Re: [PATCH, ARM] Further improve stack usage on sha512 (PR 77308)

[Ramana Radhakrishnan <ramana.gcc@googlemail.com>]

On Sun, Nov 6, 2016 at 2:18 PM, Bernd Edlinger
<bernd.edlinger@hotmail.de> wrote:
> Hi!
>
> This improves the stack usage on the sha512 test case for the case
> without hardware fpu and without iwmmxt by splitting all di-mode
> patterns right while expanding which is similar to what the shift-pattern
> does.  It does nothing in the case iwmmxt and fpu=neon or vfp as well as
> thumb1.
>

I would go further and do this in the absence of Neon, the VFP unit
being there doesn't help with DImode operations i.e. we do not have 64
bit integer arithmetic instructions without Neon. The main reason why
we have the DImode patterns split so late is to give a chance for
folks who want to do 64 bit arithmetic in Neon a chance to make this
work as well as support some of the 64 bit Neon intrinsics which IIRC
map down to these instructions. Doing this just for soft-float doesn't
improve the default case only. I don't usually test iwmmxt and I'm not
sure who has the ability to do so, thus keeping this restriction for
iwMMX is fine.


> It reduces the stack usage from 2300 to near optimal 272 bytes (!).
>
> Note this also splits many ldrd/strd instructions and therefore I will
> post a followup-patch that mitigates this effect by enabling the ldrd/strd
> peephole optimization after the necessary reg-testing.
>
>
> Bootstrapped and reg-tested on arm-linux-gnueabihf.

What do you mean by arm-linux-gnueabihf - when folks say that I
interpret it as --with-arch=armv7-a --with-float=hard
--with-fpu=vfpv3-d16 or (--with-fpu=neon).

If you've really bootstrapped and regtested it on armhf, doesn't this
patch as it stand have no effect there i.e. no change ?
arm-linux-gnueabihf usually means to me someone has configured with
--with-float=hard, so there are no regressions in the hard float ABI
case,


Ramana

> Is it OK for trunk?
>
>
> Thanks
> Bernd.