Optimize Ord trait implementation for bool

Casting the booleans to `i8`s and converting their difference
into `Ordering` generates better assembly than casting them to
`u8`s and comparing them.

1 files changed, 17 insertions, 0 deletions

diff --git a/src/test/codegen/bool-cmp.rs b/src/test/codegen/bool-cmp.rs
new file mode 100644
index 00000000000..8769a4cb5e1
--- /dev/null
+++ b/src/test/codegen/bool-cmp.rs
@@ -0,0 +1,17 @@
+// This is a test for optimal Ord trait implementation for bool.
+// See <https://github.com/rust-lang/rust/issues/66780> for more info.
+
+// compile-flags: -C opt-level=3
+
+#![crate_type = "lib"]
+
+use std::cmp::Ordering;
+
+// CHECK-LABEL: @cmp_bool
+#[no_mangle]
+pub fn cmp_bool(a: bool, b: bool) -> Ordering {
+// CHECK: zext i1
+// CHECK: zext i1
+// CHECK: sub nsw
+    a.cmp(&b)
+}