bug#17584: 24.3.91; bug of `=' operator optimization

[Shigeru Fukaya]

The following is a code with a little more optimized than
byte-optimize-predicate.  It can be used by `<', `<=', `>', `>='.

-- Shigeru


(defun byte-optimize-comparison-predicate (form)
  ;; (cmp-op arg1 [[arg2]...])
  (let (constants
        others
        (rest (cdr form)))
    (while rest
      (if (macroexp-const-p (car rest))
          (push (car rest) constants)
        (push (car rest) others))
      (setq rest (cdr rest)))
    (if constants
        (cond
         ;; only constants
         ((null others) (eval form))
         ;; constants satisfy predicate
         ((apply (car form) (nreverse constants)) form)
         ;; always nil
         (t `(progn ,@(nreverse others) nil)))
      ;; no constant
      form)))


(byte-optimize-comparison-predicate '(= 0 a b))         ==> (= 0 a b)
(byte-optimize-comparison-predicate '(= 1 1.0 1))       ==> t
(byte-optimize-comparison-predicate '(= 1 a (f) 2))     ==> (progn a (f) nil)

(byte-optimize-comparison-predicate '(<= 1 a (f) 1.0))  ==> (<= 1 a (f) 1.0)
(byte-optimize-comparison-predicate '(< 1 a (f) 1.0))   ==> (progn a (f) nil)



>>(byte-optimize-form '(lambda (a b) (= a b 0)))
>>==> (lambda (a b) (= a b 0))
>>(byte-optimize-form '(lambda (a b) (= 0 a b)))
>>==> (lambda (a b) (= a 0))
>>
>>- (put '=   'byte-optimizer 'byte-optimize-binary-predicate)
>>+ (put '=   'byte-optimizer 'byte-optimize-predicate)
>
>byte-optimize-predicate is no good, sorry.
>
>-- Shigeru