From 9169934e27c955787e94186364dcc6fcb7455e4d Mon Sep 17 00:00:00 2001
From: ljedrz <ljedrz@gmail.com>
Date: Mon, 30 Jul 2018 14:54:33 +0200
Subject: [PATCH 1/2] Use Vec::extend in SmallVec::extend when applicable

---
 src/librustc_data_structures/small_vec.rs | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/librustc_data_structures/small_vec.rs b/src/librustc_data_structures/small_vec.rs
index 83eb54fade177..bfa580eb18660 100644
--- a/src/librustc_data_structures/small_vec.rs
+++ b/src/librustc_data_structures/small_vec.rs
@@ -169,10 +169,18 @@ impl<A: Array> FromIterator<A::Element> for SmallVec<A> {
 
 impl<A: Array> Extend<A::Element> for SmallVec<A> {
     fn extend<I: IntoIterator<Item=A::Element>>(&mut self, iter: I) {
-        let iter = iter.into_iter();
-        self.reserve(iter.size_hint().0);
-        for el in iter {
-            self.push(el);
+        if self.is_array() {
+            let iter = iter.into_iter();
+            self.reserve(iter.size_hint().0);
+
+            for el in iter {
+                self.push(el);
+            }
+        } else {
+            match self.0 {
+                AccumulateVec::Heap(ref mut vec) => vec.extend(iter),
+                _ => unreachable!()
+            }
         }
     }
 }

From ca5264826430cb5dab7a3c61394e8e795bbbd851 Mon Sep 17 00:00:00 2001
From: ljedrz <ljedrz@gmail.com>
Date: Tue, 31 Jul 2018 14:11:04 +0200
Subject: [PATCH 2/2] Benchmarks for SmallVec

---
 src/librustc_data_structures/small_vec.rs | 116 ++++++++++++++++++++++
 1 file changed, 116 insertions(+)

diff --git a/src/librustc_data_structures/small_vec.rs b/src/librustc_data_structures/small_vec.rs
index bfa580eb18660..2398a6f99259c 100644
--- a/src/librustc_data_structures/small_vec.rs
+++ b/src/librustc_data_structures/small_vec.rs
@@ -225,3 +225,119 @@ impl<A> Decodable for SmallVec<A>
         })
     }
 }
+
+#[cfg(test)]
+mod tests {
+    extern crate test;
+    use self::test::Bencher;
+
+    use super::*;
+
+    #[bench]
+    fn fill_small_vec_1_10_with_cap(b: &mut Bencher) {
+        b.iter(|| {
+            let mut sv: SmallVec<[usize; 1]> = SmallVec::with_capacity(10);
+
+            sv.extend(0..10);
+        })
+    }
+
+    #[bench]
+    fn fill_small_vec_1_10_wo_cap(b: &mut Bencher) {
+        b.iter(|| {
+            let mut sv: SmallVec<[usize; 1]> = SmallVec::new();
+
+            sv.extend(0..10);
+        })
+    }
+
+    #[bench]
+    fn fill_small_vec_8_10_with_cap(b: &mut Bencher) {
+        b.iter(|| {
+            let mut sv: SmallVec<[usize; 8]> = SmallVec::with_capacity(10);
+
+            sv.extend(0..10);
+        })
+    }
+
+    #[bench]
+    fn fill_small_vec_8_10_wo_cap(b: &mut Bencher) {
+        b.iter(|| {
+            let mut sv: SmallVec<[usize; 8]> = SmallVec::new();
+
+            sv.extend(0..10);
+        })
+    }
+
+    #[bench]
+    fn fill_small_vec_32_10_with_cap(b: &mut Bencher) {
+        b.iter(|| {
+            let mut sv: SmallVec<[usize; 32]> = SmallVec::with_capacity(10);
+
+            sv.extend(0..10);
+        })
+    }
+
+    #[bench]
+    fn fill_small_vec_32_10_wo_cap(b: &mut Bencher) {
+        b.iter(|| {
+            let mut sv: SmallVec<[usize; 32]> = SmallVec::new();
+
+            sv.extend(0..10);
+        })
+    }
+
+    #[bench]
+    fn fill_small_vec_1_50_with_cap(b: &mut Bencher) {
+        b.iter(|| {
+            let mut sv: SmallVec<[usize; 1]> = SmallVec::with_capacity(50);
+
+            sv.extend(0..50);
+        })
+    }
+
+    #[bench]
+    fn fill_small_vec_1_50_wo_cap(b: &mut Bencher) {
+        b.iter(|| {
+            let mut sv: SmallVec<[usize; 1]> = SmallVec::new();
+
+            sv.extend(0..50);
+        })
+    }
+
+    #[bench]
+    fn fill_small_vec_8_50_with_cap(b: &mut Bencher) {
+        b.iter(|| {
+            let mut sv: SmallVec<[usize; 8]> = SmallVec::with_capacity(50);
+
+            sv.extend(0..50);
+        })
+    }
+
+    #[bench]
+    fn fill_small_vec_8_50_wo_cap(b: &mut Bencher) {
+        b.iter(|| {
+            let mut sv: SmallVec<[usize; 8]> = SmallVec::new();
+
+            sv.extend(0..50);
+        })
+    }
+
+    #[bench]
+    fn fill_small_vec_32_50_with_cap(b: &mut Bencher) {
+        b.iter(|| {
+            let mut sv: SmallVec<[usize; 32]> = SmallVec::with_capacity(50);
+
+            sv.extend(0..50);
+        })
+    }
+
+    #[bench]
+    fn fill_small_vec_32_50_wo_cap(b: &mut Bencher) {
+        b.iter(|| {
+            let mut sv: SmallVec<[usize; 32]> = SmallVec::new();
+
+            sv.extend(0..50);
+        })
+    }
+}