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

[Akash Dutta via llvm-commits]

akadutta wrote:

> > > Check compile time effect, it was a check to save compile time blow
> > 
> > 
> > I did not see any noticeable difference in compile time for the cases I tested. Do you have a benchmark/app in mind that would be a good candidate?
> 
> Use https://llvm-compile-time-tracker.com/

I tested CTMark locally. There's no significant difference in wall time. All differences are less than 0.2 seconds. In terms of instructions, O3 increases by 0.05% for this patch. The remaining configs are very similar.

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