diff --git a/compiler/gen/src/llvm/build.rs b/compiler/gen/src/llvm/build.rs
index d4c56854a2..dfa0c3c281 100644
--- a/compiler/gen/src/llvm/build.rs
+++ b/compiler/gen/src/llvm/build.rs
@@ -362,289 +362,24 @@ pub fn construct_optimization_passes<'a>(
     (mpm, fpm)
 }
 
-/// For communication with C (tests and platforms) we need to abide by the C calling convention
-///
-/// While small values are just returned like with the fast CC, larger structures need to
-/// be written into a pointer (into the callers stack)
-enum PassVia {
-    Register,
-    Memory,
-}
-
-impl PassVia {
-    fn from_layout(ptr_bytes: u32, layout: &Layout<'_>) -> Self {
-        let stack_size = layout.stack_size(ptr_bytes);
-        let eightbyte = 8;
-
-        if stack_size > 2 * eightbyte {
-            PassVia::Memory
-        } else {
-            PassVia::Register
-        }
-    }
-}
-
-/// entry point to roc code; uses the fastcc calling convention
-pub fn build_roc_main<'a, 'ctx, 'env>(
-    env: &Env<'a, 'ctx, 'env>,
-    layout_ids: &mut LayoutIds<'a>,
-    layout: &Layout<'a>,
-    main_body: &roc_mono::ir::Stmt<'a>,
-) -> &'a FunctionValue<'ctx> {
-    use inkwell::types::BasicType;
-
-    let context = env.context;
-    let builder = env.builder;
-    let arena = env.arena;
-    let ptr_bytes = env.ptr_bytes;
-
-    let return_type = basic_type_from_layout(&arena, context, &layout, ptr_bytes);
-    let roc_main_fn_name = "$Test.roc_main";
-
-    // make the roc main function
-    let roc_main_fn_type = return_type.fn_type(&[], false);
-
-    // Add main to the module.
-    let roc_main_fn = env
-        .module
-        .add_function(roc_main_fn_name, roc_main_fn_type, None);
-
-    // internal function, use fast calling convention
-    roc_main_fn.set_call_conventions(FAST_CALL_CONV);
-
-    // Add main's body
-    let basic_block = context.append_basic_block(roc_main_fn, "entry");
-
-    builder.position_at_end(basic_block);
-
-    // builds the function body (return statement included)
-    build_exp_stmt(
-        env,
-        layout_ids,
-        &mut Scope::default(),
-        roc_main_fn,
-        main_body,
-    );
-
-    env.arena.alloc(roc_main_fn)
-}
-
 pub fn promote_to_main_function<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     layout_ids: &mut LayoutIds<'a>,
     symbol: Symbol,
     layout: &Layout<'a>,
-) -> (&'static str, &'a FunctionValue<'ctx>) {
+) -> (&'static str, FunctionValue<'ctx>) {
     let fn_name = layout_ids
         .get(symbol, layout)
         .to_symbol_string(symbol, &env.interns);
 
-    let wrapped = env.module.get_function(&fn_name).unwrap();
-
-    make_main_function_help(env, layout, wrapped)
-}
-
-pub fn make_main_function<'a, 'ctx, 'env>(
-    env: &Env<'a, 'ctx, 'env>,
-    layout_ids: &mut LayoutIds<'a>,
-    layout: &Layout<'a>,
-    main_body: &roc_mono::ir::Stmt<'a>,
-) -> (&'static str, &'a FunctionValue<'ctx>) {
-    // internal main function
-    let roc_main_fn = *build_roc_main(env, layout_ids, layout, main_body);
-
-    make_main_function_help(env, layout, roc_main_fn)
-}
-
-fn make_main_function_help<'a, 'ctx, 'env>(
-    env: &Env<'a, 'ctx, 'env>,
-    layout: &Layout<'a>,
-    roc_main_fn: FunctionValue<'ctx>,
-) -> (&'static str, &'a FunctionValue<'ctx>) {
-    // build the C calling convention wrapper
-    use inkwell::types::BasicType;
-    use PassVia::*;
-
-    let context = env.context;
-    let builder = env.builder;
+    let roc_main_fn = env.module.get_function(&fn_name).unwrap();
 
     let main_fn_name = "$Test.main";
-    let u8_ptr = env.context.i8_type().ptr_type(AddressSpace::Generic);
-
-    let fields = [Layout::Builtin(Builtin::Int64), layout.clone()];
-    let main_return_layout = Layout::Struct(&fields);
-    let main_return_type = block_of_memory(context, &main_return_layout, env.ptr_bytes);
-
-    let register_or_memory = PassVia::from_layout(env.ptr_bytes, &main_return_layout);
-
-    let main_fn_type = match register_or_memory {
-        Memory => {
-            let return_value_ptr = context.i64_type().ptr_type(AddressSpace::Generic).into();
-            context.void_type().fn_type(&[return_value_ptr], false)
-        }
-        Register => main_return_type.fn_type(&[], false),
-    };
 
