lang: codegen: redesign codegen to use a stack-based state machine

lang/codegen/unit.c

@@ -0,0 +1,68 @@
+#include "codegen.h"
+
+#include <mie/block.h>
+#include <mie/func.h>
+#include <mie/module.h>
+
+struct unit_codegen_state {
+	struct code_generator_state s_base;
+	/* function for top-level statements */
+	struct mie_func *s_immediate;
+};
+
+static enum ivy_status switch_to_immediate_func(
+	struct ivy_codegen *gen, struct unit_codegen_state *unit)
+{
+	if (!unit->s_immediate) {
+		struct mie_type *ret_type
+			= mie_ctx_get_type(gen->c_ctx, MIE_TYPE_VOID);
+		unit->s_immediate = mie_func_create(
+			"init", MIE_FUNC_STATIC, ret_type, NULL, 0);
+
+		if (!unit->s_immediate) {
+			return IVY_ERR_NO_MEMORY;
+		}
+
+		mie_module_add_function(gen->c_module, unit->s_immediate);
+	}
+
+	struct mie_block *block = mie_func_get_last_block(unit->s_immediate);
+	if (!block || mie_block_is_terminated(block)) {
+		block = mie_func_create_block(unit->s_immediate, NULL);
+		mie_func_insert_block(unit->s_immediate, block, NULL);
+	}
+
+	mie_builder_set_insert_point(gen->c_builder, block);
+
+	return IVY_OK;
+}
+
+static struct code_generator_result gen_expr(
+	struct ivy_codegen *gen, struct code_generator_state *state,
+	struct ivy_ast_node *node)
+{
+	struct unit_codegen_state *unit = (struct unit_codegen_state *)state;
+	struct mie_builder *builder = gen->c_builder;
+	struct mie_func *current = mie_builder_get_current_func(builder);
+
+	enum ivy_status status = IVY_OK;
+	if (!current || current != unit->s_immediate) {
+		status = switch_to_immediate_func(gen, unit);
+	}
+
+	if (status != IVY_OK) {
+		return CODEGEN_RESULT_ERR(status);
+	}
+
+	codegen_push_generator(gen, CODE_GENERATOR_EXPR, NULL);
+	return CODEGEN_RESULT_OK(CODEGEN_REPEAT_NODE);
+}
+
+struct code_generator unit_generator = {
+	.g_type = CODE_GENERATOR_UNIT,
+	.g_state_size = sizeof(struct unit_codegen_state),
+	.g_node_generators_pre = {
+		[IVY_AST_INT] = gen_expr,
+		[IVY_AST_OP] = gen_expr,
+	},
+};