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

Tobias Hieta via llvm-dev
Wed, 09 Sep 2020 17:58:01 -0000

Would it make sense to have a flag to select optnone or optsize? We would
probably also do the tradeoff for a smaller binary.

On Wed, Sep 9, 2020, 19:28 Renato Golin <rengolin at gmail.com> wrote:

> On Wed, 9 Sep 2020 at 18:15, Min-Yih Hsu via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> David mentioned in D87337 that LLVM has used similar techniques on code
>> size (not sure what he was referencing, my guess will be something
related
>> to hot-cold code splitting).
>>
>
> IIUC, it's just using optsize instead of optnone. The idea is that, if
the
> code really doesn't run often/at all, then the performance impact of
> reducing the size is negligible, but the size impact is considerable.
>
> I'd wager that optsize could even be faster than optnone, as it would
> delete a lot of useless code... but not noticeable, as it wouldn't run
much.
>
> This is an idea that we (Verona Language) are interested in, too.
>
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