Avoid many CrateConfig clones.

This commit changes `ExtCtx::cfg()` so it returns a `CrateConfig`
reference instead of a clone. As a result, it also changes all of the
`cfg()` callsites to explicitly clone... except one, because the commit
also changes `macro_parser::parse()` to take `&CrateConfig`. This is
good, because that function can be hot, and `CrateConfig` is expensive
to clone.

This change almost halves the number of heap allocations done by rustc
for `html5ever` in rustc-benchmarks suite, which makes compilation 1.20x
faster.

src/libsyntax/ext/base.rs

@@ -617,11 +617,11 @@ impl<'a> ExtCtxt<'a> {
 
     pub fn new_parser_from_tts(&self, tts: &[tokenstream::TokenTree])
         -> parser::Parser<'a> {
-        parse::tts_to_parser(self.parse_sess, tts.to_vec(), self.cfg())
+        parse::tts_to_parser(self.parse_sess, tts.to_vec(), self.cfg().clone())
     }
     pub fn codemap(&self) -> &'a CodeMap { self.parse_sess.codemap() }
     pub fn parse_sess(&self) -> &'a parse::ParseSess { self.parse_sess }
-    pub fn cfg(&self) -> ast::CrateConfig { self.cfg.clone() }
+    pub fn cfg(&self) -> &ast::CrateConfig { &self.cfg }
     pub fn call_site(&self) -> Span {
         self.codemap().with_expn_info(self.backtrace(), |ei| match ei {
             Some(expn_info) => expn_info.call_site,

src/libsyntax/ext/quote.rs

@@ -331,7 +331,7 @@ pub mod rt {
             panictry!(parse::parse_item_from_source_str(
                 "<quote expansion>".to_string(),
                 s,
-                self.cfg(),
+                self.cfg().clone(),
                 self.parse_sess())).expect("parse error")
         }
 
@@ -339,7 +339,7 @@ pub mod rt {
             panictry!(parse::parse_stmt_from_source_str(
                 "<quote expansion>".to_string(),
                 s,
-                self.cfg(),
+                self.cfg().clone(),
                 self.parse_sess())).expect("parse error")
         }
 
@@ -347,7 +347,7 @@ pub mod rt {
             panictry!(parse::parse_expr_from_source_str(
                 "<quote expansion>".to_string(),
                 s,
-                self.cfg(),
+                self.cfg().clone(),
                 self.parse_sess()))
         }
 
@@ -355,7 +355,7 @@ pub mod rt {
             panictry!(parse::parse_tts_from_source_str(
                 "<quote expansion>".to_string(),
                 s,
-                self.cfg(),
+                self.cfg().clone(),
                 self.parse_sess()))
         }
     }
@@ -924,6 +924,10 @@ fn expand_parse_call(cx: &ExtCtxt,
         sp, cx.expr_ident(sp, id_ext("ext_cx")),
         id_ext("cfg"), Vec::new());
 
+    let cfg_clone_call = || cx.expr_method_call(
+        sp, cfg_call(),
+        id_ext("clone"), Vec::new());
+
     let parse_sess_call = || cx.expr_method_call(
         sp, cx.expr_ident(sp, id_ext("ext_cx")),
         id_ext("parse_sess"), Vec::new());
@@ -931,7 +935,7 @@ fn expand_parse_call(cx: &ExtCtxt,
     let new_parser_call =
         cx.expr_call(sp,
                      cx.expr_ident(sp, id_ext("new_parser_from_tts")),
-                     vec!(parse_sess_call(), cfg_call(), tts_expr));
+                     vec!(parse_sess_call(), cfg_clone_call(), tts_expr));
 
     let path = vec![id_ext("syntax"), id_ext("ext"), id_ext("quote"), id_ext(parse_method)];
     let mut args = vec![cx.expr_mut_addr_of(sp, new_parser_call)];

