Re: Parameter Modes, In In Out and Out

[Tucker Taft <stt@averstar.com>]

Robert Dewar wrote:
> 
> In article <86itno316m.fsf@acm.org>,
>   Laurent Guerby <guerby@acm.org> wrote:
> 
> > if your compiler uses by copy passing
> > for integer, you'll probably get a program_error, because the
> > generated code for exiting P will set X with an unitialized
> > stack value (the place reserved for the Y value).
> 
> All compilers MUST pass integers by copy, there is no choice.

Unless you can prove that passing them by reference would be equivalent,
of course.  E.g., for [in] out parameters, we generally pass an address
of something.  Usually that something is a temp which is initialized
by copy from the actual parameter.  However, if we can prove that
it is safe to pass the address of the actual parameter itself
(which involves checking for the presence of things like exception
handlers, local task units, aliasing, etc.) then we can do so,
and thereby avoid the space and copy [in/]out for the temp.

-- 
-Tucker Taft   stt@avercom.net   http://www.averstar.com/~stt/
Chief Technology Officer, AverCom, Inc. (A Titan Company) Burlington, MA  USA
(AverCom was formed 1/1/01 from the Commercial Division of AverStar)
(http://www.averstar.com/services/ebusiness_applications.html)