     // Add main to the module.
-    let main_fn = env.module.add_function(main_fn_name, main_fn_type, None);
+    let main_fn = expose_function_to_host_help(env, roc_main_fn, main_fn_name);
 
-    // our exposed main function adheres to the C calling convention
-    main_fn.set_call_conventions(C_CALL_CONV);
-
-    // Add main's body
-    let basic_block = context.append_basic_block(main_fn, "entry");
-    let then_block = context.append_basic_block(main_fn, "then_block");
-    let catch_block = context.append_basic_block(main_fn, "catch_block");
-    let cont_block = context.append_basic_block(main_fn, "cont_block");
-
-    builder.position_at_end(basic_block);
-
-    let result_alloca = builder.build_alloca(main_return_type, "result");
-
-    // invoke instead of call, so that we can catch any exeptions thrown in Roc code
-    let call_result = {
-        let call = builder.build_invoke(roc_main_fn, &[], then_block, catch_block, "call_roc_main");
-        call.set_call_convention(FAST_CALL_CONV);
-        call.try_as_basic_value().left().unwrap()
-    };
-
-    // exception handling
-    {
-        builder.position_at_end(catch_block);
-
-        let landing_pad_type = {
-            let exception_ptr = context.i8_type().ptr_type(AddressSpace::Generic).into();
-            let selector_value = context.i32_type().into();
-
-            context.struct_type(&[exception_ptr, selector_value], false)
-        };
-
-        let info = builder
-            .build_catch_all_landing_pad(
-                &landing_pad_type,
-                &BasicValueEnum::IntValue(context.i8_type().const_zero()),
-                context.i8_type().ptr_type(AddressSpace::Generic),
-                "main_landing_pad",
-            )
-            .into_struct_value();
-
-        let exception_ptr = builder
-            .build_extract_value(info, 0, "exception_ptr")
-            .unwrap();
-
-        let thrown = cxa_begin_catch(env, exception_ptr);
-
-        let error_msg = {
-            let exception_type = u8_ptr;
-            let ptr = builder.build_bitcast(
-                thrown,
-                exception_type.ptr_type(AddressSpace::Generic),
-                "cast",
-            );
-
-            builder.build_load(ptr.into_pointer_value(), "error_msg")
-        };
-
-        let return_type = context.struct_type(&[context.i64_type().into(), u8_ptr.into()], false);
-
-        let return_value = {
-            let v1 = return_type.const_zero();
-
-            // flag is non-zero, indicating failure
-            let flag = context.i64_type().const_int(1, false);
-
-            let v2 = builder
-                .build_insert_value(v1, flag, 0, "set_error")
-                .unwrap();
-
-            let v3 = builder
-                .build_insert_value(v2, error_msg, 1, "set_exception")
-                .unwrap();
-
-            v3
-        };
-
-        // bitcast result alloca so we can store our concrete type { flag, error_msg } in there
-        let result_alloca_bitcast = builder
-            .build_bitcast(
-                result_alloca,
-                return_type.ptr_type(AddressSpace::Generic),
-                "result_alloca_bitcast",
-            )
-            .into_pointer_value();
-
-        // store our return value
-        builder.build_store(result_alloca_bitcast, return_value);
-
-        cxa_end_catch(env);
-
-        builder.build_unconditional_branch(cont_block);
-    }
-
-    {
-        builder.position_at_end(then_block);
-
-        let actual_return_type =
-            basic_type_from_layout(env.arena, env.context, layout, env.ptr_bytes);
-        let return_type =
-            context.struct_type(&[context.i64_type().into(), actual_return_type], false);
-
-        let return_value = {
-            let v1 = return_type.const_zero();
-
-            let v2 = builder
-                .build_insert_value(v1, context.i64_type().const_zero(), 0, "set_no_error")
-                .unwrap();
-            let v3 = builder
-                .build_insert_value(v2, call_result, 1, "set_call_result")
-                .unwrap();
-
-            v3
-        };
-
-        let ptr = builder.build_bitcast(
-            result_alloca,
-            return_type.ptr_type(AddressSpace::Generic),
-            "name",
-        );
-        builder.build_store(ptr.into_pointer_value(), return_value);
-
-        builder.build_unconditional_branch(cont_block);
-    }
-
-    {
-        builder.position_at_end(cont_block);
-
-        let result = builder.build_load(result_alloca, "result");
-
-        match register_or_memory {
-            Memory => {
-                // write the result into the supplied pointer
-                let ptr_return_type = main_return_type.ptr_type(AddressSpace::Generic);
-
-                let ptr_as_int = main_fn.get_first_param().unwrap();
-
-                let ptr = builder.build_bitcast(ptr_as_int, ptr_return_type, "caller_ptr");
-
-                builder.build_store(ptr.into_pointer_value(), result);
-
-                // this is a void function, therefore return None
-                builder.build_return(None);
-            }
-            Register => {
-                // construct a normal return
-                // values are passed to the caller via registers
-                builder.build_return(Some(&result));
-            }
-        }
-    }
-
-    // MUST set the personality at the very end;
-    // doing it earlier can cause the personality to be ignored
-    let personality_func = get_gxx_personality_v0(env);
-    main_fn.set_personality_function(personality_func);
-
-    (main_fn_name, env.arena.alloc(main_fn))
+    (main_fn_name, main_fn)
 }
 
