[intro.races] It is slightly unclear whether a data race can occur if no bits are changed

[eisenwave]

See OP's confusion in https://stackoverflow.com/q/77031819/5740428.

I believe that the current wording implies the following (I've elaborated on this in my answer https://stackoverflow.com/a/77032028/5740428):

int x = 0; // global variable

void concurrently() {
    x = 0; // may be a data race, even if the value of x prior to this assignment is zero
}

I think there should be a note or example somewhere (possibly [defns.access], [intro.races], [intro.multithread]) which explains that even if the value is unchanged (based on equality comparison), changing the value (in the abstract machine sense) still counts as modification.

[frederick-vs-ja]

I think [expr.ass] p2 is a good place. All manners of modification eventually lead to that paragraph.

[eisenwave]

Perhaps add a note to [expr.ass] p2 stating:

The object is modified even if the value of the right operand compares equal ([expr.eq]) to the object's old value.