Try a different Struct approach

compiler/gen/src/llvm/build.rs

@@ -3,12 +3,14 @@ use bumpalo::Bump;
 use inkwell::builder::Builder;
 use inkwell::context::Context;
 use inkwell::module::{Linkage, Module};
-use inkwell::types::{BasicTypeEnum, PointerType, StructType};
+use inkwell::types::BasicTypeEnum;
 use inkwell::values::BasicValueEnum::{self, *};
 use inkwell::values::{FunctionValue, IntValue, PointerValue};
 use inkwell::{AddressSpace, FloatPredicate, IntPredicate};
 
-use crate::llvm::convert::{basic_type_from_layout, get_array_type, get_fn_type};
+use crate::llvm::convert::{
+    basic_type_from_layout, collection_wrapper, get_array_type, get_fn_type,
+};
 use roc_collections::all::ImMap;
 use roc_module::symbol::{Interns, Symbol};
 use roc_mono::expr::{Expr, Proc, Procs};
@@ -208,30 +210,37 @@ pub fn build_expr<'a, 'ctx, 'env>(
         Array { elem_layout, elems } => {
             let ctx = env.context;
             let elem_type = basic_type_from_layout(ctx, elem_layout);
+            let builder = env.builder;
 
             if elems.is_empty() {
                 let array_type = get_array_type(&elem_type, 0);
                 let ptr_type = array_type.ptr_type(AddressSpace::Generic);
-                let struct_type = array_wrapper(ctx, ptr_type);
-                let zero = BasicValueEnum::IntValue(ctx.i32_type().const_zero());
-                let val = struct_type.const_named_struct(&[
-                    BasicValueEnum::PointerValue(ptr_type.const_null()), // pointer
-                    zero,                                                // length
-                    zero,                                                // capacity
-                ]);
+                let struct_type = collection_wrapper(ctx, ptr_type);
+                let struct_val = struct_type.const_zero();
 
-                BasicValueEnum::StructValue(val)
+                // The first field in the struct should be the pointer.
+                builder
+                    .build_insert_value(
+                        struct_val,
+                        BasicValueEnum::PointerValue(ptr_type.const_null()),
+                        0,
+                        "insert_ptr",
+                    )
+                    .unwrap();
+
+                BasicValueEnum::StructValue(struct_val)
             } else {
-                let builder = env.builder;
                 let len_u64 = elems.len() as u64;
                 let elem_bytes = elem_layout.stack_size(env.pointer_bytes) as u64;
-                let bytes_len = elem_bytes * len_u64;
 
+                let ptr = {
+                    let bytes_len = elem_bytes * len_u64;
                     let len = ctx.i32_type().const_int(bytes_len, false);
-                let ptr = env
-                    .builder
+
+                    env.builder
                         .build_array_malloc(elem_type, len, "create_list_ptr")
-                    .unwrap();
+                        .unwrap()
+                };
 
                 // Copy the elements from the list literal into the array
                 for (index, elem) in elems.iter().enumerate() {
@@ -243,32 +252,29 @@ pub fn build_expr<'a, 'ctx, 'env>(
                     builder.build_store(elem_ptr, val);
                 }
 
-                let struct_type = array_wrapper(ctx, ptr.get_type());
-                let len = BasicValueEnum::IntValue(ctx.i32_type().const_int(len_u64, false));
-                let tuple_ptr = builder.build_alloca(struct_type, "create_list_tuple");
+                let ptr_val = BasicValueEnum::PointerValue(ptr);
+                let struct_type = collection_wrapper(ctx, ptr.get_type());
+                let len = dbg!(BasicValueEnum::IntValue(
+                    ctx.i32_type().const_int(len_u64, false)
+                ));
+                let struct_val = struct_type.const_zero();
 
-                {
-                    let field_ptr =
-                        unsafe { builder.build_struct_gep(tuple_ptr, 0, "list_tuple_ptr") };
+                // Field 0: pointer
+                builder
+                    .build_insert_value(struct_val, ptr_val, 0, "insert_ptr")
+                    .unwrap();
 
-                    builder.build_store(field_ptr, BasicValueEnum::PointerValue(ptr));
-                }
+                // Field 1: length
+                builder
+                    .build_insert_value(struct_val, len, 1, "insert_len")
+                    .unwrap();
 
-                {
-                    let field_ptr =
-                        unsafe { builder.build_struct_gep(tuple_ptr, 1, "list_tuple_len") };
+                // Field 2: capacity (initially set to length)
+                builder
+                    .build_insert_value(struct_val, len, 2, "insert_capacity")
+                    .unwrap();
 
-                    builder.build_store(field_ptr, len);
-                }
-
-                {
-                    let field_ptr =
-                        unsafe { builder.build_struct_gep(tuple_ptr, 2, "list_tuple_capacity") };
-
-                    builder.build_store(field_ptr, len);
-                }
-
-                BasicValueEnum::PointerValue(tuple_ptr)
+                BasicValueEnum::StructValue(struct_val)
             }
         }
         _ => {
@@ -608,12 +614,11 @@ fn call_with_args<'a, 'ctx, 'env>(
         Symbol::LIST_LEN => {
             debug_assert!(args.len() == 1);
 
-            let tuple_ptr = args[0].into_pointer_value();
+            let tuple_struct = dbg!(args[0].into_struct_value());
             let builder = env.builder;
-            let list_len_ptr = unsafe { builder.build_struct_gep(tuple_ptr, 1, "list_tuple_len") };
 
             // Get the 32-bit int length and cast it to a 64-bit int
-            let i32_val = builder.build_load(list_len_ptr, "List.len").into_int_value();
+            let i32_val = dbg!(builder.build_extract_value(tuple_struct, 1, "unwrapped_list_len").unwrap().into_int_value());
 
             BasicValueEnum::IntValue(builder.build_int_cast(i32_val, env.context.i64_type(), "i32_to_i64"))
         }
@@ -705,11 +710,3 @@ fn call_with_args<'a, 'ctx, 'env>(
         }
     }
 }
-
-/// (pointer: usize, length: u32, capacity: u32)
-fn array_wrapper<'ctx>(ctx: &'ctx Context, ptr_type: PointerType<'ctx>) -> StructType<'ctx> {
-    let ptr_type_enum = BasicTypeEnum::PointerType(ptr_type);
-    let u32_type = BasicTypeEnum::IntType(ctx.i32_type());
-
-    ctx.struct_type(&[ptr_type_enum, u32_type, u32_type], false)
-}

compiler/gen/src/llvm/convert.rs

@@ -1,6 +1,6 @@
 use inkwell::context::Context;
 use inkwell::types::BasicTypeEnum::{self, *};
-use inkwell::types::{ArrayType, BasicType, FunctionType};
+use inkwell::types::{ArrayType, BasicType, FunctionType, PointerType, StructType};
 use inkwell::AddressSpace;
 
