path: root/gcc/elna-generic.cc

/* Visitor generating a GENERIC tree.
   Copyright (C) 2025 Free Software Foundation, Inc.

GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include <array>

#include "elna/gcc/elna-generic.h"
#include "elna/gcc/elna-diagnostic.h"
#include "elna/gcc/elna1.h"
#include "elna/gcc/elna-builtins.h"

#include "ggc.h"
#include "function.h"
#include "cgraph.h"
#include "gimplify.h"
#include "stringpool.h"
#include "diagnostic.h"
#include "realmpfr.h"
#include "varasm.h"
#include "fold-const.h"
#include "langhooks.h"

namespace elna::gcc
{
    generic_visitor::generic_visitor(std::shared_ptr<symbol_table> symbol_table, elna::frontend::symbol_bag bag)
        : bag(bag), symbols(symbol_table)
    {
    }

    void generic_visitor::build_procedure_call(location_t call_location,
            tree procedure_address, const std::vector<frontend::expression *>& arguments)
    {
        vec<tree, va_gc> *argument_trees = nullptr;
        tree symbol_type = TREE_TYPE(TREE_TYPE(procedure_address));

        tree current_parameter = TYPE_ARG_TYPES(symbol_type);

        vec_alloc(argument_trees, arguments.size());
        for (frontend::expression *const argument : arguments)
        {
            location_t argument_location = get_location(&argument->position());
            if (VOID_TYPE_P(TREE_VALUE(current_parameter)))
            {
                error_at(argument_location, "Too many arguments, expected %i, got %lu",
                        list_length(TYPE_ARG_TYPES(symbol_type)) - 1, arguments.size());
                this->current_expression = error_mark_node;
                break;
            }
            argument->accept(this);
            this->current_expression = prepare_rvalue(this->current_expression);
            if (!is_assignable_from(TREE_VALUE(current_parameter), this->current_expression))
            {
                error_at(argument_location,
                        "Cannot assign value of type '%s' to variable of type '%s'",
                        print_type(TREE_TYPE(this->current_expression)).c_str(),
                        print_type(TREE_VALUE(current_parameter)).c_str());
                this->current_expression = error_mark_node;
            }
            current_parameter = TREE_CHAIN(current_parameter);
            argument_trees->quick_push(this->current_expression);
        }
        tree stmt = fold_build_call_array_loc(call_location, TREE_TYPE(symbol_type),
                procedure_address, vec_safe_length(argument_trees), vec_safe_address(argument_trees));

        if (!VOID_TYPE_P(TREE_VALUE(current_parameter)))
        {
                error_at(call_location, "Too few arguments, expected %i, got %lu",
                        list_length(TYPE_ARG_TYPES(symbol_type)) - 1, arguments.size());
                this->current_expression = error_mark_node;
        }
        else
        {
            this->current_expression = stmt;
        }
    }

    void generic_visitor::build_record_call(location_t call_location,
            tree symbol, const std::vector<frontend::expression *>& arguments)
    {
        vec<constructor_elt, va_gc> *tree_arguments = nullptr;
        tree record_fields = TYPE_FIELDS(symbol);
        for (frontend::expression *const argument : arguments)
        {
            location_t argument_location = get_location(&argument->position());

            if (is_void_type(record_fields))
            {
                error_at(argument_location, "Too many arguments, expected %i, got %lu",
                        list_length(TYPE_FIELDS(symbol)), arguments.size());
                this->current_expression = error_mark_node;
                break;
            }
            argument->accept(this);
            tree unqualified_field = get_qualified_type(TREE_TYPE(record_fields), TYPE_UNQUALIFIED);
            if (!is_assignable_from(unqualified_field, this->current_expression))
            {
                error_at(argument_location,
                        "Cannot assign value of type '%s' to variable of type '%s'",
                        print_type(TREE_TYPE(this->current_expression)).c_str(),
                        print_type(TREE_TYPE(record_fields)).c_str());
                this->current_expression = error_mark_node;
            }
            CONSTRUCTOR_APPEND_ELT(tree_arguments, record_fields, this->current_expression);
            record_fields = TREE_CHAIN(record_fields);
        }
        if (!is_void_type(record_fields))
        {
                error_at(call_location, "Too few arguments, expected %i, got %lu",
                        list_length(TYPE_FIELDS(symbol)), arguments.size());
                this->current_expression = error_mark_node;
        }
        else
        {
            this->current_expression = build_constructor(symbol, tree_arguments);
        }
    }

    void generic_visitor::build_assert_builtin(location_t call_location,
            const std::vector<frontend::expression *>& arguments)
    {
        if (arguments.size() != 1)
        {
            error_at(call_location, "assert expects exactly one boolean argument, got %lu", arguments.size());
            this->current_expression = error_mark_node;
        }
        else
        {
            arguments.at(0)->accept(this);
            tree argument_type = TREE_TYPE(this->current_expression);

            if (argument_type != elna_bool_type_node)
            {
                error_at(call_location, "assert expects exactly one boolean argument, got %s",
                        print_type(argument_type).c_str());
                this->current_expression = error_mark_node;
            }
            tree constant_expression = extract_constant(this->current_expression);
            if (constant_expression == boolean_false_node)
            {
                this->current_expression = call_built_in(call_location, "__builtin_unreachable", void_type_node);
            }
            else if (constant_expression != boolean_true_node)
            {
                tree assert_expression = call_built_in(call_location, "__builtin_trap", void_type_node);
                this->current_expression = build3(COND_EXPR, void_type_node, this->current_expression,
                        NULL_TREE, assert_expression);
            }
            else
            {
                this->current_expression = NULL_TREE;
            }
        }
    }

    bool generic_visitor::build_builtin_procedures(frontend::procedure_call *call)
    {
        location_t call_location = get_location(&call->position());

