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   RESET_OPTION(NoTrappingFPMath, "no-trapping-math");
  67
  68   StringRef Denormal =
  69     F.getFnAttribute("denormal-fp-math").getValueAsString();
  70   if (Denormal == "ieee")
  71     Options.FPDenormalMode = FPDenormal::IEEE;
  72   else if (Denormal == "preserve-sign")
  73     Options.FPDenormalMode = FPDenormal::PreserveSign;
  74   else if (Denormal == "positive-zero")
  75     Options.FPDenormalMode = FPDenormal::PositiveZero;
  76   else
  77     Options.FPDenormalMode = DefaultOptions.FPDenormalMode;
  78 }
  79
  80 /// Returns the code generation relocation model. The choices are static, PIC,
  81 /// and dynamic-no-pic.
  82 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
  83
  84 /// Returns the code model. The choices are small, kernel, medium, large, and
  85 /// target default.
  86 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
  87
  88 /// Get the IR-specified TLS model for Var.
  89 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
  90   switch (GV->getThreadLocalMode()) {
  91   case GlobalVariable::NotThreadLocal:
  92     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
  93     break;
  94   case GlobalVariable::GeneralDynamicTLSModel:
  95     return TLSModel::GeneralDynamic;
  96   case GlobalVariable::LocalDynamicTLSModel:
  97     return TLSModel::LocalDynamic;
  98   case GlobalVariable::InitialExecTLSModel:
  99     return TLSModel::InitialExec;
 100   case GlobalVariable::LocalExecTLSModel:
 101     return TLSModel::LocalExec;
 102   }
 103   llvm_unreachable("invalid TLS model");
 104 }
 105
 106 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
 107                                          const GlobalValue *GV) const {
 108   // If the IR producer requested that this GV be treated as dso local, obey.
 109   if (GV && GV->isDSOLocal())
 110     return true;
 111
 112   // If we are not supossed to use a PLT, we cannot assume that intrinsics are
 113   // local since the linker can convert some direct access to access via plt.
 114   if (M.getRtLibUseGOT() && !GV)
 115     return false;
 116
 117   // According to the llvm language reference, we should be able to
 118   // just return false in here if we have a GV, as we know it is
 119   // dso_preemptable.  At this point in time, the various IR producers
 120   // have not been transitioned to always produce a dso_local when it
 121   // is possible to do so.
 122   // In the case of intrinsics, GV is null and there is nowhere to put
 123   // dso_local. Returning false for those will produce worse code in some
 124   // architectures. For example, on x86 the caller has to set ebx before calling
 125   // a plt.
 126   // As a result we still have some logic in here to improve the quality of the
 127   // generated code.
 128   // FIXME: Add a module level metadata for whether intrinsics should be assumed
 129   // local.
 130
 131   Reloc::Model RM = getRelocationModel();
 132   const Triple &TT = getTargetTriple();
 133
 134   // DLLImport explicitly marks the GV as external.
 135   if (GV && GV->hasDLLImportStorageClass())
 136     return false;
 137
 138   // On MinGW, variables that haven't been declared with DLLImport may still
 139   // end up automatically imported by the linker. To make this feasible,
 140   // don't assume the variables to be DSO local unless we actually know
 141   // that for sure. This only has to be done for variables; for functions
 142   // the linker can insert thunks for calling functions from another DLL.
 143   if (TT.isWindowsGNUEnvironment() && GV && GV->isDeclarationForLinker() &&
 144       isa<GlobalVariable>(GV))
 145     return false;
 146
 147   // On COFF, don't mark 'extern_weak' symbols as DSO local. If these symbols
 148   // remain unresolved in the link, they can be resolved to zero, which is
 149   // outside the current DSO.
 150   if (TT.isOSBinFormatCOFF() && GV && GV->hasExternalWeakLinkage())
 151     return false;
 152
 153   // Every other GV is local on COFF.
 154   // Make an exception for windows OS in the triple: Some firmware builds use
 155   // *-win32-macho triples. This (accidentally?) produced windows relocations
 156   // without GOT tables in older clang versions; Keep this behaviour.
 157   if (TT.isOSBinFormatCOFF() || (TT.isOSWindows() && TT.isOSBinFormatMachO()))
 158     return true;
 159
 160   // Most PIC code sequences that assume that a symbol is local cannot
 161   // produce a 0 if it turns out the symbol is undefined. While this
 162   // is ABI and relocation depended, it seems worth it to handle it
 163   // here.
