To remove (for example) functions which we can prove will never be called or referred to as values.

• §1. Pipeline stage
• §2. Preservation
• §4. Destruction

§1. Pipeline stage. Experience shows that around 20 per cent of the code generated by Inform 7 consists of functions which are never in fact needed. Probably diligent book-keeping at the generation stage could reduce some of that, but other redundancies arise because of functions assimilated from the template, and we don't have much control over that. This stage removes everything that isn't used.

void CodeGen::Eliminate::create_pipeline_stage?Usage of CodeGen::Eliminate::create_pipeline_stage:
Stages - §2(void) {
    CodeGen::Stage::new(I"eliminate-redundant-code",
        CodeGen::Eliminate::run_pipeline_stage, NO_STAGE_ARG, FALSE);
}

int CodeGen::Eliminate::run_pipeline_stage(pipeline_step *step) {
    inter_tree *I = step->repository;
    InterTree::traverse(I, CodeGen::Eliminate::package_preserver, NULL, NULL, PACKAGE_IST);
    InterTree::traverse(I, CodeGen::Eliminate::package_destroyer, NULL, NULL, PACKAGE_IST);
    return TRUE;
}

§2. Preservation. We operate on a presumption of guilt: any package which we cannot prove is needed will be deleted. Main_fn is clearly needed, since it is where execution will begin. A handful of other functions, not called yet but needed in the final compilation stage (and which replace stubs which would otherwise be provided by the veneer), must also be included. Command packages contain grammar for command verbs typed at run-time: these affect an essential data structure (i.e., the parser grammar) implicitly, and so we can't detect the dependency here. So we require all command packages to be included.

void CodeGen::Eliminate::package_preserver?Usage of CodeGen::Eliminate::package_preserver:
§1(inter_tree *I, inter_tree_node *P, void *state) {
    inter_package *pack = Inter::Package::defined_by_frame(P);
    inter_symbol *ptype = Inter::Packages::type(pack);
    if (ptype == command_ptype_symbol)
        CodeGen::Eliminate::require(pack, NULL, I"it's a _command package");
    else if (ptype == property_ptype_symbol) {
        text_stream *N = Inter::Packages::name(pack);
        if (Str::eq(N, I"workflag_prop"))
            CodeGen::Eliminate::require(pack, NULL, I"it's workflag");
        if (Str::eq(N, I"pluralname_prop"))
            CodeGen::Eliminate::require(pack, NULL, I"it's pluralname");
        if (Str::eq(N, I"ambigpluralname_prop"))
            CodeGen::Eliminate::require(pack, NULL, I"it's ambigpluralname");
        if (Str::eq(N, I"proper_prop"))
            CodeGen::Eliminate::require(pack, NULL, I"it's proper");
    }
    else if (ptype == function_ptype_symbol) {
        text_stream *N = Inter::Packages::name(pack);
        if (Str::eq(N, I"Main_fn"))
            CodeGen::Eliminate::require(pack, NULL, I"it's Main");
    }
}

§3. Once you need a package, what else do you need?

void CodeGen::Eliminate::require?Usage of CodeGen::Eliminate::require:
§2, §3.1, §3.2, §3.3(inter_package *pack, inter_package *witness, text_stream *reason) {
    if ((pack->package_flags) & USED_PACKAGE_FLAG) return;
    pack->package_flags |= USED_PACKAGE_FLAG;
    if (witness) {
        LOGIF(ELIMINATION, "Need $6 because of $6 (because %S)\n", pack, witness, reason);
    } else {
        LOGIF(ELIMINATION, "Need $6 (because %S)\n", pack, reason);
    }
    If you need a package, you need its parent3.1;
    If you need a package, you need its external dependencies3.2;
    If you need a function or action, you need its internal resources3.3;
}

§3.1. If you need a package, you need its parent3.1 =

    inter_package *parent = Inter::Packages::parent(pack);
    if (parent) CodeGen::Eliminate::require(parent, pack, I"it's the parent");

• This code is used in §3.

§3.2. If you need a package, you need its external dependencies3.2 =

    inter_symbols_table *tab = Inter::Packages::scope(pack);
    for (int i=0; i<tab->size; i++) {
        inter_symbol *symb = tab->symbol_array[i];
        if ((symb) && (symb->equated_to)) {
            inter_symbol *to = symb;
            while ((to) && (to->equated_to)) to = to->equated_to;
            inter_package *needed = to->owning_table->owning_package;
            CodeGen::Eliminate::require(needed, pack, I"it's an external symbol");
        }
    }

• This code is used in §3.

§3.3. If you need a function or action, you need its internal resources3.3 =

    text_stream *rationale = NULL;
    inter_symbol *ptype = Inter::Packages::type(pack);
    if (ptype == function_ptype_symbol) rationale = I"it's a _function block";
    if (ptype == action_ptype_symbol) rationale = I"it's an _action subpackage";
    if (rationale) {
        inter_tree_node *D = Inter::Packages::definition(pack);
        LOOP_THROUGH_INTER_CHILDREN(C, D) {
            if (C->W.data[ID_IFLD] == PACKAGE_IST) {
                inter_package *P = Inter::Package::defined_by_frame(C);
                CodeGen::Eliminate::require(P, pack, rationale);
            }
        }
    }

• This code is used in §3.

§4. Destruction. Whatever has not been preserved, is now destroyed.

void CodeGen::Eliminate::package_destroyer?Usage of CodeGen::Eliminate::package_destroyer:
§1(inter_tree *I, inter_tree_node *P, void *state) {
    inter_package *pack = Inter::Package::defined_by_frame(P);
    if ((pack) && ((pack->package_flags & USED_PACKAGE_FLAG) == 0)) {
        LOGIF(ELIMINATION, "Striking unused package $6 (type %S)\n",
            pack, Inter::Packages::type(pack)->symbol_name);
        InterTree::remove_node(P);
    }
}