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BasicAliasAnalysis.h
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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/DenseMap.h"
18 #include "llvm/ADT/Optional.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/ADT/SmallVector.h"
24 #include "llvm/IR/CallSite.h"
25 #include "llvm/IR/PassManager.h"
26 #include "llvm/Pass.h"
27 #include <algorithm>
28 #include <cstdint>
29 #include <memory>
30 #include <utility>
31 
32 namespace llvm {
33 
34 struct AAMDNodes;
35 class APInt;
36 class AssumptionCache;
37 class BasicBlock;
38 class DataLayout;
39 class DominatorTree;
40 class Function;
41 class GEPOperator;
42 class LoopInfo;
43 class PHINode;
44 class SelectInst;
45 class TargetLibraryInfo;
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> {
56 
57  const DataLayout &DL;
58  const TargetLibraryInfo &TLI;
59  AssumptionCache &AC;
60  DominatorTree *DT;
61  LoopInfo *LI;
62 
63 public:
65  AssumptionCache &AC, DominatorTree *DT = nullptr,
66  LoopInfo *LI = nullptr)
67  : AAResultBase(), DL(DL), TLI(TLI), AC(AC), DT(DT), LI(LI) {}
68 
70  : AAResultBase(Arg), DL(Arg.DL), TLI(Arg.TLI), AC(Arg.AC), DT(Arg.DT),
71  LI(Arg.LI) {}
73  : AAResultBase(std::move(Arg)), DL(Arg.DL), TLI(Arg.TLI), AC(Arg.AC),
74  DT(Arg.DT), LI(Arg.LI) {}
75 
76  /// Handle invalidation events in the new pass manager.
77  bool invalidate(Function &F, const PreservedAnalyses &PA,
79 
80  AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB);
81 
83 
85 
86  /// Chases pointers until we find a (constant global) or not.
87  bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal);
88 
89  /// Get the location associated with a pointer argument of a callsite.
90  ModRefInfo getArgModRefInfo(ImmutableCallSite CS, unsigned ArgIdx);
91 
92  /// Returns the behavior when calling the given call site.
94 
95  /// Returns the behavior when calling the given function. For use when the
96  /// call site is not known.
98 
99 private:
100  // A linear transformation of a Value; this class represents ZExt(SExt(V,
101  // SExtBits), ZExtBits) * Scale + Offset.
102  struct VariableGEPIndex {
103  // An opaque Value - we can't decompose this further.
104  const Value *V;
105 
106  // We need to track what extensions we've done as we consider the same Value
107  // with different extensions as different variables in a GEP's linear
108  // expression;
109  // e.g.: if V == -1, then sext(x) != zext(x).
110  unsigned ZExtBits;
111  unsigned SExtBits;
112 
113  int64_t Scale;
114 
115  bool operator==(const VariableGEPIndex &Other) const {
116  return V == Other.V && ZExtBits == Other.ZExtBits &&
117  SExtBits == Other.SExtBits && Scale == Other.Scale;
118  }
119 
120  bool operator!=(const VariableGEPIndex &Other) const {
121  return !operator==(Other);
122  }
123  };
124 
125  // Represents the internal structure of a GEP, decomposed into a base pointer,
126  // constant offsets, and variable scaled indices.
127  struct DecomposedGEP {
128  // Base pointer of the GEP
129  const Value *Base;
130  // Total constant offset w.r.t the base from indexing into structs
131  int64_t StructOffset;
132  // Total constant offset w.r.t the base from indexing through
133  // pointers/arrays/vectors
134  int64_t OtherOffset;
135  // Scaled variable (non-constant) indices.
137  };
138 
139  /// Track alias queries to guard against recursion.
140  using LocPair = std::pair<MemoryLocation, MemoryLocation>;
142  AliasCacheTy AliasCache;
143 
144  /// Tracks phi nodes we have visited.
145  ///
146  /// When interpret "Value" pointer equality as value equality we need to make
147  /// sure that the "Value" is not part of a cycle. Otherwise, two uses could
148  /// come from different "iterations" of a cycle and see different values for
149  /// the same "Value" pointer.
150  ///
151  /// The following example shows the problem:
152  /// %p = phi(%alloca1, %addr2)
153  /// %l = load %ptr
154  /// %addr1 = gep, %alloca2, 0, %l
155  /// %addr2 = gep %alloca2, 0, (%l + 1)
156  /// alias(%p, %addr1) -> MayAlias !
157  /// store %l, ...
159 
160  /// Tracks instructions visited by pointsToConstantMemory.
162 
163  static const Value *
164  GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset,
165  unsigned &ZExtBits, unsigned &SExtBits,
166  const DataLayout &DL, unsigned Depth, AssumptionCache *AC,
167  DominatorTree *DT, bool &NSW, bool &NUW);
168 
169  static bool DecomposeGEPExpression(const Value *V, DecomposedGEP &Decomposed,
170  const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT);
171 
172  static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp,
173  const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject,
174  uint64_t ObjectAccessSize);
175 
176  /// \brief A Heuristic for aliasGEP that searches for a constant offset
177  /// between the variables.
178  ///
179  /// GetLinearExpression has some limitations, as generally zext(%x + 1)
180  /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression
181  /// will therefore conservatively refuse to decompose these expressions.
182  /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if
183  /// the addition overflows.
