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Re: [PATCH][AArch64] Support for LDP/STP of Q-registers
- From: James Greenhalgh <james dot greenhalgh at arm dot com>
- To: Kyrill Tkachov <kyrylo dot tkachov at foss dot arm dot com>
- Cc: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, Marcus Shawcroft <Marcus dot Shawcroft at arm dot com>, Richard Earnshaw <Richard dot Earnshaw at arm dot com>, Siddhesh Poyarekar <siddhesh at sourceware dot org>, Sameera Deshpande <sameera dot deshpande at linaro dot org>, "sellcey at cavium dot com" <sellcey at cavium dot com>, <nd at arm dot com>, <philipp dot tomsich at theobroma-systems dot com>, <e dot menezes at samsung dot com>, <benedikt dot huber at theobroma-systems dot com>
- Date: Tue, 5 Jun 2018 18:28:45 +0100
- Subject: Re: [PATCH][AArch64] Support for LDP/STP of Q-registers
- Nodisclaimer: True
- References: <5B157981.3010408@foss.arm.com> <5B16BB06.3020709@foss.arm.com>
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On Tue, Jun 05, 2018 at 11:32:06AM -0500, Kyrill Tkachov wrote:
>
> On 04/06/18 18:40, Kyrill Tkachov wrote:
> > Hi all,
> >
> > This patch adds support for generating LDPs and STPs of Q-registers.
> > This allows for more compact code generation and makes better use of the ISA.
> >
> > It's implemented in a straightforward way by allowing 16-byte modes in the
> > sched-fusion machinery and adding appropriate peepholes in aarch64-ldpstp.md
> > as well as the patterns themselves in aarch64-simd.md.
> >
> > I didn't see any non-noise performance effect on SPEC2017 on Cortex-A72 and Cortex-A53.
> >
>
> Adding some folks who know more about other CPUs as well.
> Are you okay with enabling these instructions in AArch64?
>
> If you could give this a spin on some benchmarks you
> care about on your platforms it would be really useful data.
>From an architecture perspective, I think this is the right thing for us
to do. Given the feedback from Andrew and Siddhesh I think we should support
this patch, defaulting to on; but behind a tuning flag for those who want
to disable it for their -mcpu tuning.
If you can respin it behind a tuning parameter and give the community
another 48 hours or so to respond, I think we'd have a good patch here.
I'm also adding some more contributors to the AArch64 cores file for their
thoughts on the proposal.
Thanks,
James