fix list decref

compiler/builtins/bitcode/src/utils.zig

@@ -118,11 +118,12 @@ pub fn decrefC(
 }
 
 pub fn decrefCheckNullC(
-    bytes_or_null: ?[*]isize,
+    bytes_or_null: ?[*]u8,
     alignment: u32,
 ) callconv(.C) void {
     if (bytes_or_null) |bytes| {
-        return @call(.{ .modifier = always_inline }, decref_ptr_to_refcount, .{ bytes, alignment });
+        const isizes: [*]isize = @ptrCast([*]isize, @alignCast(@sizeOf(isize), bytes));
+        return @call(.{ .modifier = always_inline }, decref_ptr_to_refcount, .{ isizes - 1, alignment });
     }
 }
 

compiler/gen_llvm/src/llvm/build.rs

@@ -8,10 +8,10 @@ use crate::llvm::build_dict::{
 };
 use crate::llvm::build_hash::generic_hash;
 use crate::llvm::build_list::{
-    allocate_list, empty_list, empty_polymorphic_list, list_append, list_concat, list_contains,
+    self, allocate_list, empty_list, empty_polymorphic_list, list_append, list_concat,
-    list_drop, list_get_unsafe, list_join, list_keep_errs, list_keep_if, list_keep_oks, list_len,
+    list_contains, list_drop, list_get_unsafe, list_join, list_keep_errs, list_keep_if,
-    list_map, list_map2, list_map3, list_map_with_index, list_prepend, list_range, list_repeat,
+    list_keep_oks, list_len, list_map, list_map2, list_map3, list_map_with_index, list_prepend,
-    list_reverse, list_set, list_single, list_sort_with, list_swap,
+    list_range, list_repeat, list_reverse, list_set, list_single, list_sort_with, list_swap,
 };
 use crate::llvm::build_str::{
     empty_str, str_concat, str_count_graphemes, str_ends_with, str_from_float, str_from_int,
@@ -2538,23 +2538,13 @@ pub fn build_exp_stmt<'a, 'ctx, 'env>(
                 DecRef(symbol) => {
                     let (value, layout) = load_symbol_and_layout(scope, symbol);
 
+                    let alignment = layout.alignment_bytes(env.ptr_bytes);
+
                     match layout {
                         Layout::Builtin(Builtin::List(_)) => {
                             debug_assert!(value.is_struct_value());
 
-                            // because of how we insert DECREF for lists, we can't guarantee that
+                            build_list::decref(env, value.into_struct_value(), alignment);
-                            // the list is non-empty. When the list is empty, the pointer to the
-                            // elements is NULL, and trying to get to the RC address will
-                            // underflow, causing a segfault. Therefore, in this case we must
-                            // manually check that the list is non-empty
-                            let refcount_ptr = PointerToRefcount::from_list_wrapper(
-                                env,
-                                value.into_struct_value(),
-                            );
-
-                            let length = list_len(env.builder, value.into_struct_value());
-
-                            decrement_with_size_check(env, parent, length, *layout, refcount_ptr);
                         }
                         Layout::Builtin(Builtin::Dict(_, _)) | Layout::Builtin(Builtin::Set(_)) => {
                             debug_assert!(value.is_struct_value());

compiler/gen_llvm/src/llvm/build_list.rs

@@ -1136,3 +1136,17 @@ pub fn store_list<'a, 'ctx, 'env>(
         "cast_collection",
     )
 }
+
+pub fn decref<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    wrapper_struct: StructValue<'ctx>,
+    alignment: u32,
+) {
+    let (_, pointer) = load_list(
+        env.builder,
+        wrapper_struct,
+        env.context.i8_type().ptr_type(AddressSpace::Generic),
+    );
+
+    crate::llvm::refcounting::decref_pointer_check_null(env, pointer, alignment);
+}

compiler/gen_llvm/src/llvm/refcounting.rs

@@ -230,7 +230,7 @@ impl<'ctx> PointerToRefcount<'ctx> {
     }
 }
 
-pub fn decref_pointer<'a, 'ctx, 'env>(
+fn decref_pointer<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     pointer: PointerValue<'ctx>,
     alignment: u32,
@@ -262,8 +262,8 @@ pub fn decref_pointer_check_null<'a, 'ctx, 'env>(
         &[
             env.builder.build_bitcast(
                 pointer,
-                env.ptr_int().ptr_type(AddressSpace::Generic),
+                env.context.i8_type().ptr_type(AddressSpace::Generic),
-                "to_isize_ptr",
+                "to_i8_ptr",
             ),
             alignment.into(),
         ],