1 //===- NoAliasAnalysis.cpp - Minimal Alias Analysis Impl ------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the default implementation of the Alias Analysis interface
11 // that simply returns "I don't know" for all queries.
13 //===----------------------------------------------------------------------===//
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"
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.
28 struct NoAA : public ImmutablePass, public AliasAnalysis {
29 static char ID; // Class identification, replacement for typeinfo
30 NoAA() : ImmutablePass(ID) {
31 initializeNoAAPass(*PassRegistry::getPassRegistry());
34 void getAnalysisUsage(AnalysisUsage &AU) const override {}
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;
43 AliasResult alias(const Location &LocA, const Location &LocB) override {
47 ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override {
48 return UnknownModRefBehavior;
50 ModRefBehavior getModRefBehavior(const Function *F) override {
51 return UnknownModRefBehavior;
54 bool pointsToConstantMemory(const Location &Loc, bool OrLocal) override {
57 Location getArgLocation(ImmutableCallSite CS, unsigned ArgIdx,
58 ModRefResult &Mask) override {
60 return Location(CS.getArgument(ArgIdx), UnknownSize,
61 CS.getInstruction()->getMetadata(LLVMContext::MD_tbaa));
64 ModRefResult getModRefInfo(ImmutableCallSite CS,
65 const Location &Loc) override {
68 ModRefResult getModRefInfo(ImmutableCallSite CS1,
69 ImmutableCallSite CS2) override {
73 void deleteValue(Value *V) override {}
74 void copyValue(Value *From, Value *To) override {}
75 void addEscapingUse(Use &U) override {}
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;
87 } // End of anonymous namespace
89 // Register this pass...
91 INITIALIZE_AG_PASS(NoAA, AliasAnalysis, "no-aa",
92 "No Alias Analysis (always returns 'may' alias)",
95 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }