NoAliasAnalysis.cpp revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338 
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"
19using namespace llvm;
20
21namespace {
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    void getAnalysisUsage(AnalysisUsage &AU) const override {}
34
35    void initializePass() override {
36      // Note: NoAA does not call InitializeAliasAnalysis because it's
37      // special and does not support chaining.
38      DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
39      DL = DLP ? &DLP->getDataLayout() : 0;
40    }
41
42    AliasResult alias(const Location &LocA, const Location &LocB) override {
43      return MayAlias;
44    }
45
46    ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override {
47      return UnknownModRefBehavior;
48    }
49    ModRefBehavior getModRefBehavior(const Function *F) override {
50      return UnknownModRefBehavior;
51    }
52
53    bool pointsToConstantMemory(const Location &Loc, bool OrLocal) override {
54      return false;
55    }
56    ModRefResult getModRefInfo(ImmutableCallSite CS,
57                               const Location &Loc) override {
58      return ModRef;
59    }
60    ModRefResult getModRefInfo(ImmutableCallSite CS1,
61                               ImmutableCallSite CS2) override {
62      return ModRef;
63    }
64
65    void deleteValue(Value *V) override {}
66    void copyValue(Value *From, Value *To) override {}
67    void addEscapingUse(Use &U) override {}
68
69    /// getAdjustedAnalysisPointer - This method is used when a pass implements
70    /// an analysis interface through multiple inheritance.  If needed, it
71    /// should override this to adjust the this pointer as needed for the
72    /// specified pass info.
73    void *getAdjustedAnalysisPointer(const void *ID) override {
74      if (ID == &AliasAnalysis::ID)
75        return (AliasAnalysis*)this;
76      return this;
77    }
78  };
79}  // End of anonymous namespace
80
81// Register this pass...
82char NoAA::ID = 0;
83INITIALIZE_AG_PASS(NoAA, AliasAnalysis, "no-aa",
84                   "No Alias Analysis (always returns 'may' alias)",
85                   true, true, true)
86
87ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
88