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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"
21 : #include "llvm/Analysis/AliasAnalysis.h"
22 : #include "llvm/Analysis/AssumptionCache.h"
23 : #include "llvm/Analysis/MemoryLocation.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 PhiValues;
47 : class 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.
55 : class 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 :
66 : public:
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 3041561 : : 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 1452970 : BasicAAResult(BasicAAResult &&Arg)
78 1452970 : : AAResultBase(std::move(Arg)), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI),
79 1452970 : 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(ImmutableCallSite CS, const MemoryLocation &Loc);
88 :
89 : ModRefInfo getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2);
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(ImmutableCallSite CS, unsigned ArgIdx);
96 :
97 : /// Returns the behavior when calling the given call site.
98 : FunctionModRefBehavior getModRefBehavior(ImmutableCallSite CS);
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 :
104 : private:
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 : int64_t Scale;
119 :
120 : bool operator==(const VariableGEPIndex &Other) const {
121 567 : return V == Other.V && ZExtBits == Other.ZExtBits &&
122 1201 : 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 13524178 : 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 : int64_t StructOffset;
137 : // Total constant offset w.r.t the base from indexing through
138 : // pointers/arrays/vectors
139 : int64_t 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 : int64_t 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.
222 : class BasicAA : public AnalysisInfoMixin<BasicAA> {
223 : friend AnalysisInfoMixin<BasicAA>;
224 :
225 : static AnalysisKey Key;
226 :
227 : public:
228 : using Result = BasicAAResult;
229 :
230 : BasicAAResult run(Function &F, FunctionAnalysisManager &AM);
231 : };
232 :
233 : /// Legacy wrapper pass to provide the BasicAAResult object.
234 : class BasicAAWrapperPass : public FunctionPass {
235 : std::unique_ptr<BasicAAResult> Result;
236 :
237 : virtual void anchor();
238 :
239 : public:
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 :
251 : FunctionPass *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.
256 : BasicAAResult 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.
261 : class LegacyAARGetter {
262 : Pass &P;
263 : Optional<BasicAAResult> BAR;
264 : Optional<AAResults> AAR;
265 :
266 : public:
267 1056143 : LegacyAARGetter(Pass &P) : P(P) {}
268 1451366 : AAResults &operator()(Function &F) {
269 1451366 : BAR.emplace(createLegacyPMBasicAAResult(P, F));
270 2902732 : AAR.emplace(createLegacyPMAAResults(P, F, *BAR));
271 1451366 : return *AAR;
272 : }
273 : };
274 :
275 : } // end namespace llvm
276 :
277 : #endif // LLVM_ANALYSIS_BASICALIASANALYSIS_H
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