CONFIG_OPT_LIB_FUNCTION is not available for thedefaultarchitecture x86.
Result is shown for architecture microblaze

Optimalized lib function


Linux Kernel Configuration
└─>Platform options
└─>Optimalized lib function
In linux kernel since version 2.6.30 (release Date: 2009-06-09)  
Allows turn on optimalized library function (memcpy and memmove).
They are optimized by using word alignment. This will work
fine if both source and destination are aligned on the same
boundary. However, if they are aligned on different boundaries
shifts will be necessary. This might result in bad performance
on MicroBlaze systems without a barrel shifter.