[llvm] [MachineSink] Add option for aggressive loop sinking (PR #117247)

[Jeffrey Byrnes via llvm-commits]

jrbyrnes wrote:

Reworked the approach to introduce CycleSinkStage . This does sinking into loops in progressively aggressive stages, with execution of each stage being dependent upon whether or not we've met our RP goals. The first stage sinks copies and honors the sink cycle limit, the second sinks low latency instructions, and the third sinks all candidates. 

Reorganized the tests to better test the new implementation.

https://github.com/llvm/llvm-project/pull/117247