        if (frontend::variable_expression *named_call = call->callable().is_variable())
        {
            if (named_call->name == "assert")
            {
                build_assert_builtin(call_location, call->arguments);
                return true;
            }
        }
        return false;
    }

    void generic_visitor::visit(frontend::procedure_call *call)
    {
        if (build_builtin_procedures(call))
        {
            return;
        }
        location_t call_location = get_location(&call->position());
        call->callable().accept(this);

        tree expression_type = TYPE_P(this->current_expression)
            ? this->current_expression
            : TREE_TYPE(this->current_expression);

        if (TREE_CODE(expression_type) == RECORD_TYPE)
        {
            build_record_call(call_location, expression_type, call->arguments);
        }
        else if (TREE_CODE(expression_type) == FUNCTION_TYPE)
        {
            this->current_expression = build1(ADDR_EXPR,
                    build_global_pointer_type(expression_type), this->current_expression);
            build_procedure_call(call_location, this->current_expression, call->arguments);
        }
        else if (POINTER_TYPE_P(expression_type) && TREE_CODE(TREE_TYPE(expression_type)) == FUNCTION_TYPE)
        {
            build_procedure_call(call_location, this->current_expression, call->arguments);
        }
        else
        {
            error_at(call_location, "'%s' cannot be called, it is neither a procedure nor record",
                    print_type(expression_type).c_str());
            this->current_expression = error_mark_node;
        }
    }

    void generic_visitor::visit(frontend::cast_expression *expression)
    {
        tree cast_target = get_inner_alias(expression->expression_type, this->symbols->scope());

        expression->value().accept(this);
        tree cast_source = TREE_TYPE(this->current_expression);

        if (is_castable_type(cast_target) && (is_castable_type(cast_source)))
        {
            this->current_expression = build1_loc(get_location(&expression->position()), CONVERT_EXPR,
                    cast_target, this->current_expression);
        }
        else
        {
            error_at(get_location(&expression->position()), "Type '%s' cannot be converted to '%s'",
                    print_type(cast_source).c_str(), print_type(cast_target).c_str());
            this->current_expression = error_mark_node;
        }
    }

    void generic_visitor::visit(frontend::program *program)
    {
        visit(static_cast<frontend::unit *>(program));

        tree declaration_type = build_function_type_list(elna_int_type_node,
                elna_int_type_node,
                build_global_pointer_type(build_global_pointer_type(elna_char_type_node)),
                NULL_TREE);
        tree fndecl = build_fn_decl("main", declaration_type);

        tree resdecl = build_decl(UNKNOWN_LOCATION, RESULT_DECL, NULL_TREE, integer_type_node);
        DECL_CONTEXT(resdecl) = fndecl;
        DECL_RESULT(fndecl) = resdecl;

        push_struct_function(fndecl, false);
        DECL_STRUCT_FUNCTION(fndecl)->language = ggc_cleared_alloc<language_function>();

        enter_scope();

        tree parameter_type = TYPE_ARG_TYPES(declaration_type);
        for (const char *argument_name : std::array<const char *, 2>{ "count", "parameters" })
        {
            tree declaration_tree = build_decl(UNKNOWN_LOCATION, PARM_DECL,
                    get_identifier(argument_name), TREE_VALUE(parameter_type));
            DECL_CONTEXT(declaration_tree) = fndecl;
            DECL_ARG_TYPE(declaration_tree) = TREE_VALUE(parameter_type);

            this->symbols->enter(argument_name, declaration_tree);
            DECL_ARGUMENTS(fndecl) = chainon(DECL_ARGUMENTS(fndecl), declaration_tree);
            parameter_type = TREE_CHAIN(parameter_type);
        }
        visit_statements(program->body);
        tree set_result = build2(INIT_EXPR, void_type_node, DECL_RESULT(fndecl),
                build_int_cst_type(integer_type_node, 0));
        tree return_stmt = build1(RETURN_EXPR, void_type_node, set_result);
        append_statement(return_stmt);
        tree mapping = leave_scope();

        BLOCK_SUPERCONTEXT(BIND_EXPR_BLOCK(mapping)) = fndecl;
        DECL_INITIAL(fndecl) = BIND_EXPR_BLOCK(mapping);
        DECL_SAVED_TREE(fndecl) = mapping;

        DECL_EXTERNAL(fndecl) = 0;
        DECL_PRESERVE_P(fndecl) = 1;

        pop_cfun();
        gimplify_function_tree(fndecl);
        cgraph_node::finalize_function(fndecl, true);
    }

    void generic_visitor::visit(frontend::unit *unit)
    {
        for (frontend::import_declaration *const declaration : unit->imports)
        {
            declaration->accept(this);
        }
        for (frontend::constant_declaration *const constant : unit->constants)
        {
            constant->accept(this);
        }
        for (frontend::variable_declaration *const variable : unit->variables)
        {
            variable->accept(this);
        }
        for (frontend::procedure_declaration *const procedure : unit->procedures)
        {
            procedure->accept(this);
        }
    }

    void generic_visitor::visit(frontend::procedure_declaration *definition)
    {
        tree fndecl = this->symbols->lookup(definition->identifier.name);

        if (!definition->body.has_value())
        {
            return;
        }
        push_struct_function(fndecl, false);
        DECL_STRUCT_FUNCTION(fndecl)->language = ggc_cleared_alloc<language_function>();

        enter_scope();
        this->bag.enter(this->bag.lookup(definition->identifier.name)->is_procedure()->scope);

        tree argument_chain = DECL_ARGUMENTS(fndecl);
        for (; argument_chain != NULL_TREE; argument_chain = TREE_CHAIN(argument_chain))
        {
            this->symbols->enter(IDENTIFIER_POINTER(DECL_NAME(argument_chain)), argument_chain);
        }
        for (frontend::constant_declaration *const constant : definition->body.value().constants())
        {
            constant->accept(this);
        }
        for (frontend::variable_declaration *const variable : definition->body.value().variables())
        {
            variable->accept(this);
        }
        visit_statements(definition->body.value().body());

        tree mapping = leave_scope();
        this->bag.leave();

