[LLVMdev] Recursion inlining

[Chandler Carruth]

On Fri, Dec 5, 2014 at 2:10 AM, Pablo Barrio <pablo.barrio at arm.com> wrote:

> The default inliner currently marks all recursive functions as “never”
> inline when calculating the cost (CallAnalyzer::analyzeCall() in
> lib/Analysis/IPA/InlineCost.cpp). Is there any reason for this?
>

The reason used to be given in a comment in the code that got lost at some
point.

The idea is that inlining recursive calls is essentially loop unrolling. We
need to model it's cost and effects more like loop unrolling intersected
with inlining, and we don't really have a good model for that yet. It would
be really nice to work up such a model, but would require loooots of
benchmarking and careful tuning to find the right mixture.
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