attempt to correct list refcount generation in dev backends

crates/compiler/can/src/builtins.rs

@@ -93,6 +93,7 @@ macro_rules! map_symbol_to_lowlevel_and_arity {
                 LowLevel::RefCountIsUnique => unimplemented!(),
                 LowLevel::ListIncref => unimplemented!(),
                 LowLevel::ListDecref => unimplemented!(),
+                LowLevel::ListElemDecFnPtr => unimplemented!(),
 
                 LowLevel::SetJmp => unimplemented!(),
                 LowLevel::LongJmp => unimplemented!(),

crates/compiler/gen_dev/src/generic64/mod.rs

@@ -2846,7 +2846,7 @@ impl<
                 self.load_layout_refcounted(element_layout, Symbol::DEV_TMP3);
 
                 let inc_elem_fn = self.increment_fn_pointer(element_layout);
-                let dec_elem_fn = self.decrement_fn_pointer(element_layout);
+                let dec_elem_fn = self.decrement_fn_pointer(element_layout, None);
 
                 //    input: RocList,
                 //    caller: CompareFn,
@@ -2925,7 +2925,7 @@ impl<
         self.load_layout_refcounted(elem_layout, Symbol::DEV_TMP3);
 
         let inc_elem_fn = self.increment_fn_pointer(elem_layout);
-        let dec_elem_fn = self.decrement_fn_pointer(elem_layout);
+        let dec_elem_fn = self.decrement_fn_pointer(elem_layout, None);
 
         // Setup the return location.
         let base_offset =
@@ -3276,7 +3276,7 @@ impl<
         self.load_layout_refcounted(elem_layout, Symbol::DEV_TMP4);
 
         let inc_elem_fn = self.increment_fn_pointer(elem_layout);
-        let dec_elem_fn = self.decrement_fn_pointer(elem_layout);
+        let dec_elem_fn = self.decrement_fn_pointer(elem_layout, None);
 
         // Setup the return location.
         let base_offset =
@@ -3387,7 +3387,7 @@ impl<
         self.load_layout_refcounted(elem_layout, Symbol::DEV_TMP3);
 
         let inc_elem_fn = self.increment_fn_pointer(elem_layout);
-        let dec_elem_fn = self.decrement_fn_pointer(elem_layout);
+        let dec_elem_fn = self.decrement_fn_pointer(elem_layout, None);
 
         // Setup the return location.
         let base_offset =

crates/compiler/gen_dev/src/lib.rs

@@ -465,12 +465,12 @@ trait Backend<'a> {
         element_increment
     }
 
-    fn decrement_fn_pointer(&mut self, layout: InLayout<'a>) -> Symbol {
+    fn decrement_fn_pointer(&mut self, layout: InLayout<'a>, out: Option<Symbol>) -> Symbol {
         let box_layout = self
             .interner_mut()
             .insert_direct_no_semantic(LayoutRepr::Ptr(layout));
 
-        let element_decrement = self.debug_symbol("element_decrement");
+        let element_decrement = out.unwrap_or(self.debug_symbol("element_decrement"));
         let element_decrement_symbol = self.build_indirect_dec(layout);
 
         let element_decrement_string = self.lambda_name_to_string(
@@ -1923,7 +1923,7 @@ trait Backend<'a> {
                     list_argument.element_refcounted,
                     start,
                     len,
-                    self.decrement_fn_pointer(element_layout),
+                    self.decrement_fn_pointer(element_layout, None),
                 ];
 
                 let layout_usize = Layout::U64;
@@ -1953,7 +1953,7 @@ trait Backend<'a> {
                 self.load_literal_i8(&update_mode, UpdateMode::Immutable as i8);
 
                 let inc_elem_fn = self.increment_fn_pointer(list_argument.element_layout);
-                let dec_elem_fn = self.decrement_fn_pointer(list_argument.element_layout);
+                let dec_elem_fn = self.decrement_fn_pointer(list_argument.element_layout, None);
 
                 let layout_usize = Layout::U64;
 
