Creating a va_list dynamically?

[Robert Dewar]

<<Consider your question in light of all of the other ISO C functions
gcc already has optimized builtin behavior for.
>>

Well many of these functions are allowed to be implemented with macros
anyway in the standard, and it definitely *is* legitimate to optimize them.
I was not aware of any optimizations of this kind for other kinds of
functions, though there may be some cases.

My point is that you have to go check the ANSI standard here. Perhaps
if you are considering optimizing a function for which optimziation
is not strictly possible, then you can put the optimization under control 
of -pedantic.