lib/LTO/LTOModule.cpp

   1 //===-- LTOModule.cpp - LLVM Link Time Optimizer --------------------------===//
   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 implements the Link Time Optimization library. This library is
  10 // intended to be used by linker to optimize code at link time.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/LTO/legacy/LTOModule.h"
  15 #include "llvm/ADT/Triple.h"
  16 #include "llvm/Bitcode/BitcodeReader.h"
  17 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  18 #include "llvm/IR/Constants.h"
  19 #include "llvm/IR/LLVMContext.h"
  20 #include "llvm/IR/Mangler.h"
  21 #include "llvm/IR/Metadata.h"
  22 #include "llvm/IR/Module.h"
  23 #include "llvm/MC/MCExpr.h"
  24 #include "llvm/MC/MCInst.h"
  25 #include "llvm/MC/MCParser/MCAsmParser.h"
  26 #include "llvm/MC/MCSection.h"
  27 #include "llvm/MC/MCSubtargetInfo.h"
  28 #include "llvm/MC/MCSymbol.h"
  29 #include "llvm/MC/SubtargetFeature.h"
  30 #include "llvm/Object/IRObjectFile.h"
  31 #include "llvm/Object/ObjectFile.h"
  32 #include "llvm/Support/FileSystem.h"
  33 #include "llvm/Support/Host.h"
  34 #include "llvm/Support/MemoryBuffer.h"
  35 #include "llvm/Support/Path.h"
  36 #include "llvm/Support/SourceMgr.h"
  37 #include "llvm/Support/TargetRegistry.h"
  38 #include "llvm/Support/TargetSelect.h"
  39 #include "llvm/Target/TargetLoweringObjectFile.h"
  40 #include "llvm/Transforms/Utils/GlobalStatus.h"
  41 #include <system_error>
  42 using namespace llvm;
  43 using namespace llvm::object;
  44
  45 LTOModule::LTOModule(std::unique_ptr<Module> M, MemoryBufferRef MBRef,
  46                      llvm::TargetMachine *TM)
  47     : Mod(std::move(M)), MBRef(MBRef), _target(TM) {
  48   SymTab.addModule(Mod.get());
  49 }
  50
  51 LTOModule::~LTOModule() {}
  52
  53 /// isBitcodeFile - Returns 'true' if the file (or memory contents) is LLVM
  54 /// bitcode.
  55 bool LTOModule::isBitcodeFile(const void *Mem, size_t Length) {
  56   Expected<MemoryBufferRef> BCData = IRObjectFile::findBitcodeInMemBuffer(
  57       MemoryBufferRef(StringRef((const char *)Mem, Length), "<mem>"));
  58   return !errorToBool(BCData.takeError());
  59 }
  60
  61 bool LTOModule::isBitcodeFile(StringRef Path) {
  62   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
  63       MemoryBuffer::getFile(Path);
  64   if (!BufferOrErr)
  65     return false;
  66
  67   Expected<MemoryBufferRef> BCData = IRObjectFile::findBitcodeInMemBuffer(
  68       BufferOrErr.get()->getMemBufferRef());
  69   return !errorToBool(BCData.takeError());
  70 }
  71
  72 bool LTOModule::isThinLTO() {
  73   Expected<BitcodeLTOInfo> Result = getBitcodeLTOInfo(MBRef);
  74   if (!Result) {
  75     logAllUnhandledErrors(Result.takeError(), errs());
  76     return false;
  77   }
  78   return Result->IsThinLTO;
  79 }
  80
  81 bool LTOModule::isBitcodeForTarget(MemoryBuffer *Buffer,
  82                                    StringRef TriplePrefix) {
  83   Expected<MemoryBufferRef> BCOrErr =
  84       IRObjectFile::findBitcodeInMemBuffer(Buffer->getMemBufferRef());
  85   if (errorToBool(BCOrErr.takeError()))
  86     return false;
  87   LLVMContext Context;
  88   ErrorOr<std::string> TripleOrErr =
  89       expectedToErrorOrAndEmitErrors(Context, getBitcodeTargetTriple(*BCOrErr));
  90   if (!TripleOrErr)
  91     return false;
  92   return StringRef(*TripleOrErr).startswith(TriplePrefix);
  93 }
  94
