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.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index f7c88073c9d..ff1986cb4a8 100644
--- a/src/libsyntax/ext/base.rs
+++ b/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,