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When possible, prefer NonNullableUnwrapped over NullableWrapped

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e.g. in the scenario of `[ A Str, B, C, D ]`, rather than having one tag be nullable, we want
to store the tag id in the pointer. This generally saves 8 bytes for
every allocation, and prevents an allocations for all tags except A.
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Folkert 2023-07-16 18:57:09 +02:00
parent 06dbe06971
commit 48fa4f7a8e
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4 changed files with 72 additions and 74 deletions
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48
crates/compiler/mono/src/layout.rs
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@ -3883,6 +3883,36 @@ where
union_sorted_tags_help(env, tags_vec, opt_rec_var, DropUninhabitedVariants(true)).value()
}
fn find_nullable_tag<'a, L, I>(tags: I) -> Option<(TagIdIntType, L)>
where
I: Iterator<Item = (&'a L, &'a [Variable])>,
L: Into<TagOrClosure> + Ord + Clone + 'a,
{
let mut length = 0;
let mut has_payload = 0;
let mut nullable = None;
for (index, (name, variables)) in tags.enumerate() {
length += 1;
if variables.is_empty() {
nullable = nullable.or_else(|| Some((index as TagIdIntType, name.clone())));
} else {
has_payload += 1;
}
}
let has_no_payload = length - has_payload;
// in the scenario of `[ A Str, B, C, D ]`, rather than having one tag be nullable, we want
// to store the tag id in the pointer. (we want NonNullableUnwrapped, not NullableWrapped)
if (has_payload > 1 && has_no_payload > 0) || has_no_payload == 1 {
nullable
} else {
None
}
}
fn union_sorted_tags_help<'a, L>(
env: &mut Env<'a, '_>,
mut tags_vec: std::vec::Vec<(L, std::vec::Vec<Variable>)>,
@ -3965,12 +3995,7 @@ where
// only recursive tag unions can be nullable
let is_recursive = opt_rec_var.is_some();
if is_recursive && GENERATE_NULLABLE {
for (index, (name, variables)) in tags_vec.iter().enumerate() {
if variables.is_empty() {
nullable = Some((index as TagIdIntType, name.clone()));
break;
}
}
nullable = find_nullable_tag(tags_vec.iter().map(|(a, b)| (a, b.as_slice())));
}
for (index, (tag_name, arguments)) in tags_vec.into_iter().enumerate() {
@ -4260,17 +4285,12 @@ where
let mut nullable = None;
if GENERATE_NULLABLE {
for (index, (_name, variables)) in tags_vec.iter().enumerate() {
if variables.is_empty() {
nullable = Some(index as TagIdIntType);
break;
}
}
nullable = find_nullable_tag(tags_vec.iter().map(|(a, b)| (*a, *b)));
}
env.insert_seen(rec_var);
for (index, &(_name, variables)) in tags_vec.iter().enumerate() {
if matches!(nullable, Some(i) if i == index as TagIdIntType) {
if matches!(nullable, Some((i, _)) if i == index as TagIdIntType) {
// don't add the nullable case
continue;
}
@ -4303,7 +4323,7 @@ where
}
env.remove_seen(rec_var);
let union_layout = if let Some(tag_id) = nullable {
let union_layout = if let Some((tag_id, _)) = nullable {
match tag_layouts.into_bump_slice() {
[one] => {
let nullable_id = tag_id != 0;