There was a weird period in JavaScript’s history where the threshold for inlining was rather fixed and counted comments as part of the function weight. So there was code that would go faster if you deleted the comments.

I believe it was counting AST nodes rather than bytes, otherwise that would have also created problems for descriptive function names as well and that would have been what we heard about instead of comments.

I ran into a similarish issue in C++ (MSVC++) where a small change that improved an error message led to a 10% slowdown.

The function was something like:

  int ReturnAnswerIfCharIsValid(char* c)
  {
    if(c == nullptr)
      throw std::exception("ERROR!");

    return 42;
  }

  throw std::exception("Char is not valid, please fix it!"); // String is now longer

I fixed it by replacing the exception call with yet another function call:

  if(c == nullptr)
     ThrowException();