The plain `*p = v` arm's storeop map handled 1- and 4-byte pointees but let a 2-byte one fall to MOVQ, an 8-byte over-store that clobbers six adjacent bytes (masked in the pinned fixture by the lone frame slot; loud with `&a[0]` of a [4]i16). cstage fldstoreop maps 2 to MOVW. Graduates r660_i16_out_param_negative.