Performance motivations for call tags?

[tlively]

In WebAssembly/gc#243 (comment) and in other recent discussions, call tags have been raised as a potential solution for various performance problems that come up when compiling to Wasm GC. The call tags explainer describes call tags primarily as a mechanism for enforcing program invariants rather than performance, so it would be good to have the performance motivations written up as well.

[RossTate]

Good point. We recently implemented the low-level feature (though not in WebAssembly) and used it to implement an object-oriented language. Our experiments found it both performs extremely well and is very flexible, which is why it's been coming up. I'll put in a PR outlining some examples of how we've made use of them (and giving intuition as to why it performs well in those examples).