[llvm] [SLP] NFC. Use InstructionsState::valid if users just want to know whether VL has same opcode. (PR #120217)

[Florian Hahn via llvm-commits]

fhahn wrote:

> > Looks like this has been crashing for a couple of hours.
> > Can we revert this to unblock people or land a fix ASAP?
> 
> It is fixed by #122443.

I see, but the fix hasn't landed yet, and it is not clear when it will land. If it takes longer, the change should be reverted

Also, if the change fixes a crash, I don't think it is really NFC :) 

https://github.com/llvm/llvm-project/pull/120217