[llvm] [SLP] Pessimistically handle unknown vector entries in SLP vectorizer (PR #75438)

[Maurice Heumann via llvm-commits]

momo5502 wrote:

> 2 of these shuffles are free,they are just identity resizing shuffles, so it is not a big issue + they will optimized later. Yes, this can be improved, working on this. It may help if you can provide the reproducer

Ah I see, so it's known, but not a big deal. Unfortunately, I am not allowed to send the code producing code, but maybe if I find time, I can have a look at it or reduce the sample.

Anyways, thank you. I'm not sure if @RKSimon wants to add an additional review, however, if not, I have no commit access and would appreciate if someone could merge this PR for me. 

https://github.com/llvm/llvm-project/pull/75438