[webkit-dev] Bring back ARMv6 support to JSC

[Yusuke SUZUKI]

On Wed, Sep 6, 2017 at 3:24 AM, Filip Pizlo <fpizlo at apple.com> wrote:

>
>
> > On Sep 5, 2017, at 10:51 AM, Olmstead, Don <Don.Olmstead at sony.com>
> wrote:
> >
> > We have plans to add a JSC-Only windows bot in the very near future.
> Would that have any bearing on the state of JIT in Windows?
>
> Not really.
>
> Because of the poor state of that code, I think we should rip it out.
>
> Also maintaining the 32_64 value representation is no value for us.
>

I think keeping Windows support would be good. I believe Sony folks are
working on Windows improvement, and it would be fine if they can keep
watching JSC on Windows.
And it means that we can keep WebKit fast at major latest architectures
including macOS / Linux / Windows (with 64bit CPUs), which is fine.

My largest concern about dropping JIT for various platforms is that LLInt
performance would be not good compared to JIT-ed environment.
We could remove DFG for 32bit (not sure). But I think PolyIC can be
critical for performance.
JS performance largely depends on this feature.

BTW, I strongly agree that newer feature should focus on 64bit
architecture. (I'm opposed to adding 32bit support to FTL).



>
> -Filip
>
>
> >
> > -----Original Message-----
> > From: webkit-dev [mailto:webkit-dev-bounces at lists.webkit.org] On Behalf
> Of Filip Pizlo
> > Sent: Tuesday, September 5, 2017 8:37 AM
> > To: Adrian Perez de Castro <aperez at igalia.com>
> > Cc: webkit-dev at lists.webkit.org
> > Subject: Re: [webkit-dev] Bring back ARMv6 support to JSC
> >
> > There isn’t anyone maintaining the 32-not JIT ports to the level of
> quality we have in our 64-not ports. Making 32-bit use the 64-bit cloop
> would be a quality progression for actual users of 32-bit.
> >
> > -Filip
> >
> >>> On Sep 5, 2017, at 8:02 AM, Adrian Perez de Castro <aperez at igalia.com>
> wrote:
> >>>
> >>> On Tue, 5 Sep 2017 16:38:09 +0200, Osztrogonác Csaba <
> oszi at inf.u-szeged.hu> wrote:
> >>>
> >>> [...]
> >>>
> >>> Maybe it will be hard to say good bye to 32-bit architecutres for
> >>> many people, but please, it's 2017 now, the first ARMv8 SoC is out 4
> >>> years ago, the first AMD64 CPU is out 14 years ago.
> >>
> >> While it's true that amd64/x86_64 has been around long enough to not
> >> have to care (much) about its 32-bit counterpart; the same cannot be
> said about ARM.
> >> It would be great to be able to say that 32-bit ARM is well dead, but
> >> we are not there yet.
> >>
> >> If we take x86_64 as an example, it has been “only” 10 years since the
> >> last new 32-bit CPU was announced and until 3-4 years ago it wasn't
> >> uncommon to see plently of people running 32-bit userlands. If things
> >> unroll in a similar way in the ARM arena, I would expect good 32-bit
> >> ARM support being relevant at least for another 3-4 years before the
> need starts to fade away.
> >>
> >> If something, I think it may make more sense to remove 32-bit x86
> >> support, and have the 32-bit ARM support around for some more time.
> >>
> >> Cheers,
> >>
> >>
> >> --
> >> Adrián 🎩
> >>
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