[m-dev.] diff: pragma c_code fix

[Fergus Henderson]

On 10-Nov-2000, Tyson Dowd <trd at cs.mu.OZ.AU> wrote:
> On 09-Nov-2000, Peter Ross <peter.ross at miscrit.be> wrote:
> > mercury/compiler/llds_out.m:
> >     Output any `pragma c_code' first for the LLDS backend.  This is
> >     because variables may be defined in a `pragma c_code' and we want
> >     the definition to appear before any use of the variable.  Also
> >     output the `pragma c_code' fragments in the same order they appear
> >     in the source file, as this is the more intuitive behaviour.
> 
> I don't think this is the right approach to take.  In fact, I think this
> is broken.

I agree.

> If you want to declare variables in the c_code that can be referenced
> from any place in the module, use pragma c_header_code, and put an
> extern declaration in for the variable.  Declarations should go in the
> c_header code, definitions in c_code.  (Perhaps the documentation should
> be clearer on this issue?).
> 
> Then it doesn't matter *where* you put the actual definition of the
> variable.
> 
> That way you can use --split-c-files and even if every procedure is put
> in a separate file, they can all see the c_header_code, and know there
> will be a variable defined somewhere to link to.
> 
> Your change will just hide this problem -- the code will work fine when
> in a single file but cannot be split into separate files without
> breaking.

Right.  Note that the causes problems for `--intermodule-optimization'
as well as for `--split-c-files', so it is something that we should
not ignore.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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