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

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();
-        items.sort_by_cached_key(|x| x.to_stable_hash_key(hcx));
-        items
+        self.collect_sorted(hcx, true)
     }
 
     #[inline]
     pub fn into_sorted_stable_ord(self) -> Vec<T>
     where
-        T: Ord + StableOrd,
+        T: StableCompare,
+    {
+        self.collect_stable_ord_by_key(|x| x)
+    }
+
+    #[inline]
+    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,
     {
-        let mut items: Vec<T> = self.0.collect();
-        if !T::CAN_USE_UNSTABLE_SORT {
-            items.sort();
-        } else {
-            items.sort_unstable()
+        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();
-        items.sort_by_cached_key(|x| x.to_stable_hash_key(hcx));
+        let mut items: C = self.0.collect();
+
+        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();
-        items.sort_unstable();
+        let mut items: Vec<&V> = self.inner.iter().collect();
+        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();
-        items.sort_unstable_by_key(|&(k, _)| k);
+        let mut items: Vec<_> = self.inner.iter().collect();
+        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!(