bjoernager/rust
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Move usefulness-specific pattern computations to usefulness

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This commit is contained in:
Nadrieril 2024-01-24 23:08:36 +01:00
parent 8ace7ea1f7
commit cb3ce6645f
2 changed files with 42 additions and 34 deletions
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39
compiler/rustc_pattern_analysis/src/pat.rs
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@ -29,7 +29,7 @@ pub struct DeconstructedPat<Cx: TypeCx> {
/// correspond to a user-supplied pattern.
data: Option<Cx::PatData>,
/// Whether removing this arm would change the behavior of the match expression.
useful: Cell<bool>,
pub(crate) useful: Cell<bool>,
}
impl<Cx: TypeCx> DeconstructedPat<Cx> {
@ -112,34 +112,17 @@ impl<Cx: TypeCx> DeconstructedPat<Cx> {
pub(crate) fn set_useful(&self) {
self.useful.set(true)
}
pub(crate) fn is_useful(&self) -> bool {
if self.useful.get() {
true
} else if self.is_or_pat() && self.iter_fields().any(|f| f.is_useful()) {
// We always expand or patterns in the matrix, so we will never see the actual
// or-pattern (the one with constructor `Or`) in the column. As such, it will not be
// marked as useful itself, only its children will. We recover this information here.
self.set_useful();
true
} else {
false
}
}
/// Report the subpatterns that were not useful, if any.
pub(crate) fn redundant_subpatterns(&self) -> Vec<&Self> {
let mut subpats = Vec::new();
self.collect_redundant_subpatterns(&mut subpats);
subpats
}
fn collect_redundant_subpatterns<'a>(&'a self, subpats: &mut Vec<&'a Self>) {
// We don't look at subpatterns if we already reported the whole pattern as redundant.
if !self.is_useful() {
subpats.push(self);
} else {
for p in self.iter_fields() {
p.collect_redundant_subpatterns(subpats);
}
/// Walk top-down and call `it` in each place where a pattern occurs
/// starting with the root pattern `walk` is called on. If `it` returns
/// false then we will descend no further but siblings will be processed.
pub fn walk<'a>(&'a self, it: &mut impl FnMut(&'a Self) -> bool) {
if !it(self) {
return;
}
for p in self.iter_fields() {
p.walk(it)
}
}
}