From 262452308a3192fecc3f4d88a2690dc67e681ef5 Mon Sep 17 00:00:00 2001
From: The 8472 <git@infinite-source.de>
Date: Wed, 4 Oct 2023 16:21:02 +0200
Subject: [PATCH 1/2] add benchmark for generic slice PartialEq impl

---
 library/core/benches/slice.rs | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/library/core/benches/slice.rs b/library/core/benches/slice.rs
index 3bfb35e684ea1..1ec51653d92ef 100644
--- a/library/core/benches/slice.rs
+++ b/library/core/benches/slice.rs
@@ -171,3 +171,17 @@ fn fold_to_last(b: &mut Bencher) {
     let slice: &[i32] = &[0; 1024];
     b.iter(|| black_box(slice).iter().fold(None, |_, r| Some(NonNull::from(r))));
 }
+
+#[bench]
+fn slice_cmp_generic(b: &mut Bencher) {
+    #[derive(PartialEq, Clone, Copy)]
+    struct Foo(u32, u32);
+
+    let left = [Foo(128, 128); 128];
+    let right = [Foo(128, 128); 128];
+
+    b.iter(|| {
+        let (left, right) = (black_box(&left), black_box(&right));
+        left.as_slice() == right.as_slice()
+    });
+}

From 9d3905f88f12308d79e9e4e0142fa44f1e214a75 Mon Sep 17 00:00:00 2001
From: The 8472 <git@infinite-source.de>
Date: Wed, 4 Oct 2023 16:21:21 +0200
Subject: [PATCH 2/2] unroll slice::equal impl

---
 library/core/src/slice/cmp.rs | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/library/core/src/slice/cmp.rs b/library/core/src/slice/cmp.rs
index 075347b80d031..e3b80226e9f12 100644
--- a/library/core/src/slice/cmp.rs
+++ b/library/core/src/slice/cmp.rs
@@ -60,7 +60,22 @@ where
             return false;
         }
 
-        self.iter().zip(other.iter()).all(|(x, y)| x == y)
+        let (chunks_a, residual_a) = self.as_chunks::<4>();
+        let (chunks_b, residual_b) = other.as_chunks::<4>();
+
+        // check the residual first to bail out fast if there's a mismatch and comparisons
+        // happen to be expensive
+        let mut result = residual_a.into_iter().zip(residual_b).all(|(a, b)| a == b);
+
+        // iter.all short-circuits which means the backend can't unroll the loop due to early exits.
+        // So we unroll it manually.
+        result = result
+            && chunks_a
+                .iter()
+                .zip(chunks_b.iter())
+                .all(|(a, b)| (a[0] == b[0]) & (a[1] == b[1]) & (a[2] == b[2]) & (a[3] == b[3]));
+
+        result
     }
 }