Rollup merge of #66881 - krishna-veerareddy:issue-66780-bool-ord-optimization, r=sfackler

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.

Fixes #66780

#### Comparison([Godbolt link](https://rust.godbolt.org/z/PjBpvF))

##### Old assembly:
```asm
example::boolean_cmp:
        mov     ecx, edi
        xor     ecx, esi
        test    esi, esi
        mov     eax, 255
        cmove   eax, ecx
        test    edi, edi
        cmovne  eax, ecx
        ret
```

##### New assembly:
```asm
example::boolean_cmp:
        mov     eax, edi
        sub     al, sil
        ret
```

##### Old LLVM-MCA statistics:
```
Iterations:        100
Instructions:      800
Total Cycles:      234
Total uOps:        1000

Dispatch Width:    6
uOps Per Cycle:    4.27
IPC:               3.42
Block RThroughput: 1.7
```

##### New LLVM-MCA statistics:
```
Iterations:        100
Instructions:      300
Total Cycles:      110
Total uOps:        500

Dispatch Width:    6
uOps Per Cycle:    4.55
IPC:               2.73
Block RThroughput: 1.0
```

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)
+}