Introduce InternedString::intern.

`InternedString::intern(x)` is preferable to
`Symbol::intern(x).as_interned_str()`, because the former involves one
call to `with_interner` while the latter involves two.

The case within InternedString::decode() is particularly hot, and this
change reduces the number of `with_interner` calls by up to 13%.

src/librustc/mir/mono.rs

@@ -1,6 +1,6 @@
 use crate::hir::def_id::{DefId, CrateNum, LOCAL_CRATE};
 use crate::hir::HirId;
-use syntax::symbol::{Symbol, InternedString};
+use syntax::symbol::InternedString;
 use crate::ty::{Instance, TyCtxt};
 use crate::util::nodemap::FxHashMap;
 use rustc_data_structures::base_n;
@@ -280,7 +280,7 @@ pub fn build_cgu_name<I, C, S>(&mut self,
             cgu_name
         } else {
             let cgu_name = &cgu_name.as_str()[..];
-            Symbol::intern(&CodegenUnit::mangle_name(cgu_name)).as_interned_str()
+            InternedString::intern(&CodegenUnit::mangle_name(cgu_name))
         }
     }
 
@@ -336,6 +336,6 @@ pub fn build_cgu_name_no_mangle<I, C, S>(&mut self,
             write!(cgu_name, ".{}", special_suffix).unwrap();
         }
 
-        Symbol::intern(&cgu_name[..]).as_interned_str()
+        InternedString::intern(&cgu_name[..])
     }
 }

src/librustc/traits/object_safety.rs

@@ -18,7 +18,8 @@
 use crate::ty::subst::{Subst, InternalSubsts};
 use std::borrow::Cow;
 use std::iter::{self};
-use syntax::ast::{self, Name};
+use syntax::ast::{self};
+use syntax::symbol::InternedString;
 use syntax_pos::Span;
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
@@ -539,7 +540,7 @@ fn receiver_is_dispatchable(
         // are implemented
         let unsized_self_ty: Ty<'tcx> = self.mk_ty_param(
             ::std::u32::MAX,
-            Name::intern("RustaceansAreAwesome").as_interned_str(),
+            InternedString::intern("RustaceansAreAwesome"),
         );
 
         // `Receiver[Self => U]`

src/librustc/traits/structural_impls.rs

@@ -312,17 +312,15 @@ fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> bool {
     }
 
     fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
-        use syntax::symbol::Symbol;
-
         match t.sty {
             ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
                 self.types.insert(
                     bound_ty.var.as_u32(),
                     match bound_ty.kind {
                         ty::BoundTyKind::Param(name) => name,
-                        ty::BoundTyKind::Anon => Symbol::intern(
-                            &format!("^{}", bound_ty.var.as_u32())
-                        ).as_interned_str(),
+                        ty::BoundTyKind::Anon =>
+                            InternedString::intern(&format!("^{}", bound_ty.var.as_u32()),
+                        ),
                     }
                 );
             }
@@ -334,8 +332,6 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
     }
 
     fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
-        use syntax::symbol::Symbol;
-
         match r {
             ty::ReLateBound(index, br) if *index == self.binder_index => {
                 match br {
@@ -344,9 +340,7 @@ fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
                     }
 
                     ty::BoundRegion::BrAnon(var) => {
-                        self.regions.insert(Symbol::intern(
-                            &format!("'^{}", var)
-                        ).as_interned_str());
+                        self.regions.insert(InternedString::intern(&format!("'^{}", var)));
                     }
 
                     _ => (),

src/librustc/ty/mod.rs

@@ -3405,7 +3405,7 @@ pub struct SymbolName {
 impl SymbolName {
     pub fn new(name: &str) -> SymbolName {
         SymbolName {
-            name: Symbol::intern(name).as_interned_str()
+            name: InternedString::intern(name)
         }
     }
 

src/librustc/ty/print/pretty.rs

@@ -7,10 +7,8 @@
 use crate::ty::{self, DefIdTree, ParamConst, Ty, TyCtxt, TypeFoldable};
 use crate::ty::subst::{Kind, Subst, UnpackedKind};
 use crate::mir::interpret::ConstValue;
-use syntax::symbol::{keywords, Symbol};
-
 use rustc_target::spec::abi::Abi;
-use syntax::symbol::InternedString;
+use syntax::symbol::{keywords, InternedString};
 
 use std::cell::Cell;
 use std::fmt::{self, Write as _};
@@ -1285,10 +1283,10 @@ pub fn pretty_in_binder<T>(
     {
         fn name_by_region_index(index: usize) -> InternedString {
             match index {
-                0 => Symbol::intern("'r"),
-                1 => Symbol::intern("'s"),
-                i => Symbol::intern(&format!("'t{}", i-2)),
-            }.as_interned_str()
+                0 => InternedString::intern("'r"),
+                1 => InternedString::intern("'s"),
+                i => InternedString::intern(&format!("'t{}", i-2)),
+            }
         }
 
         // Replace any anonymous late-bound regions with named

src/librustc/ty/query/values.rs

@@ -1,7 +1,7 @@
 use crate::ty::{self, Ty, TyCtxt, AdtSizedConstraint};
 use crate::ty::util::NeedsDrop;
 
-use syntax::symbol::Symbol;
+use syntax::symbol::InternedString;
 
 pub(super) trait Value<'tcx>: Sized {
     fn from_cycle_error<'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Self;
@@ -28,7 +28,7 @@ fn from_cycle_error<'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Ty<'tcx> {
 
 impl<'tcx> Value<'tcx> for ty::SymbolName {
     fn from_cycle_error<'a>(_: TyCtxt<'a, 'tcx, 'tcx>) -> Self {
-        ty::SymbolName { name: Symbol::intern("<error>").as_interned_str() }
+        ty::SymbolName { name: InternedString::intern("<error>") }
     }
 }
 

src/librustc_codegen_utils/symbol_names.rs

@@ -101,7 +101,7 @@
 use rustc_mir::monomorphize::item::{InstantiationMode, MonoItem, MonoItemExt};
 use rustc_mir::monomorphize::Instance;
 
-use syntax_pos::symbol::{Symbol, InternedString};
+use syntax_pos::symbol::InternedString;
 
 use log::debug;
 
@@ -238,13 +238,13 @@ fn compute_symbol_name(tcx: TyCtxt<'_, 'tcx, 'tcx>, instance: Instance<'tcx>) ->
     if def_id.is_local() {
         if tcx.plugin_registrar_fn(LOCAL_CRATE) == Some(def_id) {
             let disambiguator = tcx.sess.local_crate_disambiguator();
-            return Symbol::intern(&tcx.sess.generate_plugin_registrar_symbol(disambiguator))
-                .as_interned_str();
+            return
+                InternedString::intern(&tcx.sess.generate_plugin_registrar_symbol(disambiguator));
         }
         if tcx.proc_macro_decls_static(LOCAL_CRATE) == Some(def_id) {
             let disambiguator = tcx.sess.local_crate_disambiguator();
-            return Symbol::intern(&tcx.sess.generate_proc_macro_decls_symbol(disambiguator))
-                .as_interned_str();
+            return
+                InternedString::intern(&tcx.sess.generate_proc_macro_decls_symbol(disambiguator));
         }
     }
 
@@ -322,7 +322,7 @@ fn compute_symbol_name(tcx: TyCtxt<'_, 'tcx, 'tcx>, instance: Instance<'tcx>) ->
         let _ = printer.write_str("{{vtable-shim}}");
     }
 
-    Symbol::intern(&printer.path.finish(hash)).as_interned_str()
+    InternedString::intern(&printer.path.finish(hash))
 }
 
 // Follow C++ namespace-mangling style, see

src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs

@@ -12,7 +12,6 @@
 use rustc::ty::{self, RegionKind, RegionVid, Ty, TyCtxt};
 use rustc::ty::print::RegionHighlightMode;
 use rustc_errors::DiagnosticBuilder;
-use syntax::ast::Name;
 use syntax::symbol::keywords;
 use syntax_pos::Span;
 use syntax_pos::symbol::InternedString;
@@ -791,6 +790,6 @@ fn synthesize_region_name(&self, counter: &mut usize) -> InternedString {
         let c = *counter;
         *counter += 1;
 
