lib/Target/TargetMachine.cpp

   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/IR/Function.h"
  17 #include "llvm/IR/GlobalAlias.h"
  18 #include "llvm/IR/GlobalValue.h"
  19 #include "llvm/IR/GlobalVariable.h"
  20 #include "llvm/IR/LegacyPassManager.h"
  21 #include "llvm/IR/Mangler.h"
  22 #include "llvm/MC/MCAsmInfo.h"
  23 #include "llvm/MC/MCContext.h"
  24 #include "llvm/MC/MCInstrInfo.h"
  25 #include "llvm/MC/MCSectionMachO.h"
  26 #include "llvm/MC/MCTargetOptions.h"
  27 #include "llvm/MC/SectionKind.h"
  28 #include "llvm/Target/TargetLoweringObjectFile.h"
  29 using namespace llvm;
  30
  31 //---------------------------------------------------------------------------
  32 // TargetMachine Class
  33 //
  34
  35 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
  36                              const Triple &TT, StringRef CPU, StringRef FS,
  37                              const TargetOptions &Options)
  38     : TheTarget(T), DL(DataLayoutString), TargetTriple(TT), TargetCPU(CPU),
  39       TargetFS(FS), AsmInfo(nullptr), MRI(nullptr), MII(nullptr), STI(nullptr),
  40       RequireStructuredCFG(false), DefaultOptions(Options), Options(Options) {
  41 }
  42
  43 TargetMachine::~TargetMachine() = default;
  44
  45 bool TargetMachine::isPositionIndependent() const {
  46   return getRelocationModel() == Reloc::PIC_;
  47 }
  48
  49 /// Reset the target options based on the function's attributes.
  50 // FIXME: This function needs to go away for a number of reasons:
  51 // a) global state on the TargetMachine is terrible in general,
  52 // b) these target options should be passed only on the function
  53 //    and not on the TargetMachine (via TargetOptions) at all.
  54 void TargetMachine::resetTargetOptions(const Function &F) const {
  55 #define RESET_OPTION(X, Y)                                                     \
  56   do {                                                                         \
  57     if (F.hasFnAttribute(Y))                                                   \
  58       Options.X = (F.getFnAttribute(Y).getValueAsString() == "true");          \
  59     else                                                                       \
  60       Options.X = DefaultOptions.X;                                            \
  61   } while (0)
  62
  63   RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
  64   RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
  65   RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
  66   RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
  67   RESET_OPTION(NoTrappingFPMath, "no-trapping-math");
  68
  69   StringRef Denormal =
  70     F.getFnAttribute("denormal-fp-math").getValueAsString();
  71   if (Denormal == "ieee")
  72     Options.FPDenormalMode = FPDenormal::IEEE;
  73   else if (Denormal == "preserve-sign")
  74     Options.FPDenormalMode = FPDenormal::PreserveSign;
  75   else if (Denormal == "positive-zero")
  76     Options.FPDenormalMode = FPDenormal::PositiveZero;
  77   else
  78     Options.FPDenormalMode = DefaultOptions.FPDenormalMode;
  79 }
  80
  81 /// Returns the code generation relocation model. The choices are static, PIC,
  82 /// and dynamic-no-pic.
  83 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
  84
  85 /// Returns the code model. The choices are small, kernel, medium, large, and
  86 /// target default.
  87 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
  88
  89 /// Get the IR-specified TLS model for Var.
  90 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
  91   switch (GV->getThreadLocalMode()) {
  92   case GlobalVariable::NotThreadLocal:
  93     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
  94     break;
  95   case GlobalVariable::GeneralDynamicTLSModel:
  96     return TLSModel::GeneralDynamic;
  97   case GlobalVariable::LocalDynamicTLSModel:
  98     return TLSModel::LocalDynamic;
  99   case GlobalVariable::InitialExecTLSModel:
 100     return TLSModel::InitialExec;
 101   case GlobalVariable::LocalExecTLSModel:
 102     return TLSModel::LocalExec;
 103   }
 104   llvm_unreachable("invalid TLS model");
 105 }
 106
 107 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
 108                                          const GlobalValue *GV) const {
 109   // If the IR producer requested that this GV be treated as dso local, obey.
 110   if (GV && GV->isDSOLocal())
 111     return true;
 112
 113   // If we are not supossed to use a PLT, we cannot assume that intrinsics are
 114   // local since the linker can convert some direct access to access via plt.
 115   if (M.getRtLibUseGOT() && !GV)
 116     return false;
 117
 118   // According to the llvm language reference, we should be able to
 119   // just return false in here if we have a GV, as we know it is
 120   // dso_preemptable.  At this point in time, the various IR producers
 121   // have not been transitioned to always produce a dso_local when it
 122   // is possible to do so.
 123   // In the case of intrinsics, GV is null and there is nowhere to put
 124   // dso_local. Returning false for those will produce worse code in some
 125   // architectures. For example, on x86 the caller has to set ebx before calling
 126   // a plt.
 127   // As a result we still have some logic in here to improve the quality of the
 128   // generated code.
 129   // FIXME: Add a module level metadata for whether intrinsics should be assumed
 130   // local.
 131
 132   Reloc::Model RM = getRelocationModel();
 133   const Triple &TT = getTargetTriple();
 134
 135   // DLLImport explicitly marks the GV as external.
