Confusing warnings from GHC HEAD

Ian Lynagh igloo at
Sat Sep 4 09:28:44 EDT 2010

On Tue, Aug 31, 2010 at 09:11:13PM -0700, Bryan O'Sullivan wrote:
> On Tue, Aug 31, 2010 at 2:06 AM, Simon Peyton-Jones
> <simonpj at>wrote:
> >  I can’t reproduce this.  With the enclosed module and HEAD, I get the
> > warning; but when I add –fspec-constr-count=5, the warning goes away and I
> > get the specialised rules.
> >
> > Could Cabal not be passing on the flag or something?
> I see -fspec-constr-count=5 in the command line being passed to ghc when I
> run "cabal build -v", so I don't think that's to blame?

I've filed a ticket for this, with a standalone testcase, here:


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