Reduce the scope of allow(rustc::potential_query_instability) in rustc_trait_selection

Make InferCtxtExt use a FxIndexMap

This should be faster, because the map is only being used to iterate,
which is supposed to be faster with the IndexMap

Make the user_computed_preds use an IndexMap

It is being used mostly for iteration, so the change shouldn't result in
a perf hit

Make the RegionDeps fields use an IndexMap

This change could be a perf hit. Both `larger` and `smaller` are used
for iteration, but they are also used for insertions.

Make types_without_default_bounds use an IndexMap

It uses extend, but it also iterates and removes items. Not sure if
this will be a perf hit.

Make InferTtxt.reported_trait_errors use an IndexMap

This change brought a lot of other changes. The map seems to have been
mostly used for iteration, so the performance shouldn't suffer.

Add FIXME to change ProvisionalEvaluationCache.map to use an IndexMap

Right now this results in a perf hit. IndexMap doesn't have
the `drain_filter` API, so in `on_completion` we now need to iterate two
times over the map.

7 files changed, 24 insertions, 18 deletions

diff --git a/compiler/rustc_trait_selection/src/lib.rs b/compiler/rustc_trait_selection/src/lib.rs
index 5d52aa07523..2dce18e2d3c 100644
--- a/compiler/rustc_trait_selection/src/lib.rs
+++ b/compiler/rustc_trait_selection/src/lib.rs
@@ -10,7 +10,6 @@
 //!
 //! This API is completely unstable and subject to change.
 
-#![allow(rustc::potential_query_instability)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(box_patterns)]
 #![feature(control_flow_enum)]
diff --git a/compiler/rustc_trait_selection/src/traits/auto_trait.rs b/compiler/rustc_trait_selection/src/traits/auto_trait.rs
index ed34ab95ad6..188f8bb7e2a 100644
--- a/compiler/rustc_trait_selection/src/traits/auto_trait.rs
+++ b/compiler/rustc_trait_selection/src/traits/auto_trait.rs
@@ -12,7 +12,7 @@ use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
 use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::{PolyTraitRef, Region, RegionVid};
 
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
 
 use std::collections::hash_map::Entry;
 use std::collections::VecDeque;
@@ -27,8 +27,8 @@ pub enum RegionTarget<'tcx> {
 
 #[derive(Default, Debug, Clone)]
 pub struct RegionDeps<'tcx> {
-    larger: FxHashSet<RegionTarget<'tcx>>,
-    smaller: FxHashSet<RegionTarget<'tcx>>,
+    larger: FxIndexSet<RegionTarget<'tcx>>,
+    smaller: FxIndexSet<RegionTarget<'tcx>>,
 }
 
 pub enum AutoTraitResult<A> {
@@ -266,7 +266,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
         }));
 
         let computed_preds = param_env.caller_bounds().iter();
-        let mut user_computed_preds: FxHashSet<_> = user_env.caller_bounds().iter().collect();
+        let mut user_computed_preds: FxIndexSet<_> = user_env.caller_bounds().iter().collect();
 
         let mut new_env = param_env;
         let dummy_cause = ObligationCause::dummy();
@@ -389,7 +389,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
     /// not just one specific lifetime (e.g., `'static`).
     fn add_user_pred(
         &self,
-        user_computed_preds: &mut FxHashSet<ty::Predicate<'tcx>>,
+        user_computed_preds: &mut FxIndexSet<ty::Predicate<'tcx>>,
         new_pred: ty::Predicate<'tcx>,
     ) {
         let mut should_add_new = true;
@@ -585,7 +585,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
         &self,
         ty: Ty<'_>,
         nested: impl Iterator<Item = Obligation<'tcx, ty::Predicate<'tcx>>>,
-        computed_preds: &mut FxHashSet<ty::Predicate<'tcx>>,
+        computed_preds: &mut FxIndexSet<ty::Predicate<'tcx>>,
         fresh_preds: &mut FxHashSet<ty::Predicate<'tcx>>,
         predicates: &mut VecDeque<ty::PolyTraitPredicate<'tcx>>,
         select: &mut SelectionContext<'_, 'tcx>,
diff --git a/compiler/rustc_trait_selection/src/traits/engine.rs b/compiler/rustc_trait_selection/src/traits/engine.rs
index 21516c93efb..91bf5f0b39e 100644
--- a/compiler/rustc_trait_selection/src/traits/engine.rs
+++ b/compiler/rustc_trait_selection/src/traits/engine.rs
@@ -4,7 +4,7 @@ use std::fmt::Debug;
 use super::TraitEngine;
 use super::{ChalkFulfillmentContext, FulfillmentContext};
 use crate::infer::InferCtxtExt;
-use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_infer::infer::at::ToTrace;
 use rustc_infer::infer::canonical::{
@@ -153,10 +153,10 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         param_env: ty::ParamEnv<'tcx>,
         span: Span,
         def_id: LocalDefId,
-    ) -> FxHashSet<Ty<'tcx>> {
+    ) -> FxIndexSet<Ty<'tcx>> {
         let tcx = self.infcx.tcx;
         let assumed_wf_types = tcx.assumed_wf_types(def_id);
-        let mut implied_bounds = FxHashSet::default();
+        let mut implied_bounds = FxIndexSet::default();
         let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
         let cause = ObligationCause::misc(span, hir_id);
         for ty in assumed_wf_types {
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index c7dee4a18ac..2525b9fdd47 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -14,7 +14,7 @@ use crate::traits::query::normalize::AtExt as _;
 use crate::traits::specialize::to_pretty_impl_header;
 use on_unimplemented::OnUnimplementedNote;
 use on_unimplemented::TypeErrCtxtExt as _;
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_errors::{
     pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
     MultiSpan, Style,
@@ -378,7 +378,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             index: Option<usize>, // None if this is an old error
         }
 