 136   if (GV && GV->hasDLLImportStorageClass())
 137     return false;
 138
 139   // On MinGW, variables that haven't been declared with DLLImport may still
 140   // end up automatically imported by the linker. To make this feasible,
 141   // don't assume the variables to be DSO local unless we actually know
 142   // that for sure. This only has to be done for variables; for functions
 143   // the linker can insert thunks for calling functions from another DLL.
 144   if (TT.isWindowsGNUEnvironment() && GV && GV->isDeclarationForLinker() &&
 145       isa<GlobalVariable>(GV))
 146     return false;
 147
 148   // Every other GV is local on COFF.
 149   // Make an exception for windows OS in the triple: Some firmware builds use
 150   // *-win32-macho triples. This (accidentally?) produced windows relocations
 151   // without GOT tables in older clang versions; Keep this behaviour.
 152   if (TT.isOSBinFormatCOFF() || (TT.isOSWindows() && TT.isOSBinFormatMachO()))
 153     return true;
 154
 155   // Most PIC code sequences that assume that a symbol is local cannot
 156   // produce a 0 if it turns out the symbol is undefined. While this
 157   // is ABI and relocation depended, it seems worth it to handle it
 158   // here.
 159   if (GV && isPositionIndependent() && GV->hasExternalWeakLinkage())
 160     return false;
 161
 162   if (GV && !GV->hasDefaultVisibility())
 163     return true;
 164
 165   if (TT.isOSBinFormatMachO()) {
 166     if (RM == Reloc::Static)
 167       return true;
 168     return GV && GV->isStrongDefinitionForLinker();
 169   }
 170
 171   assert(TT.isOSBinFormatELF());
 172   assert(RM != Reloc::DynamicNoPIC);
 173
 174   bool IsExecutable =
 175       RM == Reloc::Static || M.getPIELevel() != PIELevel::Default;
 176   if (IsExecutable) {
 177     // If the symbol is defined, it cannot be preempted.
 178     if (GV && !GV->isDeclarationForLinker())
 179       return true;
 180
 181     // A symbol marked nonlazybind should not be accessed with a plt. If the
 182     // symbol turns out to be external, the linker will convert a direct
 183     // access to an access via the plt, so don't assume it is local.
 184     const Function *F = dyn_cast_or_null<Function>(GV);
 185     if (F && F->hasFnAttribute(Attribute::NonLazyBind))
 186       return false;
 187
 188     bool IsTLS = GV && GV->isThreadLocal();
 189     bool IsAccessViaCopyRelocs =
 190         GV && Options.MCOptions.MCPIECopyRelocations && isa<GlobalVariable>(GV);
 191     Triple::ArchType Arch = TT.getArch();
 192     bool IsPPC =
 193         Arch == Triple::ppc || Arch == Triple::ppc64 || Arch == Triple::ppc64le;
 194     // Check if we can use copy relocations. PowerPC has no copy relocations.
 195     if (!IsTLS && !IsPPC && (RM == Reloc::Static || IsAccessViaCopyRelocs))
 196       return true;
 197   }
 198
 199   // ELF supports preemption of other symbols.
 200   return false;
 201 }
 202
 203 bool TargetMachine::useEmulatedTLS() const {
 204   // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
 205   // was specified explicitly; otherwise uses target triple to decide default.
 206   if (Options.ExplicitEmulatedTLS)
 207     return Options.EmulatedTLS;
 208   return getTargetTriple().hasDefaultEmulatedTLS();
 209 }
 210
 211 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
 212   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
 213   Reloc::Model RM = getRelocationModel();
 214   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
 215   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
 216
 217   TLSModel::Model Model;
 218   if (IsSharedLibrary) {
 219     if (IsLocal)
 220       Model = TLSModel::LocalDynamic;
 221     else
 222       Model = TLSModel::GeneralDynamic;
 223   } else {
 224     if (IsLocal)
 225       Model = TLSModel::LocalExec;
 226     else
 227       Model = TLSModel::InitialExec;
 228   }
 229
 230   // If the user specified a more specific model, use that.
 231   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
 232   if (SelectedModel > Model)
 233     return SelectedModel;
 234
 235   return Model;
 236 }
 237
 238 /// Returns the optimization level: None, Less, Default, or Aggressive.
 239 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
 240
 241 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
 242
 243 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) {
 244   return TargetTransformInfo(F.getParent()->getDataLayout());
 245 }
 246
 247 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
 248                                       const GlobalValue *GV, Mangler &Mang,
 249                                       bool MayAlwaysUsePrivate) const {
 250   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
 251     // Simple case: If GV is not private, it is not important to find out if
 252     // private labels are legal in this case or not.
 253     Mang.getNameWithPrefix(Name, GV, false);
 254     return;
 255   }
 256   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
 257   TLOF->getNameWithPrefix(Name, GV, *this);
 258 }
 259
 260 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
 261   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
 262   SmallString<128> NameStr;
 263   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
 264   return TLOF->getContext().getOrCreateSymbol(NameStr);
 265 }
 266
 267 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
 268   // Since Analysis can't depend on Target, use a std::function to invert the
 269   // dependency.
 270   return TargetIRAnalysis(
 271       [this](const Function &F) { return this->getTargetTransformInfo(F); });
 272 }