3 element vector type

We have a need for 3 element vector support. Locally I’ve added a new type to MVT to support this. Is there any reason this shouldn’t be contributed back to the mainline?

That sounds good to me. There are various assumptions that the vectors will be a power of two (mostly in the legalizer), that will need to be fixed. However, non-power-of-two vectors would be a great improvement and definitely good for mainline.