Hi --

This is a bit of an implementation-specific problem, but I'd like to
post it here to see if there's a general answer within the auspices of
the language.

I'm developing a high(er)-level scripting language designed explicitly
to complement C++. One of the language's features is the ability to
pass "out" parameters to an MSVC __cdecl function by reference.

the C++ function returns, but before popping the parameters from the
stack, the scripting-language VM copies any out-parameters back from the
C++ stack frame to the variables they originally came from. In this way
any modifications made by the C++ function to its parameters are
propagated back to the scripting language.

As you might guess, this approach has problems when compiling with
optimization turned on. In theory the C++ compiler may decide that any
write operations to parameters which are never subsequently read can be
omitted. In practice, I haven't seen that happening, but what I *have*
seen is that the compiler likes to reuse function parameters when it
needs to allocate a temporary. Hilarity ensues when the VM retrieves an
unrelated temporary from the stack instead of the parameter it expects.

Is there a general, implementation-independent way to tell the compiler
(a) not to reuse a function parameter as a temporary; and (b) not to
perform dead-code elimination on writes to function parameters?

I experimentally tried applying "volatile" to a parameter ("volatile
Mat4x4 *SRC"), and while MSVC accepted the code, SRC still got reused as
a temporary within the body of the function.

Similarly, passing the parameters by reference rather than as pointers
("Mat4X4 &SRC") doesn't make any difference.