184  bool
185  constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices,
186  uint64_t V1Size, uint64_t V2Size, int64_t BaseOffset,
187  AssumptionCache *AC, DominatorTree *DT);
188 
189  bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
190 
191  void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
193 
194  AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
195  const AAMDNodes &V1AAInfo, const Value *V2,
196  uint64_t V2Size, const AAMDNodes &V2AAInfo,
197  const Value *UnderlyingV1, const Value *UnderlyingV2);
198 
199  AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
200  const AAMDNodes &PNAAInfo, const Value *V2,
201  uint64_t V2Size, const AAMDNodes &V2AAInfo,
202  const Value *UnderV2);
203 
204  AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
205  const AAMDNodes &SIAAInfo, const Value *V2,
206  uint64_t V2Size, const AAMDNodes &V2AAInfo,
207  const Value *UnderV2);
208 
209  AliasResult aliasCheck(const Value *V1, uint64_t V1Size, AAMDNodes V1AATag,
210  const Value *V2, uint64_t V2Size, AAMDNodes V2AATag,
211  const Value *O1 = nullptr, const Value *O2 = nullptr);
212 };
213 
214 /// Analysis pass providing a never-invalidated alias analysis result.
215 class BasicAA : public AnalysisInfoMixin<BasicAA> {
217 
218  static AnalysisKey Key;
219 
220 public:
222 
224 };
225 
226 /// Legacy wrapper pass to provide the BasicAAResult object.
228  std::unique_ptr<BasicAAResult> Result;
229 
230  virtual void anchor();
231 
232 public:
233  static char ID;
234 
236 
237  BasicAAResult &getResult() { return *Result; }
238  const BasicAAResult &getResult() const { return *Result; }
239 
240  bool runOnFunction(Function &F) override;
241  void getAnalysisUsage(AnalysisUsage &AU) const override;
242 };
243 
245 
246 /// A helper for the legacy pass manager to create a \c BasicAAResult object
247 /// populated to the best of our ability for a particular function when inside
248 /// of a \c ModulePass or a \c CallGraphSCCPass.
250 
251 /// This class is a functor to be used in legacy module or SCC passes for
252 /// computing AA results for a function. We store the results in fields so that
253 /// they live long enough to be queried, but we re-use them each time.
255  Pass &P;
258 
259 public:
260  LegacyAARGetter(Pass &P) : P(P) {}
263  AAR.emplace(createLegacyPMAAResults(P, F, *BAR));
264  return *AAR;
265  }
266 };
267 
268 } // end namespace llvm
269 
270 #endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H
Pass interface - Implemented by all &#39;passes&#39;.
Definition: Pass.h:81
bool invalidate(Function &F, const PreservedAnalyses &PA, FunctionAnalysisManager::Invalidator &Inv)
Handle invalidation events in the new pass manager.
const BasicAAResult & getResult() const
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:109
BasicAAResult(const DataLayout &DL, const TargetLibraryInfo &TLI, AssumptionCache &AC, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr)
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
Various leaf nodes.
Definition: ISDOpcodes.h:60
BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F)
A helper for the legacy pass manager to create a BasicAAResult object populated to the best of our ab...
void emplace(ArgTypes &&... Args)
Create a new object by constructing it in place with the given arguments.
Definition: Optional.h:79
A cache of .assume calls within a function.
This is the AA result object for the basic, local, and stateless alias analysis.
F(f)
bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal)
Chases pointers until we find a (constant global) or not.
Definition: BitVector.h:920
ModRefInfo
Flags indicating whether a memory access modifies or references memory.
This class represents the LLVM &#39;select&#39; instruction.
This class is a functor to be used in legacy module or SCC passes for computing AA results for a func...
AAResults createLegacyPMAAResults(Pass &P, Function &F, BasicAAResult &BAR)
A helper for the legacy pass manager to create a AAResults object populated to the best of our abilit...
AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB)
ELFYAML::ELF_STO Other
Definition: ELFYAML.cpp:736
A CRTP-driven "mixin" base class to help implement the function alias analysis results concept...
Key
PAL metadata keys.
FunctionModRefBehavior
Summary of how a function affects memory in the program.
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:140
static bool runOnFunction(Function &F, bool PostInlining)
#define P(N)
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:153
AAResults & operator()(Function &F)
A CRTP mix-in that provides informational APIs needed for analysis passes.
Definition: PassManager.h:382
FunctionModRefBehavior getModRefBehavior(ImmutableCallSite CS)
Returns the behavior when calling the given call site.
AliasResult
The possible results of an alias query.
Definition: AliasAnalysis.h:79
Represent the analysis usage information of a pass.
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:285
ModRefInfo getModRefInfo(ImmutableCallSite CS, const MemoryLocation &Loc)
Checks to see if the specified callsite can clobber the specified memory object.
Representation for a specific memory location.
Provides information about what library functions are available for the current target.
A collection of metadata nodes that might be associated with a memory access used by the alias-analys...
Definition: Metadata.h:642
Class for arbitrary precision integers.
Definition: APInt.h:69
FunctionPass * createBasicAAWrapperPass()
amdgpu Simplify well known AMD library false Value Value * Arg
Analysis pass providing a never-invalidated alias analysis result.
bool operator!=(uint64_t V1, const APInt &V2)
Definition: APInt.h:1948
BasicAAResult(BasicAAResult &&Arg)
BasicAAResult(const BasicAAResult &Arg)
This file provides utility analysis objects describing memory locations.
Establish a view to a call site for examination.
Definition: CallSite.h:713
API to communicate dependencies between analyses during invalidation.
Definition: PassManager.h:559
LLVM Value Representation.
Definition: Value.h:73
ModRefInfo getArgModRefInfo(ImmutableCallSite CS, unsigned ArgIdx)
Get the location associated with a pointer argument of a callsite.
A container for analyses that lazily runs them and caches their results.
bool operator==(uint64_t V1, const APInt &V2)
Definition: APInt.h:1946
This header defines various interfaces for pass management in LLVM.
A special type used by analysis passes to provide an address that identifies that particular analysis...
Definition: PassManager.h:70
Legacy wrapper pass to provide the BasicAAResult object.