lib/Target/TargetMachine.cpp

   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 }