Auto merge of #70674 - cjgillot:query-arena-all, r=matthewjasper

Have the per-query caches store the results on arenas

This PR leverages the cache for each query to serve as storage area for the query results.

It introduces a new cache `ArenaCache`, which moves the result to an arena,
and only stores the reference in the hash map.
This allows to remove a sizeable part of the usage of the global `TyCtxt` arena.

I only migrated queries that already used arenas before.

2 files changed, 6 insertions, 9 deletions

diff --git a/src/librustc_codegen_ssa/back/symbol_export.rs b/src/librustc_codegen_ssa/back/symbol_export.rs
index 9faddf254d7..338211ca11f 100644
--- a/src/librustc_codegen_ssa/back/symbol_export.rs
+++ b/src/librustc_codegen_ssa/back/symbol_export.rs
@@ -42,14 +42,11 @@ pub fn crates_export_threshold(crate_types: &[config::CrateType]) -> SymbolExpor
     }
 }
 
-fn reachable_non_generics_provider(
-    tcx: TyCtxt<'_>,
-    cnum: CrateNum,
-) -> &DefIdMap<SymbolExportLevel> {
+fn reachable_non_generics_provider(tcx: TyCtxt<'_>, cnum: CrateNum) -> DefIdMap<SymbolExportLevel> {
     assert_eq!(cnum, LOCAL_CRATE);
 
     if !tcx.sess.opts.output_types.should_codegen() {
-        return tcx.arena.alloc(Default::default());
+        return Default::default();
     }
 
     // Check to see if this crate is a "special runtime crate". These
@@ -145,7 +142,7 @@ fn reachable_non_generics_provider(
         reachable_non_generics.insert(id, SymbolExportLevel::C);
     }
 
-    tcx.arena.alloc(reachable_non_generics)
+    reachable_non_generics
 }
 
 fn is_reachable_non_generic_provider_local(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
@@ -281,7 +278,7 @@ fn exported_symbols_provider_local(
 fn upstream_monomorphizations_provider(
     tcx: TyCtxt<'_>,
     cnum: CrateNum,
-) -> &DefIdMap<FxHashMap<SubstsRef<'_>, CrateNum>> {
+) -> DefIdMap<FxHashMap<SubstsRef<'_>, CrateNum>> {
     debug_assert!(cnum == LOCAL_CRATE);
 
     let cnums = tcx.all_crate_nums(LOCAL_CRATE);
@@ -338,7 +335,7 @@ fn upstream_monomorphizations_provider(
         }
     }
 
-    tcx.arena.alloc(instances)
+    instances
 }
 
 fn upstream_monomorphizations_for_provider(
diff --git a/src/librustc_codegen_ssa/base.rs b/src/librustc_codegen_ssa/base.rs
index cd43ca8257e..fc6b547c5e7 100644
--- a/src/librustc_codegen_ssa/base.rs
+++ b/src/librustc_codegen_ssa/base.rs
@@ -908,7 +908,7 @@ pub fn provide_both(providers: &mut Providers<'_>) {
             .map(|id| &module_map[&id])
             .flat_map(|module| module.foreign_items.iter().cloned())
             .collect();
-        tcx.arena.alloc(dllimports)
+        dllimports
     };
 
     providers.is_dllimport_foreign_item =