2xi64 is the legalized type for wide reductions (like 16xi64) and setting the
cost to 2 makes `load-reduce` and `load-zext-reduce` patterns profitable.
The few performance measurments that I did on an aarch64 machine confirm that
these patterns are actually faster when vectorized.
Differential Revision: https://reviews.llvm.org/D130740
This changes the cost to (LT.first-1) * cost(add) + 2, where the cost of
an add is assumed to be 1. This brings it inline with the other
reductions.
Differential Revision: https://reviews.llvm.org/D106240
Simon Pilgrim