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"
21#include "llvm/Analysis/AliasAnalysis.h"
22#include "llvm/Analysis/AssumptionCache.h"
23#include "llvm/Analysis/MemoryLocation.h"
24#include "llvm/IR/InstrTypes.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
32namespace llvm {
33
34struct AAMDNodes;
35class APInt;
36class AssumptionCache;
37class BasicBlock;
38class DataLayout;
39class DominatorTree;
40class Function;
41class GEPOperator;
42class LoopInfo;
43class PHINode;
44class SelectInst;
45class TargetLibraryInfo;
46class PhiValues;
47class Value;
48
49/// This is the AA result object for the basic, local, and stateless alias
50/// analysis. It implements the AA query interface in an entirely stateless
51/// manner. As one consequence, it is never invalidated due to IR changes.
52/// While it does retain some storage, that is used as an optimization and not
53/// to preserve information from query to query. However it does retain handles
54/// to various other analyses and must be recomputed when those analyses are.
55class BasicAAResult : public AAResultBase<BasicAAResult> {
56 friend AAResultBase<BasicAAResult>;
57
58 const DataLayout &DL;
59 const Function &F;
60 const TargetLibraryInfo &TLI;
61 AssumptionCache &AC;
62 DominatorTree *DT;
63 LoopInfo *LI;
64 PhiValues *PV;
65
66public:
67 BasicAAResult(const DataLayout &DL, const Function &F,
68 const TargetLibraryInfo &TLI, AssumptionCache &AC,
69 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr,
70 PhiValues *PV = nullptr)
71 : AAResultBase(), DL(DL), F(F), TLI(TLI), AC(AC), DT(DT), LI(LI), PV(PV)
72 {}
73
74 BasicAAResult(const BasicAAResult &Arg)
75 : AAResultBase(Arg), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), AC(Arg.AC),
76 DT(Arg.DT), LI(Arg.LI), PV(Arg.PV) {}
77 BasicAAResult(BasicAAResult &&Arg)
78 : AAResultBase(std::move(Arg)), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI),
79 AC(Arg.AC), DT(Arg.DT), LI(Arg.LI), PV(Arg.PV) {}
80
81 /// Handle invalidation events in the new pass manager.
82 bool invalidate(Function &Fn, const PreservedAnalyses &PA,
83 FunctionAnalysisManager::Invalidator &Inv);
84
85 AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB);
86
87 ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc);
88
89 ModRefInfo getModRefInfo(const CallBase *Call1, const CallBase *Call2);
90
91 /// Chases pointers until we find a (constant global) or not.
92 bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal);
93
94 /// Get the location associated with a pointer argument of a callsite.
95 ModRefInfo getArgModRefInfo(const CallBase *Call, unsigned ArgIdx);
96
97 /// Returns the behavior when calling the given call site.
98 FunctionModRefBehavior getModRefBehavior(const CallBase *Call);
99
100 /// Returns the behavior when calling the given function. For use when the
101 /// call site is not known.
102 FunctionModRefBehavior getModRefBehavior(const Function *Fn);
103
104private:
105 // A linear transformation of a Value; this class represents ZExt(SExt(V,
106 // SExtBits), ZExtBits) * Scale + Offset.
107 struct VariableGEPIndex {
108 // An opaque Value - we can't decompose this further.
109 const Value *V;
110
111 // We need to track what extensions we've done as we consider the same Value
112 // with different extensions as different variables in a GEP's linear
113 // expression;
114 // e.g.: if V == -1, then sext(x) != zext(x).
115 unsigned ZExtBits;
116 unsigned SExtBits;
117
118 APInt Scale;
119
120 bool operator==(const VariableGEPIndex &Other) const {
121 return V == Other.V && ZExtBits == Other.ZExtBits &&
122 SExtBits == Other.SExtBits && Scale == Other.Scale;
123 }
124
125 bool operator!=(const VariableGEPIndex &Other) const {
126 return !operator==(Other);
127 }
128 };
129
130 // Represents the internal structure of a GEP, decomposed into a base pointer,
131 // constant offsets, and variable scaled indices.
