lld/ELF/LTO.cpp

//===- LTO.cpp ------------------------------------------------------------===//
//
//                             The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "LTO.h"
#include "Config.h"
#include "Error.h"
#include "InputFiles.h"
#include "Symbols.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Bitcode/ReaderWriter.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/Linker/IRMover.h"
#include "llvm/Support/StringSaver.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/IPO/PassManagerBuilder.h"

using namespace llvm;
using namespace llvm::object;
using namespace llvm::ELF;

using namespace lld;
using namespace lld::elf;

// This is for use when debugging LTO.
static void saveLtoObjectFile(StringRef Buffer) {
  std::error_code EC;
  raw_fd_ostream OS(Config->OutputFile.str() + ".lto.o", EC,
                    sys::fs::OpenFlags::F_None);
  check(EC);
  OS << Buffer;
}

// This is for use when debugging LTO.
static void saveBCFile(Module &M, StringRef Suffix) {
  std::error_code EC;
  raw_fd_ostream OS(Config->OutputFile.str() + Suffix.str(), EC,
                    sys::fs::OpenFlags::F_None);
  check(EC);
  WriteBitcodeToFile(&M, OS, /* ShouldPreserveUseListOrder */ true);
}

// Run LTO passes.
// FIXME: Reduce code duplication by sharing this code with the gold plugin.
static void runLTOPasses(Module &M, TargetMachine &TM) {
  legacy::PassManager LtoPasses;
  LtoPasses.add(createTargetTransformInfoWrapperPass(TM.getTargetIRAnalysis()));
  PassManagerBuilder PMB;
  PMB.LibraryInfo = new TargetLibraryInfoImpl(Triple(TM.getTargetTriple()));
  PMB.Inliner = createFunctionInliningPass();
  PMB.VerifyInput = true;
  PMB.VerifyOutput = true;
  PMB.LoopVectorize = true;
  PMB.SLPVectorize = true;
  PMB.OptLevel = 2; // FIXME: This should be an option.
  PMB.populateLTOPassManager(LtoPasses);
  LtoPasses.run(M);

  if (Config->SaveTemps)
    saveBCFile(M, ".lto.opt.bc");
}

void BitcodeCompiler::add(BitcodeFile &F) {
  std::unique_ptr<IRObjectFile> Obj =
      check(IRObjectFile::create(F.MB, Context));
  std::vector<GlobalValue *> Keep;
  unsigned BodyIndex = 0;
  ArrayRef<SymbolBody *> Bodies = F.getSymbols();

  for (const BasicSymbolRef &Sym : Obj->symbols()) {
    GlobalValue *GV = Obj->getSymbolGV(Sym.getRawDataRefImpl());
    assert(GV);
    if (GV->hasAppendingLinkage()) {
      Keep.push_back(GV);
      continue;
    }
    if (!BitcodeFile::shouldSkip(Sym)) {
      if (SymbolBody *B = Bodies[BodyIndex++])
        if (&B->repl() == B && isa<DefinedBitcode>(B)) {
          if (GV->getLinkage() == llvm::GlobalValue::LinkOnceODRLinkage)
            GV->setLinkage(GlobalValue::WeakODRLinkage);
          Keep.push_back(GV);
        }
    }
  }

  Mover.move(Obj->takeModule(), Keep,
             [](GlobalValue &, IRMover::ValueAdder) {});
}

// Merge all the bitcode files we have seen, codegen the result
// and return the resulting ObjectFile.
template <class ELFT>
std::unique_ptr<elf::ObjectFile<ELFT>> BitcodeCompiler::compile() {
  if (Config->SaveTemps)
    saveBCFile(Combined, ".lto.bc");

  StringRef TripleStr = Combined.getTargetTriple();
  Triple TheTriple(TripleStr);

  // FIXME: Should we have a default triple? The gold plugin uses
  // sys::getDefaultTargetTriple(), but that is probably wrong given that this
  // might be a cross linker.

  std::string ErrMsg;
  const Target *TheTarget = TargetRegistry::lookupTarget(TripleStr, ErrMsg);
  if (!TheTarget)
    fatal("target not found: " + ErrMsg);

  TargetOptions Options;
  Reloc::Model R = Config->Pic ? Reloc::PIC_ : Reloc::Static;
  std::unique_ptr<TargetMachine> TM(
      TheTarget->createTargetMachine(TripleStr, "", "", Options, R));

  runLTOPasses(Combined, *TM);

  raw_svector_ostream OS(OwningData);
  legacy::PassManager CodeGenPasses;
  if (TM->addPassesToEmitFile(CodeGenPasses, OS,
                              TargetMachine::CGFT_ObjectFile))
    fatal("failed to setup codegen");
  CodeGenPasses.run(Combined);
  MB = MemoryBuffer::getMemBuffer(OwningData,
                                  "LLD-INTERNAL-combined-lto-object", false);
  if (Config->SaveTemps)
    saveLtoObjectFile(MB->getBuffer());

  std::unique_ptr<InputFile> IF = createObjectFile(*MB);
  auto *OF = cast<ObjectFile<ELFT>>(IF.release());
  return std::unique_ptr<ObjectFile<ELFT>>(OF);
}

template std::unique_ptr<elf::ObjectFile<ELF32LE>> BitcodeCompiler::compile();
template std::unique_ptr<elf::ObjectFile<ELF32BE>> BitcodeCompiler::compile();
template std::unique_ptr<elf::ObjectFile<ELF64LE>> BitcodeCompiler::compile();
template std::unique_ptr<elf::ObjectFile<ELF64BE>> BitcodeCompiler::compile();