From 42b39924d87739f2dcda3e788c6e8655d310954f Mon Sep 17 00:00:00 2001
From: James Miller <james@aatch.net>
Date: Wed, 16 Apr 2014 11:35:18 +1200
Subject: [PATCH 1/2] Improve the copying code for slices and Vec

---
 src/libstd/slice.rs | 20 ++++++++++++++++----
 src/libstd/vec.rs   | 21 ++++++++++++++++++++-
 2 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/src/libstd/slice.rs b/src/libstd/slice.rs
index aedaa5b3c159f..f4f97ea8c9202 100644
--- a/src/libstd/slice.rs
+++ b/src/libstd/slice.rs
@@ -760,9 +760,20 @@ impl<'a, T: Clone> CloneableVector<T> for &'a [T] {
     /// Returns a copy of `v`.
     #[inline]
     fn to_owned(&self) -> ~[T] {
-        let mut result = with_capacity(self.len());
-        for e in self.iter() {
-            result.push((*e).clone());
+        let len = self.len();
+        let mut result = with_capacity(len);
+        unsafe {
+            // Unsafe code so this can be optimised to a memcpy (or something
+            // similarly fast) when T is Copy. LLVM is easily confused, so any
+            // extra operations during the loop can prevent this optimisation
+            result.set_len(len);
+            let mut i = 0;
+            while i < len {
+                mem::move_val_init(
+                    result.unsafe_mut_ref(i),
+                    self.unsafe_ref(i).clone());
+                i = i + 1;
+            }
         }
         result
     }
@@ -2584,7 +2595,8 @@ pub mod bytes {
 impl<A: Clone> Clone for ~[A] {
     #[inline]
     fn clone(&self) -> ~[A] {
-        self.iter().map(|item| item.clone()).collect()
+        // Use the fast to_owned on &[A] for cloning
+        self.as_slice().to_owned()
     }
 
     fn clone_from(&mut self, source: &~[A]) {
diff --git a/src/libstd/vec.rs b/src/libstd/vec.rs
index a69120de00f7d..034d53aa78bdb 100644
--- a/src/libstd/vec.rs
+++ b/src/libstd/vec.rs
@@ -311,7 +311,26 @@ impl<T: Clone> Vec<T> {
 
 impl<T:Clone> Clone for Vec<T> {
     fn clone(&self) -> Vec<T> {
-        self.iter().map(|x| x.clone()).collect()
+        let len = self.len;
+        let mut vector = Vec::with_capacity(len);
+        vector.len = len;
+        // Unsafe code so this can be optimised to a memcpy (or something
+        // similarly fast) when T is Copy. LLVM is easily confused, so any
+        // extra operations during the loop can prevent this optimisation
+        {
+            let slice = vector.as_mut_slice();
+            let this_slice = self.as_slice();
+            let mut i = 0;
+            while i < len {
+                unsafe {
+                    mem::move_val_init(
+                        slice.unsafe_mut_ref(i),
+                        this_slice.unsafe_ref(i).clone());
+                }
+                i = i + 1;
+            }
+        }
+        vector
     }
 
     fn clone_from(&mut self, other: &Vec<T>) {

From be334d582435a05ea56c1ca7fcb2e512cfc51f24 Mon Sep 17 00:00:00 2001
From: James Miller <james@aatch.net>
Date: Wed, 16 Apr 2014 14:29:36 +1200
Subject: [PATCH 2/2] Make Vec::clone and slice::to_owned failure-safe

---
 src/libstd/slice.rs | 25 +++++++++++++++----------
 src/libstd/vec.rs   | 11 ++++-------
 2 files changed, 19 insertions(+), 17 deletions(-)

diff --git a/src/libstd/slice.rs b/src/libstd/slice.rs
index f4f97ea8c9202..153e21c780c09 100644
--- a/src/libstd/slice.rs
+++ b/src/libstd/slice.rs
@@ -762,18 +762,23 @@ impl<'a, T: Clone> CloneableVector<T> for &'a [T] {
     fn to_owned(&self) -> ~[T] {
         let len = self.len();
         let mut result = with_capacity(len);
+        // Unsafe code so this can be optimised to a memcpy (or something
+        // similarly fast) when T is Copy. LLVM is easily confused, so any
+        // extra operations during the loop can prevent this optimisation
         unsafe {
-            // Unsafe code so this can be optimised to a memcpy (or something
-            // similarly fast) when T is Copy. LLVM is easily confused, so any
-            // extra operations during the loop can prevent this optimisation
-            result.set_len(len);
             let mut i = 0;
-            while i < len {
-                mem::move_val_init(
-                    result.unsafe_mut_ref(i),
-                    self.unsafe_ref(i).clone());
-                i = i + 1;
-            }
+            let p = result.as_mut_ptr();
+            // Use try_finally here otherwise the write to length
+            // inside the loop stops LLVM from optimising this.
+            try_finally(
+                &mut i, (),
+                |i, ()| while *i < len {
+                    mem::move_val_init(
+                        &mut(*p.offset(*i as int)),
+                        self.unsafe_ref(*i).clone());
+                    *i += 1;
+                },
+                |i| result.set_len(*i));
         }
         result
     }
diff --git a/src/libstd/vec.rs b/src/libstd/vec.rs
index 034d53aa78bdb..96cbac8869ef2 100644
--- a/src/libstd/vec.rs
+++ b/src/libstd/vec.rs
@@ -313,21 +313,18 @@ impl<T:Clone> Clone for Vec<T> {
     fn clone(&self) -> Vec<T> {
         let len = self.len;
         let mut vector = Vec::with_capacity(len);
-        vector.len = len;
         // Unsafe code so this can be optimised to a memcpy (or something
         // similarly fast) when T is Copy. LLVM is easily confused, so any
         // extra operations during the loop can prevent this optimisation
         {
-            let slice = vector.as_mut_slice();
             let this_slice = self.as_slice();
-            let mut i = 0;
-            while i < len {
+            while vector.len < len {
                 unsafe {
                     mem::move_val_init(
-                        slice.unsafe_mut_ref(i),
-                        this_slice.unsafe_ref(i).clone());
+                        vector.as_mut_slice().unsafe_mut_ref(vector.len),
+                        this_slice.unsafe_ref(vector.len).clone());
                 }
-                i = i + 1;
+                vector.len += 1;
             }
         }
         vector