[llvm-dev] [RFC] New Feature Proposal: De-Optimizing Cold Functions using PGO Info

[Min-Yih Hsu via llvm-dev]

HI Renato,

On Thu, Sep 10, 2020 at 10:54 AM Renato Golin <rengolin at gmail.com> wrote:

> On Thu, 10 Sep 2020 at 18:22, Min-Yih Hsu <minyihh at uci.edu> wrote:
>
>> I totally agree with Wenlei that (somewhere in the future) we should have
>> a unified FDO framework for both code size and compilation time. And I
>> think Renato and Tobias's suggestions to do the same thing for
>> size-oriented attributes (i.e. `minsize` and `optsize`) is the
>> low-hanging fruit we can support in a short time.
>> Engineering-wised I'll prefer to send out a separate review for the
>> size-oriented attributes work, since `minsize` / `optsize` are kind of in
>> conflict with `optnone` so I don't think it's a good idea to put them into
>> one flag / feature set.
>>
>
> I'm happy for this unification to happen at a later stage. Just not too
> long later.
>
> I worry exposing the flags will get people to use it and then we'll change
> it. The longer we leave it, the more people will be hit by the subtle
> change.
>
> Worse still if we release with one behaviour now and then with a different
> behaviour in the next release.
>

Yeah totally understandable. I will try to not let it happen.
I'm willing to implement the support for optsize / minsize after this
patch. As well as providing some experiment numbers to justify it.

Best,
Min

>
> Having conditional paths in build systems for different versions of the
> compiler isn't fun.
>
> --renato
>


-- 
Min-Yih Hsu
Ph.D Student in ICS Department, University of California, Irvine (UCI).
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