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

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon commented:

Are you able to create a test for the lost atomic property? I haven't checked but my guess is the x86 cases are losing the original dereferencable memory size or something as the SSE/AVX cases are splitting 512-bit loads down to 4 x 128-bits, so this patch is helping.

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