auto merge of #15256 : erickt/rust/optimizations, r=alexcrichton

The bug #11084 causes `option::collect` and `result::collect` about twice as slower as it should because llvm is having some trouble optimizing away the scan closure. This gets rid of it so now those functions perform equivalent to a hand written version.

This also adds an impl of `Default` for `Rc` along the way.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs
index a3ca72f1547..e3127030842 100644
--- a/src/liballoc/rc.rs
+++ b/src/liballoc/rc.rs
@@ -27,6 +27,7 @@ use core::mem::transmute;
 use core::cell::Cell;
 use core::clone::Clone;
 use core::cmp::{PartialEq, PartialOrd, Eq, Ord, Ordering};
+use core::default::Default;
 use core::kinds::marker;
 use core::ops::{Deref, Drop};
 use core::option::{Option, Some, None};
@@ -152,6 +153,13 @@ impl<T> Clone for Rc<T> {
     }
 }
 
+impl<T: Default> Default for Rc<T> {
+    #[inline]
+    fn default() -> Rc<T> {
+        Rc::new(Default::default())
+    }
+}
+
 impl<T: PartialEq> PartialEq for Rc<T> {
     #[inline(always)]
     fn eq(&self, other: &Rc<T>) -> bool { **self == **other }