[llvm-commits] Patch: Math Lib call optimization

[Sandeep Patel]

This seems like a -ffast-math optimization in this case.

deep

On Wed, Nov 2, 2011 at 7:42 PM, Weiming Zhao <weimingz at codeaurora.org> wrote:
> Hi Duncan,
>
> Thanks for your comments.
>
> The precision loss will happen when the results of sin((double)x) and
> sinf(x) differ within a single precision ulps. It might happen only in very
> rare cases. So, theoretically, you're right. :D
> But in practice, I did experiments by comparing the results of (float)sin(x)
> and sinf(x) for random inputs. The results are the same. And for users who
> are really concern about precision, they can disable this pass.
>
> Weiming Zhao
>
>
> -----Original Message-----
> From: llvm-commits-bounces at cs.uiuc.edu
> [mailto:llvm-commits-bounces at cs.uiuc.edu] On Behalf Of Duncan Sands
> Sent: Wednesday, November 02, 2011 11:25 AM
> To: llvm-commits at cs.uiuc.edu
> Subject: Re: [llvm-commits] Patch: Math Lib call optimization
>
> Dear Weiming Zhao,
>
>> Hence, this transformation will not result in precision loss.
>
> is this a correct statement?  For example, if sin returns a result which is
> correct to within two double precision ulps, and sinf to within two single
> precision ulps, then float->double->sin->float will probably be correct to
> one single precision ulp, so converting to use sinf loses precision.
>
> Ciao, Duncan.
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