🚀 go-pugleaf

The following code accesses an exotic Pentium instruction (reads high-resolution timer
into EAX:EDX register pair):

#include <stdio.h>
main()
{
 long long t1,t2;
 __asm__ __volatile__("rdtsc":"=a" (((unsigned long*)&t1)[0]),"=d" (((unsigned long*)&t1)[1]));
 __asm__ __volatile__("rdtsc":"=a" (((unsigned long*)&t2)[0]),"=d" (((unsigned long*)&t2)[1]));
 printf("%Ld\n",t2-t1);
}

Even at -O6 it generates rather redundant code. I don't know if it could have avoided storing
data into stack local vars, but the storing and reloading of registers seems very excessive.

Is there another form of __asm__ that I should have used?

main:
        pushl %ebp
        movl %esp,%ebp
        subl $24,%esp
#APP
        rdtsc
#NO_APP
        movl %eax,-8(%ebp)
        movl %edx,-4(%ebp)
#APP
        rdtsc
#NO_APP
        movl %eax,-16(%ebp)     <<<<<     
        movl %edx,-12(%ebp)     <<<<<     
        movl -16(%ebp),%eax     <<<<<     
        movl -12(%ebp),%edx     <<<<<     
        subl -8(%ebp),%eax
        sbbl -4(%ebp),%edx
        movl %eax,-24(%ebp)
        movl %edx,-20(%ebp)
        pushl -20(%ebp)
        pushl -24(%ebp)
        pushl $.LC0
        call printf
        leave


-- 
			przemek klosowski <przemek@nist.gov>  (301) 975-6249
			NIST Center for Neutron Research (bldg. 235), E111 
			National Institute of Standards and Technology
			Gaithersburg, MD 20899,      USA