[llvm-dev] PGO information at LTO/thinLTO link step

[Xinliang David Li via llvm-dev]

With the new PM, the profile information should be properly updated across
inline transformations. If you see otherwise, please file a bug ..

David

On Tue, Oct 3, 2017 at 12:54 PM, Graham Yiu via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hello,
>
> My team and I noticed that callsite hotness information is not preserved
> from compile to link step with LTO/thinLTO enabled. As a result, the link
> step inlining pass remains conservative when inlining callsites known to be
> hot (ie. without the 'HotCallSiteThreshold' which is set at 3000 by
> default). There are likely many cross-module inlining opportunities lost
> this way, and diminishes the benefit of using LTO/thinLTO+PGO together.
>
> In general, does LLVM pass profiling information through the IR to the
> link step other than branch probabilities and function entry counts? If
> not, are there plans to do so in the future? For inlining specifically,
> perhaps we can mark callsites with hot/cold attributes during compile step
> to ensure LTO inlining will give appropriate threshold bonuses/penalties.
>
> Any thoughts/insights/comments would be appreciated.
>
> Cheers,
>
> Graham Yiu
> LLVM Compiler Development
> IBM Toronto Software Lab
> Office: (905) 413-4077 C2-707/8200/Markham
> Email: gyiu at ca.ibm.com
>
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>
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