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%.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/libsyntax_pos/symbol.rs b/src/libsyntax_pos/symbol.rs
index 01b126f48b3..e0425220c3f 100644
--- a/src/libsyntax_pos/symbol.rs
+++ b/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 @@ impl fmt::Display for InternedString {
 
 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()?))
     }
 }