Improve the generic MIR in the default PartialOrd::le and friends

library/core/src/cmp.rs

@@ -397,6 +397,12 @@ pub enum Ordering {
 }
 
 impl Ordering {
+    #[inline]
+    const fn as_raw(self) -> i8 {
+        // FIXME(const-hack): just use `PartialOrd` against `Equal` once that's const
+        crate::intrinsics::discriminant_value(&self)
+    }
+
     /// Returns `true` if the ordering is the `Equal` variant.
     ///
     /// # Examples
@@ -413,7 +419,11 @@ impl Ordering {
     #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")]
     #[stable(feature = "ordering_helpers", since = "1.53.0")]
     pub const fn is_eq(self) -> bool {
-        matches!(self, Equal)
+        // All the `is_*` methods are implemented as comparisons against zero
+        // to follow how clang's libcxx implements their equivalents in
+        // <https://github.com/llvm/llvm-project/blob/60486292b79885b7800b082754153202bef5b1f0/libcxx/include/__compare/is_eq.h#L23-L28>
+
+        self.as_raw() == 0
     }
 
     /// Returns `true` if the ordering is not the `Equal` variant.
@@ -432,7 +442,7 @@ impl Ordering {
     #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")]
     #[stable(feature = "ordering_helpers", since = "1.53.0")]
     pub const fn is_ne(self) -> bool {
-        !matches!(self, Equal)
+        self.as_raw() != 0
     }
 
     /// Returns `true` if the ordering is the `Less` variant.
@@ -451,7 +461,7 @@ impl Ordering {
     #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")]
     #[stable(feature = "ordering_helpers", since = "1.53.0")]
     pub const fn is_lt(self) -> bool {
-        matches!(self, Less)
+        self.as_raw() < 0
     }
 
     /// Returns `true` if the ordering is the `Greater` variant.
@@ -470,7 +480,7 @@ impl Ordering {
     #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")]
     #[stable(feature = "ordering_helpers", since = "1.53.0")]
     pub const fn is_gt(self) -> bool {
-        matches!(self, Greater)
+        self.as_raw() > 0
     }
 
     /// Returns `true` if the ordering is either the `Less` or `Equal` variant.
@@ -489,7 +499,7 @@ impl Ordering {
     #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")]
     #[stable(feature = "ordering_helpers", since = "1.53.0")]
     pub const fn is_le(self) -> bool {
-        !matches!(self, Greater)
+        self.as_raw() <= 0
     }
 
     /// Returns `true` if the ordering is either the `Greater` or `Equal` variant.
@@ -508,7 +518,7 @@ impl Ordering {
     #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")]
     #[stable(feature = "ordering_helpers", since = "1.53.0")]
     pub const fn is_ge(self) -> bool {
-        !matches!(self, Less)
+        self.as_raw() >= 0
     }
 
     /// Reverses the `Ordering`.

