[llvm] [AMDGPU][SDAG] Add ISD::PTRADD DAG combines (PR #142739)

[Fabian Ritter via llvm-commits]

ritter-x2a wrote:

### Merge activity

* **Jun 26, 7:27 AM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/142739).


https://github.com/llvm/llvm-project/pull/142739