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
31namespace llvm {
32
33struct AAMDNodes;
34class APInt;
35class AssumptionCache;
36class BasicBlock;
37class DataLayout;
38class DominatorTree;
39class Function;
40class GEPOperator;
41class LoopInfo;
42class PHINode;
43class SelectInst;
44class TargetLibraryInfo;
45class PhiValues;
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 Function &F;
59  const TargetLibraryInfo &TLI;
60  AssumptionCache &AC;
61  DominatorTree *DT;
62  LoopInfo *LI;
63  PhiValues *PV;
64
65public:
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
107private:
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.
222class BasicAA : public AnalysisInfoMixin<BasicAA> {
223  friend AnalysisInfoMixin<BasicAA>;
224
225  static AnalysisKey Key;
226
227public:
228  using Result = BasicAAResult;
229
230  BasicAAResult run(Function &F, FunctionAnalysisManager &AM);
231};
232
233/// Legacy wrapper pass to provide the BasicAAResult object.
234class BasicAAWrapperPass : public FunctionPass {
235  std::unique_ptr<BasicAAResult> Result;
236
237  virtual void anchor();
238
239public:
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
251FunctionPass *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.
256BasicAAResult 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.
261class LegacyAARGetter {
262  Pass &P;
263  Optional<BasicAAResult> BAR;
264  Optional<AAResults> AAR;
265
266public:
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
278