  95 std::string LTOModule::getProducerString(MemoryBuffer *Buffer) {
  96   Expected<MemoryBufferRef> BCOrErr =
  97       IRObjectFile::findBitcodeInMemBuffer(Buffer->getMemBufferRef());
  98   if (errorToBool(BCOrErr.takeError()))
  99     return "";
 100   LLVMContext Context;
 101   ErrorOr<std::string> ProducerOrErr = expectedToErrorOrAndEmitErrors(
 102       Context, getBitcodeProducerString(*BCOrErr));
 103   if (!ProducerOrErr)
 104     return "";
 105   return *ProducerOrErr;
 106 }
 107
 108 ErrorOr<std::unique_ptr<LTOModule>>
 109 LTOModule::createFromFile(LLVMContext &Context, StringRef path,
 110                           const TargetOptions &options) {
 111   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
 112       MemoryBuffer::getFile(path);
 113   if (std::error_code EC = BufferOrErr.getError()) {
 114     Context.emitError(EC.message());
 115     return EC;
 116   }
 117   std::unique_ptr<MemoryBuffer> Buffer = std::move(BufferOrErr.get());
 118   return makeLTOModule(Buffer->getMemBufferRef(), options, Context,
 119                        /* ShouldBeLazy*/ false);
 120 }
 121
 122 ErrorOr<std::unique_ptr<LTOModule>>
 123 LTOModule::createFromOpenFile(LLVMContext &Context, int fd, StringRef path,
 124                               size_t size, const TargetOptions &options) {
 125   return createFromOpenFileSlice(Context, fd, path, size, 0, options);
 126 }
 127
 128 ErrorOr<std::unique_ptr<LTOModule>>
 129 LTOModule::createFromOpenFileSlice(LLVMContext &Context, int fd, StringRef path,
 130                                    size_t map_size, off_t offset,
 131                                    const TargetOptions &options) {
 132   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
 133       MemoryBuffer::getOpenFileSlice(fd, path, map_size, offset);
 134   if (std::error_code EC = BufferOrErr.getError()) {
 135     Context.emitError(EC.message());
 136     return EC;
 137   }
 138   std::unique_ptr<MemoryBuffer> Buffer = std::move(BufferOrErr.get());
 139   return makeLTOModule(Buffer->getMemBufferRef(), options, Context,
 140                        /* ShouldBeLazy */ false);
 141 }
 142
 143 ErrorOr<std::unique_ptr<LTOModule>>
 144 LTOModule::createFromBuffer(LLVMContext &Context, const void *mem,
 145                             size_t length, const TargetOptions &options,
 146                             StringRef path) {
 147   StringRef Data((const char *)mem, length);
 148   MemoryBufferRef Buffer(Data, path);
 149   return makeLTOModule(Buffer, options, Context, /* ShouldBeLazy */ false);
 150 }
 151
 152 ErrorOr<std::unique_ptr<LTOModule>>
 153 LTOModule::createInLocalContext(std::unique_ptr<LLVMContext> Context,
 154                                 const void *mem, size_t length,
 155                                 const TargetOptions &options, StringRef path) {
 156   StringRef Data((const char *)mem, length);
 157   MemoryBufferRef Buffer(Data, path);
 158   // If we own a context, we know this is being used only for symbol extraction,
 159   // not linking.  Be lazy in that case.
 160   ErrorOr<std::unique_ptr<LTOModule>> Ret =
 161       makeLTOModule(Buffer, options, *Context, /* ShouldBeLazy */ true);
 162   if (Ret)
 163     (*Ret)->OwnedContext = std::move(Context);
 164   return Ret;
 165 }
 166
 167 static ErrorOr<std::unique_ptr<Module>>
 168 parseBitcodeFileImpl(MemoryBufferRef Buffer, LLVMContext &Context,
 169                      bool ShouldBeLazy) {
 170   // Find the buffer.
