"simplifications"

[David Kastrup]

Hi, I've seen the following:

Author: Juanma Barranquero <address@hidden>  2007-11-17 03:50:37
Committer: Juanma Barranquero <address@hidden>  2007-11-17 03:50:37
Parent: 1797ed583c1d6224dbe93db681b112a9b0278358 ((backquote): Improve 
argument/docstring consistency.)
Child:  034e6631c9aab6db046645510214df80e67c29d4 (*** empty log message ***)
Branches: master, remotes/origin/master, remotes/origin/origin
Follows: merge-multi-tty-to-trunk
Precedes: 

    (ring-size, ring-p, ring-insert, ring-length, ring-empty-p): Use c[ad]dr.
    (ring-plus1): Use `1+'.
    (ring-minus1): Use `zerop'.
    (ring-remove): Use c[ad]dr.  Use `when'.
    (ring-copy): Use c[ad]dr.  Use `let', not `let*'.
    (ring-ref): Use `let', not `let*'.
    (ring-insert-at-beginning): Use c[ad]dr.  Doc fix.
    (ring-insert+extend): Use c[ad]dr.  Fix typo in docstring.
    (ring-member): Simplify.  Doc fix.
    (ring-convert-sequence-to-ring): Simplify.


Could people, before introducing such "optimizations", check the
bytecode?

(defun xxx (x) (cadr x))
generates
byte code for xxx:
  args: (x)
0       varref    x
1       dup       
2       varbind   x
3       cdr       
4       car       
5       unbind    1
6       return    

while
(defun xxx (x) (car (cdr x)))
generates
byte code for xxx:
  args: (x)
0       varref    x
1       cdr       
2       car       
3       return    

The former is _quite_ less efficient, so it is not a hot idea to use
it for data access primitives like the ring functions.

Personally, I think that we should make the byte compiler optimize the
unnecessary binding away.  But until that is the case, please don't
gratuitously replace (car (cdr ...)) with (cadr ...).

-- 
David Kastrup