-        let mut error_map: FxHashMap<_, Vec<_>> = self
+        let mut error_map: FxIndexMap<_, Vec<_>> = self
             .reported_trait_errors
             .borrow()
             .iter()
diff --git a/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs b/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
index b1a161c3536..e1092a788e3 100644
--- a/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
+++ b/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
@@ -2,7 +2,7 @@ use crate::infer::InferCtxt;
 use crate::traits::query::type_op::{self, TypeOp, TypeOpOutput};
 use crate::traits::query::NoSolution;
 use crate::traits::ObligationCause;
-use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::HirId;
 use rustc_middle::ty::{self, ParamEnv, Ty};
@@ -22,7 +22,7 @@ pub trait InferCtxtExt<'a, 'tcx> {
         &'a self,
         param_env: ty::ParamEnv<'tcx>,
         body_id: hir::HirId,
-        tys: FxHashSet<Ty<'tcx>>,
+        tys: FxIndexSet<Ty<'tcx>>,
     ) -> Bounds<'a, 'tcx>;
 }
 
@@ -103,7 +103,7 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
         &'a self,
         param_env: ParamEnv<'tcx>,
         body_id: HirId,
-        tys: FxHashSet<Ty<'tcx>>,
+        tys: FxIndexSet<Ty<'tcx>>,
     ) -> Bounds<'a, 'tcx> {
         tys.into_iter()
             .map(move |ty| {
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 84be1ced520..f0d9a1c9139 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -2,6 +2,12 @@
 //!
 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html#selection
 
+// FIXME: The `map` field in ProvisionalEvaluationCache should be changed to
+// a `FxIndexMap` to avoid query instability, but right now it causes a perf regression. This would be
+// fixed or at least lightened by the addition of the `drain_filter` method to `FxIndexMap`
+// Relevant: https://github.com/rust-lang/rust/pull/103723 and https://github.com/bluss/indexmap/issues/242
+#![allow(rustc::potential_query_instability)]
+
 use self::EvaluationResult::*;
 use self::SelectionCandidate::*;
 
@@ -24,7 +30,8 @@ use crate::traits::error_reporting::TypeErrCtxtExt;
 use crate::traits::project::ProjectAndUnifyResult;
 use crate::traits::project::ProjectionCacheKeyExt;
 use crate::traits::ProjectionCacheKey;
-use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::{Diagnostic, ErrorGuaranteed};
 use rustc_hir as hir;
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
index c891658582a..43819b3f490 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
@@ -16,7 +16,7 @@ use crate::errors::NegativePositiveConflict;
 use crate::infer::{InferCtxt, InferOk, TyCtxtInferExt};
 use crate::traits::select::IntercrateAmbiguityCause;
 use crate::traits::{self, coherence, FutureCompatOverlapErrorKind, ObligationCause};
-use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
+use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::{struct_span_err, DiagnosticBuilder, EmissionGuarantee};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::ty::{self, ImplSubject, TyCtxt};
@@ -435,7 +435,7 @@ pub(crate) fn to_pretty_impl_header(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Opti
 
     // FIXME: Currently only handles ?Sized.
     //        Needs to support ?Move and ?DynSized when they are implemented.
-    let mut types_without_default_bounds = FxHashSet::default();
+    let mut types_without_default_bounds = FxIndexSet::default();
     let sized_trait = tcx.lang_items().sized_trait();
 
     if !substs.is_empty() {