Inlining of vararg functions

Question

While playing about with optimisation settings, I noticed an interesting phenomenon: functions taking a variable number of arguments (...) never seemed to get i

Answer 1

The point of inlining is that it reduces function call overhead.

But for varargs, there is very little to be gained in general.
Consider this code in the body of that function:

if (blah)
{
    printf("%d", va_arg(vl, int));
}
else
{
    printf("%s", va_arg(vl, char *));
}

How is the compiler supposed to inline it? Doing that requires the compiler to push everything on the stack in the correct order anyway, even though there isn't any function being called. The only thing that's optimized away is a call/ret instruction pair (and maybe pushing/popping ebp and whatnot). The memory manipulations cannot be optimized away, and the parameters cannot be passed in registers. So it's unlikely that you'll gain anything notable by inlining varargs.