[Haskell-cafe] Profiling CAFs (re-post)

[Matthias Fischmann]

On Tue, Oct 10, 2006 at 01:59:23PM +0100, Ian Lynagh wrote:
> To: Matthias Fischmann <fis at wiwi.hu-berlin.de>
> Cc: haskell-cafe at haskell.org
> From: Ian Lynagh <igloo at earth.li>
> Date: Tue, 10 Oct 2006 13:59:23 +0100
> Subject: Re: [Haskell-cafe] Profiling CAFs (re-post)
> 
> On Tue, Oct 10, 2006 at 01:31:58PM +0200, Matthias Fischmann wrote:
> > 
> >   What qualifies as constant applicable form, and why is it not
> >   labelled in a more informative way?
> 
> CAFs are, AIUI, things that are just values (i.e. things that don't take
> an argument) that have been floated up to the top level.

Ok, this is consistent with the documentation.  However, it doesn't
explain why we would need to treat them differently.  In particular, I
don't understand why I wouldn't want to know their (module-global)
names.

> Compiling with -caf-all might give you more useful information.

Oops.  I thought i had that in my Makefile, but appearently i was
wrong...  If I add it, this is what happens:

======================================================================
module Main where

x = f [1..5] (f [2..] [3..])

f xs ys = l
    where
    l = [ if s then x else y | (x, y) <- zip xs ys ]
    s = g xs ys
    g [] _ = True
    g _ [] = False
    g (x:xs) (y:ys) = g xs ys

main = print (show x)
======================================================================

$ ghc -prof -caf-all Main.hs -o Main  # (ghc 6.4)
/tmp/ghc22775.hc:1475: error: redefinition of `Mainmain_CAF_cc_ccs'
/tmp/ghc22775.hc:1470: error: `Mainmain_CAF_cc_ccs' previously defined here
/tmp/ghc22775.hc:1490: error: redefinition of `Mainsat_CAF_cc_ccs'
/tmp/ghc22775.hc:1480: error: `Mainsat_CAF_cc_ccs' previously defined here
/tmp/ghc22775.hc:1495: error: redefinition of `Mainsat_CAF_cc_ccs'
/tmp/ghc22775.hc:1490: error: `Mainsat_CAF_cc_ccs' previously defined here

$ ghc -prof -auto-all -caf-all Main.hs -o Main
/tmp/ghc22771.hc:1517: error: redefinition of `Mainmain_CAF_cc_ccs'
/tmp/ghc22771.hc:1512: error: `Mainmain_CAF_cc_ccs' previously defined here

> If that doesn't help then you might find it helpful to look at heap
> profiles rather than just the normal profiler output.

Section 5.4, prof.hp, yes.  Probably should have thought of that
myself.  Will do.

> >   Why are there functions that inherit all of their (considerable)
> >   time and space consumption from elsewhere, but nothing in the
> >   list would allow for such a rich inheritage?
> 
> I didn't understand that. If it's possible to give a small example then
> that might help?

Small is harder in this case than with type errors.  But I'll try as
soon as I know what's wrong with the above.


thanks,
matthias
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