Fusion

[Simon Peyton Jones]

I have added a section "Ticky-ticky quick start" to our ticky-ticky profiling page, to explain how I go about dealing with the problem you describe
https://ghc.haskell.org/trac/ghc/wiki/Debugging/TickyTicky

Simon 

| -----Original Message-----
| From: David Feuer [mailto:david.feuer at gmail.com]
| Sent: 20 August 2014 09:33
| To: Simon Peyton Jones
| Subject: Re: Fusion
| 
| I'll be happy to try to expand it with some examples. I'm wondering if
| you could help me figure something out: the (simple) cons/build rule
| we discussed, along with the similar cons/augment rule,
| 
| "cons/build"    forall (x::a) (g::forall b . (a->b->b)->b->b) . x :
| build g = build (\c n -> c x (g c n))
| "cons/augment"  forall (x::a) (g::forall b . (a->b->b)->b->b)
| (xs::[a]) . x : augment g xs = augment (\c n -> c x (g c n)) xs
| 
| somehow *increase* allocation substantially (11.7%) in the "event"
| NoFib test, and also significantly (3.6%) in constraints, somewhat
| (2.4%) in nucleic2 [remember this] and 1.4% in ansi. I am having a
| heck of a time trying to figure out how to track these down, and
| burning loads of time recompiling GHC over and over again. On the flip
| side of things, the wang test reduces allocation by 45.8% if I use
| these rules (both of which fire), but only when I also use -fsimple-
| list-literals for nofib/spectral/hartel/nucleic2/Main.hs.
| nucleic2 still performs a little more allocation.
| 
| On Wed, Aug 20, 2014 at 2:56 AM, Simon Peyton Jones
| <simonpj at microsoft.com> wrote:
| > Great start, thank you. Can I suggest that for each question you
| give
| > a concrete example?  Otherwise only experts, who already know a lot
| about
| > rules, will understand the question, let alone the answer.   I’d be
| happy to
| > take another look then.
| >
| >
| > Simon
| >
| >
| >
| > From: David Feuer [mailto:david.feuer at gmail.com]
| > Sent: 19 August 2014 23:30
| > To: Simon Peyton Jones
| > Cc: Haskell Libraries
| > Subject: Re: Fusion
| >
| >
| >
| > I've started a page at
| > https://ghc.haskell.org/trac/ghc/wiki/FoldrBuildNotes
| > Please feel free to add, correct, etc.
| >
| > On Aug 19, 2014 3:10 AM, "Simon Peyton Jones"
| <simonpj at microsoft.com> wrote:
| >
| > David
| >
| > You've been doing all this work on improving fusion, and you
| probably
| > have a very good idea now about how it works, and how GHC's
| libraries
| > use phases and RULES to achieve it. A kind of design pattern, if you
| > like; tips and tricks.
| >
| > I wonder if you'd feel able to write a GHC wiki page describing what
| > you have learned, with examples and explanation about why it is done
| that way.
| > If you did this, someone who follows in your footsteps wouldn't need
| > to re-learn everything.  And maybe someone will say "oh, there's one
| > pattern you have omitted, here it is".
| >
| > Thanks
| >
| > Simon