tests/mir-opt/pre-codegen/derived_ord.demo_le.PreCodegen.after.mir

@@ -0,0 +1,89 @@
+// MIR for `demo_le` after PreCodegen
+
+fn demo_le(_1: &MultiField, _2: &MultiField) -> bool {
+    debug a => _1;
+    debug b => _2;
+    let mut _0: bool;
+    scope 1 (inlined <MultiField as PartialOrd>::le) {
+        let mut _11: std::option::Option<std::cmp::Ordering>;
+        scope 2 (inlined Option::<std::cmp::Ordering>::is_some_and::<fn(std::cmp::Ordering) -> bool {std::cmp::Ordering::is_le}>) {
+            let _12: std::cmp::Ordering;
+            scope 3 {
+                scope 4 (inlined <fn(std::cmp::Ordering) -> bool {std::cmp::Ordering::is_le} as FnOnce<(std::cmp::Ordering,)>>::call_once - shim(fn(std::cmp::Ordering) -> bool {std::cmp::Ordering::is_le})) {
+                    scope 5 (inlined std::cmp::Ordering::is_le) {
+                        let mut _13: i8;
+                        scope 6 (inlined std::cmp::Ordering::as_raw) {
+                        }
+                    }
+                }
+            }
+        }
+        scope 7 (inlined <MultiField as PartialOrd>::partial_cmp) {
+            let mut _6: std::option::Option<std::cmp::Ordering>;
+            let mut _7: i8;
+            scope 8 {
+            }
+            scope 9 (inlined std::cmp::impls::<impl PartialOrd for char>::partial_cmp) {
+                let mut _3: char;
+                let mut _4: char;
+                let mut _5: std::cmp::Ordering;
+            }
+            scope 10 (inlined std::cmp::impls::<impl PartialOrd for i16>::partial_cmp) {
+                let mut _8: i16;
+                let mut _9: i16;
+                let mut _10: std::cmp::Ordering;
+            }
+        }
+    }
+
+    bb0: {
+        StorageLive(_12);
+        StorageLive(_11);
+        StorageLive(_5);
+        StorageLive(_7);
+        StorageLive(_3);
+        _3 = copy ((*_1).0: char);
+        StorageLive(_4);
+        _4 = copy ((*_2).0: char);
+        _5 = Cmp(move _3, move _4);
+        StorageDead(_4);
+        StorageDead(_3);
+        _6 = Option::<std::cmp::Ordering>::Some(copy _5);
+        _7 = discriminant(_5);
+        switchInt(move _7) -> [0: bb1, otherwise: bb2];
+    }
+
+    bb1: {
+        StorageLive(_10);
+        StorageLive(_8);
+        _8 = copy ((*_1).1: i16);
+        StorageLive(_9);
+        _9 = copy ((*_2).1: i16);
+        _10 = Cmp(move _8, move _9);
+        StorageDead(_9);
+        StorageDead(_8);
+        _11 = Option::<std::cmp::Ordering>::Some(move _10);
+        StorageDead(_10);
+        StorageDead(_7);
+        StorageDead(_5);
+        goto -> bb3;
+    }
+
+    bb2: {
+        _11 = copy _6;
+        StorageDead(_7);
+        StorageDead(_5);
+        goto -> bb3;
+    }
+
+    bb3: {
+        _12 = move ((_11 as Some).0: std::cmp::Ordering);
+        StorageLive(_13);
+        _13 = discriminant(_12);
+        _0 = Le(move _13, const 0_i8);
+        StorageDead(_13);
+        StorageDead(_11);
+        StorageDead(_12);
+        return;
+    }
+}

tests/mir-opt/pre-codegen/derived_ord.rs

@@ -1,9 +1,33 @@
-// skip-filecheck
 //@ compile-flags: -O -Zmir-opt-level=2 -Cdebuginfo=0
 
 #![crate_type = "lib"]
 
 #[derive(PartialOrd, PartialEq)]
 pub struct MultiField(char, i16);
 
+// Because this isn't derived by the impl, it's not on the `{impl#0}-partial_cmp`,
+// and thus we need to call it to see what the inlined generic one produces.
+pub fn demo_le(a: &MultiField, b: &MultiField) -> bool {
+    // CHECK-LABEL: fn demo_le
+    // CHECK: inlined <MultiField as PartialOrd>::le
+    // CHECK: inlined{{.+}}is_some_and
+    // CHECK: inlined <MultiField as PartialOrd>::partial_cmp
+
+    // CHECK: [[A0:_[0-9]+]] = copy ((*_1).0: char);
+    // CHECK: [[B0:_[0-9]+]] = copy ((*_2).0: char);
+    // CHECK: Cmp(move [[A0]], move [[B0]]);
+
+    // CHECK: [[D0:_[0-9]+]] = discriminant({{.+}});
+    // CHECK: switchInt(move [[D0]]) -> [0: bb{{[0-9]+}}, otherwise: bb{{[0-9]+}}];
+
+    // CHECK: [[A1:_[0-9]+]] = copy ((*_1).1: i16);
+    // CHECK: [[B1:_[0-9]+]] = copy ((*_2).1: i16);
+    // CHECK: Cmp(move [[A1]], move [[B1]]);
+
+    // CHECK: [[D1:_[0-9]+]] = discriminant({{.+}});
+    // CHECK: _0 = Le(move [[D1]], const 0_i8);
+    *a <= *b
+}
+
 // EMIT_MIR derived_ord.{impl#0}-partial_cmp.PreCodegen.after.mir
+// EMIT_MIR derived_ord.demo_le.PreCodegen.after.mir

tests/mir-opt/pre-codegen/derived_ord.{impl#0}-partial_cmp.PreCodegen.after.mir

@@ -1,6 +1,6 @@
-// MIR for `<impl at $DIR/derived_ord.rs:6:10: 6:20>::partial_cmp` after PreCodegen
+// MIR for `<impl at $DIR/derived_ord.rs:5:10: 5:20>::partial_cmp` after PreCodegen
 
-fn <impl at $DIR/derived_ord.rs:6:10: 6:20>::partial_cmp(_1: &MultiField, _2: &MultiField) -> Option<std::cmp::Ordering> {
+fn <impl at $DIR/derived_ord.rs:5:10: 5:20>::partial_cmp(_1: &MultiField, _2: &MultiField) -> Option<std::cmp::Ordering> {
     debug self => _1;
     debug other => _2;
     let mut _0: std::option::Option<std::cmp::Ordering>;