@@ -2005,7 +2005,7 @@ trait Backend<'a> {
                 self.load_literal_i8(&update_mode, UpdateMode::Immutable as i8);
 
                 let inc_elem_fn = self.increment_fn_pointer(list_argument.element_layout);
-                let dec_elem_fn = self.decrement_fn_pointer(list_argument.element_layout);
+                let dec_elem_fn = self.decrement_fn_pointer(list_argument.element_layout, None);
 
                 let layout_usize = Layout::U64;
 
@@ -2079,7 +2079,7 @@ trait Backend<'a> {
                 let list_layout = arg_layouts[0];
                 let list_argument = self.list_argument(list_layout);
 
-                let dec_elem_fn = self.decrement_fn_pointer(list_argument.element_layout);
+                let dec_elem_fn = self.decrement_fn_pointer(list_argument.element_layout, None);
 
                 let layout_usize = Layout::U64;
 
@@ -2110,6 +2110,13 @@ trait Backend<'a> {
                 );
             }
 
+            LowLevel::ListElemDecFnPtr => {
+                let list_layout = arg_layouts[0];
+                let list_argument = self.list_argument(list_layout);
+
+                _ = self.decrement_fn_pointer(list_argument.element_layout, Some(*sym));
+            }
+
             LowLevel::ListDropAt => {
                 let list = args[0];
                 let drop_index = args[1];
@@ -2123,7 +2130,7 @@ trait Backend<'a> {
 
                 let layout_usize = Layout::U64;
                 let element_increment = self.increment_fn_pointer(element_layout);
-                let element_decrement = self.decrement_fn_pointer(element_layout);
+                let element_decrement = self.decrement_fn_pointer(element_layout, None);
 
                 //    list: RocList,
                 //    alignment: u32,

crates/compiler/gen_llvm/src/llvm/lowlevel.rs

@@ -1411,7 +1411,7 @@ pub(crate) fn run_low_level<'a, 'ctx>(
             call_bitcode_fn(env, &[], bitcode::UTILS_DICT_PSEUDO_SEED)
         }
 
-        ListIncref | ListDecref | SetJmp | LongJmp | SetLongJmpBuffer => {
+        ListElemDecFnPtr | ListIncref | ListDecref | SetJmp | LongJmp | SetLongJmpBuffer => {
             unreachable!("only inserted in dev backend codegen")
         }
     }

crates/compiler/gen_wasm/src/low_level.rs

@@ -368,6 +368,17 @@ impl<'a> LowLevelCall<'a> {
                 backend.call_host_fn_after_loading_args(bitcode::LIST_DECREF);
             }
 
+            ListElemDecFnPtr => {
+                let input_list: Symbol = self.arguments[0];
+                let list_layout = backend
+                    .layout_interner
+                    .get_repr(backend.storage.symbol_layouts[&input_list]);
+                let elem_in_layout = unwrap_list_elem_layout(list_layout);
+                let dec_fn_ptr = build_refcount_element_fn(backend, elem_in_layout, HelperOp::Dec);
+
+                backend.code_builder.i32_const(dec_fn_ptr);
+            }
+
             ListMap | ListMap2 | ListMap3 | ListMap4 | ListSortWith => {
                 internal_error!("HigherOrder lowlevels should not be handled here")
             }

crates/compiler/module/src/low_level.rs

@@ -50,6 +50,7 @@ pub enum LowLevel {
     ListConcatUtf8,
     ListIncref,
     ListDecref,
+    ListElemDecFnPtr,
     NumAdd,
     NumAddWrap,
     NumAddChecked,
@@ -243,6 +244,7 @@ macro_rules! map_symbol_to_lowlevel {
                 LowLevel::RefCountIsUnique => unimplemented!(),
                 LowLevel::ListIncref => unimplemented!(),
                 LowLevel::ListDecref => unimplemented!(),
+                LowLevel::ListElemDecFnPtr => unimplemented!(),
 
