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Avoid useless Vec clones in pending_obligations(). #51412

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merged 1 commit into from
Jun 9, 2018
Merged

Avoid useless Vec clones in pending_obligations(). #51412

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4 changes: 2 additions & 2 deletions src/librustc/traits/engine.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ use ty::{self, Ty, TyCtxt};
use hir::def_id::DefId;

use super::{FulfillmentContext, FulfillmentError};
use super::{ObligationCause, PendingPredicateObligation, PredicateObligation};
use super::{ObligationCause, PredicateObligation};

pub trait TraitEngine<'tcx>: 'tcx {
fn normalize_projection_type<'a, 'gcx>(
Expand Down Expand Up @@ -49,7 +49,7 @@ pub trait TraitEngine<'tcx>: 'tcx {
infcx: &InferCtxt<'a, 'gcx, 'tcx>,
) -> Result<(), Vec<FulfillmentError<'tcx>>>;

fn pending_obligations(&self) -> Vec<PendingPredicateObligation<'tcx>>;
fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>>;
}

impl<'a, 'gcx, 'tcx> dyn TraitEngine<'tcx> {
Expand Down
4 changes: 2 additions & 2 deletions src/librustc/traits/fulfill.rs
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Expand Up @@ -241,8 +241,8 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
self.select(&mut selcx)
}

fn pending_obligations(&self) -> Vec<PendingPredicateObligation<'tcx>> {
self.predicates.pending_obligations()
fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
self.predicates.map_pending_obligations(|o| o.obligation.clone())
}
}

Expand Down
6 changes: 3 additions & 3 deletions src/librustc_data_structures/obligation_forest/mod.rs
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Expand Up @@ -229,13 +229,13 @@ impl<O: ForestObligation> ObligationForest<O> {
}

/// Returns the set of obligations that are in a pending state.
pub fn pending_obligations(&self) -> Vec<O>
where O: Clone
pub fn map_pending_obligations<P, F>(&self, f: F) -> Vec<P>
where F: Fn(&O) -> P
{
self.nodes
.iter()
.filter(|n| n.state.get() == NodeState::Pending)
.map(|n| n.obligation.clone())
.map(|n| f(&n.obligation))
.collect()
}

Expand Down
2 changes: 0 additions & 2 deletions src/librustc_typeck/check/closure.rs
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Expand Up @@ -225,7 +225,6 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
let expected_sig = fulfillment_cx
.pending_obligations()
.iter()
.map(|obligation| &obligation.obligation)
.filter_map(|obligation| {
debug!(
"deduce_expectations_from_obligations: obligation.predicate={:?}",
Expand Down Expand Up @@ -257,7 +256,6 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
let expected_kind = fulfillment_cx
.pending_obligations()
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If my grepping is accurate, these are the only two call sites. Since both call iter() on the resultant vector, can we not change the method to return an iterator directly, instead of collecting?

Further, I feel like we might be able to avoid cloning the obligation entirely, since iter() would only give reference-based access to it anyway...

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I tried that originally, but hit this error: "impl Trait not allowed outside of function and inherent method return types".

Because pending_obligations is a method of the TraitEngine trait.

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Ah, unfortunate. If this is hot enough, we could write a struct that implements iterator... but I'm not sure it's worth it.

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I think this patch got most of the potential gain.

.iter()
.map(|obligation| &obligation.obligation)
.filter_map(|obligation| {
let opt_trait_ref = match obligation.predicate {
ty::Predicate::Projection(ref data) => Some(data.to_poly_trait_ref(self.tcx)),
Expand Down