[m-rev.] for review: implement solutions on the IL backend

[Fergus Henderson]

On 14-Jul-2001, Peter Ross <peter.ross at miscrit.be> wrote:
> Get solutions working on the IL backend.
> 
> compiler/mlds_to_il.m:
>     Workaround a bug where private classes aren't accessible from
>     classes in the same assembly when that assembly is created by
>     al.exe.  The workaround is to make the class public.  The only
>     assembly which is created by al.exe currently is the mercury std
>     library.

Fine.

> library/std_util.m:
>     Implement the MC++ code required for builtin__aggregate to work.

Fine.

Feel free to commit those two separately if you want.

> compiler/ml_code_gen.m:
>     Avoid generating casts and assignments from MR_Box to MR_Word as
>     these operations aren't type-safe on the IL backend.

What do you mean by "aren't type-safe"?
A little more explanation here might help.

> Index: compiler/ml_code_gen.m
> +ml_gen_pragma_c_decl(ml_c_arg(_Var, MaybeNameAndMode, Type), Decl) -->
> +	=(MLDSGenInfo),
> +	{ ml_gen_info_get_module_info(MLDSGenInfo, ModuleInfo) },
> +	{ module_info_globals(ModuleInfo, Globals) },
> +	{ globals__get_target(Globals, Target) },
> +	{
>  		MaybeNameAndMode = yes(ArgName - _Mode),
>  		\+ var_is_singleton(ArgName)
>  	->
> -		export__type_to_type_string(Type, TypeString),
> +		( 
> +			type_util__var(Type, _),
> +			Target = il
> +		->
> +			TypeString = "MR_Box"
> +		;
> +			export__type_to_type_string(Type, TypeString)
> +		),

I think "Target = il" is not the right test here, or at least not the best test.
This is really a property of the foreign language interface, rather than of
the target language, so you should be switching on
`Lang = managedcplusplus' rather than `Target = il',
where `Lang' is obtained via `foreign_language(Attributes, Lang)'
(you'll need to pass it down to ml_gen_pragma_c_decl).

This difference between the C interface and the MC++ interface really
ought to be documented.  Unfortunately the MC++ foreign code interface
is not documented at all, so for now I just suggest you put something
commented out (with @c) in doc/reference_manual.texi, e.g. see patch below.

Also, this test should be done in all of the calls to
export__type_to_type_string from this file.  (Make a new predicate to
abstract the common code.)  It might even be better in the long run to
do this inside export__type_to_type_string itself (i.e. to make the
foreign_language a parameter to that routine), but that can probably
wait for another day.

> @@ -2647,7 +2661,12 @@
>  			% a cast is for polymorphic types, which are
>  			% `Word' in the C interface but `MR_Box' in the
>  			% MLDS back-end.
> -			( type_util__var(OrigType, _) ->
> +			% Except for --grade ilc, where polymorphic types
> +			% are MR_Box.
> +			( 
> +				type_util__var(OrigType, _),
> +				Target \= il
> +			->

Likewise here you should be testing Lang \= managed_cplusplus.
Also the comment is wrong when it talks about `--grade ilc' --
that's not the only grade which has Target = il.

-- 
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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