 164   if (GV && isPositionIndependent() && GV->hasExternalWeakLinkage())
 165     return false;
 166
 167   if (GV && !GV->hasDefaultVisibility())
 168     return true;
 169
 170   if (TT.isOSBinFormatMachO()) {
 171     if (RM == Reloc::Static)
 172       return true;
 173     return GV && GV->isStrongDefinitionForLinker();
 174   }
 175
 176   // Due to the AIX linkage model, any global with default visibility is
 177   // considered non-local.
 178   if (TT.isOSBinFormatXCOFF())
 179     return false;
 180
 181   assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm());
 182   assert(RM != Reloc::DynamicNoPIC);
 183
 184   bool IsExecutable =
 185       RM == Reloc::Static || M.getPIELevel() != PIELevel::Default;
 186   if (IsExecutable) {
 187     // If the symbol is defined, it cannot be preempted.
 188     if (GV && !GV->isDeclarationForLinker())
 189       return true;
 190
 191     // A symbol marked nonlazybind should not be accessed with a plt. If the
 192     // symbol turns out to be external, the linker will convert a direct
 193     // access to an access via the plt, so don't assume it is local.
 194     const Function *F = dyn_cast_or_null<Function>(GV);
 195     if (F && F->hasFnAttribute(Attribute::NonLazyBind))
 196       return false;
 197
 198     bool IsTLS = GV && GV->isThreadLocal();
 199     bool IsAccessViaCopyRelocs =
 200         GV && Options.MCOptions.MCPIECopyRelocations && isa<GlobalVariable>(GV);
 201     Triple::ArchType Arch = TT.getArch();
 202     bool IsPPC =
 203         Arch == Triple::ppc || Arch == Triple::ppc64 || Arch == Triple::ppc64le;
 204     // Check if we can use copy relocations. PowerPC has no copy relocations.
 205     if (!IsTLS && !IsPPC && (RM == Reloc::Static || IsAccessViaCopyRelocs))
 206       return true;
 207   }
 208
 209   // ELF & wasm support preemption of other symbols.
 210   return false;
 211 }
 212
 213 bool TargetMachine::useEmulatedTLS() const {
 214   // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
 215   // was specified explicitly; otherwise uses target triple to decide default.
 216   if (Options.ExplicitEmulatedTLS)
 217     return Options.EmulatedTLS;
 218   return getTargetTriple().hasDefaultEmulatedTLS();
 219 }
 220
 221 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
 222   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
 223   Reloc::Model RM = getRelocationModel();
 224   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
 225   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
 226
 227   TLSModel::Model Model;
 228   if (IsSharedLibrary) {
 229     if (IsLocal)
 230       Model = TLSModel::LocalDynamic;
 231     else
 232       Model = TLSModel::GeneralDynamic;
 233   } else {
 234     if (IsLocal)
 235       Model = TLSModel::LocalExec;
 236     else
 237       Model = TLSModel::InitialExec;
 238   }
 239
 240   // If the user specified a more specific model, use that.
 241   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
 242   if (SelectedModel > Model)
 243     return SelectedModel;
 244
 245   return Model;
 246 }
 247
 248 /// Returns the optimization level: None, Less, Default, or Aggressive.
 249 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
 250
 251 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
 252
 253 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) {
 254   return TargetTransformInfo(F.getParent()->getDataLayout());
 255 }
 256
 257 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
 258                                       const GlobalValue *GV, Mangler &Mang,
 259                                       bool MayAlwaysUsePrivate) const {
 260   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
 261     // Simple case: If GV is not private, it is not important to find out if
 262     // private labels are legal in this case or not.
 263     Mang.getNameWithPrefix(Name, GV, false);
 264     return;
 265   }
 266   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
 267   TLOF->getNameWithPrefix(Name, GV, *this);
 268 }
 269
 270 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
 271   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
 272   SmallString<128> NameStr;
 273   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
 274   return TLOF->getContext().getOrCreateSymbol(NameStr);
 275 }
 276
 277 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
 278   // Since Analysis can't depend on Target, use a std::function to invert the
 279   // dependency.
 280   return TargetIRAnalysis(
 281       [this](const Function &F) { return this->getTargetTransformInfo(F); });
 282 }