comiss vs. ucomiss
Vladimir.Kozlov at Sun.COM
Tue Oct 14 14:57:54 PDT 2008
Even if exceptions are masked CPU need some
logic to check it. I think, a program with
ucom will be faster if a data has a lot of QNaN.
Tom Rodriguez wrote:
> I was just making some comparisons between x86_32.ad and x86_64.ad and
> noticed that x86_32.ad uses comiss/comisd for floating point compares
> with SSE but x86_64.ad uses ucomiss/ucomisd. The only difference
> between them is that the ucom versions don't signal for quiet NaNs. We
> have fp exception suppressed so functionally it doesn't make any
> difference. It does seem like they should be doing the same thing
> though. Anyone know why they emit different things?
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