Hi Andy,
Andy Wingo <wi...@pobox.com> skribis:
> I just finished work on the "wip-cse" branch and would like to merge it
> in sometime. It does a form of common subexpression elimination. It's
> a post-pass, designed to run after peval.
The examples in cse.test suggest that it does a good job. :-)
Initially, I was expecting things like:
(f (* a b) (* a b))
=>
(let ((x (* a b)))
(f x x))
but AIUI the CSE pass here eliminates duplicate references when they are
superfluous, but not when they are needed as above, right?
> I'm attaching a log of the things that it folds in a normal Guile
> build.
I’m not sure what the messages mean. Could you explain?
> I'm pretty happy with it, except for the speed.
What impact does it have on compilation time in module/?
> I'm reasonably confident as to its complexity, but once again we are
> seeing that lookup in vhashes is fairly slow. Dunno. If we can speed
> up vhashes somehow then we win in CSE, peval, and other passes, so
> probably it's best to focus there.
I think we’ll need C-level profiling to see what’s going on. Do you
have such info already? Otherwise I can look into it.
Also, a bit of CSE could help: ;-)
--8<---------------cut here---------------start------------->8---
scheme@(ice-9 vlist)> ,optimize (%vhash-assoc key vhash eq? hashq)
$3 = (begin
(define khash
(let ((size (vector-ref
(let ((s vhash))
(if (eq? (struct-vtable s) <vlist>)
(struct-ref s 0)
((@@ (srfi srfi-9) throw)
'wrong-type-arg
'vlist-base
"Wrong type argument: ~S"
(list s)
(list s))))
3)))
(and (> size 0) (hashq key size))))
(let loop ((base (let ((s vhash))
(if (eq? (struct-vtable s) <vlist>)
(struct-ref s 0)
((@@ (srfi srfi-9) throw)
'wrong-type-arg
'vlist-base
"Wrong type argument: ~S"
(list s)
(list s)))))
(khash khash)
(offset
(and khash
(vector-ref
(vector-ref
(let ((s vhash))
(if (eq? (struct-vtable s) <vlist>)
(struct-ref s 0)
((@@ (srfi srfi-9) throw)
'wrong-type-arg
'vlist-base
"Wrong type argument: ~S"
(list s)
(list s))))
5)
khash)))
(max-offset
(let ((s vhash))
(if (eq? (struct-vtable s) <vlist>)
(struct-ref s 1)
((@@ (srfi srfi-9) throw)
'wrong-type-arg
'vlist-offset
"Wrong type argument: ~S"
(list s)
(list s))))))
--8<---------------cut here---------------end--------------->8---
Here (vlist-base vhash) occurs three times; this could be reduced
manually to one. Then there’s (vlist-offset vhash), which repeats the
same struct type checking.
In the body itself I don’t see anything obvious.
Thanks,
Ludo’.
