Auto merge of #119192 - michaelwoerister:mcp533-push, r=cjgillot

Replace a number of FxHashMaps/Sets with stable-iteration-order alternatives

This PR replaces almost all of the remaining `FxHashMap`s in query results with either `FxIndexMap` or `UnordMap`. The only case that is missing is the `EffectiveVisibilities` struct which turned out to not be straightforward to transform. Once that is done too, we can remove the `HashStable` implementation from `HashMap`.

The first commit adds the `StableCompare` trait which is a companion trait to `StableOrd`. Some types like `Symbol` can be compared in a cross-session stable way, but their `Ord` implementation is not stable. In such cases, a `StableCompare` implementation can be provided to offer a lightweight way for stable sorting. The more heavyweight option is to sort via `ToStableHashKey`, but then sorting needs to have access to a stable hashing context and `ToStableHashKey` can also be expensive as in the case of `Symbol` where it has to allocate a `String`.

The rest of the commits are rather mechanical and don't overlap, so they are best reviewed individually.

Part of [MCP 533](https://github.com/rust-lang/compiler-team/issues/533).

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -3,7 +3,7 @@ use crate::base::allocator_kind_for_codegen;
 use std::collections::hash_map::Entry::*;
 
 use rustc_ast::expand::allocator::{ALLOCATOR_METHODS, NO_ALLOC_SHIM_IS_UNSTABLE};
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::unord::UnordMap;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
@@ -393,10 +393,10 @@ fn exported_symbols_provider_local(
 fn upstream_monomorphizations_provider(
     tcx: TyCtxt<'_>,
     (): (),
-) -> DefIdMap<FxHashMap<GenericArgsRef<'_>, CrateNum>> {
+) -> DefIdMap<UnordMap<GenericArgsRef<'_>, CrateNum>> {
     let cnums = tcx.crates(());
 
-    let mut instances: DefIdMap<FxHashMap<_, _>> = Default::default();
+    let mut instances: DefIdMap<UnordMap<_, _>> = Default::default();
 
     let drop_in_place_fn_def_id = tcx.lang_items().drop_in_place_fn();
 
@@ -445,7 +445,7 @@ fn upstream_monomorphizations_provider(
 fn upstream_monomorphizations_for_provider(
     tcx: TyCtxt<'_>,
     def_id: DefId,
-) -> Option<&FxHashMap<GenericArgsRef<'_>, CrateNum>> {
+) -> Option<&UnordMap<GenericArgsRef<'_>, CrateNum>> {
     debug_assert!(!def_id.is_local());
     tcx.upstream_monomorphizations(()).get(&def_id)
 }
@@ -656,7 +656,7 @@ fn maybe_emutls_symbol_name<'tcx>(
     }
 }
 
-fn wasm_import_module_map(tcx: TyCtxt<'_>, cnum: CrateNum) -> FxHashMap<DefId, String> {
+fn wasm_import_module_map(tcx: TyCtxt<'_>, cnum: CrateNum) -> DefIdMap<String> {
     // Build up a map from DefId to a `NativeLib` structure, where
     // `NativeLib` internally contains information about
     // `#[link(wasm_import_module = "...")]` for example.
@@ -665,9 +665,9 @@ fn wasm_import_module_map(tcx: TyCtxt<'_>, cnum: CrateNum) -> FxHashMap<DefId, S
     let def_id_to_native_lib = native_libs
         .iter()
         .filter_map(|lib| lib.foreign_module.map(|id| (id, lib)))
-        .collect::<FxHashMap<_, _>>();
+        .collect::<DefIdMap<_>>();
 
-    let mut ret = FxHashMap::default();
+    let mut ret = DefIdMap::default();
     for (def_id, lib) in tcx.foreign_modules(cnum).iter() {
         let module = def_id_to_native_lib.get(def_id).and_then(|s| s.wasm_import_module());
         let Some(module) = module else { continue };

compiler/rustc_codegen_ssa/src/target_features.rs

@@ -1,8 +1,8 @@
 use crate::errors;
 use rustc_ast::ast;
 use rustc_attr::InstructionSetAttr;
-use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::fx::FxIndexSet;
+use rustc_data_structures::unord::UnordMap;
 use rustc_errors::Applicability;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
@@ -18,7 +18,7 @@ use rustc_span::Span;
 pub fn from_target_feature(
     tcx: TyCtxt<'_>,
     attr: &ast::Attribute,
-    supported_target_features: &FxHashMap<String, Option<Symbol>>,
+    supported_target_features: &UnordMap<String, Option<Symbol>>,
     target_features: &mut Vec<Symbol>,
 ) {
     let Some(list) = attr.meta_item_list() else { return };

compiler/rustc_data_structures/src/stable_hasher.rs

@@ -245,6 +245,32 @@ unsafe impl<T: StableOrd> StableOrd for &T {
     const CAN_USE_UNSTABLE_SORT: bool = T::CAN_USE_UNSTABLE_SORT;
 }
 
+/// This is a companion trait to `StableOrd`. Some types like `Symbol` can be
+/// compared in a cross-session stable way, but their `Ord` implementation is
+/// not stable. In such cases, a `StableOrd` implementation can be provided
+/// to offer a lightweight way for stable sorting. (The more heavyweight option
+/// is to sort via `ToStableHashKey`, but then sorting needs to have access to
+/// a stable hashing context and `ToStableHashKey` can also be expensive as in
+/// the case of `Symbol` where it has to allocate a `String`.)
+///
+/// See the documentation of [StableOrd] for how stable sort order is defined.
+/// The same definition applies here. Be careful when implementing this trait.
+pub trait StableCompare {
+    const CAN_USE_UNSTABLE_SORT: bool;
+
+    fn stable_cmp(&self, other: &Self) -> std::cmp::Ordering;
+}
+
+/// `StableOrd` denotes that the type's `Ord` implementation is stable, so
+/// we can implement `StableCompare` by just delegating to `Ord`.
+impl<T: StableOrd> StableCompare for T {
+    const CAN_USE_UNSTABLE_SORT: bool = T::CAN_USE_UNSTABLE_SORT;
+
+    fn stable_cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.cmp(other)
+    }
+}
+
 /// Implement HashStable by just calling `Hash::hash()`. Also implement `StableOrd` for the type since
 /// that has the same requirements.
 ///

compiler/rustc_data_structures/src/unord.rs

@@ -3,9 +3,8 @@
 //! as required by the query system.
 
 use rustc_hash::{FxHashMap, FxHashSet};
-use smallvec::SmallVec;
 use std::{
-    borrow::Borrow,
+    borrow::{Borrow, BorrowMut},
     collections::hash_map::Entry,
     hash::Hash,
     iter::{Product, Sum},
@@ -14,7 +13,7 @@ use std::{
 
 use crate::{
     fingerprint::Fingerprint,
-    stable_hasher::{HashStable, StableHasher, StableOrd, ToStableHashKey},
+    stable_hasher::{HashStable, StableCompare, StableHasher, ToStableHashKey},
 };
 
 /// `UnordItems` is the order-less version of `Iterator`. It only contains methods
@@ -134,36 +133,78 @@ impl<'a, T: Copy + 'a, I: Iterator<Item = &'a T>> UnordItems<&'a T, I> {
     }
 }
 
-impl<T: Ord, I: Iterator<Item = T>> UnordItems<T, I> {
+impl<T, I: Iterator<Item = T>> UnordItems<T, I> {
+    #[inline]
     pub fn into_sorted<HCX>(self, hcx: &HCX) -> Vec<T>
     where
         T: ToStableHashKey<HCX>,
     {
-        let mut items: Vec<T> = self.0.collect();
+        self.collect_sorted(hcx, true)
-        items.sort_by_cached_key(|x| x.to_stable_hash_key(hcx));
-        items
     }
 
     #[inline]
     pub fn into_sorted_stable_ord(self) -> Vec<T>
     where
-        T: Ord + StableOrd,
+        T: StableCompare,
     {
-        let mut items: Vec<T> = self.0.collect();
+        self.collect_stable_ord_by_key(|x| x)
-        if !T::CAN_USE_UNSTABLE_SORT {
+    }
-            items.sort();
+
-        } else {
+    #[inline]
-            items.sort_unstable()
+    pub fn into_sorted_stable_ord_by_key<K, C>(self, project_to_key: C) -> Vec<T>
+    where
+        K: StableCompare,
+        C: for<'a> Fn(&'a T) -> &'a K,
+    {
+        self.collect_stable_ord_by_key(project_to_key)
+    }
+
+    #[inline]
+    pub fn collect_sorted<HCX, C>(self, hcx: &HCX, cache_sort_key: bool) -> C
+    where
+        T: ToStableHashKey<HCX>,
+        C: FromIterator<T> + BorrowMut<[T]>,
+    {
+        let mut items: C = self.0.collect();
+
+        let slice = items.borrow_mut();
+        if slice.len() > 1 {
+            if cache_sort_key {
+                slice.sort_by_cached_key(|x| x.to_stable_hash_key(hcx));
+            } else {
+                slice.sort_by_key(|x| x.to_stable_hash_key(hcx));
+            }
         }
+
         items
     }
 
-    pub fn into_sorted_small_vec<HCX, const LEN: usize>(self, hcx: &HCX) -> SmallVec<[T; LEN]>
+    #[inline]
+    pub fn collect_stable_ord_by_key<K, C, P>(self, project_to_key: P) -> C
     where
-        T: ToStableHashKey<HCX>,
+        K: StableCompare,
+        P: for<'a> Fn(&'a T) -> &'a K,
+        C: FromIterator<T> + BorrowMut<[T]>,
     {
-        let mut items: SmallVec<[T; LEN]> = self.0.collect();
+        let mut items: C = self.0.collect();
-        items.sort_by_cached_key(|x| x.to_stable_hash_key(hcx));
+
+        let slice = items.borrow_mut();
+        if slice.len() > 1 {
+            if !K::CAN_USE_UNSTABLE_SORT {
+                slice.sort_by(|a, b| {
+                    let a_key = project_to_key(a);
+                    let b_key = project_to_key(b);
+                    a_key.stable_cmp(b_key)
+                });
+            } else {
+                slice.sort_unstable_by(|a, b| {
+                    let a_key = project_to_key(a);
+                    let b_key = project_to_key(b);
+                    a_key.stable_cmp(b_key)
+                });
+            }
+        }
+
         items
     }
 }
@@ -268,16 +309,30 @@ impl<V: Eq + Hash> UnordSet<V> {
     }
 
     /// Returns the items of this set in stable sort order (as defined by
-    /// `StableOrd`). This method is much more efficient than
+    /// `StableCompare`). This method is much more efficient than
     /// `into_sorted` because it does not need to transform keys to their
     /// `ToStableHashKey` equivalent.
     #[inline]
-    pub fn to_sorted_stable_ord(&self) -> Vec<V>
+    pub fn to_sorted_stable_ord(&self) -> Vec<&V>
     where
-        V: Ord + StableOrd + Clone,
+        V: StableCompare,
     {
-        let mut items: Vec<V> = self.inner.iter().cloned().collect();
+        let mut items: Vec<&V> = self.inner.iter().collect();
-        items.sort_unstable();
+        items.sort_unstable_by(|a, b| a.stable_cmp(*b));
+        items
+    }
+
+    /// Returns the items of this set in stable sort order (as defined by
+    /// `StableCompare`). This method is much more efficient than
+    /// `into_sorted` because it does not need to transform keys to their
+    /// `ToStableHashKey` equivalent.
+    #[inline]
+    pub fn into_sorted_stable_ord(self) -> Vec<V>
+    where
+        V: StableCompare,
+    {
+        let mut items: Vec<V> = self.inner.into_iter().collect();
+        items.sort_unstable_by(V::stable_cmp);
         items
     }
 
@@ -483,16 +538,16 @@ impl<K: Eq + Hash, V> UnordMap<K, V> {
         to_sorted_vec(hcx, self.inner.iter(), cache_sort_key, |&(k, _)| k)
     }
 
