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Re: question about -ffast-math implementation
- From: Janne Blomqvist <blomqvist dot janne at gmail dot com>
- To: mike dot izbicki at gmail dot com
- Cc: gcc mailing list <gcc at gcc dot gnu dot org>
- Date: Mon, 2 Jun 2014 09:09:55 +0300
- Subject: Re: question about -ffast-math implementation
- Authentication-results: sourceware.org; auth=none
- References: <CAKKZoUUtBdU_ZR61hsztymquqDrRkqEUoxeiEE0kzmrpUq+Emg at mail dot gmail dot com>
On Sun, Jun 1, 2014 at 9:52 AM, Mike Izbicki <firstname.lastname@example.org> wrote:
> I'm trying to copy gcc's behavior with the -ffast-math compiler flag
> into haskell's ghc compiler. The only documentation I can find about
> it is at:
> I understand how floating point operations work and have come up with
> a reasonable list of optimizations to perform. But I doubt it is
> My question is: where can I find all the gory details about what gcc
> will do with this flag? I'm perfectly willing to look at source code
> if that's what it takes.
In addition to the official documentation, a nice overview is at
Though for the gory details and authoritative answers I suppose you'd
have to look into the source code.
> Also, are there any optimizations that you wish -ffast-math could
> perform, but for various architectural reasons they don't fit into
There are of course a (nearly endless?) list of optimizations that
could be done but aren't (lack of manpower, impractical, whatnot). I'm
not sure there are any interesting optimizations that would be
dependent on loosening -ffast-math further?
(One thing I wish wouldn't be included in -ffast-math is
-fcx-limited-range; the naive complex division algorithm can easily
lead to comically poor results.)