1 //===-- TargetMachine.cpp - General Target Information ---------------------==// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file describes the general parts of a Target machine. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/Target/TargetMachine.h" 14 #include "llvm/Analysis/TargetTransformInfo.h" 15 #include "llvm/IR/Function.h" 16 #include "llvm/IR/GlobalAlias.h" 17 #include "llvm/IR/GlobalValue.h" 18 #include "llvm/IR/GlobalVariable.h" 19 #include "llvm/IR/LegacyPassManager.h" 20 #include "llvm/IR/Mangler.h" 21 #include "llvm/MC/MCAsmInfo.h" 22 #include "llvm/MC/MCContext.h" 23 #include "llvm/MC/MCInstrInfo.h" 24 #include "llvm/MC/MCSectionMachO.h" 25 #include "llvm/MC/MCTargetOptions.h" 26 #include "llvm/MC/SectionKind.h" 27 #include "llvm/Target/TargetLoweringObjectFile.h" 28 using namespace llvm; 29 30 //--------------------------------------------------------------------------- 31 // TargetMachine Class 32 // 33 34 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString, 35 const Triple &TT, StringRef CPU, StringRef FS, 36 const TargetOptions &Options) 37 : TheTarget(T), DL(DataLayoutString), TargetTriple(TT), TargetCPU(CPU), 38 TargetFS(FS), AsmInfo(nullptr), MRI(nullptr), MII(nullptr), STI(nullptr), 39 RequireStructuredCFG(false), DefaultOptions(Options), Options(Options) { 40 } 41 42 TargetMachine::~TargetMachine() = default; 43 44 bool TargetMachine::isPositionIndependent() const { 45 return getRelocationModel() == Reloc::PIC_; 46 } 47 48 /// Reset the target options based on the function's attributes. 49 // FIXME: This function needs to go away for a number of reasons: 50 // a) global state on the TargetMachine is terrible in general, 51 // b) these target options should be passed only on the function 52 // and not on the TargetMachine (via TargetOptions) at all. 53 void TargetMachine::resetTargetOptions(const Function &F) const { 54 #define RESET_OPTION(X, Y) \ 55 do { \ 56 if (F.hasFnAttribute(Y)) \ 57 Options.X = (F.getFnAttribute(Y).getValueAsString() == "true"); \ 58 else \ 59 Options.X = DefaultOptions.X; \ 60 } while (0) 61 62 RESET_OPTION(UnsafeFPMath, "unsafe-fp-math"); 63 RESET_OPTION(NoInfsFPMath, "no-infs-fp-math"); 64 RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math"); 65 RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math"); 66 } 67 68 /// Returns the code generation relocation model. The choices are static, PIC, 69 /// and dynamic-no-pic. 70 Reloc::Model TargetMachine::getRelocationModel() const { return RM; } 71 72 /// Returns the code model. The choices are small, kernel, medium, large, and 73 /// target default. 74 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; } 75 76 /// Get the IR-specified TLS model for Var. 77 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) { 78 switch (GV->getThreadLocalMode()) { 79 case GlobalVariable::NotThreadLocal: 80 llvm_unreachable("getSelectedTLSModel for non-TLS variable"); 81 break; 82 case GlobalVariable::GeneralDynamicTLSModel: 83 return TLSModel::GeneralDynamic; 84 case GlobalVariable::LocalDynamicTLSModel: 85 return TLSModel::LocalDynamic; 86 case GlobalVariable::InitialExecTLSModel: 87 return TLSModel::InitialExec; 88 case GlobalVariable::LocalExecTLSModel: 89 return TLSModel::LocalExec; 90 } 91 llvm_unreachable("invalid TLS model"); 92 } 93 94 bool TargetMachine::shouldAssumeDSOLocal(const Module &M, 95 const GlobalValue *GV) const { 96 // If the IR producer requested that this GV be treated as dso local, obey. 97 if (GV && GV->isDSOLocal()) 98 return true; 99 100 // If we are not supossed to use a PLT, we cannot assume that intrinsics are 101 // local since the linker can convert some direct access to access via plt. 102 if (M.getRtLibUseGOT() && !GV) 103 return false; 104 105 // According to the llvm language reference, we should be able to 106 // just return false in here if we have a GV, as we know it is 107 // dso_preemptable. At this point in time, the various IR producers 108 // have not been transitioned to always produce a dso_local when it 109 // is possible to do so. 110 // In the case of intrinsics, GV is null and there is nowhere to put 111 // dso_local. Returning false for those will produce worse code in some 112 // architectures. For example, on x86 the caller has to set ebx before calling 113 // a plt. 114 // As a result we still have some logic in here to improve the quality of the 115 // generated code. 116 // FIXME: Add a module level metadata for whether intrinsics should be assumed 117 // local. 118 119 Reloc::Model RM = getRelocationModel(); 120 const Triple &TT = getTargetTriple(); 121 122 // DLLImport explicitly marks the GV as external. 