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, 1 insertions, 1 deletions

diff --git a/src/libsyntax_ext/asm.rs b/src/libsyntax_ext/asm.rs
index cc4fb604d6c..af79bdcb611 100644
--- a/src/libsyntax_ext/asm.rs
+++ b/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;