        BLOCK_SUPERCONTEXT(BIND_EXPR_BLOCK(mapping)) = fndecl;
        DECL_INITIAL(fndecl) = BIND_EXPR_BLOCK(mapping);
        DECL_SAVED_TREE(fndecl) = mapping;

        DECL_PRESERVE_P(fndecl) = 1;

        pop_cfun();
        gimplify_function_tree(fndecl);
        cgraph_node::finalize_function(fndecl, true);
    }

    void generic_visitor::enter_scope()
    {
        this->symbols = std::make_shared<symbol_table>(this->symbols);

        // Chain the binding levels.
        struct binding_level *new_level = ggc_cleared_alloc<binding_level>();
        new_level->level_chain = f_binding_level;
        new_level->statement_list = alloc_stmt_list();
        f_binding_level = new_level;
    }

    tree generic_visitor::leave_scope()
    {
        // Variables are only defined in the top function scope.
        tree variables = f_binding_level->level_chain == nullptr ? f_names : NULL_TREE;
        tree new_block = build_block(variables, f_binding_level->blocks, NULL_TREE, NULL_TREE);

        for (tree it = f_binding_level->blocks; it != NULL_TREE; it = BLOCK_CHAIN(it))
        {
            BLOCK_SUPERCONTEXT(it) = new_block;
        }
        tree bind_expr = build3(BIND_EXPR, void_type_node, variables, chain_defer(), new_block);
        this->symbols = this->symbols->scope();

        f_binding_level = f_binding_level->level_chain;

        if (f_binding_level != nullptr)
        {
            f_binding_level->blocks = chainon(f_binding_level->blocks, new_block);
        }
        return bind_expr;
    }

    void generic_visitor::visit(frontend::literal<std::int32_t> *literal)
    {
        this->current_expression = build_int_cst(elna_int_type_node, literal->value);
    }

    void generic_visitor::visit(frontend::literal<std::uint32_t> *literal)
    {
        this->current_expression = build_int_cstu(elna_word_type_node, literal->value);
    }

    void generic_visitor::visit(frontend::literal<double> *literal)
    {
        REAL_VALUE_TYPE real_value1;

        mpfr_t number;
        mpfr_init2(number, SIGNIFICAND_BITS);
        mpfr_set_d(number, literal->value, MPFR_RNDN);

        real_from_mpfr(&real_value1, number, double_type_node, MPFR_RNDN);

        this->current_expression = build_real(double_type_node, real_value1);

        mpfr_clear(number);
    }

    void generic_visitor::visit(frontend::literal<bool> *boolean)
    {
        this->current_expression = boolean->value ? boolean_true_node : boolean_false_node;
    }

    void generic_visitor::visit(frontend::literal<unsigned char> *character)
    {
        this->current_expression = build_int_cstu(elna_char_type_node, character->value);
    }

    void generic_visitor::visit(frontend::literal<nullptr_t> *)
    {
        this->current_expression = elna_pointer_nil_node;
    }

    void generic_visitor::visit(frontend::literal<std::string> *string)
    {
        tree index_constant = build_int_cstu(elna_word_type_node, string->value.size());
        tree string_type = build_array_type(elna_char_type_node, build_index_type(index_constant));

        tree string_literal = build_string(string->value.size(), string->value.c_str());
        TREE_TYPE(string_literal) = string_type;
        TREE_CONSTANT(string_literal) = 1;
        TREE_READONLY(string_literal) = 1;
        TREE_STATIC(string_literal) = 1;

        string_type = TREE_TYPE(elna_string_ptr_field_node);
        string_literal = build4(ARRAY_REF, elna_char_type_node,
                string_literal, integer_zero_node, NULL_TREE, NULL_TREE);
        string_literal = build1(ADDR_EXPR, string_type, string_literal);

        vec<constructor_elt, va_gc> *elms = nullptr;
        CONSTRUCTOR_APPEND_ELT(elms, elna_string_ptr_field_node, string_literal);
        CONSTRUCTOR_APPEND_ELT(elms, elna_string_length_field_node, index_constant);

        this->current_expression = build_constructor(elna_string_type_node, elms);
    }

    tree generic_visitor::build_arithmetic_operation(frontend::binary_expression *expression,
            tree_code operator_code, tree left, tree right)
    {
        return build_binary_operation(is_numeric_type(TREE_TYPE(left)),
                expression, operator_code, left, right, TREE_TYPE(left));
    }

    tree generic_visitor::build_comparison_operation(frontend::binary_expression *expression,
            tree_code operator_code, tree left, tree right)
    {
        return build_binary_operation(is_numeric_type(TREE_TYPE(left)) || POINTER_TYPE_P(TREE_TYPE(left)),
                expression, operator_code, left, right, elna_bool_type_node);
    }

    tree generic_visitor::build_bit_logic_operation(frontend::binary_expression *expression, tree left, tree right)
    {
        location_t expression_location = get_location(&expression->position());
        tree left_type = TREE_TYPE(left);
        tree right_type = TREE_TYPE(right);
        tree_code logical_code, bit_code;