 171   Expected<MemoryBufferRef> MBOrErr =
 172       IRObjectFile::findBitcodeInMemBuffer(Buffer);
 173   if (Error E = MBOrErr.takeError()) {
 174     std::error_code EC = errorToErrorCode(std::move(E));
 175     Context.emitError(EC.message());
 176     return EC;
 177   }
 178
 179   if (!ShouldBeLazy) {
 180     // Parse the full file.
 181     return expectedToErrorOrAndEmitErrors(Context,
 182                                           parseBitcodeFile(*MBOrErr, Context));
 183   }
 184
 185   // Parse lazily.
 186   return expectedToErrorOrAndEmitErrors(
 187       Context,
 188       getLazyBitcodeModule(*MBOrErr, Context, true /*ShouldLazyLoadMetadata*/));
 189 }
 190
 191 ErrorOr<std::unique_ptr<LTOModule>>
 192 LTOModule::makeLTOModule(MemoryBufferRef Buffer, const TargetOptions &options,
 193                          LLVMContext &Context, bool ShouldBeLazy) {
 194   ErrorOr<std::unique_ptr<Module>> MOrErr =
 195       parseBitcodeFileImpl(Buffer, Context, ShouldBeLazy);
 196   if (std::error_code EC = MOrErr.getError())
 197     return EC;
 198   std::unique_ptr<Module> &M = *MOrErr;
 199
 200   std::string TripleStr = M->getTargetTriple();
 201   if (TripleStr.empty())
 202     TripleStr = sys::getDefaultTargetTriple();
 203   llvm::Triple Triple(TripleStr);
 204
 205   // find machine architecture for this module
 206   std::string errMsg;
 207   const Target *march = TargetRegistry::lookupTarget(TripleStr, errMsg);
 208   if (!march)
 209     return make_error_code(object::object_error::arch_not_found);
 210
 211   // construct LTOModule, hand over ownership of module and target
 212   SubtargetFeatures Features;
 213   Features.getDefaultSubtargetFeatures(Triple);
 214   std::string FeatureStr = Features.getString();
 215   // Set a default CPU for Darwin triples.
 216   std::string CPU;
 217   if (Triple.isOSDarwin()) {
 218     if (Triple.getArch() == llvm::Triple::x86_64)
 219       CPU = "core2";
 220     else if (Triple.getArch() == llvm::Triple::x86)
 221       CPU = "yonah";
 222     else if (Triple.getArch() == llvm::Triple::aarch64)
 223       CPU = "cyclone";
 224   }
 225
 226   TargetMachine *target =
 227       march->createTargetMachine(TripleStr, CPU, FeatureStr, options, None);
 228
 229   std::unique_ptr<LTOModule> Ret(new LTOModule(std::move(M), Buffer, target));
 230   Ret->parseSymbols();
 231   Ret->parseMetadata();
 232
 233   return std::move(Ret);
 234 }
 235
 236 /// Create a MemoryBuffer from a memory range with an optional name.
 237 std::unique_ptr<MemoryBuffer>
 238 LTOModule::makeBuffer(const void *mem, size_t length, StringRef name) {
 239   const char *startPtr = (const char*)mem;
 240   return MemoryBuffer::getMemBuffer(StringRef(startPtr, length), name, false);
 241 }
 242
 243 /// objcClassNameFromExpression - Get string that the data pointer points to.
 244 bool
 245 LTOModule::objcClassNameFromExpression(const Constant *c, std::string &name) {
 246   if (const ConstantExpr *ce = dyn_cast<ConstantExpr>(c)) {
 247     Constant *op = ce->getOperand(0);
 248     if (GlobalVariable *gvn = dyn_cast<GlobalVariable>(op)) {
 249       Constant *cn = gvn->getInitializer();
 250       if (ConstantDataArray *ca = dyn_cast<ConstantDataArray>(cn)) {
 251         if (ca->isCString()) {
 252           name = (".objc_class_name_" + ca->getAsCString()).str();
 253           return true;
 254         }
 255       }
 256     }
 257   }
 258   return false;
 259 }
 260
 261 /// addObjCClass - Parse i386/ppc ObjC class data structure.
