[Webkit-unassigned] [Bug 112239] LLint uses SSE2 instructions

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Mon Apr 1 14:15:35 PDT 2013


--- Comment #11 from Filip Pizlo <fpizlo at apple.com>  2013-04-01 14:13:46 PST ---
(In reply to comment #10)
> (In reply to comment #9)
> > If you want performance, then let's do it right.  There's nothing fundamentally blocking x87 support in the LLInt.
> I don't really care about performance on these old machines. The problem is that on Linux many distributions have a policy of supporting architectures as far back as i686 (or even i486 in extreme cases). So if we use a solution that forces the switch on compile time (like cloop) it would force the distributions to compile all x86 with this switch and also slow down more modern x86 processors. Anything on runtime would be fine as long as it only hurts the slow machines. Though it would be good if it is at least as fast as the old interpreter which is what we should avoid regression compared to.

Aha!  Got it.

I would recommend seeing if you can cache the hasSSE2() (or whatever it's called) result in JSGlobalData, and then, only when compiling in this configuration, have LLInt check that flag prior to doing SSE stuff and bail out if it's not available.

It'll be one more check on the double paths of the interpreter.  You should benchmark how this affects performance but I'm guessing it won't be much.

Or just implement x87.

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