[swift-evolution] Pitch: Cross-module inlining and specialization

[Andrew Trick]

> On Oct 2, 2017, at 11:20 PM, Slava Pestov via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
>> On Oct 2, 2017, at 11:11 PM, Slava Pestov via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>>> This semantic doesn’t make sense to me, and I think we need to change it.  I think we are better served with the semantics of “the body may be inlined, but doesn’t have to.”
>> 
>> That is the effect it has today. The decision to inline or not is made by the optimizer, and @inlinable doesn’t change anything here; it makes the body available if the optimizer chooses to do so.
> 
> Also remember we have the @inline(never) attribute. It’s not underscored so I’m assuming it’s an “official” part of the language. And "@inline(never) @inlinable" is a perfectly valid combination — it serializes the SIL for the function body, and while inlining it is prohibited, it is still subject to specialization, function signature optimizations, etc.
> 
> Slava

FWIW, the @inlinable name has always confused me. Methods not marked @inlinable are still internally inlinable. "Inlining" is already a term of art with specific semantics in other languages, and even in Swift is it's own thing to be controlled independently from resilience. The real issue I have with the name is that it says nothing about resilience. I’ll never forget that fragility is the opposite of resilience. I can't see how a @fragile attribute would ever be misconstrued.

As for the various shades of fragility of data types, I don't see why that can't be handled as qualifiers or additional optional attributes for expert developers. It’s just a matter of picking a reasonable default.

-Andy
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