Does specifying the + operator on outputs remove the need for listing
the variable as an input? For example:
__CRT_INLINE SHORT AddTest(SHORT *Addend)
{
SHORT ret = 1;
__asm__ __volatile__("lock\n\txaddw %0,%1 "
: "+r" (ret), "+m" (*Addend)
: "0" (ret)
: "cc");
return ret + 1;
}
Is the "0" constraint accomplishing anything useful here (such as
ensuring the 1 is in the register)? Or is it just advertising the fact
that I don't fully understand how constraints work?
And more importantly, is the "+m" enough to ensure that any existing
values for Addend have been written to memory? Or do I need to add "m"
(*Addend) as an input?
I've run some tests, and as best I can tell, neither input constraint is
required. But I don't rule out the possibility that that's just an
artifact of my test code. I can say for sure that "1" (*Addend) is the
wrong answer (compile error).
Thanks.
