[llvm] [GVN] Permit load PRE to happen in more cases (PR #79324)

[David Sherwood via llvm-commits]

david-arm wrote:

This is a rework of https://github.com/llvm/llvm-project/pull/76063, attempting to do a proper analysis and add more loads to the available list. The performance gains with this patch are not as good, but they are still valuable.

https://github.com/llvm/llvm-project/pull/79324