DTLTO.h

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//===- DTLTO.h - Distributed ThinLTO functions and classes ----*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===---------------------------------------------------------------------===//
 
#ifndef LLVM_DTLTO_DTLTO_H
#define LLVM_DTLTO_DTLTO_H
 
#include "llvm/LTO/LTO.h"
#include "llvm/Support/MemoryBuffer.h"
 
namespace llvm {
namespace lto {
 
// The purpose of this class is to prepare inputs so that distributed ThinLTO
// backend compilations can succeed.
//
// For distributed compilation, each input must exist as an individual bitcode
// file on disk and be loadable via its ModuleID. This requirement is not met
// for archive members, as an archive is a collection of files rather than a
// standalone file. Similarly, for FatLTO objects, the bitcode is stored in a
// section of the containing ELF object file. To address this, the class ensures
// that an individual bitcode file exists for each input (by writing it out if
// necessary) and that the ModuleID is updated to point to it. Module IDs are
// also normalized on Windows to remove short 8.3 form paths that cannot be
// loaded on remote machines.
//
// The class ensures that lto::InputFile objects are preserved until enough of
// the LTO pipeline has executed to determine the required per-module
// information, such as whether a module will participate in ThinLTO.
class DTLTO : public LTO {
  using Base = LTO;
 
public:
  LLVM_ABI DTLTO(Config Conf, ThinBackend Backend,
                 unsigned ParallelCodeGenParallelismLevel, LTOKind LTOMode,
                 StringRef LinkerOutputFile, bool SaveTemps)
      : Base(std::move(Conf), Backend, ParallelCodeGenParallelismLevel,
             LTOMode),
        LinkerOutputFile(LinkerOutputFile), SaveTemps(SaveTemps) {
    assert(!LinkerOutputFile.empty() && "expected a valid linker output file");
  }
 
  // Add an input file and prepare it for distribution.
  LLVM_ABI Expected<std::shared_ptr<InputFile>>
  addInput(std::unique_ptr<InputFile> InputPtr) override;
 
protected:
  // Save the contents of ThinLTO-enabled input files that must be serialized
  // for distribution, such as archive members and FatLTO objects, to individual
  // bitcode files named after the module ID.
  LLVM_ABI llvm::Error serializeInputsForDistribution() override;
 
  LLVM_ABI void cleanup() override;
 
private:
  // Bump allocator for a purpose of saving updated module IDs.
  BumpPtrAllocator PtrAlloc;
  StringSaver Saver{PtrAlloc};
 
  /// The output file to which this LTO invocation will contribute.
  StringRef LinkerOutputFile;
 
  /// The normalized output directory, derived from LinkerOutputFile.
  StringRef LinkerOutputDir;
 
  /// Controls preservation of any created temporary files.
  bool SaveTemps;
 
  // Array of input bitcode files for LTO.
  std::vector<std::shared_ptr<lto::InputFile>> InputFiles;
 
  // Cache of whether a path refers to a thin archive.
  StringMap<bool> ArchiveIsThinCache;
 
  // Determines if the file at the given path is a thin archive.
  Expected<bool> isThinArchive(const StringRef ArchivePath);
};
 
} // namespace lto
} // namespace llvm
 
#endif // LLVM_DTLTO_DTLTO_H