Remove takeFirst and takeLast from backend

compiler/builtins/bitcode/src/list.zig

@@ -862,33 +862,6 @@ pub fn listSwap(
     return newList;
 }
 
-pub fn listTakeFirst(
-    list: RocList,
-    alignment: u32,
-    element_width: usize,
-    take_count: usize,
-) callconv(.C) RocList {
-    if (list.bytes) |source_ptr| {
-        if (take_count == 0) {
-            return RocList.empty();
-        }
-        const in_len = list.len();
-        const out_len = std.math.min(take_count, in_len);
-
-        const output = RocList.allocate(alignment, out_len, element_width);
-        const target_ptr = output.bytes orelse unreachable;
-
-        @memcpy(target_ptr, source_ptr, out_len * element_width);
-
-        utils.decref(list.bytes, in_len * element_width, alignment);
-
-        return output;
-    } else {
-        return RocList.empty();
-    }
-}
-
-
 pub fn listSublist(
     list: RocList,
     alignment: u32,
@@ -926,34 +899,6 @@ pub fn listSublist(
     return RocList.empty();
 }
 
-pub fn listTakeLast(
-    list: RocList,
-    alignment: u32,
-    element_width: usize,
-    take_count: usize,
-    dec: Dec,
-) callconv(.C) RocList {
-    if (take_count == 0) {
-        return RocList.empty();
-    }
-    if (list.bytes) |source_ptr| {
-        const size = list.len();
-        if (size <= take_count) {
-            return list;
-        }
-        const drop_count = size - take_count;
-        return listDrop(
-            list,
-            alignment,
-            element_width,
-            drop_count,
-            dec,
-        );
-    } else {
-        return RocList.empty();
-    }
-}
-
 pub fn listDrop(
     list: RocList,
     alignment: u32,

compiler/builtins/bitcode/src/main.zig

@@ -45,8 +45,6 @@ comptime {
     exportListFn(list.listReverse, "reverse");
     exportListFn(list.listSortWith, "sort_with");
     exportListFn(list.listConcat, "concat");
-    exportListFn(list.listTakeFirst, "take_first");
-    exportListFn(list.listTakeLast, "take_last");
     exportListFn(list.listSublist, "sublist");
     exportListFn(list.listDrop, "drop");
     exportListFn(list.listDropAt, "drop_at");

compiler/builtins/src/bitcode.rs

@@ -183,8 +183,6 @@ pub const LIST_CONTAINS: &str = "roc_builtins.list.contains";
 pub const LIST_REPEAT: &str = "roc_builtins.list.repeat";
 pub const LIST_APPEND: &str = "roc_builtins.list.append";
 pub const LIST_PREPEND: &str = "roc_builtins.list.prepend";
-pub const LIST_TAKE_FIRST: &str = "roc_builtins.list.take_first";
-pub const LIST_TAKE_LAST: &str = "roc_builtins.list.take_last";
 pub const LIST_SUBLIST: &str = "roc_builtins.list.sublist";
 pub const LIST_DROP: &str = "roc_builtins.list.drop";
 pub const LIST_DROP_AT: &str = "roc_builtins.list.drop_at";

compiler/can/src/builtins.rs

@@ -2020,11 +2020,13 @@ fn list_swap(symbol: Symbol, var_store: &mut VarStore) -> Def {
 fn list_take_first(symbol: Symbol, var_store: &mut VarStore) -> Def {
     let list_var = var_store.fresh();
     let len_var = var_store.fresh();
+    let zero = int(len_var, Variable::NATURAL, 0);
 
     let body = RunLowLevel {
-        op: LowLevel::ListTakeFirst,
+        op: LowLevel::ListSublist,
         args: vec![
             (list_var, Var(Symbol::ARG_1)),
+            (len_var, zero),
             (len_var, Var(Symbol::ARG_2)),
         ],
         ret_var: list_var,
@@ -2044,10 +2046,40 @@ fn list_take_last(symbol: Symbol, var_store: &mut VarStore) -> Def {
     let list_var = var_store.fresh();
     let len_var = var_store.fresh();
 
