Optimize option clone

library/core/src/option.rs

@@ -135,7 +135,8 @@ use crate::iter::{FromIterator, FusedIterator, TrustedLen};
 use crate::pin::Pin;
 use crate::{
     convert, fmt, hint, mem,
-    ops::{self, Deref, DerefMut},
+    ops::{self, Deref, DerefMut, Range},
+    ptr,
 };
 
 /// The `Option` type. See [the module level documentation](self) for more.
@@ -1228,22 +1229,46 @@ fn expect_none_failed(msg: &str, value: &dyn fmt::Debug) -> ! {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Clone> Clone for Option<T> {
     #[inline]
-    fn clone(&self) -> Self {
+    default fn clone(&self) -> Self {
         match self {
             Some(x) => Some(x.clone()),
             None => None,
         }
     }
 
     #[inline]
-    fn clone_from(&mut self, source: &Self) {
+    default fn clone_from(&mut self, source: &Self) {
         match (self, source) {
             (Some(to), Some(from)) => to.clone_from(from),
             (to, from) => *to = from.clone(),
         }
     }
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Copy> Clone for Option<T> {
+    #[inline]
+    fn clone(&self) -> Self {
+        *self
+    }
+
+    #[inline]
+    fn clone_from(&mut self, source: &Self) {
+        *self = *source
+    }
+}
+
+// Range<T> is not Copy even if T is copy (see #27186),
+// so provide an efficient implementation.
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Copy> Clone for Option<Range<T>> {
+    #[inline]
+    fn clone(&self) -> Self {
+        // SAFETY: 'self' is not Drop so memcpy is OK.
+        unsafe { ptr::read(self as *const Self) }
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Default for Option<T> {
     /// Returns [`None`][Option::None].