Add 'unchecked_disjoint_bitor' method to 'bool', 'i8', 'i16', 'i32', 'i64', 'i128', and 'isize';

Author: bjoernager

library/core/src/bool.rs

@@ -1,5 +1,8 @@
 //! impl bool {}
 
+use crate::intrinsics;
+use crate::ub_checks::assert_unsafe_precondition;
+
 impl bool {
     /// Returns `Some(t)` if the `bool` is [`true`](../std/keyword.true.html),
     /// or `None` otherwise.
@@ -128,4 +131,46 @@ impl bool {
     pub fn ok_or_else<E, F: FnOnce() -> E>(self, f: F) -> Result<(), E> {
         if self { Ok(()) } else { Err(f()) }
     }
+
+    /// Same value as `self | other`, but UB if any bit position is set in both inputs.
+    ///
+    /// This is a situational micro-optimization for places where you'd rather
+    /// use addition on some platforms and bitwise or on other platforms, based
+    /// on exactly which instructions combine better with whatever else you're
+    /// doing.  Note that there's no reason to bother using this for places
+    /// where it's clear from the operations involved that they can't overlap.
+    /// For example, if you're combining `u16`s into a `u32` with
+    /// `((a as u32) << 16) | (b as u32)`, that's fine, as the backend will
+    /// know those sides of the `|` are disjoint without needing help.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(disjoint_bitor)]
+    ///
+    /// // SAFETY: `false` and `true` have no bits in common.
+    /// unsafe { false.unchecked_disjoint_bitor(true) }
+    /// ```
+    ///
+    /// # Safety
+    ///
+    /// Requires that `self` and `rhs` are disjoint to each other, i.e. do not
+    /// have overlapping ones (thus `self & rhs == false`). By extension, requires
+    /// that `self | rhs`, `self + rhs`, and `self ^ rhs` are equivalent.
+    #[unstable(feature = "disjoint_bitor", issue = "135758")]
+    #[rustc_const_unstable(feature = "disjoint_bitor", issue = "135758")]
+    #[inline]
+    pub const unsafe fn unchecked_disjoint_bitor(self, rhs: Self) -> Self {
+        assert_unsafe_precondition!(
+            check_language_ub,
+            "attempt to disjoint or conjoint values",
+            (
+                lhs: bool = self,
+                rhs: bool = rhs,
+            ) => (lhs & rhs) == false,
+        );
+
+        // SAFETY: Same precondition.
+        unsafe { intrinsics::disjoint_bitor(self, rhs) }
+    }
 }

library/core/src/num/int_macros.rs

@@ -1216,6 +1216,50 @@ macro_rules! int_impl {
             if b { overflow_panic::rem() } else { a }
         }
 
+        /// Same value as `self | other`, but UB if any bit position is set in both inputs.
+        ///
+        /// This is a situational micro-optimization for places where you'd rather
+        /// use addition on some platforms and bitwise or on other platforms, based
+        /// on exactly which instructions combine better with whatever else you're
+        /// doing.  Note that there's no reason to bother using this for places
+        /// where it's clear from the operations involved that they can't overlap.
+        /// For example, if you're combining `u16`s into a `u32` with
+        /// `((a as u32) << 16) | (b as u32)`, that's fine, as the backend will
+        /// know those sides of the `|` are disjoint without needing help.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// #![feature(disjoint_bitor)]
+        ///
+        /// // SAFETY: `1` and `-2` have no bits in common.
+        /// unsafe {
+        #[doc = concat!("    assert_eq!(1_", stringify!($SelfT), ".unchecked_disjoint_bitor(-2), -1);")]
+        /// }
+        /// ```
+        ///
+        /// # Safety
+        ///
+        /// Requires that `self` and `rhs` are disjoint to each other, i.e. do not
+        /// have overlapping ones (thus `self & rhs == 0`). By extension, requires
+        /// that `self | rhs`, `self + rhs`, and `self ^ rhs` are equivalent.
+        #[unstable(feature = "disjoint_bitor", issue = "135758")]
+        #[rustc_const_unstable(feature = "disjoint_bitor", issue = "135758")]
+        #[inline]
+        pub const unsafe fn unchecked_disjoint_bitor(self, rhs: Self) -> Self {
+            assert_unsafe_precondition!(
+                check_language_ub,
+                "attempt to disjoint or conjoint values",
+                (
+                    lhs: $SelfT = self,
+                    rhs: $SelfT = rhs,
+                ) => (lhs & rhs) == 0,
+            );
+
+            // SAFETY: Same precondition.
+            unsafe { intrinsics::disjoint_bitor(self, rhs) }
+        }
+
         /// Checked negation. Computes `-self`, returning `None` if `self == MIN`.
         ///
         /// # Examples

library/core/src/num/uint_macros.rs

@@ -1443,24 +1443,24 @@ macro_rules! uint_impl {
         ///
         /// # Safety
         ///
-        /// Requires that `(self & other) == 0`, otherwise it's immediate UB.
-        ///
-        /// Equivalently, requires that `(self | other) == (self + other)`.
+        /// Requires that `self` and `rhs` are disjoint to each other, i.e. do not
+        /// have overlapping ones (thus `self & rhs == 0`). By extension, requires
+        /// that `self | rhs`, `self + rhs`, and `self ^ rhs` are equivalent.
         #[unstable(feature = "disjoint_bitor", issue = "135758")]
         #[rustc_const_unstable(feature = "disjoint_bitor", issue = "135758")]
         #[inline]
-        pub const unsafe fn unchecked_disjoint_bitor(self, other: Self) -> Self {
+        pub const unsafe fn unchecked_disjoint_bitor(self, rhs: Self) -> Self {
             assert_unsafe_precondition!(
                 check_language_ub,
-                concat!(stringify!($SelfT), "::unchecked_disjoint_bitor cannot have overlapping bits"),
+                "attempt to disjoint or conjoint values",
                 (
                     lhs: $SelfT = self,
-                    rhs: $SelfT = other,
+                    rhs: $SelfT = rhs,
                 ) => (lhs & rhs) == 0,
             );
 
-            // SAFETY: Same precondition
-            unsafe { intrinsics::disjoint_bitor(self, other) }
+            // SAFETY: Same precondition.
+            unsafe { intrinsics::disjoint_bitor(self, rhs) }
         }
 
         /// Returns the logarithm of the number with respect to an arbitrary base,