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Auto merge of #66821 - eddyb:global-trait-caching, r=nikomatsakis

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rustc: allow non-empty ParamEnv's in global trait select/eval caches.

*Based on #66963*

This appears to alleviate the symptoms of #65510 locally (without fixing WF directly), and is potentially easier to validate as sound (since it's a more ad-hoc version of queries we already have).

I'm opening this PR primarily to test the effects on perf.

r? @nikomatsakis cc @rust-lang/wg-traits
This commit is contained in:
bors 2019-12-11 12:29:35 +00:00
commit 90b957a17c
4 changed files with 36 additions and 26 deletions
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10
src/librustc/traits/project.rs
View File

@ -1079,12 +1079,10 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
if !is_default {
true
} else if obligation.param_env.reveal == Reveal::All {
debug_assert!(!poly_trait_ref.needs_infer());
if !poly_trait_ref.needs_subst() {
true
} else {
false
}
// NOTE(eddyb) inference variables can resolve to parameters, so
// assume `poly_trait_ref` isn't monomorphic, if it contains any.
let poly_trait_ref = selcx.infcx().resolve_vars_if_possible(&poly_trait_ref);
!poly_trait_ref.needs_infer() && !poly_trait_ref.needs_subst()
} else {
false
}

37
src/librustc/traits/select.rs
View File

@ -204,7 +204,10 @@ struct TraitObligationStack<'prev, 'tcx> {
#[derive(Clone, Default)]
pub struct SelectionCache<'tcx> {
hashmap: Lock<
FxHashMap<ty::TraitRef<'tcx>, WithDepNode<SelectionResult<'tcx, SelectionCandidate<'tcx>>>>,
FxHashMap<
ty::ParamEnvAnd<'tcx, ty::TraitRef<'tcx>>,
WithDepNode<SelectionResult<'tcx, SelectionCandidate<'tcx>>>,
>,
>,
}
@ -490,7 +493,9 @@ fn from(OverflowError: OverflowError) -> SelectionError<'tcx> {
#[derive(Clone, Default)]
pub struct EvaluationCache<'tcx> {
hashmap: Lock<FxHashMap<ty::PolyTraitRef<'tcx>, WithDepNode<EvaluationResult>>>,
hashmap: Lock<
FxHashMap<ty::ParamEnvAnd<'tcx, ty::PolyTraitRef<'tcx>>, WithDepNode<EvaluationResult>>,
>,
}
impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
@ -1143,7 +1148,7 @@ fn check_evaluation_cache(
let tcx = self.tcx();
if self.can_use_global_caches(param_env) {
let cache = tcx.evaluation_cache.hashmap.borrow();
if let Some(cached) = cache.get(&trait_ref) {
if let Some(cached) = cache.get(&param_env.and(trait_ref)) {
return Some(cached.get(tcx));
}
}
@ -1151,7 +1156,7 @@ fn check_evaluation_cache(
.evaluation_cache
.hashmap
.borrow()
.get(&trait_ref)
.get(&param_env.and(trait_ref))
.map(|v| v.get(tcx))
}
@ -1182,7 +1187,7 @@ fn insert_evaluation_cache(
.evaluation_cache
.hashmap
.borrow_mut()
.insert(trait_ref, WithDepNode::new(dep_node, result));
.insert(param_env.and(trait_ref), WithDepNode::new(dep_node, result));
return;
}
}
@ -1195,7 +1200,7 @@ fn insert_evaluation_cache(
.evaluation_cache
.hashmap
.borrow_mut()
.insert(trait_ref, WithDepNode::new(dep_node, result));
.insert(param_env.and(trait_ref), WithDepNode::new(dep_node, result));
}
/// For various reasons, it's possible for a subobligation
@ -1567,14 +1572,10 @@ fn is_knowable<'o>(&mut self, stack: &TraitObligationStack<'o, 'tcx>) -> Option<
/// Do note that if the type itself is not in the
/// global tcx, the local caches will be used.
fn can_use_global_caches(&self, param_env: ty::ParamEnv<'tcx>) -> bool {
// If there are any where-clauses in scope, then we always use
// a cache local to this particular scope. Otherwise, we
// switch to a global cache. We used to try and draw
// finer-grained distinctions, but that led to a serious of
// annoying and weird bugs like #22019 and #18290. This simple
// rule seems to be pretty clearly safe and also still retains
// a very high hit rate (~95% when compiling rustc).
if !param_env.caller_bounds.is_empty() {
// If there are any e.g. inference variables in the `ParamEnv`, then we
// always use a cache local to this particular scope. Otherwise, we
// switch to a global cache.
if param_env.has_local_value() {
return false;
}
@ -1602,7 +1603,7 @@ fn check_candidate_cache(
let trait_ref = &cache_fresh_trait_pred.skip_binder().trait_ref;
if self.can_use_global_caches(param_env) {
let cache = tcx.selection_cache.hashmap.borrow();
if let Some(cached) = cache.get(&trait_ref) {
if let Some(cached) = cache.get(&param_env.and(*trait_ref)) {
return Some(cached.get(tcx));
}
}
@ -1610,7 +1611,7 @@ fn check_candidate_cache(
.selection_cache
.hashmap
.borrow()
.get(trait_ref)
.get(&param_env.and(*trait_ref))
.map(|v| v.get(tcx))
}
@ -1671,7 +1672,7 @@ fn insert_candidate_cache(
tcx.selection_cache
.hashmap
.borrow_mut()
.insert(trait_ref, WithDepNode::new(dep_node, candidate));
.insert(param_env.and(trait_ref), WithDepNode::new(dep_node, candidate));
return;
}
}
@ -1685,7 +1686,7 @@ fn insert_candidate_cache(
.selection_cache
.hashmap
.borrow_mut()
.insert(trait_ref, WithDepNode::new(dep_node, candidate));
.insert(param_env.and(trait_ref), WithDepNode::new(dep_node, candidate));
}
fn assemble_candidates<'o>(

1
src/test/ui/type-alias-impl-trait/bound_reduction2.rs
View File

@ -9,6 +9,7 @@ trait TraitWithAssoc {
type Foo<V> = impl Trait<V>;
//~^ ERROR could not find defining uses
//~| ERROR the trait bound `T: TraitWithAssoc` is not satisfied
trait Trait<U> {}

14
src/test/ui/type-alias-impl-trait/bound_reduction2.stderr
View File

@ -1,5 +1,14 @@
error[E0277]: the trait bound `T: TraitWithAssoc` is not satisfied
--> $DIR/bound_reduction2.rs:10:1
|
LL | type Foo<V> = impl Trait<V>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TraitWithAssoc` is not implemented for `T`
...
LL | fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
| -- help: consider further restricting this bound: `T: TraitWithAssoc +`
error: defining opaque type use does not fully define opaque type: generic parameter `V` is specified as concrete type `<T as TraitWithAssoc>::Assoc`
--> $DIR/bound_reduction2.rs:17:1
--> $DIR/bound_reduction2.rs:18:1
|
LL | / fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
LL | | ()
@ -12,5 +21,6 @@ error: could not find defining uses
LL | type Foo<V> = impl Trait<V>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 2 previous errors
error: aborting due to 3 previous errors
For more information about this error, try `rustc --explain E0277`.