1 //===-- TargetMachine.cpp - General Target Information ---------------------==// 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 describes the general parts of a Target machine. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/Target/TargetMachine.h" 15 #include "llvm/Analysis/TargetTransformInfo.h" 16 #include "llvm/CodeGen/TargetLoweringObjectFile.h" 17 #include "llvm/CodeGen/TargetSubtargetInfo.h" 18 #include "llvm/IR/Function.h" 19 #include "llvm/IR/GlobalAlias.h" 20 #include "llvm/IR/GlobalValue.h" 21 #include "llvm/IR/GlobalVariable.h" 22 #include "llvm/IR/LegacyPassManager.h" 23 #include "llvm/IR/Mangler.h" 24 #include "llvm/MC/MCAsmInfo.h" 25 #include "llvm/MC/MCContext.h" 26 #include "llvm/MC/MCInstrInfo.h" 27 #include "llvm/MC/MCSectionMachO.h" 28 #include "llvm/MC/MCTargetOptions.h" 29 #include "llvm/MC/SectionKind.h" 30 using namespace llvm; 31 32 //--------------------------------------------------------------------------- 33 // TargetMachine Class 34 // 35 36 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString, 37 const Triple &TT, StringRef CPU, StringRef FS, 38 const TargetOptions &Options) 39 : TheTarget(T), DL(DataLayoutString), TargetTriple(TT), TargetCPU(CPU), 40 TargetFS(FS), AsmInfo(nullptr), MRI(nullptr), MII(nullptr), STI(nullptr), 41 RequireStructuredCFG(false), DefaultOptions(Options), Options(Options) { 42 } 43 44 TargetMachine::~TargetMachine() { 45 delete AsmInfo; 46 delete MRI; 47 delete MII; 48 delete STI; 49 } 50 51 bool TargetMachine::isPositionIndependent() const { 52 return getRelocationModel() == Reloc::PIC_; 53 } 54 55 /// \brief Reset the target options based on the function's attributes. 56 // FIXME: This function needs to go away for a number of reasons: 57 // a) global state on the TargetMachine is terrible in general, 58 // b) these target options should be passed only on the function 59 // and not on the TargetMachine (via TargetOptions) at all. 60 void TargetMachine::resetTargetOptions(const Function &F) const { 61 #define RESET_OPTION(X, Y) \ 62 do { \ 63 if (F.hasFnAttribute(Y)) \ 64 Options.X = (F.getFnAttribute(Y).getValueAsString() == "true"); \ 65 else \ 66 Options.X = DefaultOptions.X; \ 67 } while (0) 68 69 RESET_OPTION(UnsafeFPMath, "unsafe-fp-math"); 70 RESET_OPTION(NoInfsFPMath, "no-infs-fp-math"); 71 RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math"); 72 RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math"); 73 RESET_OPTION(NoTrappingFPMath, "no-trapping-math"); 74 75 StringRef Denormal = 76 F.getFnAttribute("denormal-fp-math").getValueAsString(); 77 if (Denormal == "ieee") 78 Options.FPDenormalMode = FPDenormal::IEEE; 79 else if (Denormal == "preserve-sign") 80 Options.FPDenormalMode = FPDenormal::PreserveSign; 81 else if (Denormal == "positive-zero") 82 Options.FPDenormalMode = FPDenormal::PositiveZero; 83 else 84 Options.FPDenormalMode = DefaultOptions.FPDenormalMode; 85 } 86 87 /// Returns the code generation relocation model. The choices are static, PIC, 88 /// and dynamic-no-pic. 89 Reloc::Model TargetMachine::getRelocationModel() const { return RM; } 90 91 /// Returns the code model. The choices are small, kernel, medium, large, and 92 /// target default. 93 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; } 94 95 /// Get the IR-specified TLS model for Var. 96 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) { 97 switch (GV->getThreadLocalMode()) { 98 case GlobalVariable::NotThreadLocal: 99 llvm_unreachable("getSelectedTLSModel for non-TLS variable"); 100 break; 101 case GlobalVariable::GeneralDynamicTLSModel: 102 return TLSModel::GeneralDynamic; 103 case GlobalVariable::LocalDynamicTLSModel: 104 return TLSModel::LocalDynamic; 105 case GlobalVariable::InitialExecTLSModel: 106 return TLSModel::InitialExec; 107 case GlobalVariable::LocalExecTLSModel: 108 return TLSModel::LocalExec; 109 } 110 llvm_unreachable("invalid TLS model"); 111 } 112 113 bool TargetMachine::shouldAssumeDSOLocal(const Module &M, 114 const GlobalValue *GV) const { 115 // If the IR producer requested that this GV be treated as dso local, obey. 116 if (GV && GV->isDSOLocal()) 117 return true; 118 119 // If we are not supossed to use a PLT, we cannot assume that intrinsics are 120 // local since the linker can convert some direct access to access via plt. 121 if (M.getRtLibUseGOT() && !GV) 122 return false; 123 124 // According to the llvm language reference, we should be able to 125 // just return false in here if we have a GV, as we know it is 126 // dso_preemptable. At this point in time, the various IR producers 127 // have not been transitioned to always produce a dso_local when it 128 // is possible to do so. 129 // In the case of intrinsics, GV is null and there is nowhere to put 130 // dso_local. Returning false for those will produce worse code in some 131 // architectures. For example, on x86 the caller has to set ebx before calling 132 // a plt. 133 // As a result we still have some logic in here to improve the quality of the 134 // generated code. 135 // FIXME: Add a module level metadata for whether intrinsics should be assumed 136 // local. 