        if (expression->operation() == frontend::binary_operator::conjunction)
        {
            bit_code = BIT_AND_EXPR;
            logical_code = TRUTH_ANDIF_EXPR;
        }
        else if (expression->operation() == frontend::binary_operator::disjunction)
        {
            bit_code = BIT_IOR_EXPR;
            logical_code = TRUTH_ORIF_EXPR;
        }
        else if (expression->operation() == frontend::binary_operator::exclusive_disjunction)
        {
            bit_code = BIT_XOR_EXPR;
            logical_code = TRUTH_XOR_EXPR;
        }
        else
        {
            gcc_unreachable();
        }
        if (left_type == elna_bool_type_node)
        {
            return build2_loc(expression_location, logical_code, elna_bool_type_node, left, right);
        }
        else if (is_integral_type(left_type))
        {
            return build2_loc(expression_location, bit_code, left_type, left, right);
        }
        else
        {
            error_at(expression_location, "Invalid operands of type '%s' and '%s' for operator %s",
                    print_type(left_type).c_str(), print_type(right_type).c_str(),
                    elna::frontend::print_binary_operator(expression->operation()));
            return error_mark_node;
        }
    }

    tree generic_visitor::build_equality_operation(frontend::binary_expression *expression, tree left, tree right)
    {
        location_t expression_location = get_location(&expression->position());
        tree_code equality_code, combination_code;

        if (expression->operation() == frontend::binary_operator::equals)
        {
            equality_code = EQ_EXPR;
            combination_code = TRUTH_ANDIF_EXPR;
        }
        else if (expression->operation() == frontend::binary_operator::not_equals)
        {
            equality_code = NE_EXPR;
            combination_code = TRUTH_ORIF_EXPR;
        }
        else
        {
            gcc_unreachable();
        }
        if (TREE_TYPE(left) == elna_string_type_node)
        {
            tree lhs_length = build3(COMPONENT_REF, TREE_TYPE(elna_string_length_field_node),
                    left, elna_string_length_field_node, NULL_TREE);
            tree lhs_ptr = build3(COMPONENT_REF, TREE_TYPE(elna_string_ptr_field_node),
                    left, elna_string_ptr_field_node, NULL_TREE);

            tree rhs_length = build3(COMPONENT_REF, TREE_TYPE(elna_string_length_field_node),
                    right, elna_string_length_field_node, NULL_TREE);
            tree rhs_ptr = build3(COMPONENT_REF, TREE_TYPE(elna_string_ptr_field_node),
                    right, elna_string_ptr_field_node, NULL_TREE);

            tree length_equality = build2(equality_code, elna_bool_type_node, lhs_length, rhs_length);
            tree memcmp_call = call_built_in(UNKNOWN_LOCATION, "__builtin_memcmp", integer_type_node,
                    lhs_ptr, rhs_ptr, lhs_length);
            tree equals_zero = build2(equality_code, elna_bool_type_node, memcmp_call, integer_zero_node);

            return build2(combination_code, elna_bool_type_node, length_equality, equals_zero);
        }
        else
        {
            return build2_loc(expression_location, equality_code, elna_bool_type_node, left, right);
        }
    }

    void generic_visitor::visit(frontend::binary_expression *expression)
    {
        expression->lhs().accept(this);
        tree left = this->current_expression;
        tree left_type = get_qualified_type(TREE_TYPE(left), TYPE_UNQUALIFIED);

        expression->rhs().accept(this);
        tree right = this->current_expression;
        tree right_type = get_qualified_type(TREE_TYPE(right), TYPE_UNQUALIFIED);

        location_t expression_location = get_location(&expression->position());

        if ((POINTER_TYPE_P(left_type) || POINTER_TYPE_P(right_type))
                && (expression->operation() == frontend::binary_operator::sum
                    || expression->operation() == frontend::binary_operator::subtraction))
        {
            this->current_expression = do_pointer_arithmetic(expression->operation(),
                    left, right, expression_location);
            if (this->current_expression == error_mark_node)
            {
                error_at(expression_location,
                        "invalid operation %s on a pointer and an integral type",
                        frontend::print_binary_operator(expression->operation()));
            }
            else if (TREE_TYPE(this->current_expression) == ssizetype)
            {
                this->current_expression = fold_convert(elna_int_type_node, this->current_expression);
            }
            return;
        }
        if (left_type != right_type
                && !are_compatible_pointers(left_type, right)
                && !are_compatible_pointers(right_type, left)
                && !(is_integral_type(left_type) && right_type == elna_word_type_node))
        {
            error_at(expression_location,
                    "invalid operands of type '%s' and '%s' for operator %s",
                    print_type(left_type).c_str(), print_type(right_type).c_str(),
                    frontend::print_binary_operator(expression->operation()));
            this->current_expression = error_mark_node;
            return;
        }
        switch (expression->operation())
        {
            case frontend::binary_operator::sum:
                this->current_expression = build_arithmetic_operation(expression, PLUS_EXPR, left, right);
                break;
            case frontend::binary_operator::subtraction:
                this->current_expression = build_arithmetic_operation(expression, MINUS_EXPR, left, right);
                break;
            case frontend::binary_operator::division:
                this->current_expression = build_arithmetic_operation(expression, TRUNC_DIV_EXPR, left, right);
                break;
            case frontend::binary_operator::remainder:
                this->current_expression = build_arithmetic_operation(expression, TRUNC_MOD_EXPR, left, right);
                break;
            case frontend::binary_operator::multiplication:
                this->current_expression = build_arithmetic_operation(expression, MULT_EXPR, left, right);
                break;
            case frontend::binary_operator::less:
                this->current_expression = build_comparison_operation(expression, LT_EXPR, left, right);
                break;
            case frontend::binary_operator::greater:
                this->current_expression = build_comparison_operation(expression, GT_EXPR, left, right);
                break;
            case frontend::binary_operator::less_equal:
                this->current_expression = build_comparison_operation(expression, LE_EXPR, left, right);
                break;
            case frontend::binary_operator::greater_equal:
                this->current_expression = build_comparison_operation(expression, GE_EXPR, left, right);
                break;
            case frontend::binary_operator::conjunction:
                this->current_expression = build_bit_logic_operation(expression, left, right);
                break;
            case frontend::binary_operator::disjunction:
                this->current_expression = build_bit_logic_operation(expression, left, right);
                break;
            case frontend::binary_operator::exclusive_disjunction:
                this->current_expression = build_bit_logic_operation(expression, left, right);
                break;
            case frontend::binary_operator::equals:
                this->current_expression = build_equality_operation(expression, left, right);
                break;
            case frontend::binary_operator::not_equals:
                this->current_expression = build_equality_operation(expression, left, right);
                break;
            case frontend::binary_operator::shift_left:
                this->current_expression = build_binary_operation(
                        is_numeric_type(left_type) && right_type == elna_word_type_node,
                        expression, LSHIFT_EXPR, left, right, left_type);
                break;
            case frontend::binary_operator::shift_right:
                this->current_expression = build_binary_operation(
                        is_numeric_type(left_type) && right_type == elna_word_type_node,
                        expression, RSHIFT_EXPR, left, right, left_type);
                break;
        }
    }

