[emmericp]

Swift spends 76% of the time incrementing/decrementing reference counts; ARC is just very bad at pushing tens of millions of objects through it every second.

There's some more evlauation for Swift here: https://github.com/ixy-languages/ixy.swift/tree/master/perfo...

It's just a coincidence that JavaScript and Swift end up with almost the same performance; there is nothing similar between these two runtimes and implementations.

[skohan]

This is also a clear optimization target. It is very possible to write Swift code which requires very little reference-counting overhead.

[dep_b]

The problem is that 99% of all Swift developers use the language to create front-ends for powerful devices and you never need to squeeze the last drop of performance out of them.