cfg out checks in add and sub but not offset

...because the checks in offset found bugs in a crater run.

Author: saethlin

library/core/src/ptr/const_ptr.rs

@@ -884,6 +884,7 @@ impl<T: ?Sized> *const T {
     where
         T: Sized,
     {
+        #[cfg(debug_assertions)]
         #[inline]
         const fn runtime_add_nowrap(this: *const (), count: usize, size: usize) -> bool {
             #[inline]
@@ -902,6 +903,7 @@ impl<T: ?Sized> *const T {
             intrinsics::const_eval_select((this, count, size), comptime, runtime)
         }
 
+        #[cfg(debug_assertions)] // Expensive, and doesn't catch much in the wild.
         ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::add requires that the address calculation does not overflow",
@@ -987,6 +989,7 @@ impl<T: ?Sized> *const T {
     where
         T: Sized,
     {
+        #[cfg(debug_assertions)]
         #[inline]
         const fn runtime_sub_nowrap(this: *const (), count: usize, size: usize) -> bool {
             #[inline]
@@ -1004,6 +1007,7 @@ impl<T: ?Sized> *const T {
             intrinsics::const_eval_select((this, count, size), comptime, runtime)
         }
 
+        #[cfg(debug_assertions)] // Expensive, and doesn't catch much in the wild.
         ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::sub requires that the address calculation does not overflow",

library/core/src/ptr/mut_ptr.rs

@@ -967,6 +967,7 @@ impl<T: ?Sized> *mut T {
     where
         T: Sized,
     {
+        #[cfg(debug_assertions)]
         #[inline]
         const fn runtime_add_nowrap(this: *const (), count: usize, size: usize) -> bool {
             #[inline]
@@ -985,6 +986,7 @@ impl<T: ?Sized> *mut T {
             intrinsics::const_eval_select((this, count, size), comptime, runtime)
         }
 
+        #[cfg(debug_assertions)] // Expensive, and doesn't catch much in the wild.
         ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::add requires that the address calculation does not overflow",
@@ -1070,6 +1072,7 @@ impl<T: ?Sized> *mut T {
     where
         T: Sized,
     {
+        #[cfg(debug_assertions)]
         #[inline]
         const fn runtime_sub_nowrap(this: *const (), count: usize, size: usize) -> bool {
             #[inline]
@@ -1087,6 +1090,7 @@ impl<T: ?Sized> *mut T {
             intrinsics::const_eval_select((this, count, size), comptime, runtime)
         }
 
+        #[cfg(debug_assertions)] // Expensive, and doesn't catch much in the wild.
         ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::sub requires that the address calculation does not overflow",