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      1 //===-- gold-plugin.cpp - Plugin to gold for Link Time Optimization  ------===//
      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 is a gold plugin for LLVM. It provides an LLVM implementation of the
     11 // interface described in http://gcc.gnu.org/wiki/whopr/driver .
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "llvm/Config/config.h" // plugin-api.h requires HAVE_STDINT_H
     16 #include "llvm/ADT/DenseSet.h"
     17 #include "llvm/ADT/StringSet.h"
     18 #include "llvm/Analysis/TargetLibraryInfo.h"
     19 #include "llvm/Analysis/TargetTransformInfo.h"
     20 #include "llvm/Bitcode/ReaderWriter.h"
     21 #include "llvm/CodeGen/Analysis.h"
     22 #include "llvm/CodeGen/CommandFlags.h"
     23 #include "llvm/IR/AutoUpgrade.h"
     24 #include "llvm/IR/Constants.h"
     25 #include "llvm/IR/DiagnosticInfo.h"
     26 #include "llvm/IR/DiagnosticPrinter.h"
     27 #include "llvm/IR/LLVMContext.h"
     28 #include "llvm/IR/LegacyPassManager.h"
     29 #include "llvm/IR/Module.h"
     30 #include "llvm/IR/Verifier.h"
     31 #include "llvm/Linker/Linker.h"
     32 #include "llvm/MC/SubtargetFeature.h"
     33 #include "llvm/Object/IRObjectFile.h"
     34 #include "llvm/Support/raw_ostream.h"
     35 #include "llvm/Support/Host.h"
     36 #include "llvm/Support/ManagedStatic.h"
     37 #include "llvm/Support/MemoryBuffer.h"
     38 #include "llvm/Support/TargetRegistry.h"
     39 #include "llvm/Support/TargetSelect.h"
     40 #include "llvm/Transforms/IPO.h"
     41 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
     42 #include "llvm/Transforms/Utils/GlobalStatus.h"
     43 #include "llvm/Transforms/Utils/ModuleUtils.h"
     44 #include "llvm/Transforms/Utils/ValueMapper.h"
     45 #include <list>
     46 #include <plugin-api.h>
     47 #include <system_error>
     48 #include <vector>
     49 
     50 #ifndef LDPO_PIE
     51 // FIXME: remove this declaration when we stop maintaining Ubuntu Quantal and
     52 // Precise and Debian Wheezy (binutils 2.23 is required)
     53 # define LDPO_PIE 3
     54 #endif
     55 
     56 using namespace llvm;
     57 
     58 namespace {
     59 struct claimed_file {
     60   void *handle;
     61   std::vector<ld_plugin_symbol> syms;
     62 };
     63 }
     64 
     65 static ld_plugin_status discard_message(int level, const char *format, ...) {
     66   // Die loudly. Recent versions of Gold pass ld_plugin_message as the first
     67   // callback in the transfer vector. This should never be called.
     68   abort();
     69 }
     70 
     71 static ld_plugin_get_input_file get_input_file = nullptr;
     72 static ld_plugin_release_input_file release_input_file = nullptr;
     73 static ld_plugin_add_symbols add_symbols = nullptr;
     74 static ld_plugin_get_symbols get_symbols = nullptr;
     75 static ld_plugin_add_input_file add_input_file = nullptr;
     76 static ld_plugin_set_extra_library_path set_extra_library_path = nullptr;
     77 static ld_plugin_get_view get_view = nullptr;
     78 static ld_plugin_message message = discard_message;
     79 static Reloc::Model RelocationModel = Reloc::Default;
     80 static std::string output_name = "";
     81 static std::list<claimed_file> Modules;
     82 static std::vector<std::string> Cleanup;
     83 static llvm::TargetOptions TargetOpts;
     84 
     85 namespace options {
     86   enum OutputType {
     87     OT_NORMAL,
     88     OT_DISABLE,
     89     OT_BC_ONLY,
     90     OT_SAVE_TEMPS
     91   };
     92   static bool generate_api_file = false;
     93   static OutputType TheOutputType = OT_NORMAL;
     94   static unsigned OptLevel = 2;
     95   static std::string obj_path;
     96   static std::string extra_library_path;
     97   static std::string triple;
     98   static std::string mcpu;
     99   // Additional options to pass into the code generator.
    100   // Note: This array will contain all plugin options which are not claimed
    101   // as plugin exclusive to pass to the code generator.
    102   // For example, "generate-api-file" and "as"options are for the plugin
    103   // use only and will not be passed.
    104   static std::vector<const char *> extra;
    105 
    106   static void process_plugin_option(const char* opt_)
    107   {
    108     if (opt_ == nullptr)
    109       return;
    110     llvm::StringRef opt = opt_;
    111 
    112     if (opt == "generate-api-file") {
    113       generate_api_file = true;
    114     } else if (opt.startswith("mcpu=")) {
    115       mcpu = opt.substr(strlen("mcpu="));
    116     } else if (opt.startswith("extra-library-path=")) {
    117       extra_library_path = opt.substr(strlen("extra_library_path="));
    118     } else if (opt.startswith("mtriple=")) {
    119       triple = opt.substr(strlen("mtriple="));
    120     } else if (opt.startswith("obj-path=")) {
    121       obj_path = opt.substr(strlen("obj-path="));
    122     } else if (opt == "emit-llvm") {
    123       TheOutputType = OT_BC_ONLY;
    124     } else if (opt == "save-temps") {
    125       TheOutputType = OT_SAVE_TEMPS;
    126     } else if (opt == "disable-output") {
    127       TheOutputType = OT_DISABLE;
    128     } else if (opt.size() == 2 && opt[0] == 'O') {
    129       if (opt[1] < '0' || opt[1] > '3')
    130         report_fatal_error("Optimization level must be between 0 and 3");
    131       OptLevel = opt[1] - '0';
    132     } else {
    133       // Save this option to pass to the code generator.
    134       // ParseCommandLineOptions() expects argv[0] to be program name. Lazily
    135       // add that.
    136       if (extra.empty())
    137         extra.push_back("LLVMgold");
    138 
    139       extra.push_back(opt_);
    140     }
    141   }
    142 }
    143 
    144 static ld_plugin_status claim_file_hook(const ld_plugin_input_file *file,
    145                                         int *claimed);
    146 static ld_plugin_status all_symbols_read_hook(void);
    147 static ld_plugin_status cleanup_hook(void);
    148 
    149 extern "C" ld_plugin_status onload(ld_plugin_tv *tv);
    150 ld_plugin_status onload(ld_plugin_tv *tv) {
    151   InitializeAllTargetInfos();
    152   InitializeAllTargets();
    153   InitializeAllTargetMCs();
    154   InitializeAllAsmParsers();
    155   InitializeAllAsmPrinters();
    156 
    157   // We're given a pointer to the first transfer vector. We read through them
    158   // until we find one where tv_tag == LDPT_NULL. The REGISTER_* tagged values
    159   // contain pointers to functions that we need to call to register our own
    160   // hooks. The others are addresses of functions we can use to call into gold
    161   // for services.
    162 
    163   bool registeredClaimFile = false;
    164   bool RegisteredAllSymbolsRead = false;
    165 
    166   for (; tv->tv_tag != LDPT_NULL; ++tv) {
    167     switch (tv->tv_tag) {
    168       case LDPT_OUTPUT_NAME:
    169         output_name = tv->tv_u.tv_string;
    170         break;
    171       case LDPT_LINKER_OUTPUT:
    172         switch (tv->tv_u.tv_val) {
    173           case LDPO_REL:  // .o
    174           case LDPO_DYN:  // .so
    175           case LDPO_PIE:  // position independent executable
    176             RelocationModel = Reloc::PIC_;
    177             break;
    178           case LDPO_EXEC:  // .exe
    179             RelocationModel = Reloc::Static;
    180             break;
    181           default:
    182             message(LDPL_ERROR, "Unknown output file type %d", tv->tv_u.tv_val);
    183             return LDPS_ERR;
    184         }
    185         break;
    186       case LDPT_OPTION:
    187         options::process_plugin_option(tv->tv_u.tv_string);
    188         break;
    189       case LDPT_REGISTER_CLAIM_FILE_HOOK: {
    190         ld_plugin_register_claim_file callback;
    191         callback = tv->tv_u.tv_register_claim_file;
    192 
    193         if (callback(claim_file_hook) != LDPS_OK)
    194           return LDPS_ERR;
    195 
    196         registeredClaimFile = true;
    197       } break;
    198       case LDPT_REGISTER_ALL_SYMBOLS_READ_HOOK: {
    199         ld_plugin_register_all_symbols_read callback;
    200         callback = tv->tv_u.tv_register_all_symbols_read;
    201 
    202         if (callback(all_symbols_read_hook) != LDPS_OK)
    203           return LDPS_ERR;
    204 
    205         RegisteredAllSymbolsRead = true;
    206       } break;
    207       case LDPT_REGISTER_CLEANUP_HOOK: {
    208         ld_plugin_register_cleanup callback;
