[Someone]

That doesn’t matter for the case where a compiler would like to replace x + y by x because it knows y == 0.

The compiler would have to test for the x == -0 case, and doing that ¿rarely/never? is faster than computing x + y.

[titzer]

TurboFan does reason about whether a value can be -0 and will strength reduce if it's known a -0 will not occur. Further, it reasons about observations of a value; if it is known that a -0 is never observed, e.g. the value is only ever converted to an integer, or compared, or otherwise only flows into expressions that treat 0 == -0, then it will do more aggressive optimizations.