bug#70036: 30.0.50; Move file-truename to the C level

[Theodor Thornhill via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Ihor Radchenko <yantar92@posteo.net> writes:

> Theodor Thornhill <theo@thornhill.no> writes:
>
>> Not sure I understand what you mean. I tried it again, but this time the
>> call is 100000 times and in an existing file on my system which is
>> deeply nested. I run emacs with `emacs -Q` from a build on
>> `30b1b0d7cd8e4d46a601e9737350cda970f6bab0`.
>>
>> the relevant part from the profile this time:
>> ```
>>        15478  72% - command-execute
>>        15440  72%  - funcall-interactively
>>        15439  72%   - eval-last-sexp
>>        15439  72%    - #<compiled-function 0C4>
>>        15439  72%     - elisp--eval-last-sexp
>>        15436  71%      - eval
>>        15436  71%       - benchmark-call
>>        15434  71%        - #<lambda E8B>
>>        15434  71%         - file-truename
>>        13536  63%          - file-truename
>>        12224  57%           - file-truename
>> ...
>> To me this looks like it spends a lot of time in recursive calls
>
> No. It is just that your `file-truename' is native-compiled and the
> profiler is unable to get the details from inside native subr code.
>
> You can re-evaluate the defun to reveal the details in the profiler
> output. Or use Emacs compiled without native-compilation support.
>
> -- 
> Ihor Radchenko // yantar92,
> Org mode contributor,
> Learn more about Org mode at <https://orgmode.org/>.
> Support Org development at <https://liberapay.com/org-mode>,
> or support my work at <https://liberapay.com/yantar92>

I'm sorry, but I don't see the real difference here. Yes, the profile is
more detailed this way, but it doesn't change the fact that
file-truename is slow, does it?

The question to me is whether or not this is an acceptable performance
hit to take for eglot given what it's trying to do, and my opinion is
no. Whether or not it should be moved to C is open to suggestion. I'm
preparing a patch that only targets Eglot by removing reliance on this
function.

Theo

```
       17839  63% - command-execute
       17794  63%  - funcall-interactively
       17793  63%   - eval-last-sexp
       17793  63%    - #<compiled-function EF0>
       17793  63%     - elisp--eval-last-sexp
       17791  63%      - eval
       17791  63%       - benchmark-call
       17788  63%        - #<lambda 219>
       17783  63%         - file-truename
       17576  62%          - let
       17546  62%           - while
       17529  62%            - let
       17358  61%             - if
       17356  61%              - let
       16365  58%               - or
       15969  56%                - if
       15964  56%                 - let
       15951  56%                  - file-name-as-directory
       15824  56%                   - file-truename
       15788  56%                    - let
       15768  56%                     - while
       15712  55%                      - let
       15579  55%                       - if
       15577  55%                        - let
        7224  25%                         - or
        3429  12%                          - if
        3325  11%                           - let
        3059  10%                            - file-name-as-directory
        1866   6%                             - file-truename
        1501   5%                              - let
        1276   4%                               - while
        1121   3%                                - let
        1004   3%                                   find-file-name-handler
          18   0%                                   if
          49   0%                                - setcar
          26   0%                                   1-
          37   0%                                - if
          23   0%                                   <
          36   0%                                  not
          97   0%                               - if
          46   0%                                - eq
           8   0%                                   quote
           7   0%                                 or
         218   0%                              - cond
         112   0%                               - and
          95   0%                                - string=
          73   0%                                   substring
          82   0%                               - or
          57   0%                                  string=
          17   0%                                or
         123   0%                            - setcar
          83   0%                             - cons
```