Slow down Symbol::as_str

Author: petrochenkov

compiler/rustc_macros/src/symbols.rs

@@ -201,6 +201,12 @@ fn symbols_with_errors(input: TokenStream) -> (TokenStream, Vec<syn::Error>) {
     }
     let _ = counter; // for future use
 
+    // We have finished collecting symbol strings.
+    let static_symbols_len = symbol_strings.len();
+
+    // Build the body of STATIC_SYMBOLS.
+    let symbol_strings_tokens: TokenStream = symbol_strings.iter().map(|s| quote!(#s,)).collect();
+
     // Build the PHF map. This translates from strings to Symbol values.
     let mut phf_map = phf_codegen::Map::<&str>::new();
     for (symbol_index, symbol) in symbol_strings.iter().enumerate() {
@@ -236,6 +242,10 @@ fn symbols_with_errors(input: TokenStream) -> (TokenStream, Vec<syn::Error>) {
             }
         }
 
+        static STATIC_SYMBOLS: [&str; #static_symbols_len as usize] = [
+            #symbol_strings_tokens
+        ];
+
         static STATIC_SYMBOLS_PHF: ::phf::Map<&'static str, Symbol> = #phf_map_expr;
     };
 

compiler/rustc_span/src/symbol.rs

@@ -1453,19 +1453,24 @@ impl Symbol {
 
     /// Maps a string to its interned representation.
     pub fn intern(string: &str) -> Self {
-        if let Some(symbol) = STATIC_SYMBOLS_PHF.get(string) {
-            *symbol
-        } else {
-            with_interner(|interner| interner.intern(string))
-        }
+        // if let Some(symbol) = STATIC_SYMBOLS_PHF.get(string) {
+        //     *symbol
+        // } else {
+        //     with_interner(|interner| interner.intern(string))
+        // }
+        with_interner(|interner| interner.intern(string))
     }
 
     /// Convert to a `SymbolStr`. This is a slowish operation because it
     /// requires locking the symbol interner.
     pub fn as_str(self) -> SymbolStr {
-        with_interner(|interner| unsafe {
-            SymbolStr { string: std::mem::transmute::<&str, &str>(interner.get(self)) }
-        })
+        if let Some(string) = STATIC_SYMBOLS.get(self.0.as_usize()) {
+            SymbolStr { string }
+        } else {
+            with_interner(|interner| unsafe {
+                SymbolStr { string: std::mem::transmute::<&str, &str>(interner.get(self)) }
+            })
+        }
     }
 
     pub fn as_u32(self) -> u32 {