what is the difference with and without crc extension support

[Dongjiu Geng]

Hi,
     My program does not use CRC instructions，but I find the compiled
binary has much difference between using "-march=armv8-a+crc" and
using "-march=armv8-a". Even stranger, when I use
"-march=armv8-a+crc", I find my compiled binary can not run. but when
I change -O2 to -O0 based on "-march=armv8-a+crc",  it can run. I  do
not  know what is the reason.. can you answer it? Thanks.