3 files changed, 24 insertions, 3 deletions
diff --git a/src/libcore/alloc.rs b/src/libcore/alloc.rs
index 4cfd6527deb..5c24e3d8f5d 100644
--- a/src/libcore/alloc.rs
+++ b/src/libcore/alloc.rs
@@ -239,8 +239,11 @@ impl Layout {
     #[unstable(feature = "alloc_layout_extra", issue = "55724")]
     #[inline]
     pub fn repeat(&self, n: usize) -> Result<(Self, usize), LayoutErr> {
-        let padded_size = self.size().checked_add(self.padding_needed_for(self.align()))
-            .ok_or(LayoutErr { private: () })?;
+        // This cannot overflow. Quoting from the invariant of Layout:
+        // > `size`, when rounded up to the nearest multiple of `align`,
+        // > must not overflow (i.e., the rounded value must be less than
+        // > `usize::MAX`)
+        let padded_size = self.size() + self.padding_needed_for(self.align());
         let alloc_size = padded_size.checked_mul(n)
             .ok_or(LayoutErr { private: () })?;
 
diff --git a/src/libcore/cmp.rs b/src/libcore/cmp.rs
index a5f355cd9a7..fd4be02e20f 100644
--- a/src/libcore/cmp.rs
+++ b/src/libcore/cmp.rs
@@ -1005,6 +1005,7 @@ pub fn max_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
 
 // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types
 mod impls {
+    use crate::hint::unreachable_unchecked;
     use crate::cmp::Ordering::{self, Less, Greater, Equal};
 
     macro_rules! partial_eq_impl {
@@ -1125,7 +1126,16 @@ mod impls {
     impl Ord for bool {
         #[inline]
         fn cmp(&self, other: &bool) -> Ordering {
-            (*self as u8).cmp(&(*other as u8))
+            // Casting to i8's and converting the difference to an Ordering generates
+            // more optimal assembly.
+            // See <https://github.com/rust-lang/rust/issues/66780> for more info.
+            match (*self as i8) - (*other as i8) {
+                -1 => Less,
+                0 => Equal,
+                1 => Greater,
+                // SAFETY: bool as i8 returns 0 or 1, so the difference can't be anything else
+                _ => unsafe { unreachable_unchecked() },
+            }
         }
     }
 
diff --git a/src/libcore/tests/cmp.rs b/src/libcore/tests/cmp.rs
index 5e6778e222a..56a2f4acf6e 100644
--- a/src/libcore/tests/cmp.rs
+++ b/src/libcore/tests/cmp.rs
@@ -10,6 +10,14 @@ fn test_int_totalord() {
 }
 
 #[test]
+fn test_bool_totalord() {
+    assert_eq!(true.cmp(&false), Greater);
+    assert_eq!(false.cmp(&true), Less);
+    assert_eq!(true.cmp(&true), Equal);
+    assert_eq!(false.cmp(&false), Equal);
+}
+
+#[test]
 fn test_mut_int_totalord() {
     assert_eq!((&mut 5).cmp(&&mut 10), Less);
     assert_eq!((&mut 10).cmp(&&mut 5), Greater);