Webassembly has a substantial performance hit for code containing hand-written vector loops using specialized instructions.
Things like video encoders and decoders are much slower in webassembly.
Things like video encoders and decoders are much slower in webassembly.
Of course though, you're right that it'll still incur a performance penalty.
That way, the developer can tweak the input to the compiler to get exactly the sequence of instructions they wanted.
They can also hand write the output assembly, and put a patch in to the compiler saying "this generated assembly is faster that what you generated, so please generate this in the next version".