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 createLibCallAliasAnalysisPass(LibCallInfo * LCI)26 FunctionPass *llvm::createLibCallAliasAnalysisPass(LibCallInfo *LCI) { 27 return new LibCallAliasAnalysis(LCI); 28 } 29 ~LibCallAliasAnalysis()30 LibCallAliasAnalysis::~LibCallAliasAnalysis() { 31 delete LCI; 32 } 33 getAnalysisUsage(AnalysisUsage & AU) const34 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 AnalyzeLibCallDetails(const LibCallFunctionInfo * FI,ImmutableCallSite CS,const Location & Loc)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 getModRefInfo(ImmutableCallSite CS,const Location & Loc)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 } 138