 262 void LTOModule::addObjCClass(const GlobalVariable *clgv) {
 263   const ConstantStruct *c = dyn_cast<ConstantStruct>(clgv->getInitializer());
 264   if (!c) return;
 265
 266   // second slot in __OBJC,__class is pointer to superclass name
 267   std::string superclassName;
 268   if (objcClassNameFromExpression(c->getOperand(1), superclassName)) {
 269     auto IterBool =
 270         _undefines.insert(std::make_pair(superclassName, NameAndAttributes()));
 271     if (IterBool.second) {
 272       NameAndAttributes &info = IterBool.first->second;
 273       info.name = IterBool.first->first();
 274       info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
 275       info.isFunction = false;
 276       info.symbol = clgv;
 277     }
 278   }
 279
 280   // third slot in __OBJC,__class is pointer to class name
 281   std::string className;
 282   if (objcClassNameFromExpression(c->getOperand(2), className)) {
 283     auto Iter = _defines.insert(className).first;
 284
 285     NameAndAttributes info;
 286     info.name = Iter->first();
 287     info.attributes = LTO_SYMBOL_PERMISSIONS_DATA |
 288       LTO_SYMBOL_DEFINITION_REGULAR | LTO_SYMBOL_SCOPE_DEFAULT;
 289     info.isFunction = false;
 290     info.symbol = clgv;
 291     _symbols.push_back(info);
 292   }
 293 }
 294
 295 /// addObjCCategory - Parse i386/ppc ObjC category data structure.
 296 void LTOModule::addObjCCategory(const GlobalVariable *clgv) {
 297   const ConstantStruct *c = dyn_cast<ConstantStruct>(clgv->getInitializer());
 298   if (!c) return;
 299
 300   // second slot in __OBJC,__category is pointer to target class name
 301   std::string targetclassName;
 302   if (!objcClassNameFromExpression(c->getOperand(1), targetclassName))
 303     return;
 304
 305   auto IterBool =
 306       _undefines.insert(std::make_pair(targetclassName, NameAndAttributes()));
 307
 308   if (!IterBool.second)
 309     return;
 310
 311   NameAndAttributes &info = IterBool.first->second;
 312   info.name = IterBool.first->first();
 313   info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
 314   info.isFunction = false;
 315   info.symbol = clgv;
 316 }
 317
 318 /// addObjCClassRef - Parse i386/ppc ObjC class list data structure.
 319 void LTOModule::addObjCClassRef(const GlobalVariable *clgv) {
 320   std::string targetclassName;
 321   if (!objcClassNameFromExpression(clgv->getInitializer(), targetclassName))
 322     return;
 323
 324   auto IterBool =
 325       _undefines.insert(std::make_pair(targetclassName, NameAndAttributes()));
 326
 327   if (!IterBool.second)
 328     return;
 329
 330   NameAndAttributes &info = IterBool.first->second;
 331   info.name = IterBool.first->first();
 332   info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
 333   info.isFunction = false;
 334   info.symbol = clgv;
 335 }
 336
 337 void LTOModule::addDefinedDataSymbol(ModuleSymbolTable::Symbol Sym) {
 338   SmallString<64> Buffer;
 339   {
 340     raw_svector_ostream OS(Buffer);
 341     SymTab.printSymbolName(OS, Sym);
 342     Buffer.c_str();
 343   }
 344
 345   const GlobalValue *V = Sym.get<GlobalValue *>();
 346   addDefinedDataSymbol(Buffer, V);
 347 }
 348
 349 void LTOModule::addDefinedDataSymbol(StringRef Name, const GlobalValue *v) {
 350   // Add to list of defined symbols.
