[llvm] [GVN] Skip instructions without value numbers in performScalarPRE (PR #219851)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

> @antoniofrighetto Should I fix the `undef` in the test, or leave it?

That is fine. We are loading a value from an uninitialized stack-allocated object, GVN has simply folded this value to undef.

https://github.com/llvm/llvm-project/pull/219851