[llvm-dev] How to get started with VLIW scheduler?

[jeniffer lesley via llvm-dev]

Thanks. That is useful but I am too immature to even get it kick started. I
am a beginner and I would like first understand what files I need to change
to build my scheduler. Just a simple scheduler and one step at a time. I am
reading Tanya's MS thesis about SMS but I am not sure if SchedInfo is right
way now. Moreover, what role TargetSchedule.t play? We need a beginner
guide to leverage LLVM's scheduler infra.


On Tue, Apr 27, 2021 at 1:31 AM Krzysztof Parzyszek via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> The way we do it for Hexagon is that we have our own specialization of the
> MachineScheduler pass, followed by a packetizer pass.  Actually, we run two
> schedulers: machine scheduler, and post-RA scheduler, but that doesn’t
> change much conceptually.  In the scheduler passes we don’t form
> instruction packets, at least not explicitly.  We do some sort of a
> simulation of “what if we were forming packets right now” type of thing,
> maximizing packetization opportunities ahead of time, before the
> packetization itself, hoping that enough of it will prevail.
>
>
>
> Finally, near the end of the post-RA passes we do run the DFAPacketizer
> pass which forms the actual packets (i.e. “bundles” in LLVM terminology).
> The DFA packetizer relies on tables that are generated out of your target’s
> td files describing your processor’s resources (some of which the standard
> scheduler uses as well).
>
>
>
> If you’re starting from scratch, I’d get the packetizer working first.
>
>
>
> --
>
> Krzysztof Parzyszek  kparzysz at quicinc.com   AI tools development
>
>
>
> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of *jeniffer
> lesley via llvm-dev
> *Sent:* Monday, April 26, 2021 1:33 PM
> *To:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* [EXT] [llvm-dev] How to get started with VLIW scheduler?
>
>
>
> Hi,
>
> I am building a toy target to teach at a university but I am not well
> aware of LLVM's scheduler infrastructure. My target is VLIW, 1 Load, 1
> Store and 2 ALUs. ALUs can perform almost all common mathematical
> operations.
>
>
>
> Where do I start building a scheduler for it? I watched a couple of videos
> from the LLVM dev meeting but what is the current way of building a new
> scheduler? Is there a .rst page out there which I missed reading?
>
>
>
> Thanks.
>
> Jeni.
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