ghc -O2 and class dictionaries

Dave Bayer bayer at
Mon Dec 29 17:45:06 EST 2008

Yeah, I knew it was fairly unlikely that I was the first to think of  
this optimization ;-)

I just reported the "run-time performance bug" as

I am using an Intel Core 2 Duo MacBook and GHC 6.10.1, OS X 10.5.6.  
For the toy example that I submitted, the difference is over a factor  
of 3x.


On Dec 29, 2008, at 6:23 AM, Simon Peyton-Jones wrote:

> Which version of GHC are you using?  GHC 6.10 implements  
> automatically precisely the transformation you give below.
> If the difference shows up in GHC 6.10, could you spare a moment to  
> produce a reproducible test case, and record it in GHC's bug tracker?
> Thanks
> Simon

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