Joe Groff 7b2a6e5e8d IRGen: Emit the "done" check for Builtin.once inline. ...

This matches how dispatch_once works in C, dramatically cutting the cost of a global accessor by avoiding the runtime call in the hot path and giving the global a unique branch for the CPU to predict away. For now, only do this for Darwin; non-ObjC platforms don't necessarily expose their "done" value as ABI like ours do.

While we're here, change "once" to take a thin function pointer. We don't ever emit global initializers with context dependencies, and this simplifies the runtime glue between swift_once and dispatch_once/std::call_once a bit.

Swift SVN r28166

2015-05-05 15:35:57 +00:00

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