[llvm] Move SI Lower Control Flow Up (PR #159557)

[Patrick Simmons via llvm-commits]

linuxrocks123 wrote:

@arsenm that would be a lot of work, and I don't see a lot of potential gain, but the IR changes are encapsulated to accommodate that approach.  Whoever implements that approach would need to modify all of the necessary target-independent upstream passes to understand a new Machine IR format used only by one target and may need to convince whoever maintains those passes that that new Machine IR format is beneficial to LLVM as a whole and should therefore be supported by target-independent passes.

Once all of that work has been done, I could update this PR to use the new format by updating SICustomBranchBundles.h to use whatever new IR feature has been added instead of bundles.  Doing so should only require changing a few lines of code.

https://github.com/llvm/llvm-project/pull/159557