Understanding when @inlinable is needed for generic specialization

[hassila (Joakim Hassila)]

@lukasa

In principle, you can avoid this by using cross-module optimisation.

But with care, see e.g.

What are the tradeoffs of -cross-module-optimization?

Just a small data point, tried this out on a small sample project and got a 4x reduction in performance (reproducible) with cross-module-optimization enabled on my M1 Max laptop: hassila@max ~/D/G/p/swift-benchmark (main)> swift run -c release Building for production... Build complete! (0.08s) Start test 1064784 usec hassila@max ~/D/G/p/swift-benchmark (main)> swift run -Xswiftc -cross-module-optimization -c release Building for production... [4/4] Linking swift-benchmark Build complete! (2.10s…

(I'll admit we haven't tried it again since April, so maybe something was fixed in 5.7)