Add comment.

rust-lang · Sep 20, 2015 · 77f5da7 · 77f5da7
1 parent 6beb4ba
commit 77f5da7
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/src/libcollections/vec.rs b/src/libcollections/vec.rs
@@ -1323,6 +1323,8 @@ impl<T> Drop for Vec<T> {
         // don't need unsafe_no_drop_flag shenanigans anymore.
         if self.buf.unsafe_no_drop_flag_needs_drop() {
             unsafe {
+                // The branch on needs_drop() is an -O1 performance optimization.
+                // Without the branch, dropping Vec<u8> takes linear time.
                 if needs_drop::<T>() {
                     for x in self.iter_mut() {
                         drop_in_place(x);