[llvm] [LoopInterchange] Enable it by default (PR #124911)

[Sjoerd Meijer via llvm-commits]

sjoerdmeijer wrote:

> > Yep, you're right, here are the right numbers:
> > http://llvm-compile-time-tracker.com/compare.php?from=bf60aa1c551ef5de62fd1d1cdcbff58cba55cacd&to=54b48e5d738fa763fb1f31590801b701262ce045&stat=instructions:u
> 
> I think this is quite a serious regression, especially given that there are no binary changes. Is the regression coming mostly from DA? In that case, can we try to early-exit in LoopInterchange and avoid computing DA, if there are likely going to be no binary changes?

We see geomean compile-time increases of 0.20% 0.30%, 0.13%, 0.17% and 0.18%, which I think is actually really good given that we are in fact talking about enabling/running 4 components: interchange, DependenceAnalysis, Delinearization and LoopCacheAnalysis. Most of the compile-time is spent on the required extra analysis, and we have spent significant effort on reducing it to this minimum compile time increases. You're right it's not triggering much, but that is also by design at this point, and again it still requires to calculate extra analysis info. 

https://github.com/llvm/llvm-project/pull/124911