That is something the pass verifies,

Unless I misunderstood you?

Great, I had forgotten we already did that.

There are some TODOs here, but the larger question is whether this seems worthwhile. I see a 1% code size regression on j2cl for example - do we expect the benefit to be larger than that? @tlively @jakobkummerow

This is primarily a performance improvement. ref.cast_desc is faster than other casts.

Makes sense, but do we think it is fast enough to justify a 1% size regression? Given that iiuc we think the VM can do much of this too.

This should only be run at the very end, manually - running it in every -O3 causes code size increases for various reasons (1% increase affects inlining, and also we end up with more exact types, which inhibit merging of locals etc.), that accumulates, and it does not enable other toolchain opts anyhow.

@tlively rebased and put behind a pass-arg, so that we can land it and continue evaluation.