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fixes after review

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This commit is contained in:
Folkert 2020-03-10 12:01:13 +01:00
parent c7daad8404
commit 246199ec3e
2 changed files with 79 additions and 28 deletions
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24
compiler/mono/src/layout.rs
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@ -5,6 +5,8 @@ use roc_module::ident::{Lowercase, TagName};
use roc_module::symbol::Symbol;
use roc_types::subs::{Content, FlatType, Subs, Variable};
const POINTER_SIZE: u32 = std::mem::size_of::<usize>() as u32;
/// Types for code gen must be monomorphic. No type variables allowed!
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum Layout<'a> {
@ -250,8 +252,26 @@ fn layout_from_flat_type<'a>(
}
_ => {
// Check if we can turn this tag union into an enum
// TODO rather than the arguments being empty, check whether their layout has size 0.
if tags.len() <= 256 && tags.iter().all(|(_, args)| args.is_empty()) {
// 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)
.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 {
// Up to 2 enum tags can be stored (in theory) in one bit
let mut it = tags.keys();