[llvm] [AMDGPU] Improved Lowering of abs(i16) and -abs(i16) (PR #165626)

[Patrick Simmons via llvm-commits]

linuxrocks123 wrote:

@jmmartinez @jayfoad I think this is everything.  If we're ready to merge this as a new pass, I'll update the llc-pipeline tests to pass.  If we'd rather combine this with an existing early MIR pass, such as `SILowerI1Copies`, please let me know, and I will do that instead.

https://github.com/llvm/llvm-project/pull/165626