llvm one element tag store

compiler/gen/src/llvm/build.rs

@@ -316,14 +316,20 @@ pub fn build_expr<'a, 'ctx, 'env>(
             BasicValueEnum::StructValue(struct_val.into_struct_value())
         }
         Tag {
-            tag_id, arguments, ..
+            tag_id,
+            arguments,
+            tag_layout,
+            ..
         } => {
+            /*
             // put the discriminant in the first slot
             let discriminant = (
                 Expr::Byte(*tag_id),
                 Layout::Builtin(Builtin::Byte(MutMap::default())),
             );
             let it = std::iter::once(&discriminant).chain(arguments.iter());
+            */
+            let it = arguments.iter();
 
             let ctx = env.context;
             let builder = env.builder;

compiler/gen/src/llvm/convert.rs

@@ -68,7 +68,21 @@ pub fn basic_type_from_layout<'ctx>(
                 .struct_type(field_types.into_bump_slice(), false)
                 .as_basic_type_enum()
         }
-        Union(_) => {
+        Union(tags) if tags.len() == 1 => {
+            let (_, layouts) = tags.into_iter().next().unwrap();
+
+            // Determine types
+            let mut field_types = Vec::with_capacity_in(layouts.len(), arena);
+
+            for layout in layouts.iter() {
+                field_types.push(basic_type_from_layout(arena, context, layout));
+            }
+
+            context
+                .struct_type(field_types.into_bump_slice(), false)
+                .as_basic_type_enum()
+        }
+        Union(tags) => {
             // TODO make this dynamic
             let ptr_size = std::mem::size_of::<i64>();
             let union_size = layout.stack_size(ptr_size as u32);

compiler/gen/tests/test_gen.rs

@@ -77,6 +77,7 @@ mod test_gen {
             // Populate Procs and Subs, and get the low-level Expr from the canonical Expr
             let mono_expr = Expr::new(&arena, &mut subs, loc_expr.value, &mut procs, home, &mut ident_ids, POINTER_SIZE);
 
+
             // Put this module's ident_ids back in the interns
             env.interns.all_ident_ids.insert(home, ident_ids);
 
@@ -691,6 +692,22 @@ mod test_gen {
         );
     }
 
+    #[test]
+    fn one_element_tag() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                x : [ Pair Int ]
+                x = Pair 2
+
+                0x3
+                "#
+            ),
+            3,
+            i64
+        );
+    }
+
     #[test]
     fn gen_when_one_branch() {
         assert_evals_to!(