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/LibCallSemantics.h" 16 #include "llvm/Analysis/Passes.h" 17 #include "llvm/IR/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 bool LibCallAliasAnalysis::runOnFunction(Function &F) { 40 // set up super class 41 InitializeAliasAnalysis(this, &F.getParent()->getDataLayout()); 42 return false; 43 } 44 45 /// AnalyzeLibCallDetails - Given a call to a function with the specified 46 /// LibCallFunctionInfo, see if we can improve the mod/ref footprint of the call 47 /// vs the specified pointer/size. 48 AliasAnalysis::ModRefResult 49 LibCallAliasAnalysis::AnalyzeLibCallDetails(const LibCallFunctionInfo *FI, 50 ImmutableCallSite CS, 51 const Location &Loc) { 52 // If we have a function, check to see what kind of mod/ref effects it 53 // has. Start by including any info globally known about the function. 54 AliasAnalysis::ModRefResult MRInfo = FI->UniversalBehavior; 55 if (MRInfo == NoModRef) return MRInfo; 56 57 // If that didn't tell us that the function is 'readnone', check to see 58 // if we have detailed info and if 'P' is any of the locations we know 59 // about. 60 const LibCallFunctionInfo::LocationMRInfo *Details = FI->LocationDetails; 61 if (Details == nullptr) 62 return MRInfo; 63 64 // If the details array is of the 'DoesNot' kind, we only know something if 65 // the pointer is a match for one of the locations in 'Details'. If we find a 66 // match, we can prove some interactions cannot happen. 67 // 68 if (FI->DetailsType == LibCallFunctionInfo::DoesNot) { 69 // Find out if the pointer refers to a known location. 70 for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) { 71 const LibCallLocationInfo &LocInfo = 72 LCI->getLocationInfo(Details[i].LocationID); 73 LibCallLocationInfo::LocResult Res = LocInfo.isLocation(CS, Loc); 74 if (Res != LibCallLocationInfo::Yes) continue; 75 76 // If we find a match against a location that we 'do not' interact with, 77 // learn this info into MRInfo. 78 return ModRefResult(MRInfo & ~Details[i].MRInfo); 79 } 80 return MRInfo; 81 } 82 83 // If the details are of the 'DoesOnly' sort, we know something if the pointer 84 // is a match for one of the locations in 'Details'. Also, if we can prove 85 // that the pointers is *not* one of the locations in 'Details', we know that 86 // the call is NoModRef. 87 assert(FI->DetailsType == LibCallFunctionInfo::DoesOnly); 88 89 // Find out if the pointer refers to a known location. 90 bool NoneMatch = true; 91 for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) { 92 const LibCallLocationInfo &LocInfo = 93 LCI->getLocationInfo(Details[i].LocationID); 94 LibCallLocationInfo::LocResult Res = LocInfo.isLocation(CS, Loc); 95 if (Res == LibCallLocationInfo::No) continue; 96 97 // If we don't know if this pointer points to the location, then we have to 98 // assume it might alias in some case. 99 if (Res == LibCallLocationInfo::Unknown) { 100 NoneMatch = false; 101 continue; 102 } 103 104 // If we know that this pointer definitely is pointing into the location, 105 // merge in this information. 106 return ModRefResult(MRInfo & Details[i].MRInfo); 107 } 108 109 // If we found that the pointer is guaranteed to not match any of the 110 // locations in our 'DoesOnly' rule, then we know that the pointer must point 111 // to some other location. Since the libcall doesn't mod/ref any other 112 // locations, return NoModRef. 113 if (NoneMatch) 114 return NoModRef; 115 116 // Otherwise, return any other info gained so far. 117 return MRInfo; 118 } 119 120 // getModRefInfo - Check to see if the specified callsite can clobber the 121 // specified memory object. 122 // 123 AliasAnalysis::ModRefResult 124 LibCallAliasAnalysis::getModRefInfo(ImmutableCallSite CS, 125 const Location &Loc) { 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 (const Function *F = CS.getCalledFunction()) { 132 if (const LibCallFunctionInfo *FI = LCI->getFunctionInfo(F)) { 133 MRInfo = ModRefResult(MRInfo & AnalyzeLibCallDetails(FI, CS, Loc)); 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, Loc)); 141 } 142
