[llvm-dev] Use of branch weight metadata in enhanced inliner

[Easwaran Raman via llvm-dev]

Hi Taewook,

There is no reason not do use BFI in non-PGO mode. My current priority is
to improve PGO performance and I wanted to isolate this as much as possible
- hence it is turned on only in PGO mode.

- Easwaran

On Fri, Mar 4, 2016 at 10:54 AM, Taewook Oh <twoh at fb.com> wrote:

> Thank you Easwaran for landing a great diff that enables the use of block
> frequency information in inliner. As of now, it seems that inliner can
> exploit the information only when profile data is available. However,
> instructions such as __builtin_expect may set branch weight metadata as
> well, which is useful for inliner.
>
> I think this problem can be addressed by letting llvm::getInlineCost
> function to use BlockFrequencyAnalysis regardless of availability of
> profile data, and making CallAnalyzer::updateThreshold to use callsite
> frequency instead of callsite count. Is there a reason that we allow
> inliner to use block frequency information only when profile data is given?
>
> Thanks,
> Taewook
>
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