    void generic_visitor::visit(frontend::unary_expression *expression)
    {
        expression->operand().accept(this);
        location_t location = get_location(&expression->position());

        switch (expression->operation())
        {
            case frontend::unary_operator::reference:
                this->current_expression = prepare_rvalue(this->current_expression);
                TREE_ADDRESSABLE(this->current_expression) = 1;
                this->current_expression = build_fold_addr_expr_with_type_loc(location,
                        this->current_expression,
                        build_global_pointer_type(TREE_TYPE(this->current_expression)));
                TREE_NO_TRAMPOLINE(this->current_expression) = 1;
                break;
            case frontend::unary_operator::negation:
                if (TREE_TYPE(this->current_expression) == elna_bool_type_node)
                {
                    this->current_expression = build1_loc(location, TRUTH_NOT_EXPR,
                            boolean_type_node, this->current_expression);
                }
                else if (is_integral_type(TREE_TYPE(this->current_expression)))
                {
                    this->current_expression = build1_loc(location, BIT_NOT_EXPR,
                            TREE_TYPE(this->current_expression), this->current_expression);
                }
                else
                {
                    error_at(location, "type '%s' cannot be negated",
                            print_type(TREE_TYPE(this->current_expression)).c_str());
                    this->current_expression = error_mark_node;
                }
                break;
            case frontend::unary_operator::minus:
                if (is_integral_type(TREE_TYPE(this->current_expression)))
                {
                    this->current_expression = fold_build1(NEGATE_EXPR, TREE_TYPE(this->current_expression),
                            this->current_expression);
                }
                else
                {
                    error_at(location, "type '%s' cannot be negated",
                            print_type(TREE_TYPE(this->current_expression)).c_str());
                    this->current_expression = error_mark_node;
                }
        }
    }

    void generic_visitor::visit(frontend::constant_declaration *definition)
    {
        location_t definition_location = get_location(&definition->position());
        definition->body().accept(this);

        if (assert_constant(definition_location))
        {
            this->current_expression = fold_init(this->current_expression);
        }
        else
        {
            this->current_expression = NULL_TREE;
            return;
        }
        tree definition_tree = build_decl(definition_location, CONST_DECL,
                get_identifier(definition->identifier.name.c_str()), TREE_TYPE(this->current_expression));
        auto result = this->symbols->enter(definition->identifier.name, definition_tree);

        if (result)
        {
            DECL_INITIAL(definition_tree) = this->current_expression;
            TREE_CONSTANT(definition_tree) = 1;
            TREE_READONLY(definition_tree) = 1;
            TREE_PUBLIC(definition_tree) = definition->identifier.exported;

            if (!lang_hooks.decls.global_bindings_p())
            {
                auto declaration_statement = build1_loc(definition_location, DECL_EXPR,
                        void_type_node, definition_tree);
                append_statement(declaration_statement);
            }
        }
        else
        {
            error_at(definition_location, "Variable '%s' already declared in this scope",
                    definition->identifier.name.c_str());
        }
        this->current_expression = NULL_TREE;
    }

    void generic_visitor::visit(frontend::variable_declaration *declaration)
    {
        for (const auto& variable_identifier : declaration->identifiers)
        {
            location_t declaration_location = get_location(&declaration->position());
            tree declaration_tree = this->symbols->lookup(variable_identifier.name);

            if (declaration_tree == NULL_TREE)
            {
                auto variable_symbol = this->bag.lookup(variable_identifier.name)->is_variable();

                declaration_tree = declare_variable(variable_identifier.name, *variable_symbol, this->symbols);
            }
            // Set initializer if given.
            if (declaration->body != nullptr)
            {
                declaration->body->accept(this);
                if (is_assignable_from(TREE_TYPE(declaration_tree), this->current_expression))
                {
                    DECL_INITIAL(declaration_tree) = this->current_expression;
                }
                else
                {
                    error_at(declaration_location, "Cannot initialize variable of type '%s' with a value of type '%s'",
                            print_type(TREE_TYPE(declaration_tree)).c_str(),
                            print_type(TREE_TYPE(this->current_expression)).c_str());
                }
            }
            else if (!declaration->is_extern && POINTER_TYPE_P(TREE_TYPE(declaration_tree)))
            {
                DECL_INITIAL(declaration_tree) = elna_pointer_nil_node;
            }
            this->current_expression = NULL_TREE;

            if (lang_hooks.decls.global_bindings_p())
            {
                TREE_STATIC(declaration_tree) = !variable_identifier.exported && !declaration->is_extern;
                varpool_node::get_create(declaration_tree);
                varpool_node::finalize_decl(declaration_tree);
            }
            else
            {
                DECL_CONTEXT(declaration_tree) = current_function_decl;
                f_names = chainon(f_names, declaration_tree);