 351   addDefinedSymbol(Name, v, false);
 352
 353   if (!v->hasSection() /* || !isTargetDarwin */)
 354     return;
 355
 356   // Special case i386/ppc ObjC data structures in magic sections:
 357   // The issue is that the old ObjC object format did some strange
 358   // contortions to avoid real linker symbols.  For instance, the
 359   // ObjC class data structure is allocated statically in the executable
 360   // that defines that class.  That data structures contains a pointer to
 361   // its superclass.  But instead of just initializing that part of the
 362   // struct to the address of its superclass, and letting the static and
 363   // dynamic linkers do the rest, the runtime works by having that field
 364   // instead point to a C-string that is the name of the superclass.
 365   // At runtime the objc initialization updates that pointer and sets
 366   // it to point to the actual super class.  As far as the linker
 367   // knows it is just a pointer to a string.  But then someone wanted the
 368   // linker to issue errors at build time if the superclass was not found.
 369   // So they figured out a way in mach-o object format to use an absolute
 370   // symbols (.objc_class_name_Foo = 0) and a floating reference
 371   // (.reference .objc_class_name_Bar) to cause the linker into erroring when
 372   // a class was missing.
 373   // The following synthesizes the implicit .objc_* symbols for the linker
 374   // from the ObjC data structures generated by the front end.
 375
 376   // special case if this data blob is an ObjC class definition
 377   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(v)) {
 378     StringRef Section = GV->getSection();
 379     if (Section.startswith("__OBJC,__class,")) {
 380       addObjCClass(GV);
 381     }
 382
 383     // special case if this data blob is an ObjC category definition
 384     else if (Section.startswith("__OBJC,__category,")) {
 385       addObjCCategory(GV);
 386     }
 387
 388     // special case if this data blob is the list of referenced classes
 389     else if (Section.startswith("__OBJC,__cls_refs,")) {
 390       addObjCClassRef(GV);
 391     }
 392   }
 393 }
 394
 395 void LTOModule::addDefinedFunctionSymbol(ModuleSymbolTable::Symbol Sym) {
 396   SmallString<64> Buffer;
 397   {
 398     raw_svector_ostream OS(Buffer);
 399     SymTab.printSymbolName(OS, Sym);
 400     Buffer.c_str();
 401   }
 402
 403   const Function *F = cast<Function>(Sym.get<GlobalValue *>());
 404   addDefinedFunctionSymbol(Buffer, F);
 405 }
 406
 407 void LTOModule::addDefinedFunctionSymbol(StringRef Name, const Function *F) {
 408   // add to list of defined symbols
 409   addDefinedSymbol(Name, F, true);
 410 }
 411
 412 void LTOModule::addDefinedSymbol(StringRef Name, const GlobalValue *def,
 413                                  bool isFunction) {
 414   // set alignment part log2() can have rounding errors
 415   uint32_t align = def->getAlignment();
 416   uint32_t attr = align ? countTrailingZeros(align) : 0;
 417
 418   // set permissions part
 419   if (isFunction) {
 420     attr |= LTO_SYMBOL_PERMISSIONS_CODE;
 421   } else {
 422     const GlobalVariable *gv = dyn_cast<GlobalVariable>(def);
 423     if (gv && gv->isConstant())
 424       attr |= LTO_SYMBOL_PERMISSIONS_RODATA;
 425     else
 426       attr |= LTO_SYMBOL_PERMISSIONS_DATA;
 427   }
 428
 429   // set definition part
 430   if (def->hasWeakLinkage() || def->hasLinkOnceLinkage())
 431     attr |= LTO_SYMBOL_DEFINITION_WEAK;
 432   else if (def->hasCommonLinkage())
 433     attr |= LTO_SYMBOL_DEFINITION_TENTATIVE;
 434   else
 435     attr |= LTO_SYMBOL_DEFINITION_REGULAR;
 436
 437   // set scope part
 438   if (def->hasLocalLinkage())
 439     // Ignore visibility if linkage is local.
 440     attr |= LTO_SYMBOL_SCOPE_INTERNAL;
 441   else if (def->hasHiddenVisibility())
 442     attr |= LTO_SYMBOL_SCOPE_HIDDEN;
 443   else if (def->hasProtectedVisibility())
 444     attr |= LTO_SYMBOL_SCOPE_PROTECTED;
 445   else if (def->canBeOmittedFromSymbolTable())
 446     attr |= LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN;
 447   else
 448     attr |= LTO_SYMBOL_SCOPE_DEFAULT;
 449
 450   if (def->hasComdat())
 451     attr |= LTO_SYMBOL_COMDAT;
 452
 453   if (isa<GlobalAlias>(def))
 454     attr |= LTO_SYMBOL_ALIAS;
 455
 456   auto Iter = _defines.insert(Name).first;
 457
 458   // fill information structure
 459   NameAndAttributes info;
 460   StringRef NameRef = Iter->first();
 461   info.name = NameRef;
 462   assert(NameRef.data()[NameRef.size()] == '\0');
 463   info.attributes = attr;
 464   info.isFunction = isFunction;
 465   info.symbol = def;
 466
 467   // add to table of symbols
 468   _symbols.push_back(info);
 469 }
 470
 471 /// addAsmGlobalSymbol - Add a global symbol from module-level ASM to the
 472 /// defined list.
 473 void LTOModule::addAsmGlobalSymbol(StringRef name,
 474                                    lto_symbol_attributes scope) {
 475   auto IterBool = _defines.insert(name);
 476
 477   // only add new define if not already defined
 478   if (!IterBool.second)
 479     return;
 480
 481   NameAndAttributes &info = _undefines[IterBool.first->first()];
 482
 483   if (info.symbol == nullptr) {
 484     // FIXME: This is trying to take care of module ASM like this:
 485     //
 486     //   module asm ".zerofill __FOO, __foo, _bar_baz_qux, 0"
 487     //
 488     // but is gross and its mother dresses it funny. Have the ASM parser give us
 489     // more details for this type of situation so that we're not guessing so
 490     // much.
 491
 492     // fill information structure
 493     info.name = IterBool.first->first();
 494     info.attributes =
 495       LTO_SYMBOL_PERMISSIONS_DATA | LTO_SYMBOL_DEFINITION_REGULAR | scope;
 496     info.isFunction = false;
 497     info.symbol = nullptr;
 498
 499     // add to table of symbols
 500     _symbols.push_back(info);
 501     return;
 502   }
 503
 504   if (info.isFunction)
 505     addDefinedFunctionSymbol(info.name, cast<Function>(info.symbol));
 506   else
 507     addDefinedDataSymbol(info.name, info.symbol);
 508
 509   _symbols.back().attributes &= ~LTO_SYMBOL_SCOPE_MASK;
 510   _symbols.back().attributes |= scope;
 511 }
 512
 513 /// addAsmGlobalSymbolUndef - Add a global symbol from module-level ASM to the
 514 /// undefined list.
 515 void LTOModule::addAsmGlobalSymbolUndef(StringRef name) {
 516   auto IterBool = _undefines.insert(std::make_pair(name, NameAndAttributes()));
 517
 518   _asm_undefines.push_back(IterBool.first->first());
 519
 520   // we already have the symbol
 521   if (!IterBool.second)
 522     return;
 523
 524   uint32_t attr = LTO_SYMBOL_DEFINITION_UNDEFINED;
 525   attr |= LTO_SYMBOL_SCOPE_DEFAULT;
 526   NameAndAttributes &info = IterBool.first->second;
 527   info.name = IterBool.first->first();
 528   info.attributes = attr;
 529   info.isFunction = false;
 530   info.symbol = nullptr;
 531 }
 532
 533 /// Add a symbol which isn't defined just yet to a list to be resolved later.