132 struct DecomposedGEP {
133 // Base pointer of the GEP
134 const Value *Base;
135 // Total constant offset w.r.t the base from indexing into structs
136 APInt StructOffset;
137 // Total constant offset w.r.t the base from indexing through
138 // pointers/arrays/vectors
139 APInt OtherOffset;
140 // Scaled variable (non-constant) indices.
141 SmallVector<VariableGEPIndex, 4> VarIndices;
142 };
143
144 /// Track alias queries to guard against recursion.
145 using LocPair = std::pair<MemoryLocation, MemoryLocation>;
146 using AliasCacheTy = SmallDenseMap<LocPair, AliasResult, 8>;
147 AliasCacheTy AliasCache;
148
149 /// Tracks phi nodes we have visited.
150 ///
151 /// When interpret "Value" pointer equality as value equality we need to make
152 /// sure that the "Value" is not part of a cycle. Otherwise, two uses could
153 /// come from different "iterations" of a cycle and see different values for
154 /// the same "Value" pointer.
155 ///
156 /// The following example shows the problem:
157 /// %p = phi(%alloca1, %addr2)
158 /// %l = load %ptr
159 /// %addr1 = gep, %alloca2, 0, %l
160 /// %addr2 = gep %alloca2, 0, (%l + 1)
161 /// alias(%p, %addr1) -> MayAlias !
162 /// store %l, ...
163 SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs;
164
165 /// Tracks instructions visited by pointsToConstantMemory.
166 SmallPtrSet<const Value *, 16> Visited;
167
168 static const Value *
169 GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset,
170 unsigned &ZExtBits, unsigned &SExtBits,
171 const DataLayout &DL, unsigned Depth, AssumptionCache *AC,
172 DominatorTree *DT, bool &NSW, bool &NUW);
173
174 static bool DecomposeGEPExpression(const Value *V, DecomposedGEP &Decomposed,
175 const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT);
176
177 static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp,
178 const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject,
179 LocationSize ObjectAccessSize);
180
181 /// A Heuristic for aliasGEP that searches for a constant offset
182 /// between the variables.
183 ///
184 /// GetLinearExpression has some limitations, as generally zext(%x + 1)
185 /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression
186 /// will therefore conservatively refuse to decompose these expressions.
187 /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if
188 /// the addition overflows.
189 bool
190 constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices,
191 LocationSize V1Size, LocationSize V2Size,
192 APInt BaseOffset, AssumptionCache *AC,
193 DominatorTree *DT);
194
195 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
196
197 void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
198 const SmallVectorImpl<VariableGEPIndex> &Src);
199
200 AliasResult aliasGEP(const GEPOperator *V1, LocationSize V1Size,
201 const AAMDNodes &V1AAInfo, const Value *V2,
202 LocationSize V2Size, const AAMDNodes &V2AAInfo,
203 const Value *UnderlyingV1, const Value *UnderlyingV2);
204
205 AliasResult aliasPHI(const PHINode *PN, LocationSize PNSize,
206 const AAMDNodes &PNAAInfo, const Value *V2,
207 LocationSize V2Size, const AAMDNodes &V2AAInfo,
208 const Value *UnderV2);
209
210 AliasResult aliasSelect(const SelectInst *SI, LocationSize SISize,
211 const AAMDNodes &SIAAInfo, const Value *V2,
212 LocationSize V2Size, const AAMDNodes &V2AAInfo,
213 const Value *UnderV2);
214
215 AliasResult aliasCheck(const Value *V1, LocationSize V1Size,
216 AAMDNodes V1AATag, const Value *V2,
217 LocationSize V2Size, AAMDNodes V2AATag,
218 const Value *O1 = nullptr, 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