /// Tracks instructions visited by pointsToConstantMemory.
132  SmallPtrSet<const Value *, 16> Visited;
133
134  static const Value *
135  GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset,
136                      unsigned &ZExtBits, unsigned &SExtBits,
137                      const DataLayout &DL, unsigned Depth, AssumptionCache *AC,
138                      DominatorTree *DT, bool &NSW, bool &NUW);
139
140  static const Value *
141  DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
142                         SmallVectorImpl<VariableGEPIndex> &VarIndices,
143                         bool &MaxLookupReached, const DataLayout &DL,
144                         AssumptionCache *AC, DominatorTree *DT);
145  /// \brief A Heuristic for aliasGEP that searches for a constant offset
146  /// between the variables.
147  ///
148  /// GetLinearExpression has some limitations, as generally zext(%x + 1)
149  /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression
150  /// will therefore conservatively refuse to decompose these expressions.
151  /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if
152  /// the addition overflows.
153  bool
154  constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices,
155                          uint64_t V1Size, uint64_t V2Size, int64_t BaseOffset,
156                          AssumptionCache *AC, DominatorTree *DT);
157
158  bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
159
160  void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
161                          const SmallVectorImpl<VariableGEPIndex> &Src);
162
163  AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
164                       const AAMDNodes &V1AAInfo, const Value *V2,
165                       uint64_t V2Size, const AAMDNodes &V2AAInfo,
166                       const Value *UnderlyingV1, const Value *UnderlyingV2);
167
168  AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
169                       const AAMDNodes &PNAAInfo, const Value *V2,
170                       uint64_t V2Size, const AAMDNodes &V2AAInfo);
171
172  AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
173                          const AAMDNodes &SIAAInfo, const Value *V2,
174                          uint64_t V2Size, const AAMDNodes &V2AAInfo);
175
176  AliasResult aliasCheck(const Value *V1, uint64_t V1Size, AAMDNodes V1AATag,
177                         const Value *V2, uint64_t V2Size, AAMDNodes V2AATag);
178};
179
180/// Analysis pass providing a never-invalidated alias analysis result.
181class BasicAA {
182public:
183  typedef BasicAAResult Result;
184
185  /// \brief Opaque, unique identifier for this analysis pass.
186  static void *ID() { return (void *)&PassID; }
187
188  BasicAAResult run(Function &F, AnalysisManager<Function> *AM);
189
190  /// \brief Provide access to a name for this pass for debugging purposes.
191  static StringRef name() { return "BasicAliasAnalysis"; }
192
193private:
194  static char PassID;
195};
196
197/// Legacy wrapper pass to provide the BasicAAResult object.
198class BasicAAWrapperPass : public FunctionPass {
199  std::unique_ptr<BasicAAResult> Result;
200
201  virtual void anchor();
202
203public:
204  static char ID;
205
206  BasicAAWrapperPass();
207
208  BasicAAResult &getResult() { return *Result; }
209  const BasicAAResult &getResult() const { return *Result; }
210
211  bool runOnFunction(Function &F) override;
212  void getAnalysisUsage(AnalysisUsage &AU) const override;
213};
214
215FunctionPass *createBasicAAWrapperPass();
216
217/// A helper for the legacy pass manager to create a \c BasicAAResult object
218/// populated to the best of our ability for a particular function when inside
219/// of a \c ModulePass or a \c CallGraphSCCPass.
220BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F);
221}
222
223#endif
224