Proposed resolution (approved by CWG 2023-09-15):

(Hypothetically, pointer-to-member types can be empty, but might differ in non-top-level cv-qualification.)

Change in 6.7.2 [intro.object] paragraph 9 as follows:

... Two objects with overlapping lifetimes that are not bit-fields may have the same address if one is nested within the other, or if at least one is a subobject of zero size and they are not of different similar types (7.3.6 [conv.qual]); otherwise, they have distinct addresses and occupy disjoint bytes of storage. [ Footnote: ... ]

Suggested resolution [SUPERSEDED]:

Change in 6.7.2 [intro.object] paragraph 9 as follows:

... Two objects with overlapping lifetimes that are not bit-fields may have the same address if one is nested within the other, or if at least one is a subobject of zero size and they are of different types (ignoring top-level cv-qualifiers); otherwise, they have distinct addresses and occupy disjoint bytes of storage. [ Footnote: ... ]

[Accepted as a DR at the November, 2023 meeting.]

Subclause 6.7.2 [intro.object] paragraph 9 specifies:

... Two objects with overlapping lifetimes that are not bit-fields may have the same address if one is nested within the other, or if at least one is a subobject of zero size and they are of different types; otherwise, they have distinct addresses and occupy disjoint bytes of storage. [ Footnote: ... ]

Types T and const T are different types, but it is unlikely the rule is intending to differentiate along that line.