Re: newtypes and optimization

12 Dec 2007

      You can find an example at:

graphics.cs.ucdavis.edu/~sdillard/newtype-maybe-bug.tar.gz

Here's my session with it:

ghc --make -O2 -DFAST Test
time ./Test +RTS -tstderr

<>

real	0m8.827s
user	0m7.520s
sys	0m1.224s

ghc --make -O2 -DSLOW Test -no-recomp
time ./Test +RTS -tstderr

<Ctrl-C>

Test: interrupted
<>

real	1m33.232s
user	1m31.410s
sys	0m1.020s

If you do

  ghc -c -O2 -DFAST -ddump-simpl Test.hs | grep VecMath.V

you won't find any occurrences/pattern matches on the constructor, but with

  ghc -c -O2 -DSLOW -ddump-simpl Test.hs | grep VecMath.V

you'll see lots, due to a call to peek that is not inlined.

This is with ghc-6.8.1 and ghc-6.8.2 (no difference)

Thanks for any light you can shed on this,
Scott

On Dec 12, 2007 1:48 PM, Don Stewart  wrote:
...
stefanor:
...
On Wed, Dec 12, 2007 at 11:02:15AM -0700, Scott Dillard wrote:
...
with strictness annotations and INLINEs for everything. I also tried automatic
newtype deriving, with no luck. Why does a newtype defeat so much of the
optimization?
Thanks,
Scott
(Not a GHC developer, but someone fairly familiar with how the Simons
work)
What version of GHC are you using?  The implementation of newtypes was
completely redone in the 6.7.x period.
Do you have a fairly small complete working example?  If so, link to or
attach a tarball - will make their jobs much easier.
Stefan
Yeah, this sounds like maybe a bug, or maybe something wrong. We need to
investigate! An example please.
-- Don