[PATCH] D145171: [FSAFDO] Improve FS discriminator encoding

[Rong Xu via llvm-commits]

On Mon, Mar 13, 2023 at 9:52 AM Wenlei He via Phabricator <
reviews at reviews.llvm.org> wrote:

> wenlei added a comment.
>
> > There is also a small change on the create_llvm_prof tool side. We will
> update the tool soon.
>
> What kind of change is that about? Appreciate if you could drop us a note
> when the change is up since we don't closely follow create_llvm_prof
> updates.
>

They are related to using the last/first entry of LBR stack to get some
coverage.
Also how to handle the duplicated first lbr entry (the bogus one)
I notice you when we port the change to open source verison.


>
> > BTW, I'll started the integration with CSSPGO base off here. Pseudo
> probes have a potential to allow more bits for the FS discriminator and
> additional FS passes. Implementation-wise, the potential comes from placing
> the FS discriminator field as a separate int64 operand of the pseudo probe
> intrinsic, instead of using the existing dbg metadata. I would like your
> thoughts about whether it's worth the diversion. Thanks.
>
> All thing being equal, I'd favor consistency. But there's potential
> benefit by allowing more FS profile loading, though whether that is
> material depends on whether we will actually leverage the ability to load
> more than 4 profiles. My intuition is that loading base profile + pre-RA
> profile + pre-layout profile as the way it is today is probably good enough.
>
Also allowing more bits for each pass might also help.

It's possible that we add another pass for machine function splitting.


>
>
> Repository:
>   rG LLVM Github Monorepo
>
> CHANGES SINCE LAST ACTION
>   https://reviews.llvm.org/D145171/new/
>
> https://reviews.llvm.org/D145171
>
>
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