Re: Pascal front-end integration

[Frank Heckenbach <frank at g-n-u dot de>]

Waldek Hebisch wrote:

> > > 3) AFAIU dropping support for multiple backends is considered as a
> > > pre-condition to inclusion of GPC into GCC. GPC release wold be
> > > part of GCC release. People trying GPC snapshots would automatically
> > > get backend snapshot. I am affraid that for Pascal that means
> > > 6-8 months extra delay between including a feature in GPC and first
> > > bug reports (and consequently more effort for bug fixing).
> > 
> > The way to avoid this is for front ends to have internal datastructures 
> > decoupled from those of the rest of GCC and to have a small piece of code 
> > that does the conversion (like the Ada front end's gigi), then just 
> > maintain multiple versions of that small piece of code.  This seems to 
> > work well for Ada.
> 
> GPC uses backend data structure when possible. I see no reason to
> duplicate backend functionality (Ada front is written in Ada, so they
> _had to_ duplicate a lot of infrastructure).

I see. That makes a difference I didn't know about. So what's
practical for Add might not be for us. (Unless we'd rewrite gpc in
Pascal. But that's a huge effort I don't really want to think about,
with small benefits.)

> We can hide (and are doing
> that now) most differences in macros.
>
> But there are few tricky questions: I old backends want us to call a
> function is it OK to always call a wrapper (empty for new backend)?
> 
> Or an actual sample (the most nasty case I have found):
> 
>     case FLOAT_EXPR:
> #ifndef GCC_3_4
>     case FFS_EXPR:
> #endif
> 
> here we have moderatly sized switch and moving the case constant
> to backend dependent part would move the whole switch, hence the
> function containing the switch. Is it acceptable to have something
> like:
> 
>    case FLOAT_EXPR:
>    CASE_FFS_EXPR
> 
> with `CASE_FFS_EXPR' expanding to nothing for new backend.

BTW, I suppose we can just remove this case as we don't use FFS_EXPR
anyway. (This code was originally copied from the C frontend,
without checking whether we need it all.)

But the general question remains, as there are probably other
similar cases.

Frank

-- 
Frank Heckenbach, frank@g-n-u.de
http://fjf.gnu.de/
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