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