[LLVMdev] Representing -ffast-math at the IR level

[Hal Finkel]

On Sun, 15 Apr 2012 14:38:47 +0400
Dmitry Babokin <babokin at gmail.com> wrote:

> On Sun, Apr 15, 2012 at 1:25 PM, Renato Golin
> <rengolin at systemcall.org>wrote:
> 
> > On 15 April 2012 09:22, Duncan Sands <baldrick at free.fr> wrote:
> > > Given the fact that no-one was interested enough to implement any
> > > kind of relaxed floating point mode in LLVM IR in all the years
> > > gone by, I
> > actually
> > > suspect that there might never be anything more than just this
> > > simple
> > and not
> > > very well defined 'fast-math' mode.  But at least there is a
> > > clear path
> > for
> > > how to evolve towards a more sophisticated setup.
> >
> > Once it's implemented, there will be zealots complaining that your
> > "-ffast-math" is not as good as <insert-compiler-here>.
> 
> 
> While it's certainly true, it's no different from any other
> analysis/transformation. What *is* different is the claims that clang
> -ffast-math is producing less precise code, than
> <insert-compiler-here>. And you'll have hard time explaining why. And
> it is sad that some people just expect compilers to produce faster
> code with keeping precision exactly the same... Even enabling FMA
> generation (which typically increases precision), provokes people to
> claim that you broke their precious code, just because the precision
> changed (didn't get better or worse, just changed).

To be fair, this can be a very serious validation issue.

 -Hal

> 
> 
> > But you can
> > kindly ask them to contribute with code.
> >
> > --
> > cheers,
> > --renato
> >
> > http://systemcall.org/
> >
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> >



-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory