Auto merge of #59343 - eddyb:rm-def-symbol-name, r=<try>

rustc(codegen): uncache `def_symbol_name` prefix from `symbol_name`.

The `def_symbol_name` query was an optimization to avoid recomputing the common part of a symbol name, as only the hash needs to be added to it for each symbol.

However, #57967 will add a new mangling scheme, which doesn't readily support this kind of reuse - while it's plausible, it requires a lot more effort, since you'd have to "symbolically evaluate" mangling, and keep it in a form where the backreference positions can be computed correctly in the final step.

So I want to see how much time we're actually saving with this `def_symbol_name` optimization, nowadays.

Author: bors

Diff for: src/librustc/dep_graph/dep_node.rs

@@ -523,8 +523,7 @@ rustc_dep_node_append!([define_dep_nodes!][ <'tcx>
     [] ConstEval { param_env: ParamEnvAnd<'tcx, GlobalId<'tcx>> },
     [] ConstEvalRaw { param_env: ParamEnvAnd<'tcx, GlobalId<'tcx>> },
     [] CheckMatch(DefId),
-    [] SymbolName(DefId),
-    [] InstanceSymbolName { instance: Instance<'tcx> },
+    [] SymbolName { instance: Instance<'tcx> },
     [] SpecializationGraph(DefId),
     [] ObjectSafety(DefId),
     [] FulfillObligation { param_env: ParamEnv<'tcx>, trait_ref: PolyTraitRef<'tcx> },

Diff for: src/librustc/ty/query/config.rs

@@ -999,7 +999,6 @@ impl_disk_cacheable_query!(unsafety_check_result, |_, def_id| def_id.is_local())
 impl_disk_cacheable_query!(borrowck, |_, def_id| def_id.is_local());
 impl_disk_cacheable_query!(mir_const_qualif, |_, def_id| def_id.is_local());
 impl_disk_cacheable_query!(check_match, |_, def_id| def_id.is_local());
-impl_disk_cacheable_query!(def_symbol_name, |_, _| true);
 impl_disk_cacheable_query!(predicates_of, |_, def_id| def_id.is_local());
 impl_disk_cacheable_query!(used_trait_imports, |_, def_id| def_id.is_local());
 impl_disk_cacheable_query!(codegen_fn_attrs, |_, _| true);

Diff for: src/librustc/ty/query/mod.rs

@@ -342,7 +342,6 @@ rustc_query_append! { [define_queries!][ <'tcx>
 
         [] fn mir_shims: mir_shim_dep_node(ty::InstanceDef<'tcx>) -> &'tcx mir::Mir<'tcx>,
 
-        [] fn def_symbol_name: SymbolName(DefId) -> ty::SymbolName,
         [] fn symbol_name: symbol_name_dep_node(ty::Instance<'tcx>) -> ty::SymbolName,
 
         [] fn describe_def: DescribeDef(DefId) -> Option<Def>,
@@ -780,7 +779,7 @@ fn mir_shim_dep_node<'tcx>(instance_def: ty::InstanceDef<'tcx>) -> DepConstructo
 }
 
 fn symbol_name_dep_node<'tcx>(instance: ty::Instance<'tcx>) -> DepConstructor<'tcx> {
-    DepConstructor::InstanceSymbolName { instance }
+    DepConstructor::SymbolName { instance }
 }
 
 fn typeck_item_bodies_dep_node<'tcx>(_: CrateNum) -> DepConstructor<'tcx> {

Diff for: src/librustc/ty/query/on_disk_cache.rs

@@ -218,7 +218,6 @@ impl<'sess> OnDiskCache<'sess> {
                 encode_query_results::<borrowck<'_>, _>(tcx, enc, qri)?;
                 encode_query_results::<mir_borrowck<'_>, _>(tcx, enc, qri)?;
                 encode_query_results::<mir_const_qualif<'_>, _>(tcx, enc, qri)?;
-                encode_query_results::<def_symbol_name<'_>, _>(tcx, enc, qri)?;
                 encode_query_results::<const_is_rvalue_promotable_to_static<'_>, _>(tcx, enc, qri)?;
                 encode_query_results::<symbol_name<'_>, _>(tcx, enc, qri)?;
                 encode_query_results::<check_match<'_>, _>(tcx, enc, qri)?;

Diff for: src/librustc/ty/query/plumbing.rs

@@ -1213,7 +1213,7 @@ pub fn force_from_dep_node<'tcx>(
         DepKind::Layout |
         DepKind::ConstEval |
         DepKind::ConstEvalRaw |
-        DepKind::InstanceSymbolName |
+        DepKind::SymbolName |
         DepKind::MirShim |
         DepKind::BorrowCheckKrate |
         DepKind::Specializes |
@@ -1310,7 +1310,6 @@ pub fn force_from_dep_node<'tcx>(
         DepKind::TypeckTables => { force!(typeck_tables_of, def_id!()); }
         DepKind::UsedTraitImports => { force!(used_trait_imports, def_id!()); }
         DepKind::HasTypeckTables => { force!(has_typeck_tables, def_id!()); }
-        DepKind::SymbolName => { force!(def_symbol_name, def_id!()); }
         DepKind::SpecializationGraph => { force!(specialization_graph_of, def_id!()); }
         DepKind::ObjectSafety => { force!(is_object_safe, def_id!()); }
         DepKind::TraitImpls => { force!(trait_impls_of, def_id!()); }
@@ -1496,7 +1495,6 @@ impl_load_from_cache!(
     BorrowCheck => borrowck,
     MirBorrowCheck => mir_borrowck,
     MirConstQualif => mir_const_qualif,
-    SymbolName => def_symbol_name,
     ConstIsRvaluePromotableToStatic => const_is_rvalue_promotable_to_static,
     CheckMatch => check_match,
     type_of => type_of,

Diff for: src/librustc_codegen_utils/symbol_names.rs

@@ -101,7 +101,7 @@ use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_mir::monomorphize::item::{InstantiationMode, MonoItem, MonoItemExt};
 use rustc_mir::monomorphize::Instance;
 
-use syntax_pos::symbol::Symbol;
+use syntax_pos::symbol::{Symbol, InternedString};
 
 use log::debug;
 
@@ -110,7 +110,6 @@ use std::mem::{self, discriminant};
 
 pub fn provide(providers: &mut Providers<'_>) {
     *providers = Providers {
-        def_symbol_name,
         symbol_name,
 
         ..*providers
@@ -222,21 +221,13 @@ fn get_symbol_hash<'a, 'tcx>(
     hasher.finish()
 }
 
-fn def_symbol_name<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> ty::SymbolName {
-    SymbolPrinter {
-        tcx,
-        path: SymbolPath::new(),
-        keep_within_component: false,
-    }.print_def_path(def_id, &[]).unwrap().path.into_interned()
-}
-
-fn symbol_name<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, instance: Instance<'tcx>) -> ty::SymbolName {
+fn symbol_name(tcx: TyCtxt<'_, 'tcx, 'tcx>, instance: Instance<'tcx>) -> ty::SymbolName {
     ty::SymbolName {
-        name: Symbol::intern(&compute_symbol_name(tcx, instance)).as_interned_str(),
+        name: compute_symbol_name(tcx, instance),
     }
 }
 
-fn compute_symbol_name<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, instance: Instance<'tcx>) -> String {
+fn compute_symbol_name(tcx: TyCtxt<'_, 'tcx, 'tcx>, instance: Instance<'tcx>) -> InternedString {
     let def_id = instance.def_id();
     let substs = instance.substs;
 
@@ -247,11 +238,13 @@ fn compute_symbol_name<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, instance: Instance
     if def_id.is_local() {
         if tcx.plugin_registrar_fn(LOCAL_CRATE) == Some(def_id) {
             let disambiguator = tcx.sess.local_crate_disambiguator();
-            return tcx.sess.generate_plugin_registrar_symbol(disambiguator);
+            return Symbol::intern(&tcx.sess.generate_plugin_registrar_symbol(disambiguator))
+                .as_interned_str();
         }
         if tcx.proc_macro_decls_static(LOCAL_CRATE) == Some(def_id) {
             let disambiguator = tcx.sess.local_crate_disambiguator();
-            return tcx.sess.generate_proc_macro_decls_symbol(disambiguator);
+            return Symbol::intern(&tcx.sess.generate_proc_macro_decls_symbol(disambiguator))
+                .as_interned_str();
         }
     }
 
@@ -268,20 +261,20 @@ fn compute_symbol_name<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, instance: Instance
     let attrs = tcx.codegen_fn_attrs(def_id);
     if is_foreign {
         if let Some(name) = attrs.link_name {
-            return name.to_string();
+            return name.as_interned_str();
         }
         // Don't mangle foreign items.
-        return tcx.item_name(def_id).to_string();
+        return tcx.item_name(def_id);
     }
 
     if let Some(name) = &attrs.export_name {
         // Use provided name
-        return name.to_string();
+        return name.as_interned_str();
     }
 
     if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) {
         // Don't mangle
-        return tcx.item_name(def_id).to_string();
+        return tcx.item_name(def_id);
     }
 
     // We want to compute the "type" of this item. Unfortunately, some
@@ -321,15 +314,15 @@ fn compute_symbol_name<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, instance: Instance
 
     let mut printer = SymbolPrinter {
         tcx,
-        path: SymbolPath::from_interned(tcx.def_symbol_name(def_id)),
+        path: SymbolPath::new(),
         keep_within_component: false,
-    };
+    }.print_def_path(def_id, &[]).unwrap();
 
     if instance.is_vtable_shim() {
         let _ = printer.write_str("{{vtable-shim}}");
     }
 
-    printer.path.finish(hash)
+    Symbol::intern(&printer.path.finish(hash)).as_interned_str()
 }
 
 // Follow C++ namespace-mangling style, see
@@ -361,22 +354,6 @@ impl SymbolPath {
         result
     }
 
-    fn from_interned(symbol: ty::SymbolName) -> Self {
-        let mut result = SymbolPath {
-            result: String::with_capacity(64),
-            temp_buf: String::with_capacity(16),
-        };
-        result.result.push_str(&symbol.as_str());
-        result
-    }
-
-    fn into_interned(mut self) -> ty::SymbolName {
-        self.finalize_pending_component();
-        ty::SymbolName {
-            name: Symbol::intern(&self.result).as_interned_str(),
-        }
-    }
-
     fn finalize_pending_component(&mut self) {
         if !self.temp_buf.is_empty() {
             let _ = write!(self.result, "{}{}", self.temp_buf.len(), self.temp_buf);

Diff for: src/librustc_mir/transform/lower_128bit.rs

@@ -138,7 +138,7 @@ fn check_lang_item_type<'a, 'tcx, D>(
     let place_ty = place.ty(local_decls, tcx).to_ty(tcx);
     let expected = [lhs_ty, rhs_ty, place_ty];
     assert_eq!(sig.inputs_and_output[..], expected,
-        "lang item {}", tcx.def_symbol_name(did));
+        "lang item `{}`", tcx.def_path_str(did));
     did
 }