On Thu, 27 Jun 2024 at 13:40, Maciej Cencora wrote: > > Hi, > > not sure whether I've missed some conditional that would exclude this case, > but your change seems to incorrectly handle trivial types that have a > non-zero bit pattern of value-initialized object, e.g. pointer to member.
Good point. I started working on this optimization after last week's https://gcc.gnu.org/r15-1550-g139d65d1f5a60a where is_trivial is appropriate, because valarray only supports numeric types, not pointers to members. But the uninitialized memory algos don't have that restriction, so need to be more careful. I think memset is OK for arithmetic types, enums, pointers, nullptr_t, and trivial classes ... except when those trivial classes contain pointers to members. Which we can't tell. So maybe we can only do it for is_trivial && ((is_scalar and not is_member_pointer) or (is_class and is_empty)).
