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Fix a performance regression in obligation deduplication.

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Commit 8378487 from #114611 changed the location of an obligation
deduplication step in `opt_normalize_projection_type`. This meant that
deduplication stopped happening on one path where it was still
necessary, causing a couple of drastic performance regressions.

This commit moves the deduplication back to the old location. The good
news is that #114611 had four commits and 8378487 was of minimal
importance, so the perf benefits from that PR remain.

Fixes #116780, #116797.
This commit is contained in:
Nicholas Nethercote 2023-10-17 09:51:36 +11:00
parent 99592fdfa1
commit 91f2fbc867
1 changed files with 4 additions and 4 deletions
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8
compiler/rustc_trait_selection/src/traits/project.rs
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@ -1233,7 +1233,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
let projected_term = selcx.infcx.resolve_vars_if_possible(projected_term);
let result = if projected_term.has_projections() {
let mut result = if projected_term.has_projections() {
let mut normalizer = AssocTypeNormalizer::new(
selcx,
param_env,
@ -1243,14 +1243,14 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
);
let normalized_ty = normalizer.fold(projected_term);
let mut deduped = SsoHashSet::with_capacity(projected_obligations.len());
projected_obligations.retain(|obligation| deduped.insert(obligation.clone()));
Normalized { value: normalized_ty, obligations: projected_obligations }
} else {
Normalized { value: projected_term, obligations: projected_obligations }
};
let mut deduped = SsoHashSet::with_capacity(result.obligations.len());
result.obligations.retain(|obligation| deduped.insert(obligation.clone()));
if use_cache {
infcx.inner.borrow_mut().projection_cache().insert_term(cache_key, result.clone());
}