[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 #4 from Yusuke Suzuki <utatane.tea at gmail.com> ---
(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?

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