[happycube]

There's a critical instruction for Objective C handling (I forget exactly what it is) but it's faster than intel's chips even in Rosetta 2's x86 emulation.

[wvenable]

I believe it's the `lock xadd` instruction. It's faster when combined with x86 Total Store Ordering mode that the Rosetta emulation runs under.

[saagarjha]

Looking at objc_retain apparently it's a lock cmpxchg these days