Auto merge of rust-lang#130540 - veera-sivarajan:fix-87525, r=estebank

Add a Lint for Pointer to Integer Transmutes in Consts

Fixes rust-lang#87525

This PR adds a MirLint for pointer to integer transmutes in const functions and associated consts. The implementation closely follows this comment: rust-lang#85769 (comment). More details about the implementation can be found in the comments.

Note: This could break some sound code as mentioned by RalfJung in rust-lang#85769 (comment):

> ... technically const-code could transmute/cast an int to a ptr and then transmute it back and that would be correct -- so the lint will deny some sound code. Does not seem terribly likely though.

References:
1. https://doc.rust-lang.org/std/mem/fn.transmute.html
2. https://doc.rust-lang.org/reference/items/associated-items.html#associated-constants

Author: bors

core/src/ptr/mod.rs

@@ -1909,6 +1909,7 @@ pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
 /// than trying to adapt this to accommodate that change.
 ///
 /// Any questions go to @nagisa.
+#[cfg_attr(not(bootstrap), allow(ptr_to_integer_transmute_in_consts))]
 #[lang = "align_offset"]
 pub(crate) const unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize {
     // FIXME(#75598): Direct use of these intrinsics improves codegen significantly at opt-level <=