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Remove 'speculative evaluation' of predicates

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Performing 'speculative evaluation' introduces caching bugs that
cannot be fixed without invasive changes to projection.

Hopefully, we can win back most of the performance lost by
re-adding 'cache completion'

Fixes #90662
This commit is contained in:
Aaron Hill 2021-12-17 10:27:26 -05:00
parent 34dc0d0f24
commit eee09ec426
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GPG key ID: B4087E510E98B164
2 changed files with 35 additions and 18 deletions
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19
compiler/rustc_trait_selection/src/traits/project.rs
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@ -10,7 +10,6 @@ use super::PredicateObligation;
use super::Selection;
use super::SelectionContext;
use super::SelectionError;
use super::TraitQueryMode;
use super::{
ImplSourceClosureData, ImplSourceDiscriminantKindData, ImplSourceFnPointerData,
ImplSourceGeneratorData, ImplSourcePointeeData, ImplSourceUserDefinedData,
@ -946,27 +945,11 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
};
let mut deduped: SsoHashSet<_> = Default::default();
let mut canonical =
SelectionContext::with_query_mode(selcx.infcx(), TraitQueryMode::Canonical);
result.obligations.drain_filter(|projected_obligation| {
if !deduped.insert(projected_obligation.clone()) {
return true;
}
// If any global obligations always apply, considering regions, then we don't
// need to include them. The `is_global` check rules out inference variables,
// so there's no need for the caller of `opt_normalize_projection_type`
// to evaluate them.
// Note that we do *not* discard obligations that evaluate to
// `EvaluatedtoOkModuloRegions`. Evaluating these obligations
// inside of a query (e.g. `evaluate_obligation`) can change
// the result to `EvaluatedToOkModuloRegions`, while an
// `EvaluatedToOk` obligation will never change the result.
// See #85360 for more details
projected_obligation.is_global(canonical.tcx())
&& canonical
.evaluate_root_obligation(projected_obligation)
.map_or(false, |res| res.must_apply_considering_regions())
false
});
if use_cache {