1 //===- NoAliasAnalysis.cpp - Minimal Alias Analysis Impl ------------------===// 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 // 10 // This file defines the default implementation of the Alias Analysis interface 11 // that simply returns "I don't know" for all queries. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "llvm/Analysis/Passes.h" 16 #include "llvm/Analysis/AliasAnalysis.h" 17 #include "llvm/IR/DataLayout.h" 18 #include "llvm/IR/LLVMContext.h" 19 #include "llvm/Pass.h" 20 using namespace llvm; 21 22 namespace { 23 /// NoAA - This class implements the -no-aa pass, which always returns "I 24 /// don't know" for alias queries. NoAA is unlike other alias analysis 25 /// implementations, in that it does not chain to a previous analysis. As 26 /// such it doesn't follow many of the rules that other alias analyses must. 27 /// 28 struct NoAA : public ImmutablePass, public AliasAnalysis { 29 static char ID; // Class identification, replacement for typeinfo 30 NoAA() : ImmutablePass(ID) { 31 initializeNoAAPass(*PassRegistry::getPassRegistry()); 32 } 33 34 void getAnalysisUsage(AnalysisUsage &AU) const override {} 35 36 void initializePass() override { 37 // Note: NoAA does not call InitializeAliasAnalysis because it's 38 // special and does not support chaining. 39 DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>(); 40 DL = DLP ? &DLP->getDataLayout() : nullptr; 41 } 42 43 AliasResult alias(const Location &LocA, const Location &LocB) override { 44 return MayAlias; 45 } 46 47 ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override { 48 return UnknownModRefBehavior; 49 } 50 ModRefBehavior getModRefBehavior(const Function *F) override { 51 return UnknownModRefBehavior; 52 } 53 54 bool pointsToConstantMemory(const Location &Loc, bool OrLocal) override { 55 return false; 56 } 57 Location getArgLocation(ImmutableCallSite CS, unsigned ArgIdx, 58 ModRefResult &Mask) override { 59 Mask = ModRef; 60 return Location(CS.getArgument(ArgIdx), UnknownSize, 61 CS.getInstruction()->getMetadata(LLVMContext::MD_tbaa)); 62 } 63 64 ModRefResult getModRefInfo(ImmutableCallSite CS, 65 const Location &Loc) override { 66 return ModRef; 67 } 68 ModRefResult getModRefInfo(ImmutableCallSite CS1, 69 ImmutableCallSite CS2) override { 70 return ModRef; 71 } 72 73 void deleteValue(Value *V) override {} 74 void copyValue(Value *From, Value *To) override {} 75 void addEscapingUse(Use &U) override {} 76 77 /// getAdjustedAnalysisPointer - This method is used when a pass implements 78 /// an analysis interface through multiple inheritance. If needed, it 79 /// should override this to adjust the this pointer as needed for the 80 /// specified pass info. 81 void *getAdjustedAnalysisPointer(const void *ID) override { 82 if (ID == &AliasAnalysis::ID) 83 return (AliasAnalysis*)this; 84 return this; 85 } 86 }; 87 } // End of anonymous namespace 88 89 // Register this pass... 90 char NoAA::ID = 0; 91 INITIALIZE_AG_PASS(NoAA, AliasAnalysis, "no-aa", 92 "No Alias Analysis (always returns 'may' alias)", 93 true, true, true) 94 95 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); } 96
