Program slower with local definitions

[Simon Peyton-Jones]

That's odd.  Making things more global can reduce optimisation
opportunities, but making things ore local should not.  You can say
-ddump-simpl to get an idea of what the differences are.  

If you can make a smallish repo case, I'll take a look, though perhaps
not before ICFP.

Simon

| -----Original Message-----
| From: glasgow-haskell-users-bounces at haskell.org
[mailto:glasgow-haskell-users-
| bounces at haskell.org] On Behalf Of Michael Marte
| Sent: 05 September 2006 17:40
| To: glasgow-haskell-users at haskell.org
| Subject: Program slower with local definitions
| 
| Hello *,
| 
| I noticed a five percent speed up by making local definitions global.
| 
| This is the first version with local definitions:
| 
| f = <some expression based on mySet>
|      where
|      mySet = foldl (flip Set.insert) Set.empty myList
|      myList = <some constant list>
| 
| Then I moved mySet and myList to the top level which gave me the speed
up.
| 
| Shouldn't both versions show the same behaviour with regard to run
time?
|   Doesn't the compiler lift mySet and myList to top level
automatically?
| Are myList and mySet evaluated in every call to f when defined
locally?
| 
| I am using ghc 6.4.2 on Windows XP.
| 
| Michael
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