Hi!

If I build a vector of some length (e.g. 4) from a vector of another length (e.g. 3)

then I get tons of extractelement and insertelement instructions. since

vectors of length 3 and 4 both map to an sse register it could be useful to

introduce an instruction that changes the length of a vector, either truncating

or extending by zero or undef values (whichever makes more sense).

for lengths 3 and 4 this maps to no-op but could be useful for e.g. concatenating

two vectors of length 8 to a vector of length 16 by first resizing to length 16

and then using shufflevector.

what do you think?

-jochen