[llvm] r179478 - Document the decision to assume that the cost of floats is twice as much as integers.

[Hal Finkel]

----- Original Message -----
> From: "Nadav Rotem" <nrotem at apple.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: llvm-commits at cs.uiuc.edu
> Sent: Friday, February 21, 2014 1:44:06 PM
> Subject: Re: [llvm] r179478 - Document the decision to assume that the cost of floats is twice as much as integers.
> 
> Hi Hal,
> 
> 
> > It looks like this is designed to be a throughput assumption, and
> > while this is certainly right on Sandy Bridge, Haswell and
> > similar, it is wrong for many other platforms (non-Intel cores
> > such as Bulldozer, many different PowerPC cores, etc.)
> 
> Makes sense.
> 
> > 
> > Should we add some kind of getDefaultFloatThroughput() callback to
> > handle this? Alternatively, X86TTI could return '2' for scalar
> > floating point arithmetic operations. Does anyone have a
> > preference?
> > 
> 
> I am okay with both suggestions.

Okay, thanks! I'll err on the side of not adding a new API and just update X86TTI to provide this behavior.

 -Hal

> 
> Thanks
> 

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory