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.

2 files changed, 3 insertions, 3 deletions

diff --git a/src/libsyntax/ext/tt/macro_parser.rs b/src/libsyntax/ext/tt/macro_parser.rs
index b0696a986e3..030cb303832 100644
--- a/src/libsyntax/ext/tt/macro_parser.rs
+++ b/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 {
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index 2e0c7ddb540..a74d335d604 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/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));