feat: vtable field in function blocks assigned to global

The `__vtable` field in classes and function blocks is assigned at init
time to the correct global variable

TODO: missing tests

Author: ghaith

compiler/plc_util/src/convention.rs

@@ -12,6 +12,16 @@ pub fn internal_type_name<T: AsRef<str> + Display>(prefix: T, original_type_name
     format!("__{prefix}{original_type_name}")
 }
 
+/// Returns the default vtable global variable name for a function block or class
+pub fn generate_vtable_name(name: &str) -> String {
+    format!("__vtable_{name}")
+}
+
+/// Returns the default vtable type name for a function block, class, or interface
+pub fn generate_vtable_type_name(name: &str) -> String {
+    format!("__vtable_{name}_type")
+}
+
 #[cfg(test)]
 mod tests {
     #[test]

src/codegen/tests/debug_tests.rs

@@ -349,7 +349,7 @@ fn dbg_declare_has_valid_metadata_references_for_methods() {
         ",
     );
 
-    assert_snapshot!(codegen, @r#"
+    assert_snapshot!(codegen, @r###"
     ; ModuleID = '<internal>'
     source_filename = "<internal>"
 
@@ -389,6 +389,9 @@ fn dbg_declare_has_valid_metadata_references_for_methods() {
     entry:
       %self = alloca %fb*, align 8
       store %fb* %0, %fb** %self, align 8
+      %deref = load %fb*, %fb** %self, align 8
+      %__vtable = getelementptr inbounds %fb, %fb* %deref, i32 0, i32 0
+      store i32* bitcast (%__vtable_fb_type* @__vtable_fb to i32*), i32** %__vtable, align 8
       ret void
     }
 
@@ -439,7 +442,7 @@ fn dbg_declare_has_valid_metadata_references_for_methods() {
     !26 = distinct !DISubprogram(name: "fb.foo", linkageName: "fb.foo", scope: !20, file: !2, line: 3, type: !21, scopeLine: 4, flags: DIFlagPublic, spFlags: DISPFlagDefinition, unit: !18, retainedNodes: !23)
     !27 = !DILocalVariable(name: "fb", scope: !26, file: !2, line: 4, type: !3)
     !28 = !DILocation(line: 4, column: 8, scope: !26)
-    "#);
+    "###);
 }
 
 #[test]