LLVM  9.0.0svn
BasicAliasAnalysis.h
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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"
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> {
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 
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) {}
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,
83 
84  AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB);
85 
86  ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc);
87 
88  ModRefInfo getModRefInfo(const CallBase *Call1, const CallBase *Call2);
89 
90  /// Chases pointers until we find a (constant global) or not.
91  bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal);
92 
93  /// Get the location associated with a pointer argument of a callsite.
94  ModRefInfo getArgModRefInfo(const CallBase *Call, unsigned ArgIdx);
95 
96  /// Returns the behavior when calling the given call site.
98 
99  /// Returns the behavior when calling the given function. For use when the
100  /// call site is not known.
102 
103 private:
104  // A linear transformation of a Value; this class represents ZExt(SExt(V,
105  // SExtBits), ZExtBits) * Scale + Offset.
106  struct VariableGEPIndex {
107  // An opaque Value - we can't decompose this further.
108  const Value *V;
109 
110  // We need to track what extensions we've done as we consider the same Value
111  // with different extensions as different variables in a GEP's linear
112  // expression;
113  // e.g.: if V == -1, then sext(x) != zext(x).
114  unsigned ZExtBits;
115  unsigned SExtBits;
116 
117  APInt Scale;
118 
119  bool operator==(const VariableGEPIndex &Other) const {
120  return V == Other.V && ZExtBits == Other.ZExtBits &&
121  SExtBits == Other.SExtBits && Scale == Other.Scale;
122  }
123 
124  bool operator!=(const VariableGEPIndex &Other) const {
125  return !operator==(Other);
126  }
127  };
128 
129  // Represents the internal structure of a GEP, decomposed into a base pointer,
130  // constant offsets, and variable scaled indices.
131  struct DecomposedGEP {
132  // Base pointer of the GEP
133  const Value *Base;
134  // Total constant offset w.r.t the base from indexing into structs
135  APInt StructOffset;
136  // Total constant offset w.r.t the base from indexing through
137  // pointers/arrays/vectors
138  APInt OtherOffset;
139  // Scaled variable (non-constant) indices.
141  };
142 
143  /// Track alias queries to guard against recursion.
144  using LocPair = std::pair<MemoryLocation, MemoryLocation>;
146  AliasCacheTy AliasCache;
148  IsCapturedCacheTy IsCapturedCache;
149 
150  /// Tracks phi nodes we have visited.
151  ///
152  /// When interpret "Value" pointer equality as value equality we need to make
153  /// sure that the "Value" is not part of a cycle. Otherwise, two uses could
154  /// come from different "iterations" of a cycle and see different values for
155  /// the same "Value" pointer.
156  ///
157  /// The following example shows the problem:
158  /// %p = phi(%alloca1, %addr2)
159  /// %l = load %ptr
160  /// %addr1 = gep, %alloca2, 0, %l
161  /// %addr2 = gep %alloca2, 0, (%l + 1)
162  /// alias(%p, %addr1) -> MayAlias !
163  /// store %l, ...
165 
166  /// Tracks instructions visited by pointsToConstantMemory.
168 
169  static const Value *
170  GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset,
171  unsigned &ZExtBits, unsigned &SExtBits,
172  const DataLayout &DL, unsigned Depth, AssumptionCache *AC,
173  DominatorTree *DT, bool &NSW, bool &NUW);
174 
175  static bool DecomposeGEPExpression(const Value *V, DecomposedGEP &Decomposed,
176  const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT);
177 
178  static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp,
179  const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject,
180  LocationSize ObjectAccessSize);
181 
182  /// A Heuristic for aliasGEP that searches for a constant offset
183  /// between the variables.
184  ///
185  /// GetLinearExpression has some limitations, as generally zext(%x + 1)
186  /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression
187  /// will therefore conservatively refuse to decompose these expressions.
188  /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if
189  /// the addition overflows.
190  bool
191  constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices,
192  LocationSize V1Size, LocationSize V2Size,
193  APInt BaseOffset, AssumptionCache *AC,
194  DominatorTree *DT);
195 
196  bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
197 
198  void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
200 
201  AliasResult aliasGEP(const GEPOperator *V1, LocationSize V1Size,
202  const AAMDNodes &V1AAInfo, const Value *V2,
203  LocationSize V2Size, const AAMDNodes &V2AAInfo,
204  const Value *UnderlyingV1, const Value *UnderlyingV2);
205 
206  AliasResult aliasPHI(const PHINode *PN, LocationSize PNSize,
207  const AAMDNodes &PNAAInfo, const Value *V2,
208  LocationSize V2Size, const AAMDNodes &V2AAInfo,
209  const Value *UnderV2);
210 
211  AliasResult aliasSelect(const SelectInst *SI, LocationSize SISize,
212  const AAMDNodes &SIAAInfo, const Value *V2,
213  LocationSize V2Size, const AAMDNodes &V2AAInfo,
214  const Value *UnderV2);
215 
216  AliasResult aliasCheck(const Value *V1, LocationSize V1Size,
217  AAMDNodes V1AATag, const Value *V2,
218  LocationSize V2Size, AAMDNodes V2AATag,
219  const Value *O1 = nullptr, const Value *O2 = nullptr);
220 };
221 
222 /// Analysis pass providing a never-invalidated alias analysis result.
