[PATCH] D24940: [thinlto] Add cold-callsite import heuristic

[Easwaran Raman via llvm-commits]

eraman added a comment.

How does this result in improved performance? If the

In https://reviews.llvm.org/D24940#553322, @mehdi_amini wrote:

> > Not tunned up heuristic, but with this small heuristic there is about +0.10% improvement on SPEC 2006
>
>
> This is not clear to me: I would expect only a compile time impact on this, why is there a perf improvement?


The inliner and the importer use a different metric to determine what is cold: the importer uses the ProfleSummaryInfo while the inliner checks if the entry count is less than a fraction of max_entry_count (the inliner's code is the one that needs to change, but that's dependent on porting inliner to the new PM) This would explain the performance improvement (inliner normally inlines functions that are considered cold as determined by PSI.isColdCount() but prevented from doing so if they aren't imported). If we were to fix the inliner first, then this change should be  nop in terms of performance.


https://reviews.llvm.org/D24940