                auto declaration_statement = build1_loc(declaration_location, DECL_EXPR,
                        void_type_node, declaration_tree);
                append_statement(declaration_statement);
            }
        }
    }

    void generic_visitor::visit(frontend::variable_expression *expression)
    {
        auto symbol = this->symbols->lookup(expression->name);

        if (symbol == NULL_TREE)
        {
            error_at(get_location(&expression->position()), "Symbol '%s' not declared in the current scope",
                    expression->name.c_str());
            this->current_expression = error_mark_node;
        }
        else
        {
            this->current_expression = symbol;
        }
    }

    void generic_visitor::visit(frontend::array_access_expression *expression)
    {
        expression->base().accept(this);
        tree designator = this->current_expression;
        location_t location = get_location(&expression->position());

        expression->index().accept(this);
        if (!is_integral_type(TREE_TYPE(this->current_expression)))
        {
            error_at(location, "Type '%s' cannot be used as index",
                    print_type(TREE_TYPE(this->current_expression)).c_str());
            this->current_expression = error_mark_node;
            return;
        }
        tree offset = fold_convert(elna_word_type_node, this->current_expression);

        if (TREE_CODE(TREE_TYPE(designator)) == ARRAY_TYPE)
        {
            tree element_type = TREE_TYPE(TREE_TYPE(designator));

            this->current_expression = build4_loc(location,
                    ARRAY_REF, element_type, designator, offset, size_one_node, NULL_TREE);
        }
        else if (TREE_TYPE(designator) == elna_string_type_node)
        {
            offset = build2(MINUS_EXPR, elna_word_type_node, offset, size_one_node);
            tree string_ptr = build3_loc(location, COMPONENT_REF, TREE_TYPE(elna_string_ptr_field_node),
                    designator, elna_string_ptr_field_node, NULL_TREE);

            tree target_pointer = do_pointer_arithmetic(frontend::binary_operator::sum, string_ptr, offset, location);

            this->current_expression = build1_loc(location, INDIRECT_REF,
                    elna_char_type_node, target_pointer);
        }
        else
        {
            error_at(location, "Indexing is not allowed on type '%s'",
                    print_type(TREE_TYPE(designator)).c_str());
            this->current_expression = error_mark_node;
        }
    }

    bool generic_visitor::expect_trait_type_only(frontend::traits_expression *trait)
    {
        if (trait->parameters.size() != 1)
        {
            error_at(get_location(&trait->position()), "Trait '%s' expects 1 argument, got %lu",
                    trait->name.c_str(), trait->parameters.size());
            this->current_expression = error_mark_node;
            return false;
        }
        this->current_expression = get_inner_alias(trait->types.front(), this->symbols);

        return this->current_expression != error_mark_node;
    }

    bool generic_visitor::expect_trait_for_integral_type(frontend::traits_expression *trait)
    {
        if (!expect_trait_type_only(trait))
        {
            return false;
        }
        else if (!is_integral_type(this->current_expression) && TREE_CODE(this->current_expression) != ENUMERAL_TYPE)
        {
            error_at(get_location(&trait->position()), "Type '%s' does not support trait '%s'",
                    print_type(this->current_expression).c_str(), trait->name.c_str());
            this->current_expression = error_mark_node;
            return false;
        }
        return true;
    }

    void generic_visitor::visit(frontend::traits_expression *trait)
    {
        location_t trait_location = get_location(&trait->position());

        if (trait->name == "size")
        {
            if (expect_trait_type_only(trait))
            {
                this->current_expression = build1_loc(trait_location, CONVERT_EXPR, elna_word_type_node,
                        size_in_bytes(this->current_expression));
            }
        }
        else if (trait->name == "alignment")
        {
            if (expect_trait_type_only(trait))
            {
                this->current_expression = build_int_cstu(elna_word_type_node,
                        TYPE_ALIGN_UNIT(this->current_expression));
            }
        }
        else if (trait->name == "min")
        {
            if (expect_trait_for_integral_type(trait))
            {
                this->current_expression = TYPE_MIN_VALUE(this->current_expression);
            }
        }
        else if (trait->name == "max")
        {
            if (expect_trait_for_integral_type(trait))
            {
                this->current_expression = TYPE_MAX_VALUE(this->current_expression);
            }
        }
        else if (trait->name == "offset")
        {
            if (trait->parameters.size() != 2)
            {
                error_at(trait_location, "Trait '%s' expects 2 arguments, got %lu",
                        trait->name.c_str(), trait->parameters.size());
                this->current_expression = error_mark_node;
                return;
            }
            this->current_expression = get_inner_alias(trait->types.front(), this->symbols);
            auto field_type = trait->parameters.at(1)->is_named();

            if (field_type == nullptr)
            {
                error_at(trait_location,
                        "The second argument to the offset trait is expected to be a field name,"
                        "got a type expression");
                this->current_expression = error_mark_node;
                return;
            }
            tree field_declaration = find_field_by_name(trait_location, this->current_expression, field_type->name);

            if (field_declaration != error_mark_node)
            {
                this->current_expression = build1(CONVERT_EXPR, elna_word_type_node,
                        byte_position(field_declaration));
            }
            else
            {
                this->current_expression = error_mark_node;
            }
        }
        else
        {
            error_at(get_location(&trait->position()), "Trait '%s' is unknown", trait->name.c_str());
            this->current_expression = error_mark_node;
        }
    }

    void generic_visitor::visit(frontend::field_access_expression *expression)
    {
        expression->base().accept(this);
        location_t expression_location = get_location(&expression->position());
        tree aggregate_type = TREE_TYPE(this->current_expression);

