[llvm] [Sink] Allow sinking of loads to distant blocks (PR #135986)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> The block walk must stop in the load block since the load block dominates the uses. I'll and a limit to the number of stores that are analyzed. Is a default of 6 okay?

Probably should avoid doing ad-hoc memory analysis, and use one of the existing analyses 

https://github.com/llvm/llvm-project/pull/135986