Re: RISC-V: Folding memory for FP + constant case

[Jivan Hakobyan <jivanhakobyan9@gmail.com>]

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Thank you for your effort.
I had evaluated only in intrate tests.
I am glad to see the same result on Leela.

On Tue, Aug 1, 2023 at 11:14 PM Vineet Gupta <vineetg@rivosinc.com> wrote:

>
>
> On 7/25/23 20:31, Jeff Law via Gcc-patches wrote:
> >
> >
> > On 7/25/23 05:24, Jivan Hakobyan wrote:
> >> Hi.
> >>
> >> I re-run the benchmarks and hopefully got the same profit.
> >> I also compared the leela's code and figured out the reason.
> >>
> >> Actually, my and Manolis's patches do the same thing. The difference
> >> is only execution order.
> > But shouldn't your patch also allow for for at the last the potential
> > to pull the fp+offset computation out of a loop?  I'm pretty sure
> > Manolis's patch can't do that.
> >
> >> Because of f-m-o held after the register allocation it cannot
> >> eliminate redundant move 'sp' to another register.
> > Actually that's supposed to be handled by a different patch that
> > should already be upstream.  Specifically;
> >
> >> commit 6a2e8dcbbd4bab374b27abea375bf7a921047800
> >> Author: Manolis Tsamis <manolis.tsamis@vrull.eu>
> >> Date:   Thu May 25 13:44:41 2023 +0200
> >>
> >>     cprop_hardreg: Enable propagation of the stack pointer if possible
> >>         Propagation of the stack pointer in cprop_hardreg is currenty
> >>     forbidden in all cases, due to maybe_mode_change returning NULL.
> >>     Relax this restriction and allow propagation when no mode change is
> >>     requested.
> >>         gcc/ChangeLog:
> >>                 * regcprop.cc (maybe_mode_change): Enable stack pointer
> >>             propagation.
> > I think there were a couple-follow-ups.  But that's the key change
> > that should allow propagation of copies from the stack pointer and
> > thus eliminate the mov gpr,sp instructions.  If that's not happening,
> > then it's worth investigating why.
> >
> >>
> >> Besides that, I have checked the build failure on x264_r. It is
> >> already fixed on the third version.
> > Yea, this was a problem with re-recognition.  I think it was fixed by:
> >
> >> commit ecfa870ff29d979bd2c3d411643b551f2b6915b0
> >> Author: Vineet Gupta <vineetg@rivosinc.com>
> >> Date:   Thu Jul 20 11:15:37 2023 -0700
> >>
> >>     RISC-V: optim const DF +0.0 store to mem [PR/110748]
> >>         Fixes: ef85d150b5963 ("RISC-V: Enable TARGET_SUPPORTS_WIDE_INT")
> >>         DF +0.0 is bitwise all zeros so int x0 store to mem can be
> >> used to optimize it.
> > [ ... ]
> >
> >
> > So I think the big question WRT your patch is does it still help the
> > case where we weren't pulling the fp+offset computation out of a loop.
>
> I have some numbers for f-m-o v3 vs this. Attached here (vs. inline to
> avoid the Thunderbird mangling the test formatting)
>


-- 
With the best regards
Jivan Hakobyan