        if (TREE_CODE(aggregate_type) == ARRAY_TYPE && expression->field() == "length")
        {
            this->current_expression = convert(build_qualified_type(elna_word_type_node, TYPE_QUAL_CONST),
                    TYPE_MAX_VALUE(TYPE_DOMAIN(aggregate_type)));
        }
        else if (TREE_CODE(aggregate_type) == ARRAY_TYPE && expression->field() == "ptr")
        {
            tree ptr_type = build_global_pointer_type(TREE_TYPE(aggregate_type));
            this->current_expression = build1(ADDR_EXPR,
                    build_qualified_type(ptr_type, TYPE_QUAL_CONST), this->current_expression);
        }
        else if (TREE_CODE(aggregate_type) == ENUMERAL_TYPE)
        {
            tree iterator{ NULL_TREE };

            for (iterator = TYPE_VALUES(aggregate_type); iterator != NULL_TREE; iterator = TREE_CHAIN(iterator))
            {
                if (IDENTIFIER_POINTER(TREE_PURPOSE(iterator)) == expression->field())
                {
                    this->current_expression = TREE_VALUE(iterator);
                    return;
                }
            }
            this->current_expression = error_mark_node;
            error_at(expression_location, "Unknown enumeration member '%s'", expression->field().c_str());
        }
        else
        {
            tree field_declaration = find_field_by_name(expression_location,
                    TREE_TYPE(this->current_expression), expression->field());

            if (field_declaration != error_mark_node)
            {
                this->current_expression = build3_loc(expression_location, COMPONENT_REF,
                        TREE_TYPE(field_declaration), this->current_expression,
                        field_declaration, NULL_TREE);
            }
        }
    }

    void generic_visitor::visit(frontend::dereference_expression *expression)
    {
        expression->base().accept(this);
        location_t expression_location = get_location(&expression->position());
        tree expression_type = TREE_TYPE(this->current_expression);

        if (POINTER_TYPE_P(expression_type))
        {
            this->current_expression = build1_loc(expression_location, INDIRECT_REF,
                    TREE_TYPE(expression_type), this->current_expression);
        }
        else
        {
            error_at(expression_location, "Type '%s' cannot be dereferenced, it is not a pointer",
                    print_type(expression_type).c_str());
            this->current_expression = error_mark_node;
        }
    }

    void generic_visitor::visit(frontend::assign_statement *statement)
    {
        statement->lvalue().accept(this);

        tree lvalue = this->current_expression;
        location_t statement_location = get_location(&statement->position());

        statement->rvalue().accept(this);
        tree rvalue = prepare_rvalue(this->current_expression);

        if (TREE_CODE(lvalue) == CONST_DECL)
        {
            error_at(statement_location, "Cannot modify constant '%s'",
                    statement->lvalue().is_variable()->name.c_str());
        }
        else if (TYPE_READONLY(TREE_TYPE(lvalue)))
        {
            error_at(statement_location, "Cannot modify a constant expression of type '%s'",
                    print_type(TREE_TYPE(lvalue)).c_str());
        }
        else if (is_assignable_from(TREE_TYPE(lvalue), rvalue))
        {
            tree assignment = build2_loc(statement_location, MODIFY_EXPR, void_type_node, lvalue, rvalue);

            append_statement(assignment);
        }
        else
        {
            error_at(statement_location, "Cannot assign value of type '%s' to variable of type '%s'",
                    print_type(TREE_TYPE(rvalue)).c_str(),
                    print_type(TREE_TYPE(lvalue)).c_str());
        }
        this->current_expression = NULL_TREE;
    }

    void generic_visitor::visit(frontend::if_statement *statement)
    {
        tree endif_label_decl = create_artificial_label(UNKNOWN_LOCATION);
        tree goto_endif = build1(GOTO_EXPR, void_type_node, endif_label_decl);

        make_if_branch(statement->body(), goto_endif);

        for (const auto branch : statement->branches)
        {
            make_if_branch(*branch, goto_endif);
        }
        if (statement->alternative != nullptr)
        {
            enter_scope();
            visit_statements(*statement->alternative);
            tree mapping = leave_scope();
            append_statement(mapping);
        }
        tree endif_label_expr = build1(LABEL_EXPR, void_type_node, endif_label_decl);
        append_statement(endif_label_expr);
        this->current_expression = NULL_TREE;
    }

    void generic_visitor::make_if_branch(frontend::conditional_statements& branch, tree goto_endif)
    {
        branch.prerequisite().accept(this);

        if (TREE_TYPE(this->current_expression) != elna_bool_type_node)
        {
            error_at(get_location(&branch.prerequisite().position()),
                    "Expected expression of boolean type but its type is %s",
                    print_type(TREE_TYPE(this->current_expression)).c_str());
            this->current_expression = error_mark_node;
            return;
        }
        tree then_label_decl = build_label_decl("then", UNKNOWN_LOCATION);
        tree goto_then = build1(GOTO_EXPR, void_type_node, then_label_decl);

        tree else_label_decl = build_label_decl("else", UNKNOWN_LOCATION);
        tree goto_else = build1(GOTO_EXPR, void_type_node, else_label_decl);

        auto cond_expr = build3(COND_EXPR, void_type_node, this->current_expression, goto_then, goto_else);
        append_statement(cond_expr);

        tree then_label_expr = build1(LABEL_EXPR, void_type_node, then_label_decl);
        append_statement(then_label_expr);
        enter_scope();

        visit_statements(branch.statements);
        tree mapping = leave_scope();
        append_statement(mapping);
        append_statement(goto_endif);

        tree else_label_expr = build1(LABEL_EXPR, void_type_node, else_label_decl);
        append_statement(else_label_expr);
    }