src/libsyntax/ext/source_util.rs

@@ -94,7 +94,7 @@ pub fn expand_include<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[tokenstream::T
     // The file will be added to the code map by the parser
     let p =
         parse::new_sub_parser_from_file(cx.parse_sess(),
-                                        cx.cfg(),
+                                        cx.cfg().clone(),
                                         &res_rel_file(cx,
                                                       sp,
                                                       Path::new(&file)),

src/libsyntax/ext/tt/macro_parser.rs

@@ -272,7 +272,7 @@ pub fn token_name_eq(t1 : &Token, t2 : &Token) -> bool {
 }
 
 pub fn parse(sess: &ParseSess,
-             cfg: ast::CrateConfig,
+             cfg: &ast::CrateConfig,
              mut rdr: TtReader,
              ms: &[TokenTree])
              -> NamedParseResult {

src/libsyntax/ext/tt/macro_rules.rs

@@ -120,7 +120,7 @@ fn generic_extension<'cx>(cx: &'cx ExtCtxt,
                                            Some(named_matches),
                                            imported_from,
                                            rhs);
-                let mut p = Parser::new(cx.parse_sess(), cx.cfg(), Box::new(trncbr));
+                let mut p = Parser::new(cx.parse_sess(), cx.cfg().clone(), Box::new(trncbr));
                 p.directory = cx.current_expansion.module.directory.clone();
                 p.restrictions = match cx.current_expansion.no_noninline_mod {
                     true => Restrictions::NO_NONINLINE_MOD,
@@ -225,7 +225,7 @@ pub fn compile(sess: &ParseSess, def: &ast::MacroDef) -> SyntaxExtension {
     // Parse the macro_rules! invocation (`none` is for no interpolations):
     let arg_reader = new_tt_reader(&sess.span_diagnostic, None, None, def.body.clone());
 
-    let argument_map = match parse(sess, Vec::new(), arg_reader, &argument_gram) {
+    let argument_map = match parse(sess, &Vec::new(), arg_reader, &argument_gram) {
         Success(m) => m,
         Failure(sp, str) | Error(sp, str) => {
             panic!(sess.span_diagnostic.span_fatal(sp.substitute_dummy(def.span), &str));

src/libsyntax_ext/asm.rs

@@ -107,7 +107,7 @@ pub fn expand_asm<'cx>(cx: &'cx mut ExtCtxt,
                 if p2.token != token::Eof {
                     let mut extra_tts = panictry!(p2.parse_all_token_trees());
                     extra_tts.extend(tts[first_colon..].iter().cloned());
-                    p = parse::tts_to_parser(cx.parse_sess, extra_tts, cx.cfg());
+                    p = parse::tts_to_parser(cx.parse_sess, extra_tts, cx.cfg().clone());
                 }
 
                 asm = s;

src/test/compile-fail-fulldeps/auxiliary/macro_crate_test.rs

@@ -57,7 +57,7 @@ fn expand_identity(cx: &mut ExtCtxt, _span: Span, tts: &[TokenTree])
                    -> Box<MacResult+'static> {
     // Parse an expression and emit it unchanged.
     let mut parser = parse::new_parser_from_tts(cx.parse_sess(),
-        cx.cfg(), tts.to_vec());
+        cx.cfg().clone(), tts.to_vec());
     let expr = parser.parse_expr().unwrap();
     MacEager::expr(quote_expr!(&mut *cx, $expr))
 }

src/test/run-pass-fulldeps/auxiliary/macro_crate_test.rs

@@ -60,7 +60,7 @@ fn expand_make_a_1(cx: &mut ExtCtxt, sp: Span, tts: &[TokenTree]) -> Box<MacResu
 // See Issue #15750
 fn expand_identity(cx: &mut ExtCtxt, _span: Span, tts: &[TokenTree]) -> Box<MacResult + 'static> {
     // Parse an expression and emit it unchanged.
-    let mut parser = parse::new_parser_from_tts(cx.parse_sess(), cx.cfg(), tts.to_vec());
+    let mut parser = parse::new_parser_from_tts(cx.parse_sess(), cx.cfg().clone(), tts.to_vec());
     let expr = parser.parse_expr().unwrap();
     MacEager::expr(quote_expr!(&mut *cx, $expr))
 }