[llvm] [DAG] Introduce generic shl_add node [NFC] (PR #88791)

[Philip Reames via llvm-commits]

preames wrote:

> This patch is not a NFC.
> 
> Example: https://godbolt.org/z/PMTqjf45M

Looks like maybe I missed a pattern for the .uw variant, will go track this down.  

Can I ask how you're finding these?  This is the second time you've chimed in with a really useful counter example on these threads.  Are you fuzzing the changes?  Much appreciated.

https://github.com/llvm/llvm-project/pull/88791