you can also out register preferences directly into the asm volatile line. asm ( assembler template : output operands (optional) : in

you can also out register preferences directly into the asm volatile line. asm ( assembler template : output operands (optional) : input operands (optional) : clobbered registers list (optional) ); clobbered register list will give same hints to compiler... register keyword is also a hint not a fixed thing so i cant imagine its really handled differently? might be wrong, but it seem earier to me to use all the features of the asm call itself rather than outside of it pre-specifying these preferences.