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Auto merge of #84944 - lcnr:obligation-dedup, r=jackh726

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remove obligation dedup from `impl_or_trait_obligations`

Looking at the examples from #38528 they all seem to compile fine even without this and it seems like this might be unnecessary effort
This commit is contained in:
bors 2022-03-03 15:43:42 +00:00
parent 4566094913 b9414850d2
commit 32cbc7630b
1 changed files with 0 additions and 22 deletions
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22
compiler/rustc_trait_selection/src/traits/select/mod.rs
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@ -2374,28 +2374,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
});
}
// We are performing deduplication here to avoid exponential blowups
// (#38528) from happening, but the real cause of the duplication is
// unknown. What we know is that the deduplication avoids exponential
// amount of predicates being propagated when processing deeply nested
// types.
//
// This code is hot enough that it's worth avoiding the allocation
// required for the FxHashSet when possible. Special-casing lengths 0,
// 1 and 2 covers roughly 75-80% of the cases.
if obligations.len() <= 1 {
// No possibility of duplicates.
} else if obligations.len() == 2 {
// Only two elements. Drop the second if they are equal.
if obligations[0] == obligations[1] {
obligations.truncate(1);
}
} else {
// Three or more elements. Use a general deduplication process.
let mut seen = FxHashSet::default();
obligations.retain(|i| seen.insert(i.clone()));
}
obligations
}
}