-    /// Returns the entries of this map in stable sort order (as defined by `StableOrd`).
+    /// Returns the entries of this map in stable sort order (as defined by `StableCompare`).
     /// This method can be much more efficient than `into_sorted` because it does not need
     /// to transform keys to their `ToStableHashKey` equivalent.
     #[inline]
-    pub fn to_sorted_stable_ord(&self) -> Vec<(K, &V)>
+    pub fn to_sorted_stable_ord(&self) -> Vec<(&K, &V)>
     where
-        K: Ord + StableOrd + Copy,
+        K: StableCompare,
     {
-        let mut items: Vec<(K, &V)> = self.inner.iter().map(|(&k, v)| (k, v)).collect();
+        let mut items: Vec<_> = self.inner.iter().collect();
-        items.sort_unstable_by_key(|&(k, _)| k);
+        items.sort_unstable_by(|(a, _), (b, _)| a.stable_cmp(*b));
         items
     }
 
@@ -510,6 +565,19 @@ impl<K: Eq + Hash, V> UnordMap<K, V> {
         to_sorted_vec(hcx, self.inner.into_iter(), cache_sort_key, |(k, _)| k)
     }
 
+    /// Returns the entries of this map in stable sort order (as defined by `StableCompare`).
+    /// This method can be much more efficient than `into_sorted` because it does not need
+    /// to transform keys to their `ToStableHashKey` equivalent.
+    #[inline]
+    pub fn into_sorted_stable_ord(self) -> Vec<(K, V)>
+    where
+        K: StableCompare,
+    {
+        let mut items: Vec<(K, V)> = self.inner.into_iter().collect();
+        items.sort_unstable_by(|a, b| a.0.stable_cmp(&b.0));
+        items
+    }
+
     /// Returns the values of this map in stable sort order (as defined by K's
     /// `ToStableHashKey` implementation).
     ///

compiler/rustc_hir_analysis/src/astconv/errors.rs

@@ -6,6 +6,7 @@ use crate::errors::{
 use crate::fluent_generated as fluent;
 use crate::traits::error_reporting::report_object_safety_error;
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap, FxIndexSet};
+use rustc_data_structures::unord::UnordMap;
 use rustc_errors::{pluralize, struct_span_err, Applicability, Diagnostic, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -673,7 +674,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 }))
             })
             .flatten()
-            .collect::<FxHashMap<Symbol, &ty::AssocItem>>();
+            .collect::<UnordMap<Symbol, &ty::AssocItem>>();
 
         let mut names = names
             .into_iter()
@@ -709,7 +710,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let mut where_constraints = vec![];
         let mut already_has_generics_args_suggestion = false;
         for (span, assoc_items) in &associated_types {
-            let mut names: FxHashMap<_, usize> = FxHashMap::default();
+            let mut names: UnordMap<_, usize> = Default::default();
             for item in assoc_items {
                 types_count += 1;
                 *names.entry(item.name).or_insert(0) += 1;

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -1,6 +1,6 @@
 use super::potentially_plural_count;
 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
-use hir::def_id::{DefId, LocalDefId};
+use hir::def_id::{DefId, DefIdMap, LocalDefId};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed};
 use rustc_hir as hir;
@@ -478,7 +478,7 @@ fn compare_asyncness<'tcx>(
 pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_m_def_id: LocalDefId,
-) -> Result<&'tcx FxHashMap<DefId, ty::EarlyBinder<Ty<'tcx>>>, ErrorGuaranteed> {
+) -> Result<&'tcx DefIdMap<ty::EarlyBinder<Ty<'tcx>>>, ErrorGuaranteed> {
     let impl_m = tcx.opt_associated_item(impl_m_def_id.to_def_id()).unwrap();
     let trait_m = tcx.opt_associated_item(impl_m.trait_item_def_id.unwrap()).unwrap();
     let impl_trait_ref =
@@ -706,7 +706,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
     );
     ocx.resolve_regions_and_report_errors(impl_m_def_id, &outlives_env)?;
 
-    let mut remapped_types = FxHashMap::default();
+    let mut remapped_types = DefIdMap::default();
     for (def_id, (ty, args)) in collected_types {
         match infcx.fully_resolve((ty, args)) {
             Ok((ty, args)) => {

compiler/rustc_hir_analysis/src/collect.rs

@@ -16,6 +16,7 @@
 
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::unord::UnordMap;
 use rustc_errors::{Applicability, DiagnosticBuilder, ErrorGuaranteed, StashKey};
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
@@ -979,7 +980,7 @@ fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
         })
         // Check for duplicates
         .and_then(|list| {
-            let mut set: FxHashMap<Symbol, Span> = FxHashMap::default();
+            let mut set: UnordMap<Symbol, Span> = Default::default();
             let mut no_dups = true;
 
             for ident in &*list {

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -913,7 +913,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             for ((span, add_where_or_comma), obligations) in type_params.into_iter() {
                 restrict_type_params = true;
                 // #74886: Sort here so that the output is always the same.
-                let obligations = obligations.to_sorted_stable_ord();
+                let obligations = obligations.into_sorted_stable_ord();
                 err.span_suggestion_verbose(
                     span,
                     format!(

compiler/rustc_hir_typeck/src/upvar.rs

@@ -912,7 +912,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         drop_order: bool,
     ) -> MigrationWarningReason {
         MigrationWarningReason {
-            auto_traits: auto_trait_reasons.to_sorted_stable_ord(),
+            auto_traits: auto_trait_reasons.into_sorted_stable_ord(),
             drop_order,
         }
     }

compiler/rustc_hir_typeck/src/writeback.rs

@@ -473,7 +473,7 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
         assert_eq!(fcx_typeck_results.hir_owner, self.typeck_results.hir_owner);
 
         let fcx_coercion_casts = fcx_typeck_results.coercion_casts().to_sorted_stable_ord();
-        for local_id in fcx_coercion_casts {
+        for &local_id in fcx_coercion_casts {
             self.typeck_results.set_coercion_cast(local_id);
         }
     }

compiler/rustc_incremental/src/persist/save.rs

@@ -103,7 +103,7 @@ pub fn save_work_product_index(
     // deleted during invalidation. Some object files don't change their
     // content, they are just not needed anymore.
     let previous_work_products = dep_graph.previous_work_products();
-    for (id, wp) in previous_work_products.to_sorted_stable_ord().iter() {
+    for (id, wp) in previous_work_products.to_sorted_stable_ord() {
         if !new_work_products.contains_key(id) {
             work_product::delete_workproduct_files(sess, wp);
             debug_assert!(

compiler/rustc_lint/src/foreign_modules.rs

@@ -1,5 +1,5 @@
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::stack::ensure_sufficient_stack;
+use rustc_data_structures::unord::{UnordMap, UnordSet};
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_middle::query::Providers;
@@ -72,7 +72,7 @@ struct ClashingExternDeclarations {
     /// the symbol should be reported as a clashing declaration.
     // FIXME: Technically, we could just store a &'tcx str here without issue; however, the
     // `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
-    seen_decls: FxHashMap<Symbol, hir::OwnerId>,
+    seen_decls: UnordMap<Symbol, hir::OwnerId>,
 }
 
