[llvm] [GVN] Add code to disable scalar PRE (PR #190386)

[Antonio Frighetto via llvm-commits]

https://github.com/antoniofrighetto commented:

I have been wondering whether we should rename AllowPRE in AllowScalarPRE instead, and change this:

https://github.com/llvm/llvm-project/blob/4326a54708ffe72a223c4fa831b5f4e6e10d8aa7/llvm/lib/Transforms/Scalar/GVN.cpp#L2073-L2075

Into: `if (!isScalarPREEnabled() && !isLoadPREEnabled())`.

@nikic Any thoughts?

https://github.com/llvm/llvm-project/pull/190386