[llvm] [AMDGPU][SDAG] Initial support for ISD::PTRADD (PR #141725)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> now is sreg_64 instead of sreg_64_xexec. I'm not sure if that loses us something worth
preserving; I haven't found an obvious way to avoid this.

I think the only plus is it removes one useless entry from the allocation order, since exec is always reserved and will never be used for the assignment 


https://github.com/llvm/llvm-project/pull/141725