Division by NonZero* checks for zero

[bugadani]

https://rust.godbolt.org/z/eTPzE6

Technically, NonZero* types are not meant to be used for optimizing arithmetic, but people (like myself) may or may not know that or may assume otherwise.

It is possible to create a NonZero* object with 0 inner value, but since that is a misuse of the type and deliberate violation of the safety guarantees, I think it would make sense to teach the compiler that get() can't return 0.

Edit: unfortunately, since NonZero* methods are const, it's not as simple as adding an assume.

[oli-obk]

since NonZero* methods are const, it's not as simple as adding an assume.

we can make assume const, it's a no-op in const eval anyway (though we use it to assert that the assumption holds in miri)

[tesuji]

I'm preparing a PR for that.

[bugadani]

I can add the assume after that's done.

[bugadani]

Duplicate of #49572