Auto merge of rust-lang#129498 - saethlin:ptr-read-write-precondition, r=<try>

Try enabling precondition checks on ptr::{read,write}

The overhead here is probably too much, but let's have the measurement anyway.

This will fail at least one codegen test.

r? `@ghost`

Author: bors

library/core/src/ptr/mod.rs

@@ -1387,7 +1387,6 @@ pub const unsafe fn read<T>(src: *const T) -> T {
 
     // SAFETY: the caller must guarantee that `src` is valid for reads.
     unsafe {
-        #[cfg(debug_assertions)] // Too expensive to always enable (for now?)
         ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::read requires that the pointer argument is aligned and non-null",
@@ -1596,7 +1595,6 @@ pub const unsafe fn write<T>(dst: *mut T, src: T) {
     // `dst` cannot overlap `src` because the caller has mutable access
     // to `dst` while `src` is owned by this function.
     unsafe {
-        #[cfg(debug_assertions)] // Too expensive to always enable (for now?)
         ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::write requires that the pointer argument is aligned and non-null",