Thomas Lively

The alternative would be to plan to use different type codes or operation codes for future extended versions. As far as I can see, the main drawback of this alternative...

@jan-wassenberg If I understand correctly, the proposed semantics is the same as the current bitselect semantics except that it requires that all mask bits for a particular lane have the...

Yes, WebAssembly cannot have undefined or implementation-defined behavior. Introducing a new mask type could solve the problem, but it would be a large amount of complexity to add to the...

I totally agree that having a separate mask type would make sense in a follow up SIMD proposal 👍

Because it would be a lot of work and we are trying to get SIMD into the hands of our users soon. Creating a new bitselect instruction in the future...

To be clear, you're just proposing a change to the boundary between an invalid and a malformed module, right? Not a change to the binary encoding? Seems ok to me,...

See some recent discussion of shift semantics in https://github.com/WebAssembly/simd/issues/100.

I don't quite understand why fence is allowed to be used with non-shared memories but other atomic instructions are not. Can you elaborate on that a bit?

@rossberg, I buy that a fence commits all accesses, even on a single thread, and I think that is a good argument for allowing it in modules without shared memories....

SGTM, and I think the names are appropriate as well. The `memory.init` instruction uses [dest_offset, source_offset, length] order for its operands, so it would be good to use [source_offset, length]...