John McCall 59e2ab4277 The callback to Builtin.once is a C function, not a Swift one. ...

If we want it to be a Swift function, we'll have to thunk in the
runtime when using a system implementaton like dispatch_once_f,
since the function pointer ABIs could be different, depending on
the target.  Dealing with that, or avoiding it on a per-target basis,
is more complexiity than a micro-optimization of the slow path of
this builtin could possibly be worth.

2017-12-16 02:22:13 -05:00

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