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/Pass.h"
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.
27 struct NoAA : public ImmutablePass, public AliasAnalysis {
28 static char ID; // Class identification, replacement for typeinfo
29 NoAA() : ImmutablePass(ID) {
30 initializeNoAAPass(*PassRegistry::getPassRegistry());
33 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
36 virtual void initializePass() {
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() : 0;
43 virtual AliasResult alias(const Location &LocA, const Location &LocB) {
47 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS) {
48 return UnknownModRefBehavior;
50 virtual ModRefBehavior getModRefBehavior(const Function *F) {
51 return UnknownModRefBehavior;
54 virtual bool pointsToConstantMemory(const Location &Loc,
58 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
59 const Location &Loc) {
62 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
63 ImmutableCallSite CS2) {
67 virtual void deleteValue(Value *V) {}
68 virtual void copyValue(Value *From, Value *To) {}
69 virtual void addEscapingUse(Use &U) {}
71 /// getAdjustedAnalysisPointer - This method is used when a pass implements
72 /// an analysis interface through multiple inheritance. If needed, it
73 /// should override this to adjust the this pointer as needed for the
74 /// specified pass info.
75 virtual void *getAdjustedAnalysisPointer(const void *ID) {
76 if (ID == &AliasAnalysis::ID)
77 return (AliasAnalysis*)this;
81 } // End of anonymous namespace
83 // Register this pass...
85 INITIALIZE_AG_PASS(NoAA, AliasAnalysis, "no-aa",
86 "No Alias Analysis (always returns 'may' alias)",
89 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }