lld/COFF/LTO.cpp

   1 //===- LTO.cpp ------------------------------------------------------------===//
   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 #include "LTO.h"
  10 #include "Config.h"
  11 #include "InputFiles.h"
  12 #include "Symbols.h"
  13 #include "lld/Common/Args.h"
  14 #include "lld/Common/ErrorHandler.h"
  15 #include "lld/Common/Strings.h"
  16 #include "lld/Common/TargetOptionsCommandFlags.h"
  17 #include "llvm/ADT/STLExtras.h"
  18 #include "llvm/ADT/SmallString.h"
  19 #include "llvm/ADT/StringRef.h"
  20 #include "llvm/ADT/Twine.h"
  21 #include "llvm/Bitcode/BitcodeWriter.h"
  22 #include "llvm/IR/DiagnosticPrinter.h"
  23 #include "llvm/LTO/Caching.h"
  24 #include "llvm/LTO/Config.h"
  25 #include "llvm/LTO/LTO.h"
  26 #include "llvm/Object/SymbolicFile.h"
  27 #include "llvm/Support/CodeGen.h"
  28 #include "llvm/Support/Error.h"
  29 #include "llvm/Support/FileSystem.h"
  30 #include "llvm/Support/MemoryBuffer.h"
  31 #include "llvm/Support/raw_ostream.h"
  32 #include <algorithm>
  33 #include <cstddef>
  34 #include <memory>
  35 #include <string>
  36 #include <system_error>
  37 #include <vector>
  38
  39 using namespace llvm;
  40 using namespace llvm::object;
  41 using namespace lld;
  42 using namespace lld::coff;
  43
  44 // Creates an empty file to and returns a raw_fd_ostream to write to it.
  45 static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) {
  46   std::error_code ec;
  47   auto ret =
  48       std::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::OF_None);
  49   if (ec) {
  50     error("cannot open " + file + ": " + ec.message());
  51     return nullptr;
  52   }
  53   return ret;
  54 }
  55
  56 static std::string getThinLTOOutputFile(StringRef path) {
  57   return lto::getThinLTOOutputFile(
  58       std::string(path), std::string(config->thinLTOPrefixReplace.first),
  59       std::string(config->thinLTOPrefixReplace.second));
  60 }
  61
  62 static lto::Config createConfig() {
  63   lto::Config c;
  64   c.Options = initTargetOptionsFromCodeGenFlags();
  65
  66   // Always emit a section per function/datum with LTO. LLVM LTO should get most
  67   // of the benefit of linker GC, but there are still opportunities for ICF.
  68   c.Options.FunctionSections = true;
  69   c.Options.DataSections = true;
  70
  71   // Use static reloc model on 32-bit x86 because it usually results in more
  72   // compact code, and because there are also known code generation bugs when
  73   // using the PIC model (see PR34306).
  74   if (config->machine == COFF::IMAGE_FILE_MACHINE_I386)
  75     c.RelocModel = Reloc::Static;
  76   else
  77     c.RelocModel = Reloc::PIC_;
  78   c.DisableVerify = true;
  79   c.DiagHandler = diagnosticHandler;
  80   c.OptLevel = config->ltoo;
  81   c.CPU = getCPUStr();
  82   c.MAttrs = getMAttrs();
  83   c.CGOptLevel = args::getCGOptLevel(config->ltoo);
  84
  85   if (config->saveTemps)
  86     checkError(c.addSaveTemps(std::string(config->outputFile) + ".",
  87                               /*UseInputModulePath*/ true));
  88   return c;
  89 }
  90
  91 BitcodeCompiler::BitcodeCompiler() {
  92   // Initialize indexFile.
  93   if (!config->thinLTOIndexOnlyArg.empty())
  94     indexFile = openFile(config->thinLTOIndexOnlyArg);
  95
  96   // Initialize ltoObj.
  97   lto::ThinBackend backend;
  98   if (config->thinLTOIndexOnly) {
  99     auto OnIndexWrite = [&](StringRef S) { thinIndices.erase(S); };
 100     backend = lto::createWriteIndexesThinBackend(
 101         std::string(config->thinLTOPrefixReplace.first),
 102         std::string(config->thinLTOPrefixReplace.second),
 103         config->thinLTOEmitImportsFiles, indexFile.get(), OnIndexWrite);
 104   } else {
 105     backend = lto::createInProcessThinBackend(
 106         llvm::heavyweight_hardware_concurrency(config->thinLTOJobs));
 107   }
 108
 109   ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
 110                                        config->ltoPartitions);
 111 }
 112
 113 BitcodeCompiler::~BitcodeCompiler() = default;
 114
 115 static void undefine(Symbol *s) { replaceSymbol<Undefined>(s, s->getName()); }
 116
 117 void BitcodeCompiler::add(BitcodeFile &f) {
 118   lto::InputFile &obj = *f.obj;
 119   unsigned symNum = 0;
 120   std::vector<Symbol *> symBodies = f.getSymbols();
 121   std::vector<lto::SymbolResolution> resols(symBodies.size());
 122
 123   if (config->thinLTOIndexOnly)
 124     thinIndices.insert(obj.getName());
 125
 126   // Provide a resolution to the LTO API for each symbol.
 127   for (const lto::InputFile::Symbol &objSym : obj.symbols()) {
 128     Symbol *sym = symBodies[symNum];
 129     lto::SymbolResolution &r = resols[symNum];
 130     ++symNum;
 131
 132     // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
 133     // reports two symbols for module ASM defined. Without this check, lld
 134     // flags an undefined in IR with a definition in ASM as prevailing.
 135     // Once IRObjectFile is fixed to report only one symbol this hack can
 136     // be removed.
 137     r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f;
 138     r.VisibleToRegularObj = sym->isUsedInRegularObj;
 139     if (r.Prevailing)
 140       undefine(sym);
 141   }
 142   checkError(ltoObj->add(std::move(f.obj), resols));
 143 }
 144
 145 // Merge all the bitcode files we have seen, codegen the result
 146 // and return the resulting objects.
 147 std::vector<InputFile *> BitcodeCompiler::compile() {
 148   unsigned maxTasks = ltoObj->getMaxTasks();
 149   buf.resize(maxTasks);
 150   files.resize(maxTasks);
 151
 152   // The /lldltocache option specifies the path to a directory in which to cache
 153   // native object files for ThinLTO incremental builds. If a path was
 154   // specified, configure LTO to use it as the cache directory.
 155   lto::NativeObjectCache cache;
 156   if (!config->ltoCache.empty())
 157     cache = check(lto::localCache(
 158         config->ltoCache, [&](size_t task, std::unique_ptr<MemoryBuffer> mb) {
 159           files[task] = std::move(mb);
 160         }));
 161
 162   checkError(ltoObj->run(
 163       [&](size_t task) {
 164         return std::make_unique<lto::NativeObjectStream>(
 165             std::make_unique<raw_svector_ostream>(buf[task]));
 166       },
 167       cache));
 168
 169   // Emit empty index files for non-indexed files
 170   for (StringRef s : thinIndices) {
 171     std::string path = getThinLTOOutputFile(s);
 172     openFile(path + ".thinlto.bc");
 173     if (config->thinLTOEmitImportsFiles)
 174       openFile(path + ".imports");
 175   }
 176
 177   // ThinLTO with index only option is required to generate only the index
 178   // files. After that, we exit from linker and ThinLTO backend runs in a
 179   // distributed environment.
 180   if (config->thinLTOIndexOnly) {
 181     if (!config->ltoObjPath.empty())
 182       saveBuffer(buf[0], config->ltoObjPath);
 183     if (indexFile)
 184       indexFile->close();
 185     return {};
 186   }
 187
 188   if (!config->ltoCache.empty())
 189     pruneCache(config->ltoCache, config->ltoCachePolicy);
 190
 191   std::vector<InputFile *> ret;
 192   for (unsigned i = 0; i != maxTasks; ++i) {
 193     // Assign unique names to LTO objects. This ensures they have unique names
 194     // in the PDB if one is produced. The names should look like:
 195     // - foo.exe.lto.obj
 196     // - foo.exe.lto.1.obj
 197     // - ...
 198     StringRef ltoObjName =
 199         saver.save(Twine(config->outputFile) + ".lto" +
 200                    (i == 0 ? Twine("") : Twine('.') + Twine(i)) + ".obj");
 201
 202     // Get the native object contents either from the cache or from memory.  Do
 203     // not use the cached MemoryBuffer directly, or the PDB will not be
 204     // deterministic.
 205     StringRef objBuf;
 206     if (files[i])
 207       objBuf = files[i]->getBuffer();
 208     else
 209       objBuf = buf[i];
 210     if (objBuf.empty())
 211       continue;
 212
 213     if (config->saveTemps)
 214       saveBuffer(buf[i], ltoObjName);
 215     ret.push_back(make<ObjFile>(MemoryBufferRef(objBuf, ltoObjName)));
 216   }
 217
 218   return ret;
 219 }