widenScalarDst updates the insert point to after MI, so
widenScalarSrc must be called before widenScalarDst. Otherwise
The updated Src values will appear after MI and break SSA. e.g.:
%14:_(s64), %15:_(s1) = G_UADDE %9:_, %11:_, %13:_
becomes
%14:_(s64), %16:_(s32) = G_UADDE %9:_, %11:_, %17:_ %15:_(s1) = G_TRUNC %16:_(s32) %17:_(s32) = G_ZEXT %13:_(s1)