[clang] [llvm] [AMDGPU] Enable atomic optimizer for 64 bit divergent values (PR #96473)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> Kindly review only the top commit here

If you're going to repost with a pre-commit, it would be better to have all the pieces squashed into one. Also you could look into using graphite or SPR for managing dependent pull requests 

https://github.com/llvm/llvm-project/pull/96473