 /// Differentiate between whether the name for an extern decl came from the link_name attribute or
@@ -96,7 +96,7 @@ impl SymbolName {
 
 impl ClashingExternDeclarations {
     pub(crate) fn new() -> Self {
-        ClashingExternDeclarations { seen_decls: FxHashMap::default() }
+        ClashingExternDeclarations { seen_decls: Default::default() }
     }
 
     /// Insert a new foreign item into the seen set. If a symbol with the same name already exists
@@ -209,12 +209,12 @@ fn structurally_same_type<'tcx>(
     b: Ty<'tcx>,
     ckind: types::CItemKind,
 ) -> bool {
-    let mut seen_types = FxHashSet::default();
+    let mut seen_types = UnordSet::default();
     structurally_same_type_impl(&mut seen_types, tcx, param_env, a, b, ckind)
 }
 
 fn structurally_same_type_impl<'tcx>(
-    seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
+    seen_types: &mut UnordSet<(Ty<'tcx>, Ty<'tcx>)>,
     tcx: TyCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     a: Ty<'tcx>,

compiler/rustc_lint/src/non_ascii_idents.rs

@@ -4,7 +4,8 @@ use crate::lints::{
 };
 use crate::{EarlyContext, EarlyLintPass, LintContext};
 use rustc_ast as ast;
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::FxIndexMap;
+use rustc_data_structures::unord::UnordMap;
 use rustc_span::symbol::Symbol;
 
 declare_lint! {
@@ -194,8 +195,8 @@ impl EarlyLintPass for NonAsciiIdents {
         }
 
         if has_non_ascii_idents && check_confusable_idents {
-            let mut skeleton_map: FxHashMap<Symbol, (Symbol, Span, bool)> =
+            let mut skeleton_map: UnordMap<Symbol, (Symbol, Span, bool)> =
-                FxHashMap::with_capacity_and_hasher(symbols.len(), Default::default());
+                UnordMap::with_capacity(symbols.len());
             let mut skeleton_buf = String::new();
 
             for (&symbol, &sp) in symbols.iter() {
@@ -248,8 +249,8 @@ impl EarlyLintPass for NonAsciiIdents {
                 Verified,
             }
 
-            let mut script_states: FxHashMap<AugmentedScriptSet, ScriptSetUsage> =
+            let mut script_states: FxIndexMap<AugmentedScriptSet, ScriptSetUsage> =
-                FxHashMap::default();
+                Default::default();
             let latin_augmented_script_set = AugmentedScriptSet::for_char('A');
             script_states.insert(latin_augmented_script_set, ScriptSetUsage::Verified);
 

compiler/rustc_lint_defs/src/lib.rs

@@ -9,7 +9,9 @@ pub use self::Level::*;
 use rustc_ast::node_id::NodeId;
 use rustc_ast::{AttrId, Attribute};
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
+use rustc_data_structures::stable_hasher::{
+    HashStable, StableCompare, StableHasher, ToStableHashKey,
+};
 use rustc_error_messages::{DiagnosticMessage, MultiSpan};
 use rustc_hir::HashStableContext;
 use rustc_hir::HirId;
@@ -541,6 +543,14 @@ impl<HCX> ToStableHashKey<HCX> for LintId {
     }
 }
 
+impl StableCompare for LintId {
+    const CAN_USE_UNSTABLE_SORT: bool = true;
+
+    fn stable_cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.lint_name_raw().cmp(&other.lint_name_raw())
+    }
+}
+
 #[derive(Debug)]
 pub struct AmbiguityErrorDiag {
     pub msg: String,

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -2,10 +2,8 @@ use crate::errors::{FailCreateFileEncoder, FailWriteFile};
 use crate::rmeta::*;
 
 use rustc_ast::Attribute;
-use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_data_structures::memmap::{Mmap, MmapMut};
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::{join, par_for_each_in, Lrc};
 use rustc_data_structures::temp_dir::MaybeTempDir;
 use rustc_hir as hir;
@@ -1914,14 +1912,15 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         empty_proc_macro!(self);
         let tcx = self.tcx;
         let lib_features = tcx.lib_features(LOCAL_CRATE);
-        self.lazy_array(lib_features.to_vec())
+        self.lazy_array(lib_features.to_sorted_vec())
     }
 
     fn encode_stability_implications(&mut self) -> LazyArray<(Symbol, Symbol)> {
         empty_proc_macro!(self);
         let tcx = self.tcx;
         let implications = tcx.stability_implications(LOCAL_CRATE);
-        self.lazy_array(implications.iter().map(|(k, v)| (*k, *v)))
+        let sorted = implications.to_sorted_stable_ord();
+        self.lazy_array(sorted.into_iter().map(|(k, v)| (*k, *v)))
     }
 
     fn encode_diagnostic_items(&mut self) -> LazyArray<(Symbol, DefIndex)> {
@@ -2033,14 +2032,10 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
     fn encode_incoherent_impls(&mut self) -> LazyArray<IncoherentImpls> {
         empty_proc_macro!(self);
         let tcx = self.tcx;
-        let mut all_impls: Vec<_> = tcx.crate_inherent_impls(()).incoherent_impls.iter().collect();
+        let all_impls = tcx.with_stable_hashing_context(|hcx| {
-        tcx.with_stable_hashing_context(|mut ctx| {
+            tcx.crate_inherent_impls(()).incoherent_impls.to_sorted(&hcx, true)
-            all_impls.sort_by_cached_key(|&(&simp, _)| {
-                let mut hasher = StableHasher::new();
-                simp.hash_stable(&mut ctx, &mut hasher);
-                hasher.finish::<Fingerprint>()
-            })
         });
+
         let all_impls: Vec<_> = all_impls
             .into_iter()
             .map(|(&simp, impls)| {

