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coverage: Eagerly deduplicate covspans with the same span

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Zalathar 2024-02-18 20:38:07 +11:00
parent 7168c13579
commit ec91209f96
3 changed files with 18 additions and 15 deletions
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15
compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
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@ -52,14 +52,19 @@ pub(super) fn mir_to_initial_sorted_coverage_spans(
// - Span A extends further left, or
// - Both have the same start and span A extends further right
.then_with(|| Ord::cmp(&a.span.hi(), &b.span.hi()).reverse())
// If both spans are equal, sort the BCBs in dominator order,
// so that dominating BCBs come before other BCBs they dominate.
.then_with(|| basic_coverage_blocks.cmp_in_dominator_order(a.bcb, b.bcb))
// If two spans are otherwise identical, put closure spans first,
// as this seems to be what the refinement step expects.
// If two spans have the same lo & hi, put closure spans first,
// as they take precedence over non-closure spans.
.then_with(|| Ord::cmp(&a.is_closure, &b.is_closure).reverse())
// After deduplication, we want to keep only the most-dominated BCB.
.then_with(|| basic_coverage_blocks.cmp_in_dominator_order(a.bcb, b.bcb).reverse())
});
// Among covspans with the same span, keep only one. Closure spans take
// precedence, otherwise keep the one with the most-dominated BCB.
// (Ideally we should try to preserve _all_ non-dominating BCBs, but that
// requires a lot more complexity in the span refiner, for little benefit.)
initial_spans.dedup_by(|b, a| a.span.source_equal(b.span));
initial_spans
}