137 138 Reloc::Model RM = getRelocationModel(); 139 const Triple &TT = getTargetTriple(); 140 141 // DLLImport explicitly marks the GV as external. 142 if (GV && GV->hasDLLImportStorageClass()) 143 return false; 144 145 // Every other GV is local on COFF. 146 // Make an exception for windows OS in the triple: Some firmware builds use 147 // *-win32-macho triples. This (accidentally?) produced windows relocations 148 // without GOT tables in older clang versions; Keep this behaviour. 149 if (TT.isOSBinFormatCOFF() || (TT.isOSWindows() && TT.isOSBinFormatMachO())) 150 return true; 151 152 // Most PIC code sequences that assume that a symbol is local cannot 153 // produce a 0 if it turns out the symbol is undefined. While this 154 // is ABI and relocation depended, it seems worth it to handle it 155 // here. 156 if (GV && isPositionIndependent() && GV->hasExternalWeakLinkage()) 157 return false; 158 159 if (GV && !GV->hasDefaultVisibility()) 160 return true; 161 162 if (TT.isOSBinFormatMachO()) { 163 if (RM == Reloc::Static) 164 return true; 165 return GV && GV->isStrongDefinitionForLinker(); 166 } 167 168 assert(TT.isOSBinFormatELF()); 169 assert(RM != Reloc::DynamicNoPIC); 170 171 bool IsExecutable = 172 RM == Reloc::Static || M.getPIELevel() != PIELevel::Default; 173 if (IsExecutable) { 174 // If the symbol is defined, it cannot be preempted. 175 if (GV && !GV->isDeclarationForLinker()) 176 return true; 177 178 // A symbol marked nonlazybind should not be accessed with a plt. If the 179 // symbol turns out to be external, the linker will convert a direct 180 // access to an access via the plt, so don't assume it is local. 181 const Function *F = dyn_cast_or_null<Function>(GV); 182 if (F && F->hasFnAttribute(Attribute::NonLazyBind)) 183 return false; 184 185 bool IsTLS = GV && GV->isThreadLocal(); 186 bool IsAccessViaCopyRelocs = 187 GV && Options.MCOptions.MCPIECopyRelocations && isa<GlobalVariable>(GV); 188 Triple::ArchType Arch = TT.getArch(); 189 bool IsPPC = 190 Arch == Triple::ppc || Arch == Triple::ppc64 || Arch == Triple::ppc64le; 191 // Check if we can use copy relocations. PowerPC has no copy relocations. 192 if (!IsTLS && !IsPPC && (RM == Reloc::Static || IsAccessViaCopyRelocs)) 193 return true; 194 } 195 196 // ELF supports preemption of other symbols. 197 return false; 198 } 199 200 bool TargetMachine::useEmulatedTLS() const { 201 // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls 202 // was specified explicitly; otherwise uses target triple to decide default. 203 if (Options.ExplicitEmulatedTLS) 204 return Options.EmulatedTLS; 205 return getTargetTriple().hasDefaultEmulatedTLS(); 206 } 207 208 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const { 209 bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default; 210 Reloc::Model RM = getRelocationModel(); 211 bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE; 212 bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV); 213 214 TLSModel::Model Model; 215 if (IsSharedLibrary) { 216 if (IsLocal) 217 Model = TLSModel::LocalDynamic; 218 else 219 Model = TLSModel::GeneralDynamic; 220 } else { 221 if (IsLocal) 222 Model = TLSModel::LocalExec; 223 else 224 Model = TLSModel::InitialExec; 225 } 226 227 // If the user specified a more specific model, use that. 228 TLSModel::Model SelectedModel = getSelectedTLSModel(GV); 229 if (SelectedModel > Model) 230 return SelectedModel; 231 232 return Model; 233 } 234 235 /// Returns the optimization level: None, Less, Default, or Aggressive. 236 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; } 237 238 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; } 239 240 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) { 241 return TargetTransformInfo(F.getParent()->getDataLayout()); 242 } 243 244 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name, 245 const GlobalValue *GV, Mangler &Mang, 246 bool MayAlwaysUsePrivate) const { 247 if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) { 248 // Simple case: If GV is not private, it is not important to find out if 249 // private labels are legal in this case or not. 250 Mang.getNameWithPrefix(Name, GV, false); 251 return; 252 } 253 const TargetLoweringObjectFile *TLOF = getObjFileLowering(); 254 TLOF->getNameWithPrefix(Name, GV, *this); 255 } 256 257 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const { 258 const TargetLoweringObjectFile *TLOF = getObjFileLowering(); 259 SmallString<128> NameStr; 260 getNameWithPrefix(NameStr, GV, TLOF->getMangler()); 261 return TLOF->getContext().getOrCreateSymbol(NameStr); 262 } 263 264 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() { 265 // Since Analysis can't depend on Target, use a std::function to invert the 266 // dependency. 267 return TargetIRAnalysis( 268 [this](const Function &F) { return this->getTargetTransformInfo(F); }); 269 } 270