-        Name::intern(&format!("'{:?}", c)).as_interned_str()
+        InternedString::intern(&format!("'{:?}", c))
     }
 }

src/librustc_mir/monomorphize/item.rs

@@ -10,7 +10,7 @@
 use std::fmt::{self, Write};
 use std::iter;
 use rustc::mir::mono::Linkage;
-use syntax_pos::symbol::Symbol;
+use syntax_pos::symbol::InternedString;
 use syntax::source_map::Span;
 pub use rustc::mir::mono::MonoItem;
 
@@ -61,7 +61,7 @@ fn symbol_name(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> ty::SymbolName {
             MonoItem::GlobalAsm(hir_id) => {
                 let def_id = tcx.hir().local_def_id_from_hir_id(hir_id);
                 ty::SymbolName {
-                    name: Symbol::intern(&format!("global_asm_{:?}", def_id)).as_interned_str()
+                    name: InternedString::intern(&format!("global_asm_{:?}", def_id))
                 }
             }
         }

src/librustc_mir/transform/check_unsafety.rs

@@ -12,7 +12,7 @@
 use rustc::mir::*;
 use rustc::mir::visit::{PlaceContext, Visitor, MutatingUseContext};
 
-use syntax::symbol::{Symbol, sym};
+use syntax::symbol::{InternedString, sym};
 
 use std::ops::Bound;
 
@@ -167,9 +167,9 @@ fn visit_rvalue(&mut self,
                     (CastTy::FnPtr, CastTy::Int(_)) => {
                         self.register_violations(&[UnsafetyViolation {
                             source_info: self.source_info,
-                            description: Symbol::intern("cast of pointer to int").as_interned_str(),
-                            details: Symbol::intern("casting pointers to integers in constants")
-                                     .as_interned_str(),
+                            description: InternedString::intern("cast of pointer to int"),
+                            details: InternedString::intern(
+                                "casting pointers to integers in constants"),
                             kind: UnsafetyViolationKind::General,
                         }], &[]);
                     },
@@ -185,9 +185,8 @@ fn visit_rvalue(&mut self,
                 if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(self.mir, self.tcx).sty {
                     self.register_violations(&[UnsafetyViolation {
                         source_info: self.source_info,
-                        description: Symbol::intern("pointer operation").as_interned_str(),
-                        details: Symbol::intern("operations on pointers in constants")
-                                 .as_interned_str(),
+                        description: InternedString::intern("pointer operation"),
+                        details: InternedString::intern("operations on pointers in constants"),
                         kind: UnsafetyViolationKind::General,
                     }], &[]);
                 }
@@ -212,13 +211,11 @@ fn visit_place(&mut self,
                             self.source_scope_local_data[source_info.scope].lint_root;
                         self.register_violations(&[UnsafetyViolation {
                             source_info,
-                            description: Symbol::intern("borrow of packed field").as_interned_str(),
-                            details:
-                                Symbol::intern("fields of packed structs might be misaligned: \
-                                                dereferencing a misaligned pointer or even just \
-                                                creating a misaligned reference is undefined \
-                                                behavior")
-                                    .as_interned_str(),
+                            description: InternedString::intern("borrow of packed field"),
+                            details: InternedString::intern(
+                                "fields of packed structs might be misaligned: dereferencing a \
+                                misaligned pointer or even just creating a misaligned reference \
+                                is undefined behavior"),
                             kind: UnsafetyViolationKind::BorrowPacked(lint_root)
                         }], &[]);
                     }
@@ -315,12 +312,10 @@ fn visit_place(&mut self,
                         self.source_scope_local_data[source_info.scope].lint_root;
                     self.register_violations(&[UnsafetyViolation {
                         source_info,
-                        description: Symbol::intern("use of extern static").as_interned_str(),
-                        details:
-                            Symbol::intern("extern statics are not controlled by the Rust type \
-                                            system: invalid data, aliasing violations or data \
-                                            races will cause undefined behavior")
-                                .as_interned_str(),
+                        description: InternedString::intern("use of extern static"),
+                        details: InternedString::intern(
+                            "extern statics are not controlled by the Rust type system: invalid \
+                            data, aliasing violations or data races will cause undefined behavior"),
                         kind: UnsafetyViolationKind::ExternStatic(lint_root)
                     }], &[]);
                 }
@@ -340,8 +335,8 @@ fn require_unsafe(
         let source_info = self.source_info;
         self.register_violations(&[UnsafetyViolation {
             source_info,
-            description: Symbol::intern(description).as_interned_str(),
-            details: Symbol::intern(details).as_interned_str(),
+            description: InternedString::intern(description),
+            details: InternedString::intern(details),
             kind,
         }], &[]);
     }
@@ -441,8 +436,8 @@ fn check_mut_borrowing_layout_constrained_field(
                                 let source_info = self.source_info;
                                 self.register_violations(&[UnsafetyViolation {
                                     source_info,
-                                    description: Symbol::intern(description).as_interned_str(),
-                                    details: Symbol::intern(details).as_interned_str(),
+                                    description: InternedString::intern(description),
+                                    details: InternedString::intern(details),
                                     kind: UnsafetyViolationKind::GeneralAndConstFn,
                                 }], &[]);
                             }