    void generic_visitor::visit(frontend::import_declaration *)
    {
    }

    void generic_visitor::visit(frontend::while_statement *statement)
    {
        location_t prerequisite_location = get_location(&statement->body().prerequisite().position());
        tree prerequisite_label_decl = build_label_decl("while_do", prerequisite_location);
        auto prerequisite_label_expr = build1_loc(prerequisite_location, LABEL_EXPR,
                void_type_node, prerequisite_label_decl);
        auto goto_check = build1(GOTO_EXPR, void_type_node, prerequisite_label_decl);
        tree branch_end_declaration = build_label_decl("while_end", UNKNOWN_LOCATION);
        tree branch_end_expression = build1_loc(UNKNOWN_LOCATION, LABEL_EXPR, void_type_node, branch_end_declaration);

        append_statement(prerequisite_label_expr);
        make_if_branch(statement->body(), goto_check);

        for (const auto branch : statement->branches)
        {
            make_if_branch(*branch, goto_check);
        }
        append_statement(branch_end_expression);
        this->current_expression = NULL_TREE;
    }

    void generic_visitor::visit_statements(const std::vector<frontend::statement *>& statements)
    {
        for (frontend::statement *const statement : statements)
        {
            statement->accept(this);

            if (this->current_expression != NULL_TREE && this->current_expression != error_mark_node)
            {
                append_statement(this->current_expression);
                this->current_expression = NULL_TREE;
            }
        }
    }

    void generic_visitor::visit(frontend::return_statement *statement)
    {
        frontend::expression *return_expression = &statement->return_expression();
        location_t statement_position = get_location(&statement->position());
        tree set_result{ NULL_TREE };
        tree return_type = TREE_TYPE(TREE_TYPE(current_function_decl));

        if (TREE_THIS_VOLATILE(current_function_decl) == 1)
        {
            error_at(statement_position, "This procedure is not allowed to return");
            return;
        }
        if (return_expression != nullptr)
        {
            return_expression->accept(this);

            set_result = build2(INIT_EXPR, void_type_node, DECL_RESULT(current_function_decl),
                    this->current_expression);
        }
        if (return_type == void_type_node && set_result != NULL_TREE)
        {
            error_at(statement_position, "Proper procedure is not allowed to return a value");
        }
        else if (return_type != void_type_node && set_result == NULL_TREE)
        {
            error_at(statement_position, "Procedure is expected to return a value of type '%s'",
                    print_type(return_type).c_str());
        }
        else if (return_type != void_type_node && !is_assignable_from(return_type, this->current_expression))
        {
            error_at(statement_position, "Cannot return '%s' from a procedure returning '%s'",
                    print_type(return_type).c_str(),
                    print_type(TREE_TYPE(this->current_expression)).c_str());
        }
        else
        {
            tree return_stmt = build1_loc(statement_position, RETURN_EXPR, void_type_node, set_result);
            append_statement(return_stmt);
        }
        this->current_expression = NULL_TREE;
    }

    void generic_visitor::visit(frontend::defer_statement *statement)
    {
        enter_scope();
        visit_statements(statement->statements);
        defer(leave_scope());
    }

    void generic_visitor::visit(frontend::case_statement *statement)
    {
        statement->condition().accept(this);
        tree condition_expression = this->current_expression;
        tree unqualified_condition = get_qualified_type(TREE_TYPE(this->current_expression), TYPE_UNQUALIFIED);

        if (!INTEGRAL_TYPE_P(unqualified_condition))
        {
            error_at(get_location(&statement->condition().position()),
                    "Case expressions can only be integral numbers, characters and enumerations, given '%s'",
                    print_type(unqualified_condition).c_str());
            this->current_expression = NULL_TREE;
            return;
        }
        tree end_label_declaration = create_artificial_label(get_location(&statement->position()));
        tree switch_statements = alloc_stmt_list();

        for (const frontend::switch_case& case_block : statement->cases)
        {
            for (frontend::expression *const case_label : case_block.labels)
            {
                case_label->accept(this);
                location_t case_location = get_location(&case_label->position());

                if (assert_constant(case_location)
                        && !is_assignable_from(unqualified_condition, this->current_expression))
                {
                    error_at(case_location, "Case type '%s' does not match the expression type '%s'",
                            print_type(TREE_TYPE(this->current_expression)).c_str(),
                            print_type(unqualified_condition).c_str());
                    this->current_expression = error_mark_node;
                }
                tree case_label_declaration = create_artificial_label(case_location);
                tree case_expression = build_case_label(this->current_expression, NULL_TREE, case_label_declaration);

                append_to_statement_list(case_expression, &switch_statements);
            }
            enter_scope();
            visit_statements(case_block.statements);
            append_to_statement_list(leave_scope(), &switch_statements);
            tree goto_end = build1(GOTO_EXPR, void_type_node, end_label_declaration);

            append_to_statement_list(goto_end, &switch_statements);
            TREE_USED(end_label_declaration) = 1;
        }
        if (statement->alternative != nullptr)
        {
            tree case_label_declaration = create_artificial_label(UNKNOWN_LOCATION);
            tree case_expression = build_case_label(NULL_TREE, NULL_TREE, case_label_declaration);

            append_to_statement_list(case_expression, &switch_statements);

            enter_scope();
            visit_statements(*statement->alternative);
            append_to_statement_list(leave_scope(), &switch_statements);

            TREE_USED(end_label_declaration) = 1;
        }
        tree switch_expression = build2(SWITCH_EXPR, TREE_TYPE(condition_expression),
                condition_expression, switch_statements);

        append_statement(switch_expression);

        tree end_label_expression = build1(LABEL_EXPR, void_type_node, end_label_declaration);
        append_statement(end_label_expression);

        this->current_expression = NULL_TREE;
    }

    bool generic_visitor::assert_constant(location_t expression_location)
    {
        tree constant_expression = extract_constant(this->current_expression);

        if (constant_expression == NULL_TREE)
        {
            error_at(expression_location, "Expected a constant expression");
            this->current_expression = error_mark_node;
        }
        else
        {
            this->current_expression = constant_expression;
        }
        return this->current_expression != error_mark_node;
    }
}