[m-rev.] for review: avoid passing type infos to C code

[Fergus Henderson]

On 09-Jul-2001, David Jeffery <dgj at cs.mu.OZ.AU> wrote:
> mercury/compiler/polymorphism.m:
> 	Do not pass a type-info to C code that does not use the variable. 
> 	To check if the C code uses the variable, we simply check for the
> 	occurence of the variable name in the string that represents the C 
> 	code. This is potentially unsafe if the user decides to do something
> 	horrible with the preprocessor, but I don't think this needs to be
> 	specially documented --- AFAIK there is no user-visible documentation
> 	about passing type-infos to and from C anyway.

That change looks OK.  I think it's an improvement on the current status
quo, so I'd be happy for you to commit it as is.  But I do have some
suggestions for improvments.

Shouldn't you do the same thing for the typeclass_info variables,
as well as for the type_info variables?

Also, I'd prefer it if the code which checks whether the foreign code
references the variable was put in a separate sub-routine.
As you say, there might possibly be some ramifications for other
languages, so ideally the foreign_language would be passed in
as a parameter to this routine, so that it can easily be changed
to handle different languages differently if need be.

P.S.
The routines that you're modifying are misleadingly named;
they're called *c_code* but actually they handle foreign procs,
whatever the language.  We should fix that... but as a separate change.

-- 
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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