    209         callback = tv->tv_u.tv_register_cleanup;
    210 
    211         if (callback(cleanup_hook) != LDPS_OK)
    212           return LDPS_ERR;
    213       } break;
    214       case LDPT_GET_INPUT_FILE:
    215         get_input_file = tv->tv_u.tv_get_input_file;
    216         break;
    217       case LDPT_RELEASE_INPUT_FILE:
    218         release_input_file = tv->tv_u.tv_release_input_file;
    219         break;
    220       case LDPT_ADD_SYMBOLS:
    221         add_symbols = tv->tv_u.tv_add_symbols;
    222         break;
    223       case LDPT_GET_SYMBOLS_V2:
    224         get_symbols = tv->tv_u.tv_get_symbols;
    225         break;
    226       case LDPT_ADD_INPUT_FILE:
    227         add_input_file = tv->tv_u.tv_add_input_file;
    228         break;
    229       case LDPT_SET_EXTRA_LIBRARY_PATH:
    230         set_extra_library_path = tv->tv_u.tv_set_extra_library_path;
    231         break;
    232       case LDPT_GET_VIEW:
    233         get_view = tv->tv_u.tv_get_view;
    234         break;
    235       case LDPT_MESSAGE:
    236         message = tv->tv_u.tv_message;
    237         break;
    238       default:
    239         break;
    240     }
    241   }
    242 
    243   if (!registeredClaimFile) {
    244     message(LDPL_ERROR, "register_claim_file not passed to LLVMgold.");
    245     return LDPS_ERR;
    246   }
    247   if (!add_symbols) {
    248     message(LDPL_ERROR, "add_symbols not passed to LLVMgold.");
    249     return LDPS_ERR;
    250   }
    251 
    252   if (!RegisteredAllSymbolsRead)
    253     return LDPS_OK;
    254 
    255   if (!get_input_file) {
    256     message(LDPL_ERROR, "get_input_file not passed to LLVMgold.");
    257     return LDPS_ERR;
    258   }
    259   if (!release_input_file) {
    260     message(LDPL_ERROR, "relesase_input_file not passed to LLVMgold.");
    261     return LDPS_ERR;
    262   }
    263 
    264   return LDPS_OK;
    265 }
    266 
    267 static const GlobalObject *getBaseObject(const GlobalValue &GV) {
    268   if (auto *GA = dyn_cast<GlobalAlias>(&GV))
    269     return GA->getBaseObject();
    270   return cast<GlobalObject>(&GV);
    271 }
    272 
    273 static bool shouldSkip(uint32_t Symflags) {
    274   if (!(Symflags & object::BasicSymbolRef::SF_Global))
    275     return true;
    276   if (Symflags & object::BasicSymbolRef::SF_FormatSpecific)
    277     return true;
    278   return false;
    279 }
    280 
    281 static void diagnosticHandler(const DiagnosticInfo &DI, void *Context) {
    282   if (const auto *BDI = dyn_cast<BitcodeDiagnosticInfo>(&DI)) {
    283     std::error_code EC = BDI->getError();
    284     if (EC == BitcodeError::InvalidBitcodeSignature)
    285       return;
    286   }
    287 
    288   std::string ErrStorage;
    289   {
    290     raw_string_ostream OS(ErrStorage);
    291     DiagnosticPrinterRawOStream DP(OS);
    292     DI.print(DP);
    293   }
    294   ld_plugin_level Level;
    295   switch (DI.getSeverity()) {
    296   case DS_Error:
    297     message(LDPL_FATAL, "LLVM gold plugin has failed to create LTO module: %s",
    298             ErrStorage.c_str());
    299     llvm_unreachable("Fatal doesn't return.");
    300   case DS_Warning:
    301     Level = LDPL_WARNING;
    302     break;
    303   case DS_Note:
    304   case DS_Remark:
    305     Level = LDPL_INFO;
    306     break;
    307   }
    308   message(Level, "LLVM gold plugin: %s",  ErrStorage.c_str());
    309 }
    310 
    311 /// Called by gold to see whether this file is one that our plugin can handle.
    312 /// We'll try to open it and register all the symbols with add_symbol if
    313 /// possible.
    314 static ld_plugin_status claim_file_hook(const ld_plugin_input_file *file,
    315                                         int *claimed) {
    316   LLVMContext Context;
    317   MemoryBufferRef BufferRef;
    318   std::unique_ptr<MemoryBuffer> Buffer;
    319   if (get_view) {
    320     const void *view;
    321     if (get_view(file->handle, &view) != LDPS_OK) {
    322       message(LDPL_ERROR, "Failed to get a view of %s", file->name);
    323       return LDPS_ERR;
    324     }
    325     BufferRef = MemoryBufferRef(StringRef((const char *)view, file->filesize), "");
    326   } else {
    327     int64_t offset = 0;
    328     // Gold has found what might be IR part-way inside of a file, such as
    329     // an .a archive.
    330     if (file->offset) {
    331       offset = file->offset;
    332     }
    333     ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
    334         MemoryBuffer::getOpenFileSlice(file->fd, file->name, file->filesize,
    335                                        offset);
    336     if (std::error_code EC = BufferOrErr.getError()) {
    337       message(LDPL_ERROR, EC.message().c_str());
    338       return LDPS_ERR;
    339     }
    340     Buffer = std::move(BufferOrErr.get());
    341     BufferRef = Buffer->getMemBufferRef();
    342   }
    343 
    344   Context.setDiagnosticHandler(diagnosticHandler);
    345   ErrorOr<std::unique_ptr<object::IRObjectFile>> ObjOrErr =
    346       object::IRObjectFile::create(BufferRef, Context);
    347   std::error_code EC = ObjOrErr.getError();
    348   if (EC == object::object_error::invalid_file_type ||
    349       EC == object::object_error::bitcode_section_not_found)
    350     return LDPS_OK;
    351 
    352   *claimed = 1;
    353 
    354   if (EC) {
    355     message(LDPL_ERROR, "LLVM gold plugin has failed to create LTO module: %s",
    356             EC.message().c_str());
    357     return LDPS_ERR;
    358   }
    359   std::unique_ptr<object::IRObjectFile> Obj = std::move(*ObjOrErr);
    360 
    361   Modules.resize(Modules.size() + 1);
    362   claimed_file &cf = Modules.back();
    363 
    364   cf.handle = file->handle;
    365 
    366   for (auto &Sym : Obj->symbols()) {
    367     uint32_t Symflags = Sym.getFlags();
    368     if (shouldSkip(Symflags))
    369       continue;
    370 
    371     cf.syms.push_back(ld_plugin_symbol());
    372     ld_plugin_symbol &sym = cf.syms.back();
    373     sym.version = nullptr;
    374 
    375     SmallString<64> Name;
    376     {
    377       raw_svector_ostream OS(Name);
    378       Sym.printName(OS);
    379     }
    380     sym.name = strdup(Name.c_str());
    381 
    382     const GlobalValue *GV = Obj->getSymbolGV(Sym.getRawDataRefImpl());
    383 
    384     sym.visibility = LDPV_DEFAULT;
    385     if (GV) {
    386       switch (GV->getVisibility()) {
    387       case GlobalValue::DefaultVisibility:
    388         sym.visibility = LDPV_DEFAULT;
    389         break;
    390       case GlobalValue::HiddenVisibility:
    391         sym.visibility = LDPV_HIDDEN;
    392         break;
    393       case GlobalValue::ProtectedVisibility:
    394         sym.visibility = LDPV_PROTECTED;
    395         break;
    396       }
    397     }
    398 
    399     if (Symflags & object::BasicSymbolRef::SF_Undefined) {
    400       sym.def = LDPK_UNDEF;
    401       if (GV && GV->hasExternalWeakLinkage())
    402         sym.def = LDPK_WEAKUNDEF;
    403     } else {
    404       sym.def = LDPK_DEF;
    405       if (GV) {
    406         assert(!GV->hasExternalWeakLinkage() &&
    407                !GV->hasAvailableExternallyLinkage() && "Not a declaration!");
    408         if (GV->hasCommonLinkage())
    409           sym.def = LDPK_COMMON;
    410         else if (GV->isWeakForLinker())
    411           sym.def = LDPK_WEAKDEF;
    412       }
    413     }
    414 
    415     sym.size = 0;
    416     sym.comdat_key = nullptr;
    417     if (GV) {
    418       const GlobalObject *Base = getBaseObject(*GV);
    419       if (!Base)
    420         message(LDPL_FATAL, "Unable to determine comdat of alias!");
    421       const Comdat *C = Base->getComdat();
    422       if (C)
    423         sym.comdat_key = strdup(C->getName().str().c_str());
    424       else if (Base->hasWeakLinkage() || Base->hasLinkOnceLinkage())
    425         sym.comdat_key = strdup(sym.name);
    426     }
    427 
    428     sym.resolution = LDPR_UNKNOWN;
    429   }
    430 
    431   if (!cf.syms.empty()) {
    432     if (add_symbols(cf.handle, cf.syms.size(), &cf.syms[0]) != LDPS_OK) {
    433       message(LDPL_ERROR, "Unable to add symbols!");
    434       return LDPS_ERR;
    435     }
    436   }
    437 
    438   return LDPS_OK;
    439 }
    440 
    441 static void keepGlobalValue(GlobalValue &GV,
    442                             std::vector<GlobalAlias *> &KeptAliases) {
    443   assert(!GV.hasLocalLinkage());
    444 
    445   if (auto *GA = dyn_cast<GlobalAlias>(&GV))
    446     KeptAliases.push_back(GA);
    447 
    448   switch (GV.getLinkage()) {
    449   default:
    450     break;
    451   case GlobalValue::LinkOnceAnyLinkage:
    452     GV.setLinkage(GlobalValue::WeakAnyLinkage);
    453     break;
    454   case GlobalValue::LinkOnceODRLinkage:
    455     GV.setLinkage(GlobalValue::WeakODRLinkage);
    456     break;
    457   }
    458 
    459   assert(!GV.isDiscardableIfUnused());
    460 }
    461 
    462 static void internalize(GlobalValue &GV) {
    463   if (GV.isDeclarationForLinker())
    464     return; // We get here if there is a matching asm definition.
    465   if (!GV.hasLocalLinkage())
    466     GV.setLinkage(GlobalValue::InternalLinkage);
    467 }
    468 
    469 static void drop(GlobalValue &GV) {
    470   if (auto *F = dyn_cast<Function>(&GV)) {
    471     F->deleteBody();
    472     F->setComdat(nullptr); // Should deleteBody do this?
    473     return;
    474   }
    475 
    476   if (auto *Var = dyn_cast<GlobalVariable>(&GV)) {
    477     Var->setInitializer(nullptr);
    478     Var->setLinkage(
    479         GlobalValue::ExternalLinkage); // Should setInitializer do this?
    480     Var->setComdat(nullptr); // and this?
    481     return;
    482   }
    483 
    484   auto &Alias = cast<GlobalAlias>(GV);
    485   Module &M = *Alias.getParent();
    486   PointerType &Ty = *cast<PointerType>(Alias.getType());
    487   GlobalValue::LinkageTypes L = Alias.getLinkage();
    488   auto *Var =
    489       new GlobalVariable(M, Ty.getElementType(), /*isConstant*/ false, L,
    490                          /*Initializer*/ nullptr);
    491   Var->takeName(&Alias);
    492   Alias.replaceAllUsesWith(Var);
    493   Alias.eraseFromParent();
    494 }
    495 
    496 static const char *getResolutionName(ld_plugin_symbol_resolution R) {
    497   switch (R) {
    498   case LDPR_UNKNOWN:
    499     return "UNKNOWN";
    500   case LDPR_UNDEF:
    501     return "UNDEF";
    502   case LDPR_PREVAILING_DEF:
    503     return "PREVAILING_DEF";
    504   case LDPR_PREVAILING_DEF_IRONLY:
    505     return "PREVAILING_DEF_IRONLY";
    506   case LDPR_PREEMPTED_REG:
    507     return "PREEMPTED_REG";
    508   case LDPR_PREEMPTED_IR:
    509     return "PREEMPTED_IR";
    510   case LDPR_RESOLVED_IR:
    511     return "RESOLVED_IR";
    512   case LDPR_RESOLVED_EXEC:
    513     return "RESOLVED_EXEC";
    514   case LDPR_RESOLVED_DYN:
    515     return "RESOLVED_DYN";
    516   case LDPR_PREVAILING_DEF_IRONLY_EXP:
    517     return "PREVAILING_DEF_IRONLY_EXP";
    518   }
    519   llvm_unreachable("Unknown resolution");
    520 }
    521 
    522 namespace {
    523 class LocalValueMaterializer : public ValueMaterializer {
    524   DenseSet<GlobalValue *> &Dropped;
    525   DenseMap<GlobalObject *, GlobalObject *> LocalVersions;
    526 
    527 public:
    528   LocalValueMaterializer(DenseSet<GlobalValue *> &Dropped) : Dropped(Dropped) {}
    529   Value *materializeValueFor(Value *V) override;
    530 };
    531 }
    532 
    533 Value *LocalValueMaterializer::materializeValueFor(Value *V) {
    534   auto *GO = dyn_cast<GlobalObject>(V);
    535   if (!GO)
    536     return nullptr;
    537 
    538   auto I = LocalVersions.find(GO);
    539   if (I != LocalVersions.end())
    540     return I->second;
    541 
    542   if (!Dropped.count(GO))
    543     return nullptr;
    544 
    545   Module &M = *GO->getParent();
    546   GlobalValue::LinkageTypes L = GO->getLinkage();
    547   GlobalObject *Declaration;
    548   if (auto *F = dyn_cast<Function>(GO)) {
    549     Declaration = Function::Create(F->getFunctionType(), L, "", &M);
    550   } else {
    551     auto *Var = cast<GlobalVariable>(GO);
    552     Declaration = new GlobalVariable(M, Var->getType()->getElementType(),
    553                                      Var->isConstant(), L,
    554                                      /*Initializer*/ nullptr);
    555   }
    556   Declaration->takeName(GO);
    557   Declaration->copyAttributesFrom(GO);
    558 
    559   GO->setLinkage(GlobalValue::InternalLinkage);
    560   GO->setName(Declaration->getName());
    561   Dropped.erase(GO);
    562   GO->replaceAllUsesWith(Declaration);
    563 
    564   LocalVersions[Declaration] = GO;
    565 
    566   return GO;
    567 }
    568 
    569 static Constant *mapConstantToLocalCopy(Constant *C, ValueToValueMapTy &VM,
    570                                         LocalValueMaterializer *Materializer) {
    571   return MapValue(C, VM, RF_IgnoreMissingEntries, nullptr, Materializer);
    572 }
    573 
    574 static void freeSymName(ld_plugin_symbol &Sym) {
    575   free(Sym.name);
    576   free(Sym.comdat_key);
    577   Sym.name = nullptr;
    578   Sym.comdat_key = nullptr;
    579 }
    580 
    581 static std::unique_ptr<Module>
    582 getModuleForFile(LLVMContext &Context, claimed_file &F,
    583                  ld_plugin_input_file &Info, raw_fd_ostream *ApiFile,
    584                  StringSet<> &Internalize, StringSet<> &Maybe) {
    585 
    586   if (get_symbols(F.handle, F.syms.size(), &F.syms[0]) != LDPS_OK)
    587     message(LDPL_FATAL, "Failed to get symbol information");
    588 
    589   const void *View;
    590   if (get_view(F.handle, &View) != LDPS_OK)
    591     message(LDPL_FATAL, "Failed to get a view of file");
    592 
    593   MemoryBufferRef BufferRef(StringRef((const char *)View, Info.filesize),
    594                             Info.name);
    595   ErrorOr<std::unique_ptr<object::IRObjectFile>> ObjOrErr =
    596       object::IRObjectFile::create(BufferRef, Context);
    597 
    598   if (std::error_code EC = ObjOrErr.getError())
    599     message(LDPL_FATAL, "Could not read bitcode from file : %s",
    600             EC.message().c_str());
    601 
    602   object::IRObjectFile &Obj = **ObjOrErr;
    603 
    604   Module &M = Obj.getModule();
    605 
    606   M.materializeMetadata();
    607   UpgradeDebugInfo(M);
    608 
    609   SmallPtrSet<GlobalValue *, 8> Used;
    610   collectUsedGlobalVariables(M, Used, /*CompilerUsed*/ false);
    611 
    612   DenseSet<GlobalValue *> Drop;
    613   std::vector<GlobalAlias *> KeptAliases;
    614 
    615   unsigned SymNum = 0;
    616   for (auto &ObjSym : Obj.symbols()) {
    617     if (shouldSkip(ObjSym.getFlags()))
    618       continue;
    619     ld_plugin_symbol &Sym = F.syms[SymNum];
    620     ++SymNum;
    621 
    622     ld_plugin_symbol_resolution Resolution =
    623         (ld_plugin_symbol_resolution)Sym.resolution;
    624 
    625     if (options::generate_api_file)
    626       *ApiFile << Sym.name << ' ' << getResolutionName(Resolution) << '\n';
    627 
    628     GlobalValue *GV = Obj.getSymbolGV(ObjSym.getRawDataRefImpl());
    629     if (!GV) {
    630       freeSymName(Sym);
    631       continue; // Asm symbol.
    632     }
    633 
    634     if (Resolution != LDPR_PREVAILING_DEF_IRONLY && GV->hasCommonLinkage()) {
    635       // Common linkage is special. There is no single symbol that wins the
    636       // resolution. Instead we have to collect the maximum alignment and size.
    637       // The IR linker does that for us if we just pass it every common GV.
    638       // We still have to keep track of LDPR_PREVAILING_DEF_IRONLY so we
    639       // internalize once the IR linker has done its job.
    640       freeSymName(Sym);
    641       continue;
    642     }
    643 
    644     switch (Resolution) {
    645     case LDPR_UNKNOWN:
    646       llvm_unreachable("Unexpected resolution");
    647 
    648     case LDPR_RESOLVED_IR:
    649     case LDPR_RESOLVED_EXEC:
    650     case LDPR_RESOLVED_DYN:
    651       assert(GV->isDeclarationForLinker());
    652       break;
    653 
    654     case LDPR_UNDEF:
    655       if (!GV->isDeclarationForLinker()) {
    656         assert(GV->hasComdat());
    657         Drop.insert(GV);
    658       }
    659       break;
    660 
    661     case LDPR_PREVAILING_DEF_IRONLY: {
    662       keepGlobalValue(*GV, KeptAliases);
    663       if (!Used.count(GV)) {
    664         // Since we use the regular lib/Linker, we cannot just internalize GV
    665         // now or it will not be copied to the merged module. Instead we force
    666         // it to be copied and then internalize it.
    667         Internalize.insert(GV->getName());
    668       }
    669       break;
    670     }
    671 
    672     case LDPR_PREVAILING_DEF:
    673       keepGlobalValue(*GV, KeptAliases);
    674       break;
    675 
    676     case LDPR_PREEMPTED_IR:
    677       // Gold might have selected a linkonce_odr and preempted a weak_odr.
    678       // In that case we have to make sure we don't end up internalizing it.
    679       if (!GV->isDiscardableIfUnused())
    680         Maybe.erase(GV->getName());
    681 
    682       // fall-through
    683     case LDPR_PREEMPTED_REG:
    684       Drop.insert(GV);
    685       break;
    686 
    687     case LDPR_PREVAILING_DEF_IRONLY_EXP: {
    688       // We can only check for address uses after we merge the modules. The
    689       // reason is that this GV might have a copy in another module
    690       // and in that module the address might be significant, but that
    691       // copy will be LDPR_PREEMPTED_IR.