 fn get_inplace_from_layout(layout: &Layout<'_>) -> InPlace {
@@ -1875,9 +1610,19 @@ fn expose_function_to_host<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     roc_function: FunctionValue<'ctx>,
 ) {
+    let c_function_name: String = format!("{}_exposed", roc_function.get_name().to_str().unwrap());
+
+    expose_function_to_host_help(env, roc_function, &c_function_name);
+}
+
+fn expose_function_to_host_help<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    roc_function: FunctionValue<'ctx>,
+    c_function_name: &str,
+) -> FunctionValue<'ctx> {
     use inkwell::types::BasicType;
 
-    let roc_wrapper_function = make_exception_catching_wrapper(env, roc_function);
+    let roc_wrapper_function = make_exception_catcher(env, roc_function);
 
     let roc_function_type = roc_wrapper_function.get_type();
 
@@ -1888,13 +1633,10 @@ fn expose_function_to_host<'a, 'ctx, 'env>(
     argument_types.push(output_type.into());
 
     let c_function_type = env.context.void_type().fn_type(&argument_types, false);
-    let c_function_name: String = format!("{}_exposed", roc_function.get_name().to_str().unwrap());
 
-    let c_function = env.module.add_function(
-        c_function_name.as_str(),
-        c_function_type,
-        Some(Linkage::External),
-    );
+    let c_function =
+        env.module
+            .add_function(c_function_name, c_function_type, Some(Linkage::External));
 
     // STEP 2: build the exposed function's body
     let builder = env.builder;
@@ -1942,6 +1684,8 @@ fn expose_function_to_host<'a, 'ctx, 'env>(
 
     let size: BasicValueEnum = return_type.size_of().unwrap().into();
     builder.build_return(Some(&size));
+
+    c_function
 }
 
 fn invoke_and_catch<'a, 'ctx, 'env, F, T>(
@@ -2095,9 +1839,19 @@ where
     result
 }
 
+fn make_exception_catcher<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    roc_function: FunctionValue<'ctx>,
+) -> FunctionValue<'ctx> {
+    let wrapper_function_name = format!("{}_catcher", roc_function.get_name().to_str().unwrap());
+
+    make_exception_catching_wrapper(env, roc_function, &wrapper_function_name)
+}
+
 fn make_exception_catching_wrapper<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     roc_function: FunctionValue<'ctx>,
+    wrapper_function_name: &str,
 ) -> FunctionValue<'ctx> {
     // build the C calling convention wrapper
 
@@ -2107,8 +1861,6 @@ fn make_exception_catching_wrapper<'a, 'ctx, 'env>(
     let roc_function_type = roc_function.get_type();
     let argument_types = roc_function_type.get_param_types();
 
-    let wrapper_function_name = format!("{}_catcher", roc_function.get_name().to_str().unwrap());
-
     let wrapper_return_type = context.struct_type(
         &[
             context.i64_type().into(),
@@ -2328,70 +2080,6 @@ pub fn build_closure_caller<'a, 'ctx, 'env>(
     builder.build_return(Some(&size));
 }
 
