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Auto merge of #90996 - the8472:obligation-hashes2, r=matthewjasper
Optimize `impl Hash for ObligationCauseData` by not hashing `ObligationCauseCode` variant fields
Split out from #90913 since it's a [clear performance win](https://perf.rust-lang.org/compare.html?start=ad442399756573dccacb314b6bf8079964bcc72a&end=223f5e877fe93b5f437c2d703f883797913cd2b7) and should be easier to review.
It speeds up hashing for `Obligation` [deduplication](c9c4b5d727/compiler/rustc_trait_selection/src/traits/select/mod.rs (L2355-L2356)
) by only hashing the discriminant of the `ObligationCauseCode` enum instead of its contents. That shouldn't affect hash quality much since there are several other fields in `Obligation` which should be unique enough, especially the predicate itself which is hashed as an interned pointer.
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commit
18fa4342fc
@ -23,6 +23,7 @@ use smallvec::SmallVec;
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use std::borrow::Cow;
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use std::fmt;
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use std::hash::{Hash, Hasher};
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use std::ops::Deref;
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pub use self::select::{EvaluationCache, EvaluationResult, OverflowError, SelectionCache};
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@ -108,7 +109,7 @@ impl Deref for ObligationCause<'tcx> {
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}
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}
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#[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
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#[derive(Clone, Debug, PartialEq, Eq, Lift)]
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pub struct ObligationCauseData<'tcx> {
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pub span: Span,
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@ -123,6 +124,14 @@ pub struct ObligationCauseData<'tcx> {
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pub code: ObligationCauseCode<'tcx>,
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}
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impl Hash for ObligationCauseData<'_> {
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fn hash<H: Hasher>(&self, state: &mut H) {
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self.body_id.hash(state);
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self.span.hash(state);
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std::mem::discriminant(&self.code).hash(state);
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}
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}
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impl<'tcx> ObligationCause<'tcx> {
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#[inline]
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pub fn new(
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