That's a common strategy for Intel: get the instruction out the door and let programmers build on top of it, and then in the next revision, make the instruction

That's a common strategy for Intel: get the instruction out the door and let programmers build on top of it, and then in the next revision, make the instruction fast. One benefit of this strategy is that it makes it more difficult for 'other' x86 vendors to maintain binary compatibility if the industry leader is constantly changing what 'binary compatibility' means.