[PATCH] D93761: [libObject/Decompressor] - Use `resize_for_overwrite` in Decompressor::resizeAndDecompress().

[George Rimar via Phabricator via llvm-commits]

grimar added a comment.

Ok. I've used the following piece of code to construct a 1Gb of random compressed data and estimated
the difference between the old and the new code in Release.

  auto T1 = std::chrono::high_resolution_clock::now();
  constexpr uint64_t Size = 1024 * 1024 * 1024uLL;
  std::vector<uint8_t> Data;
  Data.reserve(Size);
  for (size_t I = 0; I != Size; ++I)
    Data.push_back(rand());
  
  auto T2 = std::chrono::high_resolution_clock::now();
  outs()
      << "Create data (microseconds): "
      << std::chrono::duration_cast<std::chrono::microseconds>(T2 - T1).count()
      << "\n";
  
  SmallVector<char, 1> CompressedData;
  T1 = std::chrono::high_resolution_clock::now();
  if (Error Err = zlib::compress(
          StringRef(reinterpret_cast<const char *>(Data.data()), Size),
          CompressedData)) {
    return 1;
  }
  T2 = std::chrono::high_resolution_clock::now();
  outs()
      << "Compress data (microseconds): "
      << std::chrono::duration_cast<std::chrono::microseconds>(T2 - T1).count()
      << "\n";
  outs() << "Compressed data size: " << CompressedData.size() << "\n";
  
  object::Decompressor Decompressor(
      StringRef(CompressedData.data(), CompressedData.size()));
  Decompressor.DecompressedSize = Size;
  
  T1 = std::chrono::high_resolution_clock::now();
  SmallString<0> DecompressedData;
  Decompressor.resizeAndDecompress(DecompressedData);
  T2 = std::chrono::high_resolution_clock::now();
  outs()
      << "Decompress data (microseconds): "
      << std::chrono::duration_cast<std::chrono::microseconds>(T2 - T1).count()
      << "\n";

Selected an average result from 3 runs:

  ----------------------------------------
  With `resize`:
  ----------------------------------------
  
  D:\XXX\LLVM\llvm-project\build\Release\bin>yaml2obj.exe
  Create data (microseconds): 16963852
  Compress data (microseconds): 27999644
  Compressed data size: 1074069335
  Decompress data (microseconds): 836237
  
  ----------------------------------------
  With `resize_for_overwrite`:
  ----------------------------------------
  
  D:\XXX\LLVM\llvm-project\build\Release\bin>yaml2obj.exe
  Create data (microseconds): 17025348
  Compress data (microseconds): 27997363
  Compressed data size: 1074069335
  Decompress data (microseconds): 549606

836237 * 0.657 == 549606, i.e. the new code is about 35% faster for me.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D93761/new/

https://reviews.llvm.org/D93761