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -12,7 +12,7 @@ use rustc_attr as attr;
 use rustc_data_structures::svh::Svh;
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, DefKind, DocLinkResMap};
-use rustc_hir::def_id::{CrateNum, DefId, DefIndex, DefPathHash, StableCrateId};
+use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, DefIndex, DefPathHash, StableCrateId};
 use rustc_hir::definitions::DefKey;
 use rustc_hir::lang_items::LangItem;
 use rustc_index::bit_set::BitSet;
@@ -459,7 +459,7 @@ define_tables! {
     macro_definition: Table<DefIndex, LazyValue<ast::DelimArgs>>,
     proc_macro: Table<DefIndex, MacroKind>,
     deduced_param_attrs: Table<DefIndex, LazyArray<DeducedParamAttrs>>,
-    trait_impl_trait_tys: Table<DefIndex, LazyValue<FxHashMap<DefId, ty::EarlyBinder<Ty<'static>>>>>,
+    trait_impl_trait_tys: Table<DefIndex, LazyValue<DefIdMap<ty::EarlyBinder<Ty<'static>>>>>,
     doc_link_resolutions: Table<DefIndex, LazyValue<DocLinkResMap>>,
     doc_link_traits_in_scope: Table<DefIndex, LazyArray<DefId>>,
     assumed_wf_types_for_rpitit: Table<DefIndex, LazyArray<(Ty<'static>, Span)>>,

compiler/rustc_middle/src/arena.rs

@@ -103,7 +103,7 @@ macro_rules! arena_types {
             [] dep_kind: rustc_middle::dep_graph::DepKindStruct<'tcx>,
 
             [decode] trait_impl_trait_tys:
-                rustc_data_structures::fx::FxHashMap<
+                rustc_data_structures::unord::UnordMap<
                     rustc_hir::def_id::DefId,
                     rustc_middle::ty::EarlyBinder<rustc_middle::ty::Ty<'tcx>>
                 >,

compiler/rustc_middle/src/middle/mod.rs

@@ -4,7 +4,7 @@ pub mod dependency_format;
 pub mod exported_symbols;
 pub mod lang_items;
 pub mod lib_features {
-    use rustc_data_structures::fx::FxHashMap;
+    use rustc_data_structures::unord::UnordMap;
     use rustc_span::{symbol::Symbol, Span};
 
     #[derive(Copy, Clone, Debug, PartialEq, Eq)]
@@ -16,15 +16,16 @@ pub mod lib_features {
 
     #[derive(HashStable, Debug, Default)]
     pub struct LibFeatures {
-        pub stability: FxHashMap<Symbol, (FeatureStability, Span)>,
+        pub stability: UnordMap<Symbol, (FeatureStability, Span)>,
     }
 
     impl LibFeatures {
-        pub fn to_vec(&self) -> Vec<(Symbol, FeatureStability)> {
+        pub fn to_sorted_vec(&self) -> Vec<(Symbol, FeatureStability)> {
-            let mut all_features: Vec<_> =
+            self.stability
-                self.stability.iter().map(|(&sym, &(stab, _))| (sym, stab)).collect();
+                .to_sorted_stable_ord()
-            all_features.sort_unstable_by(|(a, _), (b, _)| a.as_str().cmp(b.as_str()));
+                .iter()
-            all_features
+                .map(|(&sym, &(stab, _))| (sym, stab))
+                .collect()
         }
     }
 }

compiler/rustc_middle/src/middle/region.rs

@@ -7,12 +7,11 @@
 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/borrow_check.html
 
 use crate::ty::TyCtxt;
-use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
+use rustc_data_structures::fx::FxIndexMap;
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::unord::UnordMap;
 use rustc_hir as hir;
 use rustc_hir::{HirIdMap, Node};
 use rustc_macros::HashStable;
-use rustc_query_system::ich::StableHashingContext;
 use rustc_span::{Span, DUMMY_SP};
 
 use std::fmt;
@@ -205,7 +204,7 @@ impl Scope {
 pub type ScopeDepth = u32;
 
 /// The region scope tree encodes information about region relationships.
-#[derive(Default, Debug)]
+#[derive(Default, Debug, HashStable)]
 pub struct ScopeTree {
     /// If not empty, this body is the root of this region hierarchy.
     pub root_body: Option<hir::HirId>,
@@ -306,7 +305,7 @@ pub struct ScopeTree {
     /// The reason is that semantically, until the `box` expression returns,
     /// the values are still owned by their containing expressions. So
     /// we'll see that `&x`.
-    pub yield_in_scope: FxHashMap<Scope, Vec<YieldData>>,
+    pub yield_in_scope: UnordMap<Scope, Vec<YieldData>>,
 }
 
 /// Identifies the reason that a given expression is an rvalue candidate
@@ -404,23 +403,3 @@ impl ScopeTree {
         self.yield_in_scope.get(&scope).map(Deref::deref)
     }
 }
-
-impl<'a> HashStable<StableHashingContext<'a>> for ScopeTree {
-    fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
-        let ScopeTree {
-            root_body,
-            ref parent_map,
-            ref var_map,
-            ref destruction_scopes,
-            ref rvalue_candidates,
-            ref yield_in_scope,
-        } = *self;
-
-        root_body.hash_stable(hcx, hasher);
-        parent_map.hash_stable(hcx, hasher);
-        var_map.hash_stable(hcx, hasher);
-        destruction_scopes.hash_stable(hcx, hasher);
-        rvalue_candidates.hash_stable(hcx, hasher);
-        yield_in_scope.hash_stable(hcx, hasher);
-    }
-}

compiler/rustc_middle/src/middle/resolve_bound_vars.rs

@@ -2,7 +2,7 @@
 
 use crate::ty;
 
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def_id::DefId;
 use rustc_hir::{ItemLocalId, OwnerId};
@@ -51,7 +51,7 @@ pub enum ObjectLifetimeDefault {
 pub struct ResolveBoundVars {
     /// Maps from every use of a named (not anonymous) lifetime to a
     /// `Region` describing how that region is bound
-    pub defs: FxHashMap<OwnerId, FxHashMap<ItemLocalId, ResolvedArg>>,
+    pub defs: FxIndexMap<OwnerId, FxIndexMap<ItemLocalId, ResolvedArg>>,
 
