Reference (section label): [intro.memory]

Issue description

union U { int x, y; } u;
(u.x = 1, 0) + (u.y = 2, 0);

The latter statement makes two unsequenced modifications which target the same storage within u but are not the same memory location by definition. Therefore, the statement is well-defined, but it should not be.

Suggested resolution

Update [intro.memory] paragraph 3 as follows:

A memory location is a set of elements which occupy overlapping storage, where each element is either an object of scalar type that is not a bit-field or a maximal sequence of adjacent bit-fields all having nonzero width.