-#[allow(dead_code)]
-pub fn build_closure_caller_old<'a, 'ctx, 'env>(
-    env: &'a Env<'a, 'ctx, 'env>,
-    closure_function: FunctionValue<'ctx>,
-) {
-    let context = env.context;
-    let builder = env.builder;
-    // asuming the closure has type `a, b, closure_data -> c`
-    // change that into `a, b, *const closure_data, *mut output -> ()`
-
-    // a function `a, b, closure_data -> RocCallResult<c>`
-    let wrapped_function = make_exception_catching_wrapper(env, closure_function);
-
-    let closure_function_type = closure_function.get_type();
-    let wrapped_function_type = wrapped_function.get_type();
-
-    let mut arguments = closure_function_type.get_param_types();
-
-    // require that the closure data is passed by reference
-    let closure_data_type = arguments.pop().unwrap();
-    let closure_data_ptr_type = get_ptr_type(&closure_data_type, AddressSpace::Generic);
-    arguments.push(closure_data_ptr_type.into());
-
-    // require that a pointer is passed in to write the result into
-    let output_type = get_ptr_type(
-        &wrapped_function_type.get_return_type().unwrap(),
-        AddressSpace::Generic,
-    );
-    arguments.push(output_type.into());
-
-    let caller_function_type = env.context.void_type().fn_type(&arguments, false);
-    let caller_function_name: String =
-        format!("{}_caller", closure_function.get_name().to_str().unwrap());
-
-    let caller_function = env.module.add_function(
-        caller_function_name.as_str(),
-        caller_function_type,
-        Some(Linkage::External),
-    );
-
-    caller_function.set_call_conventions(C_CALL_CONV);
-
-    let entry = context.append_basic_block(caller_function, "entry");
-
-    builder.position_at_end(entry);
-
-    let mut parameters = caller_function.get_params();
-    let output = parameters.pop().unwrap();
-    let closure_data_ptr = parameters.pop().unwrap();
-
-    let closure_data =
-        builder.build_load(closure_data_ptr.into_pointer_value(), "load_closure_data");
-    parameters.push(closure_data);
-
-    let call = builder.build_call(wrapped_function, &parameters, "call_wrapped_function");
-    call.set_call_convention(FAST_CALL_CONV);
-
-    let result = call.try_as_basic_value().left().unwrap();
-
-    builder.build_store(output.into_pointer_value(), result);
-
-    builder.build_return(None);
-}
-
 pub fn build_proc<'a, 'ctx, 'env>(
     env: &'a Env<'a, 'ctx, 'env>,
     layout_ids: &mut LayoutIds<'a>,
diff --git a/compiler/gen/src/run_roc.rs b/compiler/gen/src/run_roc.rs
index c9b0aff8d3..024a5198ca 100644
--- a/compiler/gen/src/run_roc.rs
+++ b/compiler/gen/src/run_roc.rs
@@ -36,15 +36,20 @@ macro_rules! run_jit_function {
     ($lib: expr, $main_fn_name: expr, $ty:ty, $transform:expr, $errors:expr) => {{
         use inkwell::context::Context;
         use roc_gen::run_roc::RocCallResult;
+        use std::mem::MaybeUninit;
 
         unsafe {
-            let main: libloading::Symbol<unsafe extern "C" fn() -> RocCallResult<$ty>> = $lib
-                .get($main_fn_name.as_bytes())
-                .ok()
-                .ok_or(format!("Unable to JIT compile `{}`", $main_fn_name))
-                .expect("errored");
+            let main: libloading::Symbol<unsafe extern "C" fn(*mut RocCallResult<$ty>) -> ()> =
+                $lib.get($main_fn_name.as_bytes())
+                    .ok()
+                    .ok_or(format!("Unable to JIT compile `{}`", $main_fn_name))
+                    .expect("errored");
 
-            match main().into() {
+            let mut result = MaybeUninit::uninit();
+
+            main(result.as_mut_ptr());
+
+            match result.assume_init().into() {
                 Ok(success) => {
                     // only if there are no exceptions thrown, check for errors
                     assert_eq!(
diff --git a/compiler/gen/tests/gen_primitives.rs b/compiler/gen/tests/gen_primitives.rs
index 6a6a9dbc29..b0dacec440 100644
--- a/compiler/gen/tests/gen_primitives.rs
+++ b/compiler/gen/tests/gen_primitives.rs
@@ -1088,7 +1088,6 @@ mod gen_primitives {
     }
 
     #[test]
-    #[ignore]
     fn return_wrapped_closure() {
         assert_non_opt_evals_to!(
             indoc!(
@@ -1101,7 +1100,7 @@ mod gen_primitives {
                 foo =
                     x = 5
 
-                    @Effect \{} -> if x > 3 then {} else {}
+                    @Effect (\{} -> if x > 3 then {} else {})
 
                 main : Effect {}
                 main = foo