-    pub late_bound_vars: FxHashMap<OwnerId, FxHashMap<ItemLocalId, Vec<ty::BoundVariableKind>>>,
+    pub late_bound_vars: FxIndexMap<OwnerId, FxIndexMap<ItemLocalId, Vec<ty::BoundVariableKind>>>,
 }

compiler/rustc_middle/src/middle/stability.rs

@@ -8,11 +8,11 @@ use rustc_ast::NodeId;
 use rustc_attr::{
     self as attr, ConstStability, DefaultBodyStability, DeprecatedSince, Deprecation, Stability,
 };
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::unord::UnordMap;
 use rustc_errors::{Applicability, Diagnostic};
 use rustc_feature::GateIssue;
 use rustc_hir::def::DefKind;
-use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_hir::def_id::{DefId, LocalDefId, LocalDefIdMap};
 use rustc_hir::{self as hir, HirId};
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_session::lint::builtin::{DEPRECATED, DEPRECATED_IN_FUTURE, SOFT_UNSTABLE};
@@ -61,10 +61,10 @@ impl DeprecationEntry {
 pub struct Index {
     /// This is mostly a cache, except the stabilities of local items
     /// are filled by the annotator.
-    pub stab_map: FxHashMap<LocalDefId, Stability>,
+    pub stab_map: LocalDefIdMap<Stability>,
-    pub const_stab_map: FxHashMap<LocalDefId, ConstStability>,
+    pub const_stab_map: LocalDefIdMap<ConstStability>,
-    pub default_body_stab_map: FxHashMap<LocalDefId, DefaultBodyStability>,
+    pub default_body_stab_map: LocalDefIdMap<DefaultBodyStability>,
-    pub depr_map: FxHashMap<LocalDefId, DeprecationEntry>,
+    pub depr_map: LocalDefIdMap<DeprecationEntry>,
     /// Mapping from feature name to feature name based on the `implied_by` field of `#[unstable]`
     /// attributes. If a `#[unstable(feature = "implier", implied_by = "impliee")]` attribute
     /// exists, then this map will have a `impliee -> implier` entry.
@@ -77,7 +77,7 @@ pub struct Index {
     /// to know that the feature implies another feature. If it were reversed, and the `#[stable]`
     /// attribute had an `implies` meta item, then a map would be necessary when avoiding a "use of
     /// unstable feature" error for a feature that was implied.
-    pub implications: FxHashMap<Symbol, Symbol>,
+    pub implications: UnordMap<Symbol, Symbol>,
 }
 
 impl Index {

compiler/rustc_middle/src/query/mod.rs

@@ -57,11 +57,11 @@ use rustc_ast as ast;
 use rustc_ast::expand::{allocator::AllocatorKind, StrippedCfgItem};
 use rustc_attr as attr;
 use rustc_data_structures::fingerprint::Fingerprint;
-use rustc_data_structures::fx::{FxHashMap, FxIndexMap, FxIndexSet};
+use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::steal::Steal;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::Lrc;
-use rustc_data_structures::unord::UnordSet;
+use rustc_data_structures::unord::{UnordMap, UnordSet};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, DocLinkResMap};
@@ -264,7 +264,7 @@ rustc_queries! {
     }
 
     query collect_return_position_impl_trait_in_trait_tys(key: DefId)
-        -> Result<&'tcx FxHashMap<DefId, ty::EarlyBinder<Ty<'tcx>>>, ErrorGuaranteed>
+        -> Result<&'tcx DefIdMap<ty::EarlyBinder<Ty<'tcx>>>, ErrorGuaranteed>
     {
         desc { "comparing an impl and trait method signature, inferring any hidden `impl Trait` types in the process" }
         cache_on_disk_if { key.is_local() }
@@ -611,7 +611,7 @@ rustc_queries! {
         desc { "erasing regions from `{}`", ty }
     }
 
-    query wasm_import_module_map(_: CrateNum) -> &'tcx FxHashMap<DefId, String> {
+    query wasm_import_module_map(_: CrateNum) -> &'tcx DefIdMap<String> {
         arena_cache
         desc { "getting wasm import module map" }
     }
@@ -1537,7 +1537,7 @@ rustc_queries! {
     /// added or removed in any upstream crate. Instead use the narrower
     /// `upstream_monomorphizations_for`, `upstream_drop_glue_for`, or, even
     /// better, `Instance::upstream_monomorphization()`.
-    query upstream_monomorphizations(_: ()) -> &'tcx DefIdMap<FxHashMap<GenericArgsRef<'tcx>, CrateNum>> {
+    query upstream_monomorphizations(_: ()) -> &'tcx DefIdMap<UnordMap<GenericArgsRef<'tcx>, CrateNum>> {
         arena_cache
         desc { "collecting available upstream monomorphizations" }
     }
@@ -1550,7 +1550,7 @@ rustc_queries! {
     /// You likely want to call `Instance::upstream_monomorphization()`
     /// instead of invoking this query directly.
     query upstream_monomorphizations_for(def_id: DefId)
-        -> Option<&'tcx FxHashMap<GenericArgsRef<'tcx>, CrateNum>>
+        -> Option<&'tcx UnordMap<GenericArgsRef<'tcx>, CrateNum>>
     {
         desc { |tcx|
             "collecting available upstream monomorphizations for `{}`",
@@ -1662,7 +1662,7 @@ rustc_queries! {
         desc { "resolving lifetimes" }
     }
     query named_variable_map(_: hir::OwnerId) ->
-        Option<&'tcx FxHashMap<ItemLocalId, ResolvedArg>> {
+        Option<&'tcx FxIndexMap<ItemLocalId, ResolvedArg>> {
         desc { "looking up a named region" }
     }
     query is_late_bound_map(_: hir::OwnerId) -> Option<&'tcx FxIndexSet<ItemLocalId>> {
@@ -1678,7 +1678,7 @@ rustc_queries! {
         separate_provide_extern
     }
     query late_bound_vars_map(_: hir::OwnerId)
-        -> Option<&'tcx FxHashMap<ItemLocalId, Vec<ty::BoundVariableKind>>> {
+        -> Option<&'tcx FxIndexMap<ItemLocalId, Vec<ty::BoundVariableKind>>> {
         desc { "looking up late bound vars" }
     }
 
@@ -1734,7 +1734,7 @@ rustc_queries! {
         separate_provide_extern
         arena_cache
     }
-    query stability_implications(_: CrateNum) -> &'tcx FxHashMap<Symbol, Symbol> {
+    query stability_implications(_: CrateNum) -> &'tcx UnordMap<Symbol, Symbol> {
         arena_cache
         desc { "calculating the implications between `#[unstable]` features defined in a crate" }
         separate_provide_extern
@@ -1786,7 +1786,7 @@ rustc_queries! {
     }
     /// Collects the "trimmed", shortest accessible paths to all items for diagnostics.
     /// See the [provider docs](`rustc_middle::ty::print::trimmed_def_paths`) for more info.
-    query trimmed_def_paths(_: ()) -> &'tcx FxHashMap<DefId, Symbol> {
+    query trimmed_def_paths(_: ()) -> &'tcx DefIdMap<Symbol> {
         arena_cache
         desc { "calculating trimmed def paths" }
     }
@@ -2077,7 +2077,7 @@ rustc_queries! {
         desc { "computing autoderef types for `{}`", goal.value.value }
     }
 
-    query supported_target_features(_: CrateNum) -> &'tcx FxHashMap<String, Option<Symbol>> {
+    query supported_target_features(_: CrateNum) -> &'tcx UnordMap<String, Option<Symbol>> {
         arena_cache
         eval_always
         desc { "looking up supported target features" }

compiler/rustc_middle/src/query/on_disk_cache.rs

@@ -2,7 +2,7 @@ use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
 use rustc_data_structures::memmap::Mmap;
 use rustc_data_structures::sync::{HashMapExt, Lock, Lrc, RwLock};
 use rustc_data_structures::unhash::UnhashMap;
-use rustc_data_structures::unord::UnordSet;
+use rustc_data_structures::unord::{UnordMap, UnordSet};
 use rustc_hir::def_id::{CrateNum, DefId, DefIndex, LocalDefId, StableCrateId, LOCAL_CRATE};
 use rustc_hir::definitions::DefPathHash;
 use rustc_index::{Idx, IndexVec};
@@ -764,7 +764,7 @@ impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx UnordSet<LocalDefId>
 }
 
 impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>>
-    for &'tcx FxHashMap<DefId, ty::EarlyBinder<Ty<'tcx>>>
+    for &'tcx UnordMap<DefId, ty::EarlyBinder<Ty<'tcx>>>
 {
     #[inline]
     fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Self {

compiler/rustc_middle/src/ty/mod.rs

@@ -38,6 +38,7 @@ use rustc_data_structures::intern::Interned;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::steal::Steal;
 use rustc_data_structures::tagged_ptr::CopyTaggedPtr;
+use rustc_data_structures::unord::UnordMap;
 use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed, StashKey};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, CtorOf, DefKind, DocLinkResMap, LifetimeRes, Res};
@@ -655,7 +656,7 @@ pub struct CratePredicatesMap<'tcx> {
     /// For each struct with outlive bounds, maps to a vector of the
     /// predicate of its outlive bounds. If an item has no outlives
     /// bounds, it will have no entry.
-    pub predicates: FxHashMap<DefId, &'tcx [(Clause<'tcx>, Span)]>,
+    pub predicates: DefIdMap<&'tcx [(Clause<'tcx>, Span)]>,
 }
 
 impl<'tcx> Clause<'tcx> {
@@ -2658,7 +2659,7 @@ pub fn provide(providers: &mut Providers) {
 #[derive(Clone, Debug, Default, HashStable)]
 pub struct CrateInherentImpls {
     pub inherent_impls: LocalDefIdMap<Vec<DefId>>,
-    pub incoherent_impls: FxHashMap<SimplifiedType, Vec<LocalDefId>>,
+    pub incoherent_impls: UnordMap<SimplifiedType, Vec<LocalDefId>>,
 }
 
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, TyEncodable, HashStable)]

compiler/rustc_middle/src/ty/parameterized.rs

@@ -1,6 +1,7 @@
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::unord::UnordMap;
 use rustc_hir::def_id::DefIndex;
 use rustc_index::{Idx, IndexVec};
+use std::hash::Hash;
 
 use crate::ty;
 
@@ -24,8 +25,8 @@ impl<I: Idx + 'static, T: ParameterizedOverTcx> ParameterizedOverTcx for IndexVe
     type Value<'tcx> = IndexVec<I, T::Value<'tcx>>;
 }
 
-impl<I: 'static, T: ParameterizedOverTcx> ParameterizedOverTcx for FxHashMap<I, T> {
+impl<I: Hash + Eq + 'static, T: ParameterizedOverTcx> ParameterizedOverTcx for UnordMap<I, T> {
-    type Value<'tcx> = FxHashMap<I, T::Value<'tcx>>;
+    type Value<'tcx> = UnordMap<I, T::Value<'tcx>>;
 }
 
 impl<T: ParameterizedOverTcx> ParameterizedOverTcx for ty::Binder<'static, T> {

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -12,7 +12,7 @@ use rustc_apfloat::Float;
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_hir as hir;
 use rustc_hir::def::{self, CtorKind, DefKind, Namespace};
-use rustc_hir::def_id::{DefIdSet, ModDefId, CRATE_DEF_ID, LOCAL_CRATE};
+use rustc_hir::def_id::{DefIdMap, DefIdSet, ModDefId, CRATE_DEF_ID, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPathDataName};
 use rustc_hir::LangItem;
 use rustc_session::config::TrimmedDefPaths;
@@ -3049,8 +3049,8 @@ fn for_each_def(tcx: TyCtxt<'_>, mut collect_fn: impl for<'b> FnMut(&'b Ident, N
 ///
 /// See also [`DelayDm`](rustc_error_messages::DelayDm) and [`with_no_trimmed_paths!`].
 // this is pub to be able to intra-doc-link it
-pub fn trimmed_def_paths(tcx: TyCtxt<'_>, (): ()) -> FxHashMap<DefId, Symbol> {
+pub fn trimmed_def_paths(tcx: TyCtxt<'_>, (): ()) -> DefIdMap<Symbol> {
-    let mut map: FxHashMap<DefId, Symbol> = FxHashMap::default();
+    let mut map: DefIdMap<Symbol> = Default::default();
 
     if let TrimmedDefPaths::GoodPath = tcx.sess.opts.trimmed_def_paths {
         // Trimming paths is expensive and not optimized, since we expect it to only be used for error reporting.

