Auto merge of #103556 - clubby789:specialize-option-partial-eq, r=scottmcm

Manually implement PartialEq for Option<T> and specialize non-nullable types

This PR manually implements `PartialEq` and `StructuralPartialEq` for `Option`, which seems to produce slightly better codegen than the automatically derived implementation.

It also allows specializing on the `core::num::NonZero*` and `core::ptr::NonNull` types, taking advantage of the niche optimization by transmuting the `Option<T>` to `T` to be compared directly, which can be done in just two instructions.

A comparison of the original, new and specialized code generation is available [here](https://godbolt.org/z/dE4jxdYsa).

1 files changed, 34 insertions, 0 deletions

diff --git a/src/test/codegen/option-nonzero-eq.rs b/src/test/codegen/option-nonzero-eq.rs
new file mode 100644
index 00000000000..598dcc19b49
--- /dev/null
+++ b/src/test/codegen/option-nonzero-eq.rs
@@ -0,0 +1,34 @@
+// compile-flags: -O -Zmerge-functions=disabled
+
+#![crate_type = "lib"]
+
+extern crate core;
+use core::num::{NonZeroU32, NonZeroI64};
+use core::ptr::NonNull;
+
+// CHECK-lABEL: @non_zero_eq
+#[no_mangle]
+pub fn non_zero_eq(l: Option<NonZeroU32>, r: Option<NonZeroU32>) -> bool {
+    // CHECK: start:
+    // CHECK-NEXT: icmp eq i32
+    // CHECK-NEXT: ret i1
+    l == r
+}
+
+// CHECK-lABEL: @non_zero_signed_eq
+#[no_mangle]
+pub fn non_zero_signed_eq(l: Option<NonZeroI64>, r: Option<NonZeroI64>) -> bool {
+    // CHECK: start:
+    // CHECK-NEXT: icmp eq i64
+    // CHECK-NEXT: ret i1
+    l == r
+}
+
+// CHECK-lABEL: @non_null_eq
+#[no_mangle]
+pub fn non_null_eq(l: Option<NonNull<u8>>, r: Option<NonNull<u8>>) -> bool {
+    // CHECK: start:
+    // CHECK-NEXT: icmp eq {{(i8\*|ptr)}}
+    // CHECK-NEXT: ret i1
+    l == r
+}