To make sure certain symbol names translate into globally unique target symbols.

§1. Pipeline stage. 

void DetectIndirectCalls::create_pipeline_stage(void) {
    CodeGen::Stage::new(I"detect-indirect-calls", DetectIndirectCalls::run_pipeline_stage, NO_STAGE_ARG, FALSE);
}

int DetectIndirectCalls::run_pipeline_stage(pipeline_step *step) {
    InterTree::traverse(step->repository, DetectIndirectCalls::visitor, NULL, NULL, PACKAGE_IST);
    return TRUE;
}

void DetectIndirectCalls::visitor(inter_tree *I, inter_tree_node *P, void *state) {
    inter_package *pack = Inter::Package::defined_by_frame(P);
    if (Inter::Packages::is_codelike(pack)) {
        inter_tree_node *D = Inter::Packages::definition(pack);
        DetectIndirectCalls::traverse_code_tree(D);
    }
}

§2. iden[0] and iden[1] hold left and right identity elements for these binary operations: 

void DetectIndirectCalls::traverse_code_tree(inter_tree_node *P) {
    PROTECTED_LOOP_THROUGH_INTER_CHILDREN(F, P) {
        DetectIndirectCalls::traverse_code_tree(F);
    }
    PROTECTED_LOOP_THROUGH_INTER_CHILDREN(F, P) {
        if ((F->W.data[ID_IFLD] == INV_IST) &&
            (F->W.data[METHOD_INV_IFLD] == INVOKED_ROUTINE)) {
            inter_symbol *routine = InterSymbolsTables::symbol_from_frame_data(F, INVOKEE_INV_IFLD);
            if (routine == NULL) internal_error("bad routine");
            inter_tree_node *D = routine->definition;
            if ((D) && (D->W.data[ID_IFLD] == VARIABLE_IST)) {
                inter_tree *I = F->tree;
                F->W.data[METHOD_INV_IFLD] = INVOKED_PRIMITIVE;
                int arity = 0;
                PROTECTED_LOOP_THROUGH_INTER_CHILDREN(X, F) arity++;
                inter_ti bip = Primitives::indirect_interp(arity);
                inter_symbol *prim_symb = Primitives::get(I, bip);
                F->W.data[INVOKEE_INV_IFLD] = InterSymbolsTables::id_from_symbol_F(F, NULL, prim_symb);
                inter_bookmark IBM = Inter::Bookmarks::first_child_of_this_node(I, F);
                inter_ti val1 = 0, val2 = 0;
                Inter::Symbols::to_data(Inter::Bookmarks::tree(&IBM), Inter::Bookmarks::package(&IBM), routine, &val1, &val2);
                Inter::Val::new(&IBM, unchecked_kind_symbol, (int) F->W.data[LEVEL_IFLD] + 1, val1, val2, NULL);
            }
        }
    }
}