    692       if (GV->hasLinkOnceODRLinkage())
    693         Maybe.insert(GV->getName());
    694       keepGlobalValue(*GV, KeptAliases);
    695       break;
    696     }
    697     }
    698 
    699     freeSymName(Sym);
    700   }
    701 
    702   ValueToValueMapTy VM;
    703   LocalValueMaterializer Materializer(Drop);
    704   for (GlobalAlias *GA : KeptAliases) {
    705     // Gold told us to keep GA. It is possible that a GV usied in the aliasee
    706     // expression is being dropped. If that is the case, that GV must be copied.
    707     Constant *Aliasee = GA->getAliasee();
    708     Constant *Replacement = mapConstantToLocalCopy(Aliasee, VM, &Materializer);
    709     GA->setAliasee(Replacement);
    710   }
    711 
    712   for (auto *GV : Drop)
    713     drop(*GV);
    714 
    715   return Obj.takeModule();
    716 }
    717 
    718 static void runLTOPasses(Module &M, TargetMachine &TM) {
    719   if (const DataLayout *DL = TM.getDataLayout())
    720     M.setDataLayout(*DL);
    721 
    722   legacy::PassManager passes;
    723   passes.add(createTargetTransformInfoWrapperPass(TM.getTargetIRAnalysis()));
    724 
    725   PassManagerBuilder PMB;
    726   PMB.LibraryInfo = new TargetLibraryInfoImpl(Triple(TM.getTargetTriple()));
    727   PMB.Inliner = createFunctionInliningPass();
    728   PMB.VerifyInput = true;
    729   PMB.VerifyOutput = true;
    730   PMB.LoopVectorize = true;
    731   PMB.SLPVectorize = true;
    732   PMB.OptLevel = options::OptLevel;
    733   PMB.populateLTOPassManager(passes);
    734   passes.run(M);
    735 }
    736 
    737 static void saveBCFile(StringRef Path, Module &M) {
    738   std::error_code EC;
    739   raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::F_None);
    740   if (EC)
    741     message(LDPL_FATAL, "Failed to write the output file.");
    742   WriteBitcodeToFile(&M, OS, /* ShouldPreserveUseListOrder */ true);
    743 }
    744 
    745 static void codegen(Module &M) {
    746   const std::string &TripleStr = M.getTargetTriple();
    747   Triple TheTriple(TripleStr);
    748 
    749   std::string ErrMsg;
    750   const Target *TheTarget = TargetRegistry::lookupTarget(TripleStr, ErrMsg);
    751   if (!TheTarget)
    752     message(LDPL_FATAL, "Target not found: %s", ErrMsg.c_str());
    753 
    754   if (unsigned NumOpts = options::extra.size())
    755     cl::ParseCommandLineOptions(NumOpts, &options::extra[0]);
    756 
    757   SubtargetFeatures Features;
    758   Features.getDefaultSubtargetFeatures(TheTriple);
    759   for (const std::string &A : MAttrs)
    760     Features.AddFeature(A);
    761 
    762   TargetOptions Options = InitTargetOptionsFromCodeGenFlags();
    763   CodeGenOpt::Level CGOptLevel;
    764   switch (options::OptLevel) {
    765   case 0:
    766     CGOptLevel = CodeGenOpt::None;
    767     break;
    768   case 1:
    769     CGOptLevel = CodeGenOpt::Less;
    770     break;
    771   case 2:
    772     CGOptLevel = CodeGenOpt::Default;
    773     break;
    774   case 3:
    775     CGOptLevel = CodeGenOpt::Aggressive;
    776     break;
    777   }
    778   std::unique_ptr<TargetMachine> TM(TheTarget->createTargetMachine(
    779       TripleStr, options::mcpu, Features.getString(), Options, RelocationModel,
    780       CodeModel::Default, CGOptLevel));
    781 
    782   runLTOPasses(M, *TM);
    783 
    784   if (options::TheOutputType == options::OT_SAVE_TEMPS)
    785     saveBCFile(output_name + ".opt.bc", M);
    786 
    787   legacy::PassManager CodeGenPasses;
    788 
    789   SmallString<128> Filename;
    790   int FD;
    791   if (options::obj_path.empty()) {
    792     std::error_code EC =
    793         sys::fs::createTemporaryFile("lto-llvm", "o", FD, Filename);
    794     if (EC)
    795       message(LDPL_FATAL, "Could not create temporary file: %s",
    796               EC.message().c_str());
    797   } else {
    798     Filename = options::obj_path;
    799     std::error_code EC =
    800         sys::fs::openFileForWrite(Filename.c_str(), FD, sys::fs::F_None);
    801     if (EC)
    802       message(LDPL_FATAL, "Could not open file: %s", EC.message().c_str());
    803   }
    804 
    805   {
    806     raw_fd_ostream OS(FD, true);
    807 
    808     if (TM->addPassesToEmitFile(CodeGenPasses, OS,
    809                                 TargetMachine::CGFT_ObjectFile))
    810       message(LDPL_FATAL, "Failed to setup codegen");
    811     CodeGenPasses.run(M);
    812   }
    813 
    814   if (add_input_file(Filename.c_str()) != LDPS_OK)
    815     message(LDPL_FATAL,
    816             "Unable to add .o file to the link. File left behind in: %s",
    817             Filename.c_str());
    818 
    819   if (options::obj_path.empty())
    820     Cleanup.push_back(Filename.c_str());
    821 }
    822 
    823 /// gold informs us that all symbols have been read. At this point, we use
    824 /// get_symbols to see if any of our definitions have been overridden by a
    825 /// native object file. Then, perform optimization and codegen.
