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clean up tag pattern match conversion

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This commit is contained in:
Folkert 2020-03-23 17:12:44 +01:00
parent a7b5768c47
commit b9613fcdc5
4 changed files with 121 additions and 139 deletions
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127
compiler/mono/src/layout.rs
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@ -287,7 +287,7 @@ fn layout_from_flat_type<'a>(
TagUnion(tags, ext_var) => {
debug_assert!(ext_var_is_empty_tag_union(subs, ext_var));
layout_from_tag_union(arena, &tags, subs, pointer_size)
Ok(layout_from_tag_union(arena, tags, subs, pointer_size))
}
RecursiveTagUnion(_, _, _) => {
panic!("TODO make Layout for non-empty Tag Union");
@ -394,18 +394,27 @@ fn union_sorted_tags_help<'a>(
UnionVariant::ByteUnion(tag_names)
}
1 => {
// special-case NUM_AT_NUM: if its argument is a FlexVar, make it Int
let (tag_name, arguments) = tags_vec.remove(0);
// just one tag in the union (but with arguments) can be a struct
let mut layouts = Vec::with_capacity_in(tags_vec.len(), arena);
let arguments = tags_vec.remove(0).1;
for var in arguments.iter() {
let layout = Layout::from_var(arena, *var, subs, pointer_size)
.expect("invalid layout from var");
layouts.push(layout);
match tag_name {
TagName::Private(Symbol::NUM_AT_NUM) => {
layouts.push(unwrap_num_tag(subs, arguments[0]).expect("invalid num layout"));
}
_ => {
for var in arguments.iter() {
let layout = Layout::from_var(arena, *var, subs, pointer_size)
.expect("invalid layout from var");
layouts.push(layout);
}
}
}
UnionVariant::Unwrapped(layouts)
}
_ => {
// default path
let mut result = Vec::with_capacity_in(tags_vec.len(), arena);
@ -432,94 +441,38 @@ fn union_sorted_tags_help<'a>(
pub fn layout_from_tag_union<'a>(
arena: &'a Bump,
tags: &MutMap<TagName, std::vec::Vec<Variable>>,
tags: MutMap<TagName, std::vec::Vec<Variable>>,
subs: &Subs,
pointer_size: u32,
) -> Result<Layout<'a>, ()> {
match tags.len() {
0 => {
panic!("TODO gracefully handle trying to instantiate Never");
}
// We can only unwrap a wrapper if it never becomes part of a bigger union
// therefore, the ext_var must be the literal empty tag union
1 => {
// This is a wrapper. Unwrap it!
let (tag_name, arguments) = tags.iter().next().unwrap();
) -> Layout<'a> {
use UnionVariant::*;
match &tag_name {
TagName::Private(Symbol::NUM_AT_NUM) => {
debug_assert!(arguments.len() == 1);
let tags_vec: std::vec::Vec<_> = tags.into_iter().collect();
let first_tag = tags_vec[0].clone();
let variant = union_sorted_tags_help(arena, tags_vec, subs, pointer_size);
let var = arguments.iter().next().unwrap();
match variant {
Never => panic!("TODO gracefully handle trying to instantiate Never"),
Unit => Layout::Struct(&[]),
BoolUnion { .. } => Layout::Builtin(Builtin::Bool),
ByteUnion(_) => Layout::Builtin(Builtin::Byte),
Unwrapped(field_layouts) => match first_tag.0 {
TagName::Private(Symbol::NUM_AT_NUM) => {
let arguments = first_tag.1;
debug_assert!(arguments.len() == 1);
let var = arguments.iter().next().unwrap();
unwrap_num_tag(subs, *var)
}
TagName::Private(_) | TagName::Global(_) => {
let mut arg_layouts = Vec::with_capacity_in(arguments.len(), arena);
for arg in arguments {
arg_layouts.push(Layout::from_var(arena, *arg, subs, pointer_size)?);
}
let layouts = [arg_layouts.into_bump_slice()];
Ok(Layout::Union(arena.alloc(layouts)))
}
unwrap_num_tag(subs, *var).expect("invalid Num argument")
}
}
_ => {
// Check if we can turn this tag union into an enum
// The arguments of all tags must have size 0.
// That is trivially the case when there are no arguments
//
// [ Orange, Apple, Banana ]
//
// But when one-tag tag unions are optimized away, we can also use an enum for
//
// [ Foo [ Unit ], Bar [ Unit ] ]
_ => Layout::Struct(field_layouts.into_bump_slice()),
},
Wrapped(tags) => {
let mut tag_layouts = Vec::with_capacity_in(tags.len(), arena);
let arguments_have_size_0 = || {
tags.iter().all(|(_, args)| {
args.iter().all(|var| {
Layout::from_var(arena, *var, subs, pointer_size)
.map(|v| v.stack_size(pointer_size))
== Ok(0)
})
})
};
// up to 256 enum keys can be stored in a byte
if tags.len() <= std::u8::MAX as usize + 1 && arguments_have_size_0() {
if tags.len() <= 2 {
Ok(Layout::Builtin(Builtin::Bool))
} else {
// up to 256 enum tags can be stored in a byte
Ok(Layout::Builtin(Builtin::Byte))
}
} else {
let add_discriminant = tags.len() != 1;
let mut layouts = Vec::with_capacity_in(tags.len(), arena);
for arguments in tags.values() {
// add a field for the discriminant if there is more than one tag in the union
let mut arg_layouts = if add_discriminant {
let discriminant = Layout::Builtin(Builtin::Int64);
let mut result = Vec::with_capacity_in(arguments.len() + 1, arena);
result.push(discriminant);
result
} else {
Vec::with_capacity_in(arguments.len(), arena)
};
for arg in arguments {
arg_layouts.push(Layout::from_var(arena, *arg, subs, pointer_size)?);
}
layouts.push(arg_layouts.into_bump_slice());
}
Ok(Layout::Union(arena.alloc(layouts)))
for (_, tag_layout) in tags {
tag_layouts.push(tag_layout);
}
Layout::Union(tag_layouts.into_bump_slice())
}
}
}