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Simplify empty pattern logic some more

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Nadrieril 2024-01-10 23:08:31 +01:00
parent de77f1a86e
commit d95644d3ae
1 changed files with 7 additions and 8 deletions
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15
compiler/rustc_pattern_analysis/src/usefulness.rs
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@ -1450,23 +1450,19 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
is_top_level && matches!(ctors_for_ty, ConstructorSet::NoConstructors); is_top_level && matches!(ctors_for_ty, ConstructorSet::NoConstructors);
// Whether empty patterns can be omitted for exhaustiveness. // Whether empty patterns can be omitted for exhaustiveness.
let can_omit_empty_arms = is_toplevel_exception || mcx.tycx.is_exhaustive_patterns_feature_on(); let can_omit_empty_arms = is_toplevel_exception || mcx.tycx.is_exhaustive_patterns_feature_on();
// Whether empty patterns are counted as useful or not.
let empty_arms_are_unreachable = place_validity.is_known_valid() && can_omit_empty_arms;
// Analyze the constructors present in this column. // Analyze the constructors present in this column.
let ctors = matrix.heads().map(|p| p.ctor()); let ctors = matrix.heads().map(|p| p.ctor());
let mut split_set = ctors_for_ty.split(ctors); let mut split_set = ctors_for_ty.split(ctors);
if !can_omit_empty_arms {
// Treat all missing constructors as nonempty.
// This clears `missing_empty`.
split_set.missing.append(&mut split_set.missing_empty);
}
let all_missing = split_set.present.is_empty(); let all_missing = split_set.present.is_empty();
// Build the set of constructors we will specialize with. It must cover the whole type. // Build the set of constructors we will specialize with. It must cover the whole type.
// We need to iterate over a full set of constructors, so we add `Missing` to represent the // We need to iterate over a full set of constructors, so we add `Missing` to represent the
// missing ones. This is explained under "Constructor Splitting" at the top of this file. // missing ones. This is explained under "Constructor Splitting" at the top of this file.
let mut split_ctors = split_set.present; let mut split_ctors = split_set.present;
if !(split_set.missing.is_empty() if !(split_set.missing.is_empty()
&& (split_set.missing_empty.is_empty() || place_validity.is_known_valid())) && (split_set.missing_empty.is_empty() || empty_arms_are_unreachable))
{ {
split_ctors.push(Constructor::Missing); split_ctors.push(Constructor::Missing);
} }
@ -1479,7 +1475,10 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
// Which constructors are considered missing. We ensure that `!missing_ctors.is_empty() => // Which constructors are considered missing. We ensure that `!missing_ctors.is_empty() =>
// split_ctors.contains(Missing)`. The converse usually holds except when // split_ctors.contains(Missing)`. The converse usually holds except when
// `!place_validity.is_known_valid()`. // `!place_validity.is_known_valid()`.
let missing_ctors = split_set.missing; let mut missing_ctors = split_set.missing;
if !can_omit_empty_arms {
missing_ctors.append(&mut split_set.missing_empty);
}
let mut ret = WitnessMatrix::empty(); let mut ret = WitnessMatrix::empty();
for ctor in split_ctors { for ctor in split_ctors {