[llvm] [llvm][Comment] removing out-of-date comment, ARM backend no longer uses ScheduleDAGRRList (PR #117803)

[via llvm-commits]

CBSears wrote:

The ARM backend still uses ScheduleDAG and ScheduleDAGRRList ... 

> if (TLI->getSchedulingPreference() == Sched::RegPressure)

> if (isMClass() && hasMinSize())

So the comment needs to be improved/fixed rather than deleted. I'll look further.

> Also find it hard to believe that ARM, or any backend for that matter has 100% switched from SelectionDAG to GlobalISel. I thought they are all stuck somewhere in-between (but admittedly I did not follow this development closely).

As for GlobalISel, DirectX (2022) and SPIRV (2021) don't use SelectionDAG at all. In fact those newer backends needlessly include selectionDAG in their CMake files and SPIRV even has SelectionDAGTargetInfo.h in SPIRVSubtarget.h. So I commented those out and LLVM still built and passed the ninja check-llvm tests. I'll submit them as patches.

https://github.com/llvm/llvm-project/pull/117803