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Report arm intersections

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This commit is contained in:
Nadrieril 2024-03-17 15:48:27 +01:00
parent 3c85e56249
commit 3dfd0fd858
1 changed files with 21 additions and 4 deletions
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25
compiler/rustc_pattern_analysis/src/usefulness.rs
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@ -1042,7 +1042,7 @@ struct MatrixRow<'p, Cx: PatCx> {
is_under_guard: bool, is_under_guard: bool,
/// When we specialize, we remember which row of the original matrix produced a given row of the /// When we specialize, we remember which row of the original matrix produced a given row of the
/// specialized matrix. When we unspecialize, we use this to propagate usefulness back up the /// specialized matrix. When we unspecialize, we use this to propagate usefulness back up the
/// callstack. /// callstack. On creation, this stores the index of the original match arm.
parent_row: usize, parent_row: usize,
/// False when the matrix is just built. This is set to `true` by /// False when the matrix is just built. This is set to `true` by
/// [`compute_exhaustiveness_and_usefulness`] if the arm is found to be useful. /// [`compute_exhaustiveness_and_usefulness`] if the arm is found to be useful.
@ -1163,10 +1163,10 @@ fn new(arms: &[MatchArm<'p, Cx>], scrut_ty: Cx::Ty, scrut_validity: PlaceValidit
place_info: smallvec![place_info], place_info: smallvec![place_info],
wildcard_row_is_relevant: true, wildcard_row_is_relevant: true,
}; };
for (row_id, arm) in arms.iter().enumerate() { for (arm_id, arm) in arms.iter().enumerate() {
let v = MatrixRow { let v = MatrixRow {
pats: PatStack::from_pattern(arm.pat), pats: PatStack::from_pattern(arm.pat),
parent_row: row_id, // dummy, we don't read it parent_row: arm_id,
is_under_guard: arm.has_guard, is_under_guard: arm.has_guard,
useful: false, useful: false,
intersects: BitSet::new_empty(0), // Initialized in `Matrix::expand_and_push`. intersects: BitSet::new_empty(0), // Initialized in `Matrix::expand_and_push`.
@ -1738,6 +1738,9 @@ pub struct UsefulnessReport<'p, Cx: PatCx> {
/// If the match is exhaustive, this is empty. If not, this contains witnesses for the lack of /// If the match is exhaustive, this is empty. If not, this contains witnesses for the lack of
/// exhaustiveness. /// exhaustiveness.
pub non_exhaustiveness_witnesses: Vec<WitnessPat<Cx>>, pub non_exhaustiveness_witnesses: Vec<WitnessPat<Cx>>,
/// For each arm, a set of indices of arms above it that have non-empty intersection, i.e. there
/// is a value matched by both arms. This may miss real intersections.
pub arm_intersections: Vec<BitSet<usize>>,
} }
/// Computes whether a match is exhaustive and which of its arms are useful. /// Computes whether a match is exhaustive and which of its arms are useful.
@ -1769,5 +1772,19 @@ pub fn compute_match_usefulness<'p, Cx: PatCx>(
}) })
.collect(); .collect();
Ok(UsefulnessReport { arm_usefulness, non_exhaustiveness_witnesses }) let mut arm_intersections: Vec<_> =
arms.iter().enumerate().map(|(i, _)| BitSet::new_empty(i)).collect();
for row in matrix.rows() {
let arm_id = row.parent_row;
for intersection in row.intersects.iter() {
// Convert the matrix row ids into arm ids (they can differ because we expand or-patterns).
let arm_intersection = matrix.rows[intersection].parent_row;
// Note: self-intersection can happen with or-patterns.
if arm_intersection != arm_id {
arm_intersections[arm_id].insert(arm_intersection);
}
}
}
Ok(UsefulnessReport { arm_usefulness, non_exhaustiveness_witnesses, arm_intersections })
} }