[llvm] [GlobalISel] Add G_ABDS and G_ABDU instructions (PR #118122)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

Alternative / teaser:
Add 20 pseudo opcodes, map them to AArch64ISDs (AArch64usdot), and add a ton of combines into the pseudos.

https://github.com/llvm/llvm-project/pull/118122