Instead of splatting a single lane, to initialise a build_vector, lower to scalar_to_vector which can be selected to load_zero. Also add load_zero and load_lane patterns for f32x4 and f64x2.
Instead of splatting a single lane, to initialise a build_vector, lower to scalar_to_vector which can be selected to load_zero. Also add load_zero and load_lane patterns for f32x4 and f64x2.