From a7eae239f037cfe724cf74f7c559fed9dd87bfde Mon Sep 17 00:00:00 2001
From: Brendan Hansknecht <brendan.hansknecht@gmail.com>
Date: Mon, 16 Sep 2024 16:47:20 -0700
Subject: [PATCH] Avoid explicit tag padding

Explicit padding changes the c-abi when passed to/returned from functions.
This is leading to incorrect loading of types like `Task U64 {}`.
---
 crates/compiler/gen_llvm/src/llvm/convert.rs | 12 ------------
 crates/glue/src/RustGlue.roc                 | 20 --------------------
 2 files changed, 32 deletions(-)

diff --git a/crates/compiler/gen_llvm/src/llvm/convert.rs b/crates/compiler/gen_llvm/src/llvm/convert.rs
index 73eb20f344..257f661363 100644
--- a/crates/compiler/gen_llvm/src/llvm/convert.rs
+++ b/crates/compiler/gen_llvm/src/llvm/convert.rs
@@ -315,17 +315,6 @@ impl<'ctx> RocUnion<'ctx> {
             .as_basic_type_enum();
 
         let struct_type = if let Some(tag_type) = tag_type {
-            let tag_width = match tag_type {
-                TagType::I8 => 1,
-                TagType::I16 => 2,
-            };
-
-            let tag_padding = round_up_to_alignment(tag_width, data_align) - tag_width;
-            let tag_padding_type = context
-                .i8_type()
-                .array_type(tag_padding)
-                .as_basic_type_enum();
-
             context.struct_type(
                 &[
                     alignment_array_type,
@@ -334,7 +323,6 @@ impl<'ctx> RocUnion<'ctx> {
                         TagType::I8 => context.i8_type().into(),
                         TagType::I16 => context.i16_type().into(),
                     },
-                    tag_padding_type,
                 ],
                 false,
             )
diff --git a/crates/glue/src/RustGlue.roc b/crates/glue/src/RustGlue.roc
index 61402a838d..0531aaa602 100644
--- a/crates/glue/src/RustGlue.roc
+++ b/crates/glue/src/RustGlue.roc
@@ -1288,7 +1288,6 @@ generateRecursiveTagUnion = \buf, types, id, tagUnionName, tags, discriminantSiz
         union $(unionName) {
         """
     |> \b -> List.walk tags b (generateUnionField types)
-    |> generateTagUnionSizer types id tags
     |> Str.concat "}\n\n"
     |> generateRocRefcounted types unionType escapedName
 
@@ -1337,25 +1336,6 @@ writeTagImpls = \buf, tags, discriminantName, indents, f ->
     |> writeIndents indents
     |> Str.concat "}\n"
 
-generateTagUnionSizer : Str, Types, TypeId, _ -> Str
-generateTagUnionSizer = \buf, types, id, tags ->
-    if List.len tags > 1 then
-        # When there's a discriminant (so, multiple tags) and there is
-        # no alignment padding after the largest variant,
-        # the compiler will make extra room for the discriminant.
-        # We need that to be reflected in the overall size of the enum,
-        # so add an extra variant with the appropriate size.
-        #
-        # (Do this even if theoretically shouldn't be necessary, since
-        # there's no runtime cost and it more explicitly syncs the
-        # union's size with what we think it should be.)
-        size = getSizeRoundedToAlignment types id
-        sizeStr = Num.toStr size
-
-        Str.concat buf "$(indent)_sizer: [u8; $(sizeStr)],\n"
-    else
-        buf
-
 generateDiscriminant = \buf, types, name, tags, size ->
     if size > 0 then
         enumType =