lib/Analysis/NoAliasAnalysis.cpp

   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/AliasAnalysis.h"
  16 #include "llvm/Analysis/Passes.h"
  17 #include "llvm/Pass.h"
  18 #include "llvm/Target/TargetData.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<TargetData>();
  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(); }