How reuse inline assembler conditionals?

[Benjamin K.]

Example (need x86 compatible system):

int Increment(int a){
    int tmp;
    asm volatile(
    "inc %0\n"
    : "=r" (tmp)
    : "0" (a)
    );
    return tmp;
}

x86 cpu will set conditional flags after using INC
instruction, but this conditional will no be used by
gcc, why?

Gcc will produce something like:

if (Increment(10)==0) {
}

mov eax,10
inc eax
test eax,eax
jnz Lxx

But "test eax,eax" isn't needed here.
How can the function be declared to reuse asm conditional flags?

Benjamin Kalytta