After D75689 we lost the ability to emitturns the faddp instructions:
VectorCombine prefers an extract after apattern into a shuffle with vector add and splatdd.
Change the cost model so that the extracts are free when they feed intoMatch this new pattern in target-specific DAG combine, rather than ISel,
a pairwise add. This reflects the cost of an faddp more accurately, andbecause legalization (for v2f32) turns it into a bit of a mess.
leaves the pattern intact for ISel to pick up.