Re: Q: access to subprogram

[dewar@cs.nyu.edu (Robert Dewar)]

Ronald Cole said (commenting on my claim that GCC did not have multiple
backends)

Not true.  A single instance of GCC doesn't support multiple machine
targets (other than the -m options for some processor families).  GCC
has to be recompiled to support different machine descriptions (that's
what the -b and -V options of gcc are for).  I consider this as having
multiple backends.

That's not what I meant, yes, of course there are multiple backends at
the object level, but not at the source level. If you look back in this
thread, you will see that this is the critical issue. If you have a
technology where each backend is a completely different source program,
separately written (such technoologies are pretty common, most Ada 83
compiler technologies were like this), then the point is that the impact
of anything that affects the backend is greatly multiplied, and that is
why during the design, we were very cautious about changes that affect
the backend.

Most Ada technologies have a single front end for all targets (though
Ronald Cole would presumably call these multiple front ends too, because
there are certanly separate object versions), but again the important
thing is that there is only one source program. Thus changes to the front
end are potentially less troublesome, since the change only has to be made
once.

But for technologies like GCC, where there is only one source program for
both front end and backend (though in both cases multiple executables),
this distinction is not significant.