Previously, the logic was wrong on two counts:
- It used the bits of the entire vector (e.g. i32x4 -> 128) instead of just the lane bits (e.g. i32x4 -> 32).
- It used the type of the first operand before it was bitcast to its correct type. Remember that, by default, vectors are handed around as i8x16 and we must bitcast them to their correct type for Cranelift's verifier; see https://github.com/bytecodealliance/wasmtime/issues/1147 for discussion on this. This fix simply uses the type of the instruction itself, which is equivalent and hopefully less fragile to any changes.
4155d15e69