                 LowLevel::SetJmp => unimplemented!(),
                 LowLevel::LongJmp => unimplemented!(),

crates/compiler/mono/src/code_gen_help/refcount.rs

@@ -953,7 +953,7 @@ fn refcount_list<'a>(
     ctx: &mut Context<'a>,
     layout_interner: &mut STLayoutInterner<'a>,
     element_layout: InLayout<'a>,
-    structure: Symbol,
+    _structure: Symbol,
 ) -> Stmt<'a> {
     let arena = root.arena;
     let layout_isize = root.layout_isize;
@@ -1016,29 +1016,38 @@ fn refcount_list<'a>(
                 Expr::Literal(Literal::Int((element_alignment as u128).to_ne_bytes()));
             let alignment_stmt = |next| Stmt::Let(alignment, alignment_expr, LAYOUT_U32, next);
 
-            // let orig_op = ctx.op;
+            let dec_elem_ptr = root.create_symbol(ident_ids, "dec_elem_ptr");
-            // ctx.op = HelperOp::IndirectDec;
+            let dec_elem_ptr_expr = Expr::Call(Call {
-            // let dec_elem_fn =
+                call_type: CallType::LowLevel {
-            //     root.find_or_create_proc(ident_ids, ctx, layout_interner, element_layout);
+                    op: LowLevel::ListElemDecFnPtr,
-            // ctx.op = orig_op;
+                    update_mode: UpdateModeId::BACKEND_DUMMY,
-            // TODO: How do I load a proc symbol to a pointer???
+                },
+                arguments: root.arena.alloc([list]),
+            });
+            let dec_elem_ptr_stmt =
+                |next| Stmt::Let(dec_elem_ptr, dec_elem_ptr_expr, Layout::OPAQUE_PTR, next);
 
             let rc_list_expr = Expr::Call(Call {
                 call_type: CallType::LowLevel {
                     op: LowLevel::ListDecref,
                     update_mode: UpdateModeId::BACKEND_DUMMY,
                 },
-                arguments: root.arena.alloc([list, alignment, width, is_refcounted]),
+                arguments: root
+                    .arena
+                    .alloc([list, alignment, width, is_refcounted, dec_elem_ptr]),
             });
             width_stmt(arena.alloc(
                 //
                 alignment_stmt(arena.alloc(
+                    //
+                    dec_elem_ptr_stmt(arena.alloc(
                         //
                         is_refcounted_stmt(arena.alloc(
                             //
                             Stmt::Let(rc_list_unit, rc_list_expr, LAYOUT_UNIT, ret_stmt),
                         )),
                     )),
+                )),
             ))
         }
         _ => unreachable!(),

crates/compiler/mono/src/drop_specialization.rs

@@ -1621,8 +1621,8 @@ fn low_level_no_rc(lowlevel: &LowLevel) -> RC {
         PtrLoad => RC::NoRc,
         PtrCast => RC::NoRc,
 
-        PtrClearTagId | RefCountIncRcPtr | RefCountDecRcPtr | RefCountIncDataPtr
+        ListElemDecFnPtr | PtrClearTagId | RefCountIncRcPtr | RefCountDecRcPtr
-        | RefCountDecDataPtr | RefCountIsUnique => {
+        | RefCountIncDataPtr | RefCountDecDataPtr | RefCountIsUnique => {
             unreachable!("Only inserted *after* borrow checking: {:?}", lowlevel);
         }
 

crates/compiler/mono/src/inc_dec.rs

@@ -1357,6 +1357,8 @@ pub(crate) fn lowlevel_borrow_signature(op: LowLevel) -> &'static [Ownership] {
         StrReleaseExcessCapacity => &[OWNED],
         ListIncref => &[OWNED],
         ListDecref => &[OWNED],
+        // This doesn't really use the list. It just generates a functions from the layout.
+        ListElemDecFnPtr => &[BORROWED],
 
         Eq | NotEq => &[BORROWED, BORROWED],