The default code generation model for Embedded Swift is "inlinable".
DeferredCodeGen made the default code generation model
"implementation", and there was no spelling for "interface".
Introduce the experimental feature CodeGenerationModel=<model>, which
can be any of those three options. The default remains "inlinable", but
one can now specify "implementation" (which keeps most everything in
SIL) or "interface" (which only keeps the generic things in SIL). The
"interface" mode is more like non-embedded Swift for non-generic
declarations, emitting them into the IR (only) but not SIL. Generic
declarations would remain in SIL.
Implements rdar://172433062.
For a given function, we might end up emitting it's definition as
object code, serialized SIL, or both. The @export, @inlinable, and
@inline(always) attributes provide control of this behavior at the
declaration level.
Centralize the query function that will look for each of these
attributes and map down to a specific "code generation model", whose 3
options follow the naming from SE-0497: interface, inlinable, and
implementation. Use this one computation to back the queries for
"always emit into client", "never emit into client", and "inlinable"
so we can't get inconsistent results from places that are doing
one-off checks for these attributes.
Doug Gregor