+    let zero = int(len_var, Variable::NATURAL, 0);
+    let bool_var = var_store.fresh();
+
+    let get_list_len = RunLowLevel {
+        op: LowLevel::ListLen,
+        args: vec![(list_var, Var(Symbol::ARG_1))],
+        ret_var: len_var,
+    };
+
+    let get_sub = RunLowLevel {
+        op: LowLevel::NumSubWrap,
+        args: vec![(len_var, get_list_len), (len_var, Var(Symbol::ARG_2))],
+        ret_var: len_var,
+    };
+
+    let get_start = If {
+        cond_var: bool_var,
+        branch_var: len_var,
+        branches: vec![(
+            no_region(RunLowLevel {
+                op: LowLevel::NumGt,
+                args: vec![(len_var, get_sub.clone()), (len_var, zero.clone())],
+                ret_var: bool_var,
+            }),
+            no_region(get_sub),
+        )],
+        final_else: Box::new(no_region(zero)),
+    };
+
     let body = RunLowLevel {
-        op: LowLevel::ListTakeLast,
+        op: LowLevel::ListSublist,
         args: vec![
             (list_var, Var(Symbol::ARG_1)),
+            (len_var, get_start),
             (len_var, Var(Symbol::ARG_2)),
         ],
         ret_var: list_var,

compiler/gen_llvm/src/llvm/build.rs

@@ -12,8 +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_sublist, list_swap, list_take_first,
-    list_take_last,
+    list_reverse, list_set, list_single, list_sort_with, list_sublist, list_swap,
 };
 use crate::llvm::build_str::{
     empty_str, str_concat, str_count_graphemes, str_ends_with, str_from_float, str_from_int,
@@ -5169,47 +5168,6 @@ fn run_low_level<'a, 'ctx, 'env>(
                 _ => unreachable!("Invalid layout {:?} in List.swap", list_layout),
             }
         }
-        ListTakeFirst => {
-            // List.takeFirst : List elem, 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 count = load_symbol(scope, &args[1]);
-
-            match list_layout {
-                Layout::Builtin(Builtin::EmptyList) => empty_list(env),
-                Layout::Builtin(Builtin::List(element_layout)) => list_take_first(
-                    env,
-                    original_wrapper,
-                    count.into_int_value(),
-                    element_layout,
-                ),
-                _ => unreachable!("Invalid layout {:?} in List.takeFirst", list_layout),
-            }
-        }
-        ListTakeLast => {
-            // List.takeLast : List elem, 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 count = load_symbol(scope, &args[1]);
-
-            match list_layout {
-                Layout::Builtin(Builtin::EmptyList) => empty_list(env),
-                Layout::Builtin(Builtin::List(element_layout)) => list_take_last(
-                    env,
-                    layout_ids,
-                    original_wrapper,
-                    count.into_int_value(),
-                    element_layout,
-                ),
-                _ => unreachable!("Invalid layout {:?} in List.takeLast", list_layout),
-            }
-        }
         ListSublist => {
             // List.sublist : List elem, { start : Nat, len : Nat } -> List elem
             //

compiler/gen_llvm/src/llvm/build_list.rs

@@ -297,47 +297,6 @@ pub fn list_swap<'a, 'ctx, 'env>(
     )
 }
 
-/// List.takeFirst : List elem, Nat -> List elem
-pub fn list_take_first<'a, 'ctx, 'env>(
-    env: &Env<'a, 'ctx, 'env>,
-    original_wrapper: StructValue<'ctx>,
-    count: IntValue<'ctx>,
-    element_layout: &Layout<'a>,
-) -> BasicValueEnum<'ctx> {
-    call_bitcode_fn_returns_list(
-        env,
-        &[
-            pass_list_cc(env, original_wrapper.into()),
-            env.alignment_intvalue(element_layout),
-            layout_width(env, element_layout),
-            count.into(),
-        ],
-        bitcode::LIST_TAKE_FIRST,
-    )
-}
-
-/// List.takeLast : List elem, Nat -> List elem
-pub fn list_take_last<'a, 'ctx, 'env>(
-    env: &Env<'a, 'ctx, 'env>,
-    layout_ids: &mut LayoutIds<'a>,
-    original_wrapper: StructValue<'ctx>,
-    count: IntValue<'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),
-            count.into(),
-            dec_element_fn.as_global_value().as_pointer_value().into(),
-        ],
-        bitcode::LIST_TAKE_LAST,
-    )
-}
-
 /// List.sublist : List elem, { start : Nat, len : Nat } -> List elem
 pub fn list_sublist<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,

compiler/gen_wasm/src/low_level.rs

@@ -33,11 +33,10 @@ pub fn build_call_low_level<'a>(
         | ListGetUnsafe | ListSet | ListSingle | ListRepeat | ListReverse | ListConcat
         | ListContains | ListAppend | ListPrepend | ListJoin | ListRange | ListMap | ListMap2
         | ListMap3 | ListMap4 | ListMapWithIndex | ListKeepIf | ListWalk | ListWalkUntil
-        | ListWalkBackwards | ListKeepOks | ListKeepErrs | ListSortWith | ListTakeFirst
-        | ListTakeLast | ListSublist | ListDrop | ListDropAt | ListSwap | ListAny
-        | ListFindUnsafe | DictSize | DictEmpty | DictInsert | DictRemove | DictContains
-        | DictGetUnsafe | DictKeys | DictValues | DictUnion | DictIntersection | DictDifference
-        | DictWalk | SetFromList => {
+        | ListWalkBackwards | ListKeepOks | ListKeepErrs | ListSortWith | ListSublist
+        | ListDrop | ListDropAt | ListSwap | ListAny | ListFindUnsafe | DictSize | DictEmpty
+        | DictInsert | DictRemove | DictContains | DictGetUnsafe | DictKeys | DictValues
+        | DictUnion | DictIntersection | DictDifference | DictWalk | SetFromList => {
             return NotImplemented;
         }
 

compiler/module/src/low_level.rs

@@ -43,8 +43,6 @@ pub enum LowLevel {
     ListKeepOks,
     ListKeepErrs,
     ListSortWith,
-    ListTakeFirst,
-    ListTakeLast,
     ListSublist,
     ListDrop,
     ListDropAt,
@@ -137,8 +135,6 @@ macro_rules! first_order {
             | ListLen
             | ListGetUnsafe
             | ListSet
-            | ListTakeFirst
-            | ListTakeLast
             | ListSublist
             | ListDrop
             | ListDropAt

compiler/mono/src/borrow.rs

@@ -966,8 +966,6 @@ pub fn lowlevel_borrow_signature(arena: &Bump, op: LowLevel) -> &[bool] {
         // TODO when we have lists with capacity (if ever)
         // List.append should own its first argument
         ListAppend => arena.alloc_slice_copy(&[owned, owned]),
-        ListTakeFirst => arena.alloc_slice_copy(&[owned, irrelevant]),
-        ListTakeLast => arena.alloc_slice_copy(&[owned, irrelevant]),
         ListSublist => arena.alloc_slice_copy(&[owned, irrelevant, irrelevant]),
         ListDrop => arena.alloc_slice_copy(&[owned, irrelevant]),
         ListDropAt => arena.alloc_slice_copy(&[owned, irrelevant]),

compiler/mono/src/low_level.rs

@@ -100,8 +100,6 @@ enum FirstOrder {
     ListLen,
     ListGetUnsafe,
     ListSet,
-    ListTakeFirst,
-    ListTakeLast,
     ListSublist,
     ListDrop,
     ListDropAt,