That’s true, even if the semantics are the same (and parsing time isn’t a big factor) the assumptions for what optimizations have been applied to bytecode might be different. I remember seeing in one of the meeting notes that they didn’t expect browsers to end up making assumptions about the optimization level of the SPIR-V they ingest anyway but I don’t remember the specific rationale for that.

There’s of course also the time for the SPIR-V -> gpu native step. It would be nice if they could just cache that and skip the whole process most of the time.