This occurs when the constant value is out of range of the type being assigned to. This is likely indicative of an error, or of code that assumes types have larger ranges than they do in ORCA/C (e.g. 32-bit int).
This intentionally does not report cases where a value is assigned to a signed type but is within the range of the corresponding unsigned type, or vice versa. These may be done intentionally, e.g. setting an unsigned value to "-1" or setting a signed value using a hex constant with the high bit set. Also, only conversions to 8-bit or 16-bit integer types are currently checked.