The compiler looses vector capacity information

In this example:
```Rust
pub fn test() -> Vec<u32> {
    let mut vec = Vec::with_capacity(3);
    let mut i = 0;
    while i < 3 {
        vec.push(32);
        i += 1;
    }
    vec
}
```
the compiler produces sub-optimal assembly.
https://rust.godbolt.org/z/1T3Knodn8