 use roc_mono::layout::Layout;
@@ -62,15 +62,36 @@ pub fn basic_type_from_layout<'ctx>(
         Builtin(builtin) => match builtin {
             Int64 => context.i64_type().as_basic_type_enum(),
             Float64 => context.f64_type().as_basic_type_enum(),
-            Str => context
+            Str | EmptyStr => context
                 .i8_type()
                 .ptr_type(AddressSpace::Generic)
                 .as_basic_type_enum(),
-            Map(_, _) => panic!("TODO layout_to_basic_type for Builtin::Map"),
-            Set(_) => panic!("TODO layout_to_basic_type for Builtin::Set"),
-            List(elem_layout) => basic_type_from_layout(context, elem_layout)
-                .ptr_type(AddressSpace::Generic)
-                .as_basic_type_enum(),
+            Map(_, _) | EmptyMap => panic!("TODO layout_to_basic_type for Builtin::Map"),
+            Set(_) | EmptySet => panic!("TODO layout_to_basic_type for Builtin::Set"),
+            List(elem_layout) => {
+                let ptr_type =
+                    basic_type_from_layout(context, elem_layout).ptr_type(AddressSpace::Generic);
+
+                collection_wrapper(context, ptr_type).into()
+            }
+            EmptyList => {
+                let array_type =
+                    get_array_type(&context.opaque_struct_type("empty_list_elem").into(), 0);
+                let ptr_type = array_type.ptr_type(AddressSpace::Generic);
+
+                collection_wrapper(context, ptr_type).into()
+            }
         },
     }
 }
+
+/// (pointer: usize, length: u32, capacity: u32)
+pub fn collection_wrapper<'ctx>(
+    ctx: &'ctx Context,
+    ptr_type: PointerType<'ctx>,
+) -> StructType<'ctx> {
+    let ptr_type_enum = BasicTypeEnum::PointerType(ptr_type);
+    let u32_type = BasicTypeEnum::IntType(ctx.i32_type());
+
+    ctx.struct_type(&[ptr_type_enum, u32_type, u32_type], false)
+}

compiler/gen/tests/test_gen.rs

@@ -482,6 +482,12 @@ mod test_gen {
         assert_evals_to!("1234.0", 1234.0, f64);
     }
 
+    #[test]
+    fn empty_list_len() {
+        // assert_evals_to!("List.len [ 12, 9, 6, 3 ]", 4, i64);
+        assert_llvm_evals_to!("List.len []", 0, i64, |x| x);
+    }
+
     #[test]
     fn int_list_len() {
         // assert_evals_to!("List.len [ 12, 9, 6, 3 ]", 4, i64);

compiler/mono/src/layout.rs

@@ -23,6 +23,10 @@ pub enum Builtin<'a> {
     Map(&'a Layout<'a>, &'a Layout<'a>),
     Set(&'a Layout<'a>),
     List(&'a Layout<'a>),
+    EmptyStr,
+    EmptyList,
+    EmptyMap,
+    EmptySet,
 }
 
 impl<'a> Layout<'a> {
@@ -94,10 +98,10 @@ impl<'a> Builtin<'a> {
         match self {
             Int64 => Builtin::I64_SIZE,
             Float64 => Builtin::F64_SIZE,
-            Str => Builtin::STR_WORDS * pointer_size,
-            Map(_, _) => Builtin::MAP_WORDS * pointer_size,
-            Set(_) => Builtin::SET_WORDS * pointer_size,
-            List(_) => Builtin::LIST_WORDS * pointer_size,
+            Str | EmptyStr => Builtin::STR_WORDS * pointer_size,
+            Map(_, _) | EmptyMap => Builtin::MAP_WORDS * pointer_size,
+            Set(_) | EmptySet => Builtin::SET_WORDS * pointer_size,
+            List(_) | EmptyList => Builtin::LIST_WORDS * pointer_size,
         }
     }
 }
@@ -131,10 +135,17 @@ fn layout_from_flat_type<'a>(
                 }
                 Symbol::STR_STR => Ok(Layout::Builtin(Builtin::Str)),
                 Symbol::LIST_LIST => {
-                    let elem_layout = Layout::from_var(arena, args[0], subs)?;
+                    use roc_types::subs::Content::*;
+
+                    match subs.get_without_compacting(args[0]).content {
+                        FlexVar(_) | RigidVar(_) => Ok(Layout::Builtin(Builtin::EmptyList)),
+                        content => {
+                            let elem_layout = Layout::from_content(arena, content, subs)?;
 
                             Ok(Layout::Builtin(Builtin::List(arena.alloc(elem_layout))))
                         }
+                    }
+                }
                 Symbol::ATTR_ATTR => {
                     debug_assert!(args.len() == 2);