;;; find-gc.el --- detect functions that call the garbage collector  -*- lexical-binding: t; -*-

;; Copyright (C) 1992, 2001-2024 Free Software Foundation, Inc.

;; Maintainer: emacs-devel@gnu.org

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; Produce in find-gc-unsafe-list the set of all functions that may invoke GC.
;; This expects the Emacs sources to live in find-gc-source-directory.

;;; Code:

(defvar find-gc-unsafe-list nil
  "The list of unsafe functions is placed here by `find-gc-unsafe'.")

(defvar find-gc-source-directory
  (file-name-as-directory (expand-file-name "src" source-directory))
  "Directory containing Emacs C sources.")

(defvar find-gc-subrs-callers nil
  "Alist of users of subrs, from GC testing.
Each entry has the form (FUNCTION . FUNCTIONS-THAT-CALL-IT).")

(defvar find-gc-subrs-called nil
  "Alist of subrs called, in GC testing.
Each entry has the form (FUNCTION . FUNCTIONS-IT-CALLS).")


;; Functions on this list are safe, even if they appear to be able
;; to call the target.

(defvar find-gc-noreturn-list '(Fsignal Fthrow wrong_type_argument))

;; This was originally generated directory-files, but there were
;; too many files there that were not actually compiled.  The
;; list below was created for a HP-UX 7.0 system.

(defvar find-gc-source-files
  '("dispnew.c" "scroll.c" "xdisp.c" "window.c"
    "term.c" "cm.c" "emacs.c" "keyboard.c" "macros.c"
    "keymap.c" "sysdep.c" "buffer.c" "filelock.c"
    "insdel.c" "marker.c" "minibuf.c" "fileio.c"
    "dired.c" "cmds.c" "casefiddle.c"
    "indent.c" "search.c" "regex-emacs.c" "undo.c"
    "alloc.c" "data.c" "doc.c" "editfns.c"
    "callint.c" "eval.c" "fns.c" "print.c" "lread.c"
    "syntax.c" "unexcoff.c"
    "bytecode.c" "process.c" "callproc.c" "doprnt.c"
    "xterm.c" "xfns.c"))


(defun find-gc-unsafe ()
  "Return a list of unsafe functions--that is, which can call GC.
Also store it in `find-gc-unsafe-list'."
  (trace-call-tree nil)
  (trace-use-tree)
  (find-unsafe-funcs 'Fgarbage_collect)
  (setq find-gc-unsafe-list
	(sort find-gc-unsafe-list
              (lambda (x y)
                (string-lessp (car x) (car y))))))

;; This does a depth-first search to find all functions that can
;; ultimately call the function "target".  The result is an a-list
;; in find-gc-unsafe-list; the cars are the unsafe functions, and the cdrs
;; are (one of) the unsafe functions that these functions directly
;; call.

(defun find-unsafe-funcs (target)
  (setq find-gc-unsafe-list (list (list target)))
  (trace-unsafe target))

(defun trace-unsafe (func)
  (let ((used (assq func find-gc-subrs-callers)))
    (or used
	(error "No find-gc-subrs-callers for %s" (car find-gc-unsafe-list)))
    (while (setq used (cdr used))
      (or (assq (car used) find-gc-unsafe-list)
	  (memq (car used) find-gc-noreturn-list)
	  (progn
	    (push (cons (car used) func) find-gc-unsafe-list)
	    (trace-unsafe (car used)))))))




(defun trace-call-tree (&optional ignored)
  (message "Setting up directories...")
  (setq find-gc-subrs-called nil)
  (let ((case-fold-search nil)
	(default-directory find-gc-source-directory)
	(files find-gc-source-files)
	name entry rtlfile)
    (dolist (file files)
      (message "Compiling %s..." file)
      (call-process "gcc" nil nil nil "-I" "." "-I" "../lib"
		    "-fdump-rtl-expand" "-o" null-device "-c" file)
      (setq rtlfile
	    (file-expand-wildcards (format "%s.*.expand" file) t))
      (if (/= 1 (length rtlfile))
	  (message "Error compiling `%s'?" file)
	(with-temp-buffer
	  (insert-file-contents (setq rtlfile (car rtlfile)))
	  (delete-file rtlfile)
	  (while (re-search-forward ";; Function \\|(call_insn " nil t)
	    (if (= (char-after (- (point) 3)) ?o)
		(progn
		  (looking-at "[a-zA-Z0-9_]+")
		  (setq name (intern (match-string 0)))
		  (message "%s : %s" (car files) name)
		  (setq entry (list name)
			find-gc-subrs-called
			(cons entry find-gc-subrs-called)))
	      (if (looking-at ".*\n?.*\"\\([A-Za-z0-9_]+\\)\"")
		  (progn
		    (setq name (intern (match-string 1)))
		    (or (memq name (cdr entry))
			(setcdr entry (cons name (cdr entry)))))))))))))

(defun trace-use-tree ()
  (setq find-gc-subrs-callers
        (mapcar #'list (mapcar #'car find-gc-subrs-called)))
  (let ((ptr find-gc-subrs-called)
	p2 found)
    (while ptr
      (setq p2 (car ptr))
      (while (setq p2 (cdr p2))
	(if (setq found (assq (car p2) find-gc-subrs-callers))
	    (setcdr found (cons (car (car ptr)) (cdr found)))))
      (setq ptr (cdr ptr)))))

(provide 'find-gc)

;;; find-gc.el ends here