How to express the fact that arguments don't escape?

[Richard Guenther]

On Sat, Aug 15, 2009 at 1:32 PM, N.M. Maclaren<nmm1@cam.ac.uk> wrote:
> On Aug 15 2009, Richard Guenther wrote:
>>
>> It's of course one area where the Fortran choice of passing everything by
>> reference pessimizes it quite a bit compared to other frontends ...
>
> Can the back-end distinguish traditional call by reference (as in Algol 60
> and 68) from call by pointer value (and in C and C++)?  The former does

No it can't.  Well - the backend has the DECL_BY_REFERENCE, but it's
semantics are poorly documented.  Note that Fortran overly uses that
predicate anyway - likely because it is also used for debug information
annotation IIRC.

> not have the same pessimisation problem, and is actually what Fortran needs
> for 'ordinary' objects.
>
> The difference could be useful for the C++ STL and possibly Ada, but I have
> forgotten the little of the latter that I once knew and so am not sure.

I don't think so.  You can take the address of even passed by value objects in
C++ if you make sure to remove all references in the destructor that runs after
the call completes.  See some previous bugs we had in this area.

Richard.