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modify the comment on `in_cycle` to reflect changes requested by ariel and myself.
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pnkfelix committed May 13, 2019
1 parent bd005a2 commit decd6d366018823a8b1116b346bc778eb010accd
Showing with 7 additions and 2 deletions.
  1. +7 −2 src/librustc/traits/select.rs
@@ -173,10 +173,15 @@ struct TraitObligationStack<'prev, 'tcx: 'prev> {
/// well as the second instance of `A: AutoTrait`) to supress
/// caching.
///
/// This is a simple, targeted fix. The correct fix requires
/// This is a simple, targeted fix. A more-performant fix requires
/// deeper changes, but would permit more caching: we could
/// basically defer caching until we have fully evaluated the
/// tree, and then cache the entire tree at once.
/// tree, and then cache the entire tree at once. In any case, the
/// performance impact here shouldn't be so horrible: every time
/// this is hit, we do cache at least one trait, so we only
/// evaluate each member of a cycle up to N times, where N is the
/// length of the cycle. This means the performance impact is
/// bounded and we shouldn't have any terrible worst-cases.
in_cycle: Cell<bool>,

previous: TraitObligationStackList<'prev, 'tcx>,

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