lib/Analysis/LibCallAliasAnalysis.cpp

   1 //===- LibCallAliasAnalysis.cpp - Implement AliasAnalysis for libcalls ----===//
   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 implements the LibCallAliasAnalysis class.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Analysis/LibCallAliasAnalysis.h"
  15 #include "llvm/Analysis/Passes.h"
  16 #include "llvm/Analysis/LibCallSemantics.h"
  17 #include "llvm/Function.h"
  18 #include "llvm/Pass.h"
  19 using namespace llvm;
  20
  21 // Register this pass...
  22 char LibCallAliasAnalysis::ID = 0;
  23 static RegisterPass<LibCallAliasAnalysis>
  24 X("libcall-aa", "LibCall Alias Analysis", false, true);
  25
  26 // Declare that we implement the AliasAnalysis interface
  27 static RegisterAnalysisGroup<AliasAnalysis> Y(X);
  28
  29 FunctionPass *llvm::createLibCallAliasAnalysisPass(LibCallInfo *LCI) {
  30   return new LibCallAliasAnalysis(LCI);
  31 }
  32
  33 LibCallAliasAnalysis::~LibCallAliasAnalysis() {
  34   delete LCI;
  35 }
  36
  37 void LibCallAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
  38   AliasAnalysis::getAnalysisUsage(AU);
  39   AU.setPreservesAll();                         // Does not transform code
  40 }
  41
  42
  43
  44 /// AnalyzeLibCallDetails - Given a call to a function with the specified
  45 /// LibCallFunctionInfo, see if we can improve the mod/ref footprint of the call
  46 /// vs the specified pointer/size.
  47 AliasAnalysis::ModRefResult
  48 LibCallAliasAnalysis::AnalyzeLibCallDetails(const LibCallFunctionInfo *FI,
  49                                             CallSite CS, Value *P,
  50                                             unsigned Size) {
  51   // If we have a function, check to see what kind of mod/ref effects it
  52   // has.  Start by including any info globally known about the function.
  53   AliasAnalysis::ModRefResult MRInfo = FI->UniversalBehavior;
  54   if (MRInfo == NoModRef) return MRInfo;
  55
  56   // If that didn't tell us that the function is 'readnone', check to see
  57   // if we have detailed info and if 'P' is any of the locations we know
  58   // about.
  59   const LibCallFunctionInfo::LocationMRInfo *Details = FI->LocationDetails;
  60   if (Details == 0)
  61     return MRInfo;
  62
  63   // If the details array is of the 'DoesNot' kind, we only know something if
  64   // the pointer is a match for one of the locations in 'Details'.  If we find a
  65   // match, we can prove some interactions cannot happen.
  66   //
  67   if (FI->DetailsType == LibCallFunctionInfo::DoesNot) {
  68     // Find out if the pointer refers to a known location.
  69     for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) {
  70       const LibCallLocationInfo &Loc =
  71       LCI->getLocationInfo(Details[i].LocationID);
  72       LibCallLocationInfo::LocResult Res = Loc.isLocation(CS, P, Size);
  73       if (Res != LibCallLocationInfo::Yes) continue;
  74
  75       // If we find a match against a location that we 'do not' interact with,
  76       // learn this info into MRInfo.
  77       return ModRefResult(MRInfo & ~Details[i].MRInfo);
  78     }
  79     return MRInfo;
  80   }
  81
  82   // If the details are of the 'DoesOnly' sort, we know something if the pointer
  83   // is a match for one of the locations in 'Details'.  Also, if we can prove
  84   // that the pointers is *not* one of the locations in 'Details', we know that
  85   // the call is NoModRef.
  86   assert(FI->DetailsType == LibCallFunctionInfo::DoesOnly);
  87
  88   // Find out if the pointer refers to a known location.
  89   bool NoneMatch = true;
  90   for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) {
  91     const LibCallLocationInfo &Loc =
  92     LCI->getLocationInfo(Details[i].LocationID);
  93     LibCallLocationInfo::LocResult Res = Loc.isLocation(CS, P, Size);
  94     if (Res == LibCallLocationInfo::No) continue;
  95
  96     // If we don't know if this pointer points to the location, then we have to
  97     // assume it might alias in some case.
  98     if (Res == LibCallLocationInfo::Unknown) {
  99       NoneMatch = false;
 100       continue;
 101     }
 102
 103     // If we know that this pointer definitely is pointing into the location,
 104     // merge in this information.
 105     return ModRefResult(MRInfo & Details[i].MRInfo);
 106   }
 107
 108   // If we found that the pointer is guaranteed to not match any of the
 109   // locations in our 'DoesOnly' rule, then we know that the pointer must point
 110   // to some other location.  Since the libcall doesn't mod/ref any other
 111   // locations, return NoModRef.
 112   if (NoneMatch)
 113     return NoModRef;
 114
 115   // Otherwise, return any other info gained so far.
 116   return MRInfo;
 117 }
 118
 119 // getModRefInfo - Check to see if the specified callsite can clobber the
 120 // specified memory object.
 121 //
 122 AliasAnalysis::ModRefResult
 123 LibCallAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
 124   ModRefResult MRInfo = ModRef;
 125
 126   // If this is a direct call to a function that LCI knows about, get the
 127   // information about the runtime function.
 128   if (LCI) {
 129     if (Function *F = CS.getCalledFunction()) {
 130       if (const LibCallFunctionInfo *FI = LCI->getFunctionInfo(F)) {
 131         MRInfo = ModRefResult(MRInfo & AnalyzeLibCallDetails(FI, CS, P, Size));
 132         if (MRInfo == NoModRef) return NoModRef;
 133       }
 134     }
 135   }
 136
 137   // The AliasAnalysis base class has some smarts, lets use them.
 138   return (ModRefResult)(MRInfo | AliasAnalysis::getModRefInfo(CS, P, Size));
 139 }