223 class BasicAA : public AnalysisInfoMixin<BasicAA> {
225 
226  static AnalysisKey Key;
227 
228 public:
230 
232 };
233 
234 /// Legacy wrapper pass to provide the BasicAAResult object.
236  std::unique_ptr<BasicAAResult> Result;
237 
238  virtual void anchor();
239 
240 public:
241  static char ID;
242 
244 
245  BasicAAResult &getResult() { return *Result; }
246  const BasicAAResult &getResult() const { return *Result; }
247 
248  bool runOnFunction(Function &F) override;
249  void getAnalysisUsage(AnalysisUsage &AU) const override;
250 };
251 
253 
254 /// A helper for the legacy pass manager to create a \c BasicAAResult object
255 /// populated to the best of our ability for a particular function when inside
256 /// of a \c ModulePass or a \c CallGraphSCCPass.
258 
259 /// This class is a functor to be used in legacy module or SCC passes for
260 /// computing AA results for a function. We store the results in fields so that
261 /// they live long enough to be queried, but we re-use them each time.
263  Pass &P;
266 
267 public:
268  LegacyAARGetter(Pass &P) : P(P) {}
271  AAR.emplace(createLegacyPMAAResults(P, F, *BAR));
272  return *AAR;
273  }
274 };
275 
276 } // end namespace llvm
277 
278 #endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H
Pass interface - Implemented by all &#39;passes&#39;.
Definition: Pass.h:80
const BasicAAResult & getResult() const
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:110
This class represents lattice values for constants.
Definition: AllocatorList.h:23
Various leaf nodes.
Definition: ISDOpcodes.h:59
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:136
A cache of @llvm.assume calls within a function.
This is the AA result object for the basic, local, and stateless alias analysis.
Base class for all callable instructions (InvokeInst and CallInst) Holds everything related to callin...
Definition: InstrTypes.h:1014
ModRefInfo getArgModRefInfo(const CallBase *Call, unsigned ArgIdx)
Get the location associated with a pointer argument of a callsite.
bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal)
Chases pointers until we find a (constant global) or not.
Definition: BitVector.h:937
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:810
A CRTP-driven "mixin" base class to help implement the function alias analysis results concept...
Key
PAL metadata keys.
#define F(x, y, z)
Definition: MD5.cpp:55
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:144
AliasResult
The possible results of an alias query.
Definition: AliasAnalysis.h:77
BasicAAResult(const DataLayout &DL, const Function &F, const TargetLibraryInfo &TLI, AssumptionCache &AC, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr, PhiValues *PV=nullptr)
static bool runOnFunction(Function &F, bool PostInlining)
#define P(N)
FunctionModRefBehavior getModRefBehavior(const CallBase *Call)
Returns the behavior when calling the given call site.
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
Represent the analysis usage information of a pass.
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:284
amdgpu Simplify well known AMD library false FunctionCallee Value * Arg
bool invalidate(Function &Fn, const PreservedAnalyses &PA, FunctionAnalysisManager::Invalidator &Inv)
Handle invalidation events in the new pass manager.
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:643
ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc)
Checks to see if the specified callsite can clobber the specified memory object.
Class for arbitrary precision integers.
Definition: APInt.h:69
FunctionPass * createBasicAAWrapperPass()
Analysis pass providing a never-invalidated alias analysis result.
bool operator!=(uint64_t V1, const APInt &V2)
Definition: APInt.h:1968
BasicAAResult(BasicAAResult &&Arg)
BasicAAResult(const BasicAAResult &Arg)
This file provides utility analysis objects describing memory locations.
Class for calculating and caching the underlying values of phis in a function.
Definition: PhiValues.h:42
API to communicate dependencies between analyses during invalidation.
Definition: PassManager.h:641
LLVM Value Representation.
Definition: Value.h:72
ModRefInfo
Flags indicating whether a memory access modifies or references memory.
A container for analyses that lazily runs them and caches their results.
bool operator==(uint64_t V1, const APInt &V2)
Definition: APInt.h:1966
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.