[Webkit-unassigned] [Bug 184909] Disable usage of fused multiply-add instructions for JSC with compiler flag

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=184909

--- Comment #5 from Filip Pizlo <fpizlo at apple.com> ---
(In reply to Yusuke Suzuki from comment #4)
> (In reply to Filip Pizlo from comment #3)
> > Fused multiply-add gives a precision boost that results in double math
> > returning a result that does not match bit-for-bit what you would have
> > gotten without the fusion. Based on this, I think it might be a good idea to
> > disable it for all of JSC. 
> > 
> > I would definitely want to disable it if it’s free to disable it.
> 
> Interesting. After considering about this, I think, in JSC, we do not have
> performance sensitive FMAs (I believe). So disabling is OK.
> I'm a bit worried about disabling this in the entire WebKit tree due to,
> 
> 1. performance reason. If we have a non-result-sensitive
> performance-sensitive FMAs, this can affect on that (like, implementing some
> graphic filters)
> 2. coordination with third party libraries.
> 
> what do you think of?

Sounds like a good reason to only disable fused fma in JSC and leave it elsewhere.

-- 
You are receiving this mail because:
You are the assignee for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.webkit.org/pipermail/webkit-unassigned/attachments/20180426/17a60f33/attachment.html>