    826 static ld_plugin_status allSymbolsReadHook(raw_fd_ostream *ApiFile) {
    827   if (Modules.empty())
    828     return LDPS_OK;
    829 
    830   LLVMContext Context;
    831   Context.setDiagnosticHandler(diagnosticHandler, nullptr, true);
    832 
    833   std::unique_ptr<Module> Combined(new Module("ld-temp.o", Context));
    834   Linker L(Combined.get());
    835 
    836   std::string DefaultTriple = sys::getDefaultTargetTriple();
    837 
    838   StringSet<> Internalize;
    839   StringSet<> Maybe;
    840   for (claimed_file &F : Modules) {
    841     ld_plugin_input_file File;
    842     if (get_input_file(F.handle, &File) != LDPS_OK)
    843       message(LDPL_FATAL, "Failed to get file information");
    844     std::unique_ptr<Module> M =
    845         getModuleForFile(Context, F, File, ApiFile, Internalize, Maybe);
    846     if (!options::triple.empty())
    847       M->setTargetTriple(options::triple.c_str());
    848     else if (M->getTargetTriple().empty()) {
    849       M->setTargetTriple(DefaultTriple);
    850     }
    851 
    852     if (L.linkInModule(M.get()))
    853       message(LDPL_FATAL, "Failed to link module");
    854     if (release_input_file(F.handle) != LDPS_OK)
    855       message(LDPL_FATAL, "Failed to release file information");
    856   }
    857 
    858   for (const auto &Name : Internalize) {
    859     GlobalValue *GV = Combined->getNamedValue(Name.first());
    860     if (GV)
    861       internalize(*GV);
    862   }
    863 
    864   for (const auto &Name : Maybe) {
    865     GlobalValue *GV = Combined->getNamedValue(Name.first());
    866     if (!GV)
    867       continue;
    868     GV->setLinkage(GlobalValue::LinkOnceODRLinkage);
    869     if (canBeOmittedFromSymbolTable(GV))
    870       internalize(*GV);
    871   }
    872 
    873   if (options::TheOutputType == options::OT_DISABLE)
    874     return LDPS_OK;
    875 
    876   if (options::TheOutputType != options::OT_NORMAL) {
    877     std::string path;
    878     if (options::TheOutputType == options::OT_BC_ONLY)
    879       path = output_name;
    880     else
    881       path = output_name + ".bc";
    882     saveBCFile(path, *L.getModule());
    883     if (options::TheOutputType == options::OT_BC_ONLY)
    884       return LDPS_OK;
    885   }
    886 
    887   codegen(*L.getModule());
    888 
    889   if (!options::extra_library_path.empty() &&
    890       set_extra_library_path(options::extra_library_path.c_str()) != LDPS_OK)
    891     message(LDPL_FATAL, "Unable to set the extra library path.");
    892 
    893   return LDPS_OK;
    894 }
    895 
    896 static ld_plugin_status all_symbols_read_hook(void) {
    897   ld_plugin_status Ret;
    898   if (!options::generate_api_file) {
    899     Ret = allSymbolsReadHook(nullptr);
    900   } else {
    901     std::error_code EC;
    902     raw_fd_ostream ApiFile("apifile.txt", EC, sys::fs::F_None);
    903     if (EC)
    904       message(LDPL_FATAL, "Unable to open apifile.txt for writing: %s",
    905               EC.message().c_str());
    906     Ret = allSymbolsReadHook(&ApiFile);
    907   }
    908 
    909   llvm_shutdown();
    910 
    911   if (options::TheOutputType == options::OT_BC_ONLY ||
    912       options::TheOutputType == options::OT_DISABLE) {
    913     if (options::TheOutputType == options::OT_DISABLE)
    914       // Remove the output file here since ld.bfd creates the output file
    915       // early.
    916       sys::fs::remove(output_name);
    917     exit(0);
    918   }
    919 
    920   return Ret;
    921 }
    922 
    923 static ld_plugin_status cleanup_hook(void) {
    924   for (std::string &Name : Cleanup) {
    925     std::error_code EC = sys::fs::remove(Name);
    926     if (EC)
    927       message(LDPL_ERROR, "Failed to delete '%s': %s", Name.c_str(),
    928               EC.message().c_str());
    929   }
    930 
    931   return LDPS_OK;
    932 }
    933