[llvm] SLPVectorizer: Avoid looking at uselists of constants (PR #134578)

[Alexander Kornienko via llvm-commits]

alexfh wrote:

As I mentioned, the reproducer is tricky here. I haven't yet figured out how to build a clang that would reliably crash on the inputs I have without the specific profiles gathered from our code. I'm still working on this though.

https://github.com/llvm/llvm-project/pull/134578