Re: byte-compiler very slow

[David Ponce]

Hi All,

I think I found the cause of the byte-compiler slow down.  I profiled
the byte-compiler and finally found that most of the byte-compilation
time was spent in the function `symbol-file' called from
`byte-compile-cl-warn'.  In fact I found that the time spent in
`symbol-file' is proportional to the size of `load-history'.

Here is a summary profiling result I got when byte-compiling edebug.el
in my normal working environment where `load-history' is quite big:

Function Name            Call Count  Elapsed Time  Average Time
=======================  ==========  ============  ============
emacs-lisp-byte-compile  1           12.077        12.077
symbol-file              3590        9.0729999999  0.0025272980

That clearly shows that 75% of compilation time is spent in
`symbol-file'!

Here is the result I got just after `emacs -q --no-site-file' when
`load-history' should be at minimal size:

Function Name            Call Count  Elapsed Time  Average Time
=======================  ==========  ============  ============
emacs-lisp-byte-compile  1           3.235         3.235
symbol-file              3589        0.9410000000  0.0002621900

In that case only 29% of time is spent in `symbol-file'!

To confirm these results I hacked a version of bytecomp.el where I
replaced `byte-compile-cl-warn' with the following:

(defsubst byte-compile-cl-warn (form)
 "Warn if FORM is a call of a function from the CL package."
 form)

And magically, the byte-compiler recovered its speed :-)

Hope this will help.

Sincerely,
David