bug#37321: 27.0.50; Excessive gc in a use case (el-search)

[Michael Heerdegen <michael_heerdegen@web.de>]

Michael Heerdegen <michael_heerdegen@web.de> writes:

> #+begin_src emacs-lisp
> (defun el-search--flatten-tree (tree)
>   "Return a list of `el-search--atomic-p' objects in TREE."
>   (let ((elements ())
>         (walked-objects ;to avoid infinite recursion for circular TREEs
>          (make-hash-table :test #'eq))
>          (gc-cons-percentage 0.8)
>         ) ;Why is binding it here more effective than binding it more top-level?
>     (cl-labels ((walker (object)
>                         (if (el-search--atomic-p object)
>                             (push object elements)
>                           (unless (gethash object walked-objects)
>                             (puthash object t walked-objects)
>                             (if (consp object)
>                                 (progn
>                                   (while (consp object)
>                                     (walker (car object))
>                                     (setq object (cdr object))
>                                     (if (gethash object walked-objects)
>                                         (setq object nil)
>                                       (puthash object t walked-objects)))
>                                   (when object ;dotted list
>                                     (walker object)))
>                               (cl-loop for elt being the elements of object do (walker elt)))))))
>       (walker tree)
>       elements)))
> #+end_src

It doesn't seem to be related to the hash table usage - if I remove the
hash table test based infloop check part of the function, the behavior
wrt gc doesn't change.  So I wonder what in this function does it make
so much depend on gc behavior?

Michael.