[m-rev.] for review: fix problems with --split-c-files

[Fergus Henderson]

On 08-Aug-2002, Zoltan Somogyi <zs at cs.mu.OZ.AU> wrote:
> On 08-Aug-2002, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> > Why not just qualify the names of the conflicting symbols with the module
> > name?
> 
> That was the approach I started with.
> 
> One problem with it is that the straightforward way of implementing it
> required adding the module name as a new argument to a very large number
> of predicates; pretty much everything in llds_out, and many in other modules
> too.
> 
> I then got around this by adding the module name to the globals in the I/O
> state. This field had to be updated when the compiler started compiling
> a new module, but that could done.
> 
> Then I discovered the problem that made the approach untenable, which is that
> module qualifying the names of the conflicting symbols doesn't actually solve
> the problem, because you get conflicts with different .c files GENERATED FROM
> THE SAME MERCURY MODULE defining the same symbol.
> 
> The problem is that --split-c-files splits up the list of data structures,
> but a single comp_gen_c_data item can now expand to multiple C global data
> definitions. For example, --split-c-files puts the definitions of the
> type_ctor_infos of ra_list/1 and ra_list_bintree/1 in bt_array.m in different
> C source files, but both of those will include a pseudotypeinfo representing
> ra_list_bintree(T), since both those type constructors have a function symbol
> argument with that type. Since we construct the name of the C global containing
> a pseudotypeinfo's representation from the value of the pseudotypeinfo, this
> guarantees a name collision. The only way to avoid the name collision causing
> a link failure is to make the globals involved static.

Hmm.  Perhaps changing the llds__comp_gen_c_data type so that it
corresponded to more than one C definition was a mistake.

Anyway, I guess --split-c-files is not so important, especially since the
latest versions of the GNU C compiler now supports -ffunction-sections,
which achieves the same effect, on some platforms.  So I guess this
change is OK for now.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  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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