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