[llvm] [Transforms] Introduce BuildBuiltins.h atomic helpers (PR #134455)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> @jyknight Here the proof that emitting sized libcall atomics early is better than letting AtomicExpandPass do it: https://godbolt.org/z/bGW37TMYh. In this case it skips tail call elimination.

That's only proof that AtomicExpand doesn't bother setting the tail flag, which it could simply do 

https://github.com/llvm/llvm-project/pull/134455