From 911736dd8527bad44f7d939ebab484a6530123ba Mon Sep 17 00:00:00 2001
From: Dylan MacKenzie <ecstaticmorse@gmail.com>
Date: Mon, 29 Nov 2021 19:06:44 -0800
Subject: [PATCH 1/2] Mark defaulted `PartialEq`/`PartialOrd` methods as const

---
 library/core/src/cmp.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/library/core/src/cmp.rs b/library/core/src/cmp.rs
index 7456f886ea5d8..deed9901cc9e4 100644
--- a/library/core/src/cmp.rs
+++ b/library/core/src/cmp.rs
@@ -215,6 +215,7 @@ pub trait PartialEq<Rhs: ?Sized = Self> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[default_method_body_is_const]
     fn ne(&self, other: &Rhs) -> bool {
         !self.eq(other)
     }
@@ -1031,6 +1032,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[default_method_body_is_const]
     fn lt(&self, other: &Rhs) -> bool {
         matches!(self.partial_cmp(other), Some(Less))
     }
@@ -1050,6 +1052,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[default_method_body_is_const]
     fn le(&self, other: &Rhs) -> bool {
         // Pattern `Some(Less | Eq)` optimizes worse than negating `None | Some(Greater)`.
         // FIXME: The root cause was fixed upstream in LLVM with:
@@ -1072,6 +1075,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[default_method_body_is_const]
     fn gt(&self, other: &Rhs) -> bool {
         matches!(self.partial_cmp(other), Some(Greater))
     }
@@ -1091,6 +1095,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[default_method_body_is_const]
     fn ge(&self, other: &Rhs) -> bool {
         matches!(self.partial_cmp(other), Some(Greater | Equal))
     }

From dc18d507de30c0e27ed41994a863b9b54b445c67 Mon Sep 17 00:00:00 2001
From: Dylan MacKenzie <ecstaticmorse@gmail.com>
Date: Wed, 1 Dec 2021 14:37:51 -0800
Subject: [PATCH 2/2] Test const impl of `cmp` traits

---
 library/core/tests/cmp.rs | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/library/core/tests/cmp.rs b/library/core/tests/cmp.rs
index 11cf7add07ada..c9d29ed3a83f4 100644
--- a/library/core/tests/cmp.rs
+++ b/library/core/tests/cmp.rs
@@ -203,3 +203,31 @@ fn cmp_default() {
     assert!(Fool(false) != Fool(false));
     assert_eq!(Fool(false), Fool(true));
 }
+
+struct S(i32);
+
+impl const PartialEq for S {
+    fn eq(&self, other: &Self) -> bool {
+        self.0 == other.0
+    }
+}
+
+impl const PartialOrd for S {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        let ret = match (self.0, other.0) {
+            (a, b) if a > b => Ordering::Greater,
+            (a, b) if a < b => Ordering::Less,
+            _ => Ordering::Equal,
+        };
+
+        Some(ret)
+    }
+}
+
+const _: () = assert!(S(1) == S(1));
+const _: () = assert!(S(0) != S(1));
+
+const _: () = assert!(S(1) <= S(1));
+const _: () = assert!(S(1) >= S(1));
+const _: () = assert!(S(0) <  S(1));
+const _: () = assert!(S(1) >  S(0));