Comment by zozbot234

> However, they still lack an actual operational semantics in MIR -- and the way they are represented in MIR doesn't lend itself to a sensible semantics

That's an issue with how the MIR for this feature has been defined, not with the feature itself. The claim that the implementation should be reworked from the ground up is one that I might agree with, but the recent proposal to back out of an existing RFC suggests that the devs see alloca itself as problematic. And that's bad news if you intend to use alloca throughout as a foundation for your Swift-like ABI support...