[llvm] [DAGCombiner] Don't drop atomic property of original load. (PR #75626)

[Jonas Paulsson via llvm-commits]

JonPsson1 wrote:

> See also @preames comment in commit [a0dde7b](https://github.com/llvm/llvm-project/commit/a0dde7b8d16842005d6f5247dda6f17c77a5906f). I think the idea is to delete the support for atomic LoadSDNode, after moving SystemZ off of it.

Made a patch for this: https://github.com/llvm/llvm-project/pull/75879

https://github.com/llvm/llvm-project/pull/75626