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 #include "llvm/Target/TargetData.h"
  20 using namespace llvm;
  21
  22 // Register this pass...
  23 char LibCallAliasAnalysis::ID = 0;
  24 static RegisterPass<LibCallAliasAnalysis>
  25 X("libcall-aa", "LibCall Alias Analysis", false, true);
  26
  27 // Declare that we implement the AliasAnalysis interface
  28 static RegisterAnalysisGroup<AliasAnalysis> Y(X);
  29
  30 FunctionPass *llvm::createLibCallAliasAnalysisPass(LibCallInfo *LCI) {
  31   return new LibCallAliasAnalysis(LCI);
  32 }
  33
  34 LibCallAliasAnalysis::~LibCallAliasAnalysis() {
  35   delete LCI;
  36 }
  37
  38 void LibCallAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
  39   AliasAnalysis::getAnalysisUsage(AU);
  40   AU.addRequired<TargetData>();
  41   AU.setPreservesAll();                         // Does not transform code
  42 }
  43
  44
  45
  46 /// AnalyzeLibCallDetails - Given a call to a function with the specified
  47 /// LibCallFunctionInfo, see if we can improve the mod/ref footprint of the call
  48 /// vs the specified pointer/size.
  49 AliasAnalysis::ModRefResult
  50 LibCallAliasAnalysis::AnalyzeLibCallDetails(const LibCallFunctionInfo *FI,
  51                                             CallSite CS, Value *P,
  52                                             unsigned Size) {
  53   // If we have a function, check to see what kind of mod/ref effects it
  54   // has.  Start by including any info globally known about the function.
  55   AliasAnalysis::ModRefResult MRInfo = FI->UniversalBehavior;
  56   if (MRInfo == NoModRef) return MRInfo;
  57
  58   // If that didn't tell us that the function is 'readnone', check to see
  59   // if we have detailed info and if 'P' is any of the locations we know
  60   // about.
  61   const LibCallFunctionInfo::LocationMRInfo *Details = FI->LocationDetails;
  62   if (Details == 0)
  63     return MRInfo;
  64
  65   // If the details array is of the 'DoesNot' kind, we only know something if
  66   // the pointer is a match for one of the locations in 'Details'.  If we find a
  67   // match, we can prove some interactions cannot happen.
  68   //
  69   if (FI->DetailsType == LibCallFunctionInfo::DoesNot) {
  70     // Find out if the pointer refers to a known location.
  71     for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) {
  72       const LibCallLocationInfo &Loc =
  73       LCI->getLocationInfo(Details[i].LocationID);
  74       LibCallLocationInfo::LocResult Res = Loc.isLocation(CS, P, Size);
  75       if (Res != LibCallLocationInfo::Yes) continue;
  76
  77       // If we find a match against a location that we 'do not' interact with,
  78       // learn this info into MRInfo.
  79       return ModRefResult(MRInfo & ~Details[i].MRInfo);
  80     }
  81     return MRInfo;
  82   }
  83
  84   // If the details are of the 'DoesOnly' sort, we know something if the pointer
  85   // is a match for one of the locations in 'Details'.  Also, if we can prove
  86   // that the pointers is *not* one of the locations in 'Details', we know that
  87   // the call is NoModRef.
  88   assert(FI->DetailsType == LibCallFunctionInfo::DoesOnly);
  89
  90   // Find out if the pointer refers to a known location.
  91   bool NoneMatch = true;
  92   for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) {
  93     const LibCallLocationInfo &Loc =
  94     LCI->getLocationInfo(Details[i].LocationID);
  95     LibCallLocationInfo::LocResult Res = Loc.isLocation(CS, P, Size);
  96     if (Res == LibCallLocationInfo::No) continue;
  97
  98     // If we don't know if this pointer points to the location, then we have to
  99     // assume it might alias in some case.
 100     if (Res == LibCallLocationInfo::Unknown) {
 101       NoneMatch = false;
 102       continue;
 103     }
 104
 105     // If we know that this pointer definitely is pointing into the location,
 106     // merge in this information.
 107     return ModRefResult(MRInfo & Details[i].MRInfo);
 108   }
 109
 110   // If we found that the pointer is guaranteed to not match any of the
 111   // locations in our 'DoesOnly' rule, then we know that the pointer must point
 112   // to some other location.  Since the libcall doesn't mod/ref any other
 113   // locations, return NoModRef.
 114   if (NoneMatch)
 115     return NoModRef;
 116
 117   // Otherwise, return any other info gained so far.
 118   return MRInfo;
 119 }
 120
 121 // getModRefInfo - Check to see if the specified callsite can clobber the
 122 // specified memory object.
 123 //
 124 AliasAnalysis::ModRefResult
 125 LibCallAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
 126   ModRefResult MRInfo = ModRef;
 127
 128   // If this is a direct call to a function that LCI knows about, get the
 129   // information about the runtime function.
 130   if (LCI) {
 131     if (Function *F = CS.getCalledFunction()) {
 132       if (const LibCallFunctionInfo *FI = LCI->getFunctionInfo(F)) {
 133         MRInfo = ModRefResult(MRInfo & AnalyzeLibCallDetails(FI, CS, P, Size));
 134         if (MRInfo == NoModRef) return NoModRef;
 135       }
 136     }
 137   }
 138
 139   // The AliasAnalysis base class has some smarts, lets use them.
 140   return (ModRefResult)(MRInfo | AliasAnalysis::getModRefInfo(CS, P, Size));
 141 }