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[WIP] traits/select: use global vs per-infcx caches more uniformly. #69294

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[WIP] traits/select: use global vs per-infcx caches more uniformly. #69294

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b71da57
traits/select: simplify "has inference vars" check.
eddyb Feb 24, 2020
8b9e4ba
traits/select: use global vs per-infcx caches more uniformly.
eddyb Feb 19, 2020
2bc133c
traits/select: pass the whole cache key to can_use_global_caches.
eddyb Feb 19, 2020
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130 changes: 59 additions & 71 deletions src/librustc_infer/traits/select.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -835,18 +835,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
trait_ref: ty::PolyTraitRef<'tcx>,
) -> Option<EvaluationResult> {
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(&param_env.and(trait_ref)) {
return Some(cached.get(tcx));
}
}
self.infcx
.evaluation_cache
.hashmap
.borrow()
.get(&param_env.and(trait_ref))
.map(|v| v.get(tcx))
let cache = if self.can_use_global_caches(param_env) && !trait_ref.has_local_value() {
&tcx.evaluation_cache
} else {
&self.infcx.evaluation_cache
};

cache.hashmap.borrow().get(&param_env.and(trait_ref)).map(|v| v.get(tcx))
}

fn insert_evaluation_cache(
Expand All @@ -862,28 +857,22 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
return;
}

if self.can_use_global_caches(param_env) {
if !trait_ref.has_local_value() {
debug!(
"insert_evaluation_cache(trait_ref={:?}, candidate={:?}) global",
trait_ref, result,
);
// This may overwrite the cache with the same value
// FIXME: Due to #50507 this overwrites the different values
// This should be changed to use HashMapExt::insert_same
// when that is fixed
self.tcx()
.evaluation_cache
.hashmap
.borrow_mut()
.insert(param_env.and(trait_ref), WithDepNode::new(dep_node, result));
return;
}
}
let cache = if self.can_use_global_caches(param_env) && !trait_ref.has_local_value() {
debug!(
"insert_evaluation_cache(trait_ref={:?}, candidate={:?}) global",
trait_ref, result,
);
// This may overwrite the cache with the same value
// FIXME: Due to #50507 this overwrites the different values
// This should be changed to use HashMapExt::insert_same
// when that is fixed
&self.tcx().evaluation_cache
} else {
debug!("insert_evaluation_cache(trait_ref={:?}, candidate={:?})", trait_ref, result,);
&self.infcx.evaluation_cache
};

debug!("insert_evaluation_cache(trait_ref={:?}, candidate={:?})", trait_ref, result,);
self.infcx
.evaluation_cache
cache
.hashmap
.borrow_mut()
.insert(param_env.and(trait_ref), WithDepNode::new(dep_node, result));
Expand Down Expand Up @@ -982,6 +971,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
cache_fresh_trait_pred,
dep_node,
candidate.clone(),
stack.obligation.cause.span,
);
candidate
}
Expand Down Expand Up @@ -1250,18 +1240,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
) -> Option<SelectionResult<'tcx, SelectionCandidate<'tcx>>> {
let tcx = self.tcx();
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(&param_env.and(*trait_ref)) {
return Some(cached.get(tcx));
}
}
self.infcx
.selection_cache
.hashmap
.borrow()
.get(&param_env.and(*trait_ref))
.map(|v| v.get(tcx))
let cache = if self.can_use_global_caches(param_env) && !trait_ref.has_local_value() {
&tcx.selection_cache
} else {
&self.infcx.selection_cache
};

cache.hashmap.borrow().get(&param_env.and(*trait_ref)).map(|v| v.get(tcx))
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to be clear, this commit is just a "logical cleanup", right?

}

/// Determines whether can we safely cache the result
Expand All @@ -1285,9 +1270,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
result: &SelectionResult<'tcx, SelectionCandidate<'tcx>>,
) -> bool {
match result {
Ok(Some(SelectionCandidate::ParamCandidate(trait_ref))) => {
!trait_ref.skip_binder().input_types().any(|t| t.walk().any(|t_| t_.is_ty_infer()))
}
Ok(Some(SelectionCandidate::ParamCandidate(trait_ref))) => !trait_ref.needs_infer(),
Comment on lines -1288 to +1280
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This is a fix for #55258 (comment), I should make a separate commit but I didn't want to lose track of this.

_ => true,
}
}
Expand All @@ -1298,6 +1281,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
cache_fresh_trait_pred: ty::PolyTraitPredicate<'tcx>,
dep_node: DepNodeIndex,
candidate: SelectionResult<'tcx, SelectionCandidate<'tcx>>,
span: rustc_span::Span,
) {
let tcx = self.tcx();
let trait_ref = cache_fresh_trait_pred.skip_binder().trait_ref;
Expand All @@ -1311,31 +1295,35 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
return;
}

if self.can_use_global_caches(param_env) {
if let Err(Overflow) = candidate {
// Don't cache overflow globally; we only produce this in certain modes.
} else if !trait_ref.has_local_value() {
if !candidate.has_local_value() {
debug!(
"insert_candidate_cache(trait_ref={:?}, candidate={:?}) global",
trait_ref, candidate,
);
// This may overwrite the cache with the same value.
tcx.selection_cache
.hashmap
.borrow_mut()
.insert(param_env.and(trait_ref), WithDepNode::new(dep_node, candidate));
return;
}
}
// HACK(eddyb) never cache overflow (this check used to be global-only).
if let Err(Overflow) = candidate {
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with the exception of this tiny logic change, I guess

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I can't really think why we would want to cache overflow locally anyhow, that seems like a bug...

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@eddyb eddyb Mar 2, 2020 •
edited
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Pfft, that's nothing, here's something more fun: I don't think we ever use the local caches except for the intercrate mode, because we're doing freshening all the time.

So we could put intercrate in Reveal or w/e then replace freshening with canonicalization, and have only global caching (either that or I'm seriously misunderstanding the implementation).

return;
}

debug!(
"insert_candidate_cache(trait_ref={:?}, candidate={:?}) local",
trait_ref, candidate,
);
self.infcx
.selection_cache
let cache = if self.can_use_global_caches(param_env) && !trait_ref.has_local_value() {
if candidate.has_local_value() {
span_bug!(
span,
"selecting inference-free `{}` resulted in `{:?}`?!",
trait_ref,
candidate,
);
}
debug!(
"insert_candidate_cache(trait_ref={:?}, candidate={:?}) global",
trait_ref, candidate,
);
// This may overwrite the cache with the same value.
&tcx.selection_cache
} else {
debug!(
"insert_candidate_cache(trait_ref={:?}, candidate={:?}) local",
trait_ref, candidate,
);
&self.infcx.selection_cache
};

cache
.hashmap
.borrow_mut()
.insert(param_env.and(trait_ref), WithDepNode::new(dep_node, candidate));
Expand Down