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Specialize polymorphic lists against non-polymorphic ones

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Ayaz Hafiz 2023-11-20 20:56:02 -06:00 • committed by Brendan Hansknecht
parent 37a8bbd87c
commit f72b8c2c30
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1 changed files with 43 additions and 27 deletions
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70
crates/compiler/exhaustive/src/lib.rs
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@ -399,34 +399,19 @@ pub fn is_useful(mut old_matrix: PatternMatrix, mut vector: Row) -> bool {
&mut spec_matrix, &mut spec_matrix,
); );
// Add Anythings for the missing elements. let mut vector = vector.clone();
let full_args = if let ListArity::Slice(before, _) = arity { specialize_row_with_polymorphic_list(
if arity.min_len() < list_ctor.min_len() { &mut vector,
let (before, after) = args.split_at(before); &args,
let num_extra_wildcards = arity,
list_ctor.min_len() - arity.min_len(); list_ctor,
let extra_wildcards = );
std::iter::repeat(&Anything).take(num_extra_wildcards);
before if is_useful(spec_matrix, vector) {
.iter()
.chain(extra_wildcards)
.chain(after)
.cloned()
.collect()
} else {
args.clone()
}
} else {
args.clone()
};
let mut nested_vector = vector.clone();
nested_vector.extend(full_args);
if is_useful(spec_matrix, nested_vector) {
return true; return true;
} }
} }
return false; return false;
} }
} }
@ -527,6 +512,36 @@ fn specialize_matrix_by_list(
} }
} }
fn specialize_row_with_polymorphic_list(
row: &mut Vec<Pattern>,
list_element_patterns: &[Pattern],
polymorphic_list_ctor: ListArity,
specialized_list_ctor: ListArity,
) {
let min_len = specialized_list_ctor.min_len();
if list_element_patterns.len() > min_len {
row.extend(list_element_patterns.iter().cloned());
}
let (patterns_before, patterns_after) = match polymorphic_list_ctor {
ListArity::Slice(before, after) => (
&list_element_patterns[..before],
&list_element_patterns[after..],
),
ListArity::Exact(_) => (list_element_patterns, &[] as &[Pattern]),
};
let middle_any_patterns_needed =
specialized_list_ctor.min_len() - polymorphic_list_ctor.min_len();
let middle_patterns = std::iter::repeat(Anything).take(middle_any_patterns_needed);
row.extend(
(patterns_before.iter().cloned())
.chain(middle_patterns)
.chain(patterns_after.iter().cloned()),
);
}
// Specialize a row that matches a list's constructor(s). // Specialize a row that matches a list's constructor(s).
// //
// See the docs on [build_list_ctors_covering_patterns] for more information on how list // See the docs on [build_list_ctors_covering_patterns] for more information on how list
@ -550,8 +565,9 @@ fn specialize_row_by_list(spec_arity: ListArity, mut row: Row) -> Option<Row> {
debug_assert!(spec_arity.min_len() > this_arity.min_len()); debug_assert!(spec_arity.min_len() > this_arity.min_len());
match this_arity { match this_arity {
ListArity::Exact(_) => internal_error!("exact-sized lists cannot cover lists of other minimum length"), ListArity::Exact(_) => internal_error!("exact-sized lists cannot cover lists of other minimum length"),
ListArity::Slice(before, _) => { ListArity::Slice(before, after) => {
let (before, after) = args.split_at(before); let before = &args[..before];
let after = &args[this_arity.min_len() - after..];
let num_extra_wildcards = spec_arity.min_len() - this_arity.min_len(); let num_extra_wildcards = spec_arity.min_len() - this_arity.min_len();
let extra_wildcards = std::iter::repeat(&Anything).take(num_extra_wildcards); let extra_wildcards = std::iter::repeat(&Anything).take(num_extra_wildcards);
@ -869,7 +885,7 @@ fn build_list_ctors_covering_patterns(
} }
(max_prefix_len, max_suffix_len) (max_prefix_len, max_suffix_len)
}; };
let l = inf_cover_prefix + inf_cover_suffix + 1; let l = inf_cover_prefix + inf_cover_suffix;
let exact_size_lists = (min_len..l) // exclusive let exact_size_lists = (min_len..l) // exclusive
.map(ListArity::Exact); .map(ListArity::Exact);