Full name of submitter (unless configured in github; will be published with the issue): Jiang An

Reference (section label): [expr.new], [basic.life]

Link to reflector thread (if any):

Issue description:
It seems that nothing in [expr.new] says that non-allocating placement new at an unaligned address has undefined behavior. [basic.life] p1.1 may be related, but one may think that such a new-expression just fails to create an object while being well-defined (however, the value of the new-expression seems underspecified if so).

For example, assuming alignof(double) == 8.

#include <new>

int main() {
  alignas(double) unsigned char buf[sizeof(double) + 1];
  new ((void*)(buf + 1)) double{};
}

Does the above program have undefined behavior? Or is the behavior well-defined despite that the new-expression doesn't create a double object?

It seems that the behavior should be undefined, because it generally requests unaligned access.

Suggested resolution: