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_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" }