move List.sublist to backend

compiler/gen_llvm/src/llvm/build.rs

@@ -12,7 +12,7 @@ use crate::llvm::build_list::{
     list_contains, list_drop, list_drop_at, list_find_trivial_not_found, list_find_unsafe,
     list_get_unsafe, list_join, list_keep_errs, list_keep_if, list_keep_oks, list_len, list_map,
     list_map2, list_map3, list_map4, list_map_with_index, list_prepend, list_range, list_repeat,
-    list_reverse, list_set, list_single, list_sort_with, list_swap, list_take_first,
+    list_reverse, list_set, list_single, list_sort_with, list_sublist, list_swap, list_take_first,
     list_take_last,
 };
 use crate::llvm::build_str::{
@@ -5210,6 +5210,27 @@ fn run_low_level<'a, 'ctx, 'env>(
                 _ => unreachable!("Invalid layout {:?} in List.takeLast", list_layout),
             }
         }
+        ListSublist => {
+            // List.sublist : List elem, { start : Nat, len : Nat } -> List elem
+            debug_assert_eq!(args.len(), 2);
+
+            let (list, list_layout) = load_symbol_and_layout(scope, &args[0]);
+            let original_wrapper = list.into_struct_value();
+
+            let rec = load_symbol(scope, &args[1]);
+
+            match list_layout {
+                Layout::Builtin(Builtin::EmptyList) => empty_list(env),
+                Layout::Builtin(Builtin::List(element_layout)) => list_sublist(
+                    env,
+                    layout_ids,
+                    original_wrapper,
+                    rec.into_struct_value(),
+                    element_layout,
+                ),
+                _ => unreachable!("Invalid layout {:?} in List.sublist", list_layout),
+            }
+        }
         ListDrop => {
             // List.drop : List elem, Nat -> List elem
             debug_assert_eq!(args.len(), 2);

compiler/gen_llvm/src/llvm/build_list.rs

@@ -338,6 +338,33 @@ pub fn list_take_last<'a, 'ctx, 'env>(
     )
 }
 
+/// List.sublist : List elem, { start : Nat, len : Nat } -> List elem
+pub fn list_sublist<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    layout_ids: &mut LayoutIds<'a>,
+    original_wrapper: StructValue<'ctx>,
+    len_and_start: StructValue<'ctx>,
+    element_layout: &Layout<'a>,
+) -> BasicValueEnum<'ctx> {
+    let dec_element_fn = build_dec_wrapper(env, layout_ids, element_layout);
+    call_bitcode_fn_returns_list(
+        env,
+        &[
+            pass_list_cc(env, original_wrapper.into()),
+            env.alignment_intvalue(element_layout),
+            layout_width(env, element_layout),
+            complex_bitcast(
+                env.builder,
+                len_and_start.into(),
+                env.str_list_c_abi().into(),
+                "to_i128",
+            ),
+            dec_element_fn.as_global_value().as_pointer_value().into(),
+        ],
+        bitcode::LIST_SUBLIST,
+    )
+}
+
 /// List.drop : List elem, Nat -> List elem
 pub fn list_drop<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,