src/librustc_typeck/check/intrinsic.rs

@@ -7,7 +7,7 @@
 use crate::require_same_types;
 
 use rustc_target::spec::abi::Abi;
-use syntax::symbol::Symbol;
+use syntax::symbol::InternedString;
 
 use rustc::hir;
 
@@ -80,7 +80,7 @@ pub fn intrisic_operation_unsafety(intrinsic: &str) -> hir::Unsafety {
 /// and in libcore/intrinsics.rs
 pub fn check_intrinsic_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                       it: &hir::ForeignItem) {
-    let param = |n| tcx.mk_ty_param(n, Symbol::intern(&format!("P{}", n)).as_interned_str());
+    let param = |n| tcx.mk_ty_param(n, InternedString::intern(&format!("P{}", n)));
     let name = it.ident.as_str();
 
     let mk_va_list_ty = || {
@@ -397,7 +397,7 @@ pub fn check_intrinsic_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 pub fn check_platform_intrinsic_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                                it: &hir::ForeignItem) {
     let param = |n| {
-        let name = Symbol::intern(&format!("P{}", n)).as_interned_str();
+        let name = InternedString::intern(&format!("P{}", n));
         tcx.mk_ty_param(n, name)
     };
 

src/librustc_typeck/collect.rs

@@ -39,7 +39,7 @@
 use syntax::attr::{InlineAttr, OptimizeAttr, list_contains_name, mark_used};
 use syntax::source_map::Spanned;
 use syntax::feature_gate;
-use syntax::symbol::{keywords, Symbol, sym};
+use syntax::symbol::{InternedString, keywords, Symbol, sym};
 use syntax_pos::{Span, DUMMY_SP};
 
 use rustc::hir::def::{CtorKind, Res, DefKind};
@@ -1082,7 +1082,7 @@ fn generics_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx ty
                 .enumerate()
                 .map(|(i, &arg)| ty::GenericParamDef {
                     index: type_start + i as u32,
-                    name: Symbol::intern(arg).as_interned_str(),
+                    name: InternedString::intern(arg),
                     def_id,
                     pure_wrt_drop: false,
                     kind: ty::GenericParamDefKind::Type {
@@ -1097,7 +1097,7 @@ fn generics_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx ty
             params.extend(upvars.iter().zip((dummy_args.len() as u32)..).map(|(_, i)| {
                 ty::GenericParamDef {
                     index: type_start + i,
-                    name: Symbol::intern("<upvar>").as_interned_str(),
+                    name: InternedString::intern("<upvar>"),
                     def_id,
                     pure_wrt_drop: false,
                     kind: ty::GenericParamDefKind::Type {

src/libsyntax_pos/symbol.rs

@@ -1134,6 +1134,13 @@ pub struct InternedString {
 }
 
 impl InternedString {
+    /// Maps a string to its interned representation.
+    pub fn intern(string: &str) -> Self {
+        InternedString {
+            symbol: Symbol::intern(string)
+        }
+    }
+
     pub fn with<F: FnOnce(&str) -> R, R>(self, f: F) -> R {
         let str = with_interner(|interner| {
             interner.get(self.symbol) as *const str
@@ -1236,7 +1243,7 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 
 impl Decodable for InternedString {
     fn decode<D: Decoder>(d: &mut D) -> Result<InternedString, D::Error> {
-        Ok(Symbol::intern(&d.read_str()?).as_interned_str())
+        Ok(InternedString::intern(&d.read_str()?))
     }
 }