[Design] confusing `target_pointer_width = "64"` usize convertion design

Title

confusing target_pointer_width = "64" usize convertion design

Actual

        #[cfg(target_pointer_width = "64")]
        {
            let _ = usize::try_from(42u64).unwrap();
            let _ = usize::try_from(42u32).unwrap();
            let _ = usize::from(42u16);
        }

Expected

When under target_pointer_width 64, should always success, and try is not necessary.

        #[cfg(CONDITION)]
        {
            let _ = usize::from(42u64);
            let _ = usize::from(42u32);
            let _ = usize::from(42u16);
        }

Related

https://github.com/rust-lang/rust/blob/master/library/core/src/convert/num.rs

Read library/core/src/convert/num.rs and inspect the existing usize conversion implementations related to target_pointer_width. Compare the requested 64-bit behavior with the current conversion design and determine the appropriate condition and API implications. Done means the design is settled and the relevant conversions have consistent, justified behavior under the requested target width.