diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index 7d11dd2800fd4..590f4e46c1d2f 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -71,6 +71,8 @@
 #![feature(cfg_target_has_atomic)]
 #![feature(concat_idents)]
 #![feature(const_fn)]
+#![feature(const_if_match)]
+#![feature(const_panic)]
 #![feature(const_fn_union)]
 #![feature(const_generics)]
 #![feature(const_ptr_offset_from)]
diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index 8a32479b2ff7d..14540394caba1 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -1416,18 +1416,14 @@ $EndFeature, "
 ```"),
             #[stable(feature = "no_panic_abs", since = "1.13.0")]
             #[rustc_const_stable(feature = "const_int_methods", since = "1.32.0")]
+            #[allow_internal_unstable(const_if_match)]
             #[inline]
             pub const fn wrapping_abs(self) -> Self {
-                // sign is -1 (all ones) for negative numbers, 0 otherwise.
-                let sign = self >> ($BITS - 1);
-                // For positive self, sign == 0 so the expression is simply
-                // (self ^ 0).wrapping_sub(0) == self == abs(self).
-                //
-                // For negative self, self ^ sign == self ^ all_ones.
-                // But all_ones ^ self == all_ones - self == -1 - self.
-                // So for negative numbers, (self ^ sign).wrapping_sub(sign) is
-                // (-1 - self).wrapping_sub(-1) == -self == abs(self).
-                (self ^ sign).wrapping_sub(sign)
+                 if self.is_negative() {
+                     self.wrapping_neg()
+                 } else {
+                     self
+                 }
             }
         }
 
@@ -1713,8 +1709,13 @@ assert_eq!(", stringify!($SelfT), "::MIN.overflowing_neg(), (", stringify!($Self
             #[inline]
             #[stable(feature = "wrapping", since = "1.7.0")]
             #[rustc_const_stable(feature = "const_int_methods", since = "1.32.0")]
+            #[allow_internal_unstable(const_if_match)]
             pub const fn overflowing_neg(self) -> (Self, bool) {
-                ((!self).wrapping_add(1), self == Self::min_value())
+                if self == Self::min_value() {
+                    (Self::min_value(), true)
+                } else {
+                    (-self, false)
+                }
             }
         }
 
@@ -2041,7 +2042,11 @@ $EndFeature, "
             #[rustc_const_unstable(feature = "const_int_sign", issue = "53718")]
             #[inline]
             pub const fn signum(self) -> Self {
-                (self > 0) as Self - (self < 0) as Self
+                match self {
+                    n if n > 0 =>  1,
+                    0          =>  0,
+                    _          => -1,
+                }
             }
         }
 
diff --git a/src/libcore/ptr/const_ptr.rs b/src/libcore/ptr/const_ptr.rs
index e5297a0c1e094..fc3c02e1f066d 100644
--- a/src/libcore/ptr/const_ptr.rs
+++ b/src/libcore/ptr/const_ptr.rs
@@ -288,10 +288,7 @@ impl<T: ?Sized> *const T {
         T: Sized,
     {
         let pointee_size = mem::size_of::<T>();
-        let ok = 0 < pointee_size && pointee_size <= isize::max_value() as usize;
-        // assert that the pointee size is valid in a const eval compatible way
-        // FIXME: do this with a real assert at some point
-        [()][(!ok) as usize];
+        assert!(0 < pointee_size && pointee_size <= isize::max_value() as usize);
         intrinsics::ptr_offset_from(self, origin)
     }