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 @@ impl<'a, 'gcx: 'tcx, 'tcx: 'a> CodegenUnitNameBuilder<'a, 'gcx, 'tcx> {
             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 @@ impl<'a, 'gcx: 'tcx, 'tcx: 'a> CodegenUnitNameBuilder<'a, 'gcx, 'tcx> {
             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::{self, Ty, TyCtxt, TypeFoldable, Predicate, ToPredicate};
 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 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
         // 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 @@ impl<'tcx> TypeVisitor<'tcx> for BoundNamesCollector {
     }
 
     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 @@ impl<'tcx> TypeVisitor<'tcx> for BoundNamesCollector {
     }
 
     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 @@ impl<'tcx> TypeVisitor<'tcx> for BoundNamesCollector {
                     }
 
                     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 @@ impl_stable_hash_for!(struct self::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::middle::region;
 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 @@ impl<F: fmt::Write> FmtPrinter<'_, 'gcx, 'tcx, F> {
     {
         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 @@ impl<'tcx> Value<'tcx> for 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>") }
     }
 }