[clang] [clang][CodeGen] Emit atomic IR in place of optimized libcalls. (PR #73176)

[James Y Knight via cfe-commits]

https://github.com/jyknight commented:

Overall, I think this is a great improvement.

And I believe it should be correct to do now, after fixing the backends' MaxAtomicSizeInBitsSupported in #75703 #75185 #75112 #74385 #74389, and fixing Clang's propagation of alignment to atomicrmw/cmpxchg in #74349.

Just a few more comments.

https://github.com/llvm/llvm-project/pull/73176