123 if (GV && GV->hasDLLImportStorageClass()) 124 return false; 125 126 // On MinGW, variables that haven't been declared with DLLImport may still 127 // end up automatically imported by the linker. To make this feasible, 128 // don't assume the variables to be DSO local unless we actually know 129 // that for sure. This only has to be done for variables; for functions 130 // the linker can insert thunks for calling functions from another DLL. 131 if (TT.isWindowsGNUEnvironment() && GV && GV->isDeclarationForLinker() && 132 isa<GlobalVariable>(GV)) 133 return false; 134 135 // On COFF, don't mark 'extern_weak' symbols as DSO local. If these symbols 136 // remain unresolved in the link, they can be resolved to zero, which is 137 // outside the current DSO. 138 if (TT.isOSBinFormatCOFF() && GV && GV->hasExternalWeakLinkage()) 139 return false; 140 141 // Every other GV is local on COFF. 142 // Make an exception for windows OS in the triple: Some firmware builds use 143 // *-win32-macho triples. This (accidentally?) produced windows relocations 144 // without GOT tables in older clang versions; Keep this behaviour. 145 if (TT.isOSBinFormatCOFF() || (TT.isOSWindows() && TT.isOSBinFormatMachO())) 146 return true; 147 148 // Most PIC code sequences that assume that a symbol is local cannot 149 // produce a 0 if it turns out the symbol is undefined. While this 150 // is ABI and relocation depended, it seems worth it to handle it 151 // here. 152 if (GV && isPositionIndependent() && GV->hasExternalWeakLinkage()) 153 return false; 154 155 if (GV && !GV->hasDefaultVisibility()) 156 return true; 157 158 if (TT.isOSBinFormatMachO()) { 159 if (RM == Reloc::Static) 160 return true; 161 return GV && GV->isStrongDefinitionForLinker(); 162 } 163 164 // Due to the AIX linkage model, any global with default visibility is 165 // considered non-local. 166 if (TT.isOSBinFormatXCOFF()) 167 return false; 168 169 assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm()); 170 assert(RM != Reloc::DynamicNoPIC); 171 172 bool IsExecutable = 173 RM == Reloc::Static || M.getPIELevel() != PIELevel::Default; 174 if (IsExecutable) { 175 // If the symbol is defined, it cannot be preempted. 176 if (GV && !GV->isDeclarationForLinker()) 177 return true; 178 179 // A symbol marked nonlazybind should not be accessed with a plt. If the 180 // symbol turns out to be external, the linker will convert a direct 181 // access to an access via the plt, so don't assume it is local. 182 const Function *F = dyn_cast_or_null<Function>(GV); 183 if (F && F->hasFnAttribute(Attribute::NonLazyBind)) 184 return false; 185 186 bool IsTLS = GV && GV->isThreadLocal(); 187 bool IsAccessViaCopyRelocs = 188 GV && Options.MCOptions.MCPIECopyRelocations && isa<GlobalVariable>(GV); 189 Triple::ArchType Arch = TT.getArch(); 190 bool IsPPC = 191 Arch == Triple::ppc || Arch == Triple::ppc64 || Arch == Triple::ppc64le; 192 // Check if we can use copy relocations. PowerPC has no copy relocations. 193 if (!IsTLS && !IsPPC && (RM == Reloc::Static || IsAccessViaCopyRelocs)) 194 return true; 195 } 196 197 // ELF & wasm support preemption of other symbols. 198 return false; 199 } 200 201 bool TargetMachine::useEmulatedTLS() const { 202 // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls 203 // was specified explicitly; otherwise uses target triple to decide default. 204 if (Options.ExplicitEmulatedTLS) 205 return Options.EmulatedTLS; 206 return getTargetTriple().hasDefaultEmulatedTLS(); 207 } 208 209 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const { 210 bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default; 211 Reloc::Model RM = getRelocationModel(); 212 bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE; 213 bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV); 214 215 TLSModel::Model Model; 216 if (IsSharedLibrary) { 217 if (IsLocal) 218 Model = TLSModel::LocalDynamic; 219 else 220 Model = TLSModel::GeneralDynamic; 221 } else { 222 if (IsLocal) 223 Model = TLSModel::LocalExec; 224 else 225 Model = TLSModel::InitialExec; 226 } 227 228 // If the user specified a more specific model, use that. 229 TLSModel::Model SelectedModel = getSelectedTLSModel(GV); 230 if (SelectedModel > Model) 231 return SelectedModel; 232 233 return Model; 234 } 235 236 /// Returns the optimization level: None, Less, Default, or Aggressive. 237 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; } 238 239 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; } 240 241 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) { 242 return TargetTransformInfo(F.getParent()->getDataLayout()); 243 } 244 245 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name, 246 const GlobalValue *GV, Mangler &Mang, 247 bool MayAlwaysUsePrivate) const { 248 if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) { 249 // Simple case: If GV is not private, it is not important to find out if 250 // private labels are legal in this case or not. 251 Mang.getNameWithPrefix(Name, GV, false); 252 return; 253 } 254 const TargetLoweringObjectFile *TLOF = getObjFileLowering(); 255 TLOF->getNameWithPrefix(Name, GV, *this); 256 } 257 258 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const { 259 const TargetLoweringObjectFile *TLOF = getObjFileLowering(); 260 SmallString<128> NameStr; 261 getNameWithPrefix(NameStr, GV, TLOF->getMangler()); 262 return TLOF->getContext().getOrCreateSymbol(NameStr); 263 } 264 265 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() { 266 // Since Analysis can't depend on Target, use a std::function to invert the 267 // dependency. 268 return TargetIRAnalysis( 269 [this](const Function &F) { return this->getTargetTransformInfo(F); }); 270 } 271