Re: Nonsensical byte compiler warning.

[Markus Triska <markus.triska@gmx.at>]

Richard Stallman <rms@gnu.org> writes:

> I agree this is too hard to change now.
> However, it would have been premature to give up without
> checking.

Sure; here's a rather trivial compromise for `char-before': It makes
the compiler rewrite calls to char-before at the time the byte-code is
emitted instead of during the optimisation phase. This retains the
correct function call in the warning. It can yield slightly inferior
byte-code though (with usage-patterns that don't occur in Emacs trunk
and are probably rather atypical). If you find this change advisable,
I'll implement analogous changes for backward-char and backward-word.

2007-04-08  Markus Triska  <markus.triska@gmx.at>

	* emacs-lisp/byte-opt.el: remove char-before rewriting
	* emacs-lisp/bytecomp.el: add char-before rewriting


*** byte-opt.el	04 Apr 2007 19:36:54 +0200	1.88
--- byte-opt.el	08 Apr 2007 21:33:44 +0200	
***************
*** 1158,1171 ****
  	 '(forward-word -1))
  	(t form)))
  
- (put 'char-before 'byte-optimizer 'byte-optimize-char-before)
- (defun byte-optimize-char-before (form)
-   (cond ((= 2 (safe-length form))
- 	 `(char-after (1- ,(nth 1 form))))
- 	((= 1 (safe-length form))
- 	 '(char-after (1- (point))))
- 	(t form)))
- 
  ;; Fixme: delete-char -> delete-region (byte-coded)
  ;; optimize string-as-unibyte, string-as-multibyte, string-make-unibyte,
  ;; string-make-multibyte for constant args.
--- 1158,1163 ----
*** bytecomp.el	27 Mar 2007 08:08:58 +0200	2.196
--- bytecomp.el	08 Apr 2007 21:52:58 +0200	
***************
*** 3148,3153 ****
--- 3148,3154 ----
  \f
  ;; more complicated compiler macros
  
+ (byte-defop-compiler char-before)
  (byte-defop-compiler list)
  (byte-defop-compiler concat)
  (byte-defop-compiler fset)
***************
*** 3159,3164 ****
--- 3160,3172 ----
  (byte-defop-compiler19 (/ byte-quo) byte-compile-quo)
  (byte-defop-compiler19 nconc)
  
+ (defun byte-compile-char-before (form)
+   (cond ((= 2 (length form))
+ 	 (byte-compile-form `(char-after (1- ,(nth 1 form)))))
+ 	((= 1 (length form))
+ 	 (byte-compile-form '(char-after (1- (point)))))
+ 	(t (byte-compile-subr-wrong-args form "0-1"))))
+ 
  (defun byte-compile-list (form)
    (let ((count (length (cdr form))))
      (cond ((= count 0)