/// cheaper to allocate caller saved registers.
///
/// These methods take a MachineFunction argument, which can be used to tune
- /// the allocatable registers based on the characteristics of the function.
- /// One simple example is that the frame pointer register can be used if
- /// frame-pointer-elimination is performed.
+ /// the allocatable registers based on the characteristics of the function,
+ /// subtarget, or other criteria.
+ ///
+ /// Register allocators should account for the fact that an allocation
+ /// order iterator may return a reserved register and always check
+ /// if the register is allocatable (getAllocatableSet()) before using it.
///
/// By default, these methods return all registers in the class.
///