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/IR/Module.h"
20 #include "llvm/Pass.h"
24 /// NoAA - This class implements the -no-aa pass, which always returns "I
25 /// don't know" for alias queries. NoAA is unlike other alias analysis
26 /// implementations, in that it does not chain to a previous analysis. As
27 /// such it doesn't follow many of the rules that other alias analyses must.
29 struct NoAA : public ImmutablePass, public AliasAnalysis {
30 static char ID; // Class identification, replacement for typeinfo
31 NoAA() : ImmutablePass(ID) {
32 initializeNoAAPass(*PassRegistry::getPassRegistry());
35 void getAnalysisUsage(AnalysisUsage &AU) const override {}
37 bool doInitialization(Module &M) override {
38 // Note: NoAA does not call InitializeAliasAnalysis because it's
39 // special and does not support chaining.
40 DL = &M.getDataLayout();
44 AliasResult alias(const MemoryLocation &LocA,
45 const MemoryLocation &LocB) override {
49 ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override {
50 return UnknownModRefBehavior;
52 ModRefBehavior getModRefBehavior(const Function *F) override {
53 return UnknownModRefBehavior;
56 bool pointsToConstantMemory(const MemoryLocation &Loc,
57 bool OrLocal) override {
60 ModRefResult getArgModRefInfo(ImmutableCallSite CS,
61 unsigned ArgIdx) override {
65 ModRefResult getModRefInfo(ImmutableCallSite CS,
66 const MemoryLocation &Loc) override {
69 ModRefResult getModRefInfo(ImmutableCallSite CS1,
70 ImmutableCallSite CS2) override {
74 void deleteValue(Value *V) 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(); }