Re: Knowing where a function has been used (bis) [Was: Re: Optimising Elisp code]

[Emanuel Berg]

Stefan Monnier wrote:

> Try M-x disassemble RET add-it RET
> to see how the two calls where compiled.

OK, here goes:

(defsubst add-it-inline (i j)
  (+ i j) )

(defun add-it (a b)
  (+ a b) )

(defun test-normal ()
  (add-it 1 2) )
;; (test-normal)

;; byte code for test-normal:
;;   args: nil
;; 0       constant  add-it
;; 1       constant  1
;; 2       constant  2
;; 3       call      2
;; 4       return

(defun test-inline ()
  (add-it-inline 10 20) )
;; (test-inline)

;; byte code for test-inline:
;;   args: nil
;; 0       constant  10
;; 1       constant  20
;; 2       varbind   j
;; 3       dup
;; 4       varbind   i
;; 5       varref    j
;; 6       plus
;; 7       unbind    2
;; 8       return

OK, so there is no call, instead the code
is inserted. I suppose this is a glitch in the
Matrix, becuase what I can reCALL this is what
I've been saying this whole time...

But anyway, instead of dwelling on the past,
meditate on this:

;; byte code for add-it:
;;  args: (a b)
;; 0       varref    a
;; 1       varref    b
;; 2       plus      
;; 3       return

So as for machine instructions, the inline
version, "test-inline", has 9.
The "test-normal" has 5. The non-inlined
"add-it" has 4. 5 + 4 = 9. And I've saved the
best forst last: 9 = 9!

So there is no gain as to the number of machine
instructions. So where is the gain? The `call'
instruction specifically, or the implied
funcall overhead not visible in
the disassembly?

-- 
underground experts united
http://user.it.uu.se/~embe8573