[llvm] [ARM] Replace ABS and tABS machine nodes with custom lowering (PR #156717)

[via llvm-commits]

AZero13 wrote:

> > Is 2 not accurate since it is just cmp+cmov?
> 
> Yeah It depends on how much a cmp costs. The BasicTTI seems to use ICmp+Select+Sub costs, even if the default expansion is via asr+xor+sub. The cost of i64 seems too low, and the costsize costs of the others you could argue should be higher than 2.

Well, ICmp+Select+Sub is the custom lowering we are going with. We are not doing that in THUMB. 

https://github.com/llvm/llvm-project/pull/156717