 534 void LTOModule::addPotentialUndefinedSymbol(ModuleSymbolTable::Symbol Sym,
 535                                             bool isFunc) {
 536   SmallString<64> name;
 537   {
 538     raw_svector_ostream OS(name);
 539     SymTab.printSymbolName(OS, Sym);
 540     name.c_str();
 541   }
 542
 543   auto IterBool = _undefines.insert(std::make_pair(name, NameAndAttributes()));
 544
 545   // we already have the symbol
 546   if (!IterBool.second)
 547     return;
 548
 549   NameAndAttributes &info = IterBool.first->second;
 550
 551   info.name = IterBool.first->first();
 552
 553   const GlobalValue *decl = Sym.dyn_cast<GlobalValue *>();
 554
 555   if (decl->hasExternalWeakLinkage())
 556     info.attributes = LTO_SYMBOL_DEFINITION_WEAKUNDEF;
 557   else
 558     info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
 559
 560   info.isFunction = isFunc;
 561   info.symbol = decl;
 562 }
 563
 564 void LTOModule::parseSymbols() {
 565   for (auto Sym : SymTab.symbols()) {
 566     auto *GV = Sym.dyn_cast<GlobalValue *>();
 567     uint32_t Flags = SymTab.getSymbolFlags(Sym);
 568     if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
 569       continue;
 570
 571     bool IsUndefined = Flags & object::BasicSymbolRef::SF_Undefined;
 572
 573     if (!GV) {
 574       SmallString<64> Buffer;
 575       {
 576         raw_svector_ostream OS(Buffer);
 577         SymTab.printSymbolName(OS, Sym);
 578         Buffer.c_str();
 579       }
 580       StringRef Name(Buffer);
 581
 582       if (IsUndefined)
 583         addAsmGlobalSymbolUndef(Name);
 584       else if (Flags & object::BasicSymbolRef::SF_Global)
 585         addAsmGlobalSymbol(Name, LTO_SYMBOL_SCOPE_DEFAULT);
 586       else
 587         addAsmGlobalSymbol(Name, LTO_SYMBOL_SCOPE_INTERNAL);
 588       continue;
 589     }
 590
 591     auto *F = dyn_cast<Function>(GV);
 592     if (IsUndefined) {
 593       addPotentialUndefinedSymbol(Sym, F != nullptr);
 594       continue;
 595     }
 596
 597     if (F) {
 598       addDefinedFunctionSymbol(Sym);
 599       continue;
 600     }
 601
 602     if (isa<GlobalVariable>(GV)) {
 603       addDefinedDataSymbol(Sym);
 604       continue;
 605     }
 606
 607     assert(isa<GlobalAlias>(GV));
 608     addDefinedDataSymbol(Sym);
 609   }
 610
 611   // make symbols for all undefines
 612   for (StringMap<NameAndAttributes>::iterator u =_undefines.begin(),
 613          e = _undefines.end(); u != e; ++u) {
 614     // If this symbol also has a definition, then don't make an undefine because
 615     // it is a tentative definition.
 616     if (_defines.count(u->getKey())) continue;
 617     NameAndAttributes info = u->getValue();
 618     _symbols.push_back(info);
 619   }
 620 }
 621
 622 /// parseMetadata - Parse metadata from the module
 623 void LTOModule::parseMetadata() {
 624   raw_string_ostream OS(LinkerOpts);
 625
 626   // Linker Options
 627   if (NamedMDNode *LinkerOptions =
 628           getModule().getNamedMetadata("llvm.linker.options")) {
 629     for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
 630       MDNode *MDOptions = LinkerOptions->getOperand(i);
 631       for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
 632         MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
 633         OS << " " << MDOption->getString();
 634       }
 635     }
 636   }
 637
 638   // Globals - we only need to do this for COFF.
 639   const Triple TT(_target->getTargetTriple());
 640   if (!TT.isOSBinFormatCOFF())
 641     return;
 642   Mangler M;
 643   for (const NameAndAttributes &Sym : _symbols) {
 644     if (!Sym.symbol)
 645       continue;
 646     emitLinkerFlagsForGlobalCOFF(OS, Sym.symbol, TT, M);
 647   }
 648
 649   // Add other interesting metadata here.
 650 }