It’s a bit of a moveable feast.  With –fno-spec-constr-count you allow GHC to specialise as much as it pleases, which is good for perf (maybe) but can lead to major code size expansion. 

S

From: Johan Tibell [mailto:johan.tibell@gmail.com]
Sent: 31 August 2010 10:16
To: Simon Peyton-Jones
Cc: Bryan O'Sullivan; glasgow-haskell-users@haskell.org
Subject: Re: Confusing warnings from GHC HEAD

On Tue, Aug 31, 2010 at 11:06 AM, Simon Peyton-Jones <simonpj@microsoft.com> 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.

Is this the right fix in general? I try to keep my code warning free but I don't want to bump the count unless it's always a win. If it's not always a win perhaps it should be a warning that's on by default?

-- Johan