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optimize tag union layout calculation

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Folkert 2020-03-18 22:42:10 +01:00
parent 0996f264e7
commit b28a6ffa33
2 changed files with 110 additions and 120 deletions
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164
compiler/mono/src/layout.rs
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@ -175,7 +175,6 @@ impl<'a> Builtin<'a> {
}
}
#[allow(clippy::cognitive_complexity)]
fn layout_from_flat_type<'a>(
arena: &'a Bump,
flat_type: FlatType,
@ -308,83 +307,7 @@ fn layout_from_flat_type<'a>(
TagUnion(tags, ext_var) => {
debug_assert!(ext_var_is_empty_tag_union(subs, ext_var));
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.into_iter().next().unwrap();
match &tag_name {
TagName::Private(Symbol::NUM_AT_NUM) => {
debug_assert!(arguments.len() == 1);
let var = arguments.into_iter().next().unwrap();
unwrap_num_tag(subs, var)
}
TagName::Private(_) | TagName::Global(_) => {
let mut layouts = MutMap::default();
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)?);
}
layouts.insert(tag_name.clone(), arg_layouts.into_bump_slice());
Ok(Layout::Union(arena.alloc(layouts)))
}
}
}
_ => {
// 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 ] ]
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 mut layouts = MutMap::default();
for (tag_name, arguments) in tags {
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)?);
}
layouts.insert(tag_name, arg_layouts.into_bump_slice());
}
Ok(Layout::Union(arena.alloc(layouts)))
}
}
}
layout_from_tag_union(arena, tags, subs, pointer_size)
}
RecursiveTagUnion(_, _, _) => {
panic!("TODO make Layout for non-empty Tag Union");
@ -400,6 +323,91 @@ fn layout_from_flat_type<'a>(
}
}
pub fn layout_from_tag_union<'a>(
arena: &'a Bump,
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.into_iter().next().unwrap();
match &tag_name {
TagName::Private(Symbol::NUM_AT_NUM) => {
debug_assert!(arguments.len() == 1);
let var = arguments.into_iter().next().unwrap();
unwrap_num_tag(subs, var)
}
TagName::Private(_) | TagName::Global(_) => {
let mut layouts = MutMap::default();
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)?);
}
layouts.insert(tag_name.clone(), arg_layouts.into_bump_slice());
Ok(Layout::Union(arena.alloc(layouts)))
}
}
}
_ => {
// 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 ] ]
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 mut layouts = MutMap::default();
for (tag_name, arguments) in tags {
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)?);
}
layouts.insert(tag_name, arg_layouts.into_bump_slice());
}
Ok(Layout::Union(arena.alloc(layouts)))
}
}
}
}
fn ext_var_is_empty_tag_union(subs: &Subs, ext_var: Variable) -> bool {
// the ext_var is empty
let mut ext_fields = std::vec::Vec::new();