[llvm] [SLP] Relax store chain user limit to 2 (PR #215700)

[Akash Dutta via llvm-commits]

akadutta wrote:

> > > Use https://llvm-compile-time-tracker.com/
> > 
> > 
> > Please see results here. https://llvm-compile-time-tracker.com/index.php?config=Overview&stat=instructions%3Au&remote=akadutta
> 
> Yep, as expected. Would be good to try to reduce compile time effect

Just to clarify, is 0.05% compile time hit unacceptable? I'm seeing upwards of 8% performance hit on several kernels if the store chain limit is kept at 1.

https://github.com/llvm/llvm-project/pull/215700