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pattern_analysis: factor out unspecialization #121324

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Feb 25, 2024
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pattern_analysis: factor out unspecialization #121324

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36 changes: 21 additions & 15 deletions compiler/rustc_pattern_analysis/src/usefulness.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1118,6 +1118,25 @@ impl<'p, Cx: TypeCx> Matrix<'p, Cx> {
}
Ok(matrix)
}

/// Recover row usefulness and intersection information from a processed specialized matrix.
/// `specialized` must come from `self.specialize_constructor`.
fn unspecialize(&mut self, specialized: Self) {
for child_row in specialized.rows() {
let parent_row_id = child_row.parent_row;
let parent_row = &mut self.rows[parent_row_id];
// A parent row is useful if any of its children is.
parent_row.useful |= child_row.useful;
for child_intersection in child_row.intersects.iter() {
// Convert the intersecting ids into ids for the parent matrix.
let parent_intersection = specialized.rows[child_intersection].parent_row;
// Note: self-intersection can happen with or-patterns.
if parent_intersection != parent_row_id {
parent_row.intersects.insert(parent_intersection);
}
}
}
}
}

/// Pretty-printer for matrices of patterns, example:
Expand Down Expand Up @@ -1542,21 +1561,6 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
// Accumulate the found witnesses.
ret.extend(witnesses);

for child_row in spec_matrix.rows() {
let parent_row_id = child_row.parent_row;
let parent_row = &mut matrix.rows[parent_row_id];
// A parent row is useful if any of its children is.
parent_row.useful |= child_row.useful;
for child_intersection in child_row.intersects.iter() {
// Convert the intersecting ids into ids for the parent matrix.
let parent_intersection = spec_matrix.rows[child_intersection].parent_row;
// Note: self-intersection can happen with or-patterns.
if parent_intersection != parent_row_id {
parent_row.intersects.insert(parent_intersection);
}
}
}

// Detect ranges that overlap on their endpoints.
if let Constructor::IntRange(overlap_range) = ctor {
if overlap_range.is_singleton()
Expand All @@ -1566,6 +1570,8 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
collect_overlapping_range_endpoints(mcx, overlap_range, matrix, &spec_matrix);
}
}

matrix.unspecialize(spec_matrix);
}

// Record usefulness in the patterns.
Expand Down