[m-rev.] diff: Delete unused imports.

[Peter Wang]

On Wed, 30 Mar 2022 10:01:12 +1100 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> 
> 
> On Wed, 30 Mar 2022 06:07:17 +1100 (AEDT), "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> > Indeed there was. The attached diff, which I am asking you to review,
> > fixes two of them. I haven't had time yet to test whether it fixes the issue
> > you reported, or whether that is a separate bug. Though it could also be
> > a known limitation rather than a bug, for anyone who cares about
> > the distinction :-)
> 
> Actually, the reason why the import of vartypes was flagged as unused
> with --intermod-opt was a known limitation that we discussed in october:
> the absence of a record of which modules expanded type equivalences
> came from. Here is the diff from the HLDS dump of the generate_generic_call predicate
> in call_gen.m without and with --intermod-opt:
> 
> --- NO_IMO      2022-03-30 09:34:24.727602291 +1100
> +++ IMO 2022-03-30 09:35:34.267873128 +1100
> @@ -33,7 +33,7 @@
>  % OutputArg_34 (number 34): term.var(parse_tree.prog_data.prog_var_type)
>  % ModuleInfo_35 (number 35): hlds.hlds_module.module_info
>  % ProcInfo_36 (number 36): hlds.hlds_pred.proc_info
> -% VarTypes_37 (number 37): hlds.vartypes.vartypes
> +% VarTypes_37 (number 37): tree234.tree234(term.var(parse_tree.prog_data.prog_var_type), parse_tree.prog_data.mer_type)
>  % Rval_38 (number 38): backend_libs.builtin_ops.simple_expr(term.var(parse_tree.prog_data.prog_var_type))
>  % STATE_VARIABLE_CI_0_39 (number 39): ll_backend.code_info.code_info
>  % STATE_VARIABLE_CI_40 (number 40): ll_backend.code_info.code_info
> 
> It just so happened that the type of the VarTypes variable was the
> only reference to the vartypes module in call_gen.m. With intermodule optimization,
> the compiler read in hlds.vartypes.opt, found the definition of the
> "vartypes" type, which is an equivalence, expanded it, and then
> promptly forgot that it expanded it :-(

Do you mean that call_gen.m _should_ import hlds.vartypes because it
contains a call to proc_info_get_vartypes, and one of the arguments
of that call has a type defined in hlds.vartypes?

So far, by my understanding, a variable merely having a certain type
would not be considered a "use" of that type.

> That discussion on oct 8 was about a description of the problem I added
> as a comment on an import in hlds_out_module.m, which exhibits
> the same problem. Would people be ok with me fixing this problem
> using the first approach outlined in that comment? The discussion
> ended in october without a decision on that.

It seems fine.

(I had trouble finding the discussion; the date was actually 2021-08-10,
the thread subject: for post-commit review: "unused" eqv types)

Peter