compiler/rustc_middle/src/ty/typeck_results.rs

@@ -527,7 +527,7 @@ impl<'a, V> LocalTableInContext<'a, V> {
     }
 
     pub fn items_in_stable_order(&self) -> Vec<(ItemLocalId, &'a V)> {
-        self.data.to_sorted_stable_ord()
+        self.data.items().map(|(&k, v)| (k, v)).into_sorted_stable_ord_by_key(|(k, _)| k)
     }
 }
 

compiler/rustc_passes/src/stability.rs

@@ -6,7 +6,8 @@ use rustc_attr::{
     self as attr, ConstStability, DeprecatedSince, Stability, StabilityLevel, StableSince,
     Unstable, UnstableReason, VERSION_PLACEHOLDER,
 };
-use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
+use rustc_data_structures::fx::FxIndexMap;
+use rustc_data_structures::unord::{ExtendUnord, UnordMap, UnordSet};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{LocalDefId, LocalModDefId, CRATE_DEF_ID, LOCAL_CRATE};
@@ -923,7 +924,7 @@ pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
     }
 
     let declared_lang_features = &tcx.features().declared_lang_features;
-    let mut lang_features = FxHashSet::default();
+    let mut lang_features = UnordSet::default();
     for &(feature, span, since) in declared_lang_features {
         if let Some(since) = since {
             // Warn if the user has enabled an already-stable lang feature.
@@ -980,11 +981,11 @@ pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
     fn check_features<'tcx>(
         tcx: TyCtxt<'tcx>,
         remaining_lib_features: &mut FxIndexMap<&Symbol, Span>,
-        remaining_implications: &mut FxHashMap<Symbol, Symbol>,
+        remaining_implications: &mut UnordMap<Symbol, Symbol>,
         defined_features: &LibFeatures,
-        all_implications: &FxHashMap<Symbol, Symbol>,
+        all_implications: &UnordMap<Symbol, Symbol>,
     ) {
-        for (feature, since) in defined_features.to_vec() {
+        for (feature, since) in defined_features.to_sorted_vec() {
             if let FeatureStability::AcceptedSince(since) = since
                 && let Some(span) = remaining_lib_features.get(&feature)
             {
@@ -1021,7 +1022,8 @@ pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
         // `remaining_lib_features`.
         let mut all_implications = remaining_implications.clone();
         for &cnum in tcx.crates(()) {
-            all_implications.extend(tcx.stability_implications(cnum));
+            all_implications
+                .extend_unord(tcx.stability_implications(cnum).items().map(|(k, v)| (*k, *v)));
         }
 
         check_features(
@@ -1050,10 +1052,7 @@ pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
         tcx.dcx().emit_err(errors::UnknownFeature { span, feature: *feature });
     }
 
-    // We only use the hash map contents to emit errors, and the order of
+    for (&implied_by, &feature) in remaining_implications.to_sorted_stable_ord() {
-    // emitted errors do not affect query stability.
-    #[allow(rustc::potential_query_instability)]
-    for (implied_by, feature) in remaining_implications {
         let local_defined_features = tcx.lib_features(LOCAL_CRATE);
         let span = local_defined_features
             .stability

compiler/rustc_span/src/def_id.rs

@@ -1,6 +1,8 @@
 use crate::{HashStableContext, Symbol};
 use rustc_data_structures::fingerprint::Fingerprint;
-use rustc_data_structures::stable_hasher::{Hash64, HashStable, StableHasher, ToStableHashKey};
+use rustc_data_structures::stable_hasher::{
+    Hash64, HashStable, StableHasher, StableOrd, ToStableHashKey,
+};
 use rustc_data_structures::unhash::Unhasher;
 use rustc_data_structures::AtomicRef;
 use rustc_index::Idx;
@@ -132,6 +134,11 @@ impl Default for DefPathHash {
     }
 }
 
+// Safety: `DefPathHash` sort order is not affected (de)serialization.
+unsafe impl StableOrd for DefPathHash {
+    const CAN_USE_UNSTABLE_SORT: bool = true;
+}
+
 /// A [`StableCrateId`] is a 64-bit hash of a crate name, together with all
 /// `-Cmetadata` arguments, and some other data. It is to [`CrateNum`] what [`DefPathHash`] is to
 /// [`DefId`]. It is stable across compilation sessions.
@@ -490,6 +497,15 @@ impl<CTX: HashStableContext> ToStableHashKey<CTX> for CrateNum {
     }
 }
 
+impl<CTX: HashStableContext> ToStableHashKey<CTX> for DefPathHash {
+    type KeyType = DefPathHash;
+
+    #[inline]
+    fn to_stable_hash_key(&self, _: &CTX) -> DefPathHash {
+        *self
+    }
+}
+
 macro_rules! typed_def_id {
     ($Name:ident, $LocalName:ident) => {
         #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Encodable, Decodable, HashStable_Generic)]

compiler/rustc_span/src/symbol.rs

@@ -4,7 +4,9 @@
 
 use rustc_arena::DroplessArena;
 use rustc_data_structures::fx::FxIndexSet;
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
+use rustc_data_structures::stable_hasher::{
+    HashStable, StableCompare, StableHasher, ToStableHashKey,
+};
 use rustc_data_structures::sync::Lock;
 use rustc_macros::HashStable_Generic;
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
@@ -2104,6 +2106,14 @@ impl<CTX> ToStableHashKey<CTX> for Symbol {
     }
 }
 
+impl StableCompare for Symbol {
+    const CAN_USE_UNSTABLE_SORT: bool = true;
+
+    fn stable_cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.as_str().cmp(other.as_str())
+    }
+}
+
 pub(crate) struct Interner(Lock<InternerInner>);
 
 // The `&'static str`s in this type actually point into the arena.