compiler/rust: Use std::mem::offset_of!()

It got stabilized with Rust 1.77.

Reviewed-by: Faith Ekstrand <[email protected]>
Reviewed-by: Karol Herbst <[email protected]>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31510>

Author: LingMan

src/compiler/rust/nir.rs

@@ -5,31 +5,10 @@ use crate::bindings::*;
 
 use std::ffi::{c_void, CStr};
 use std::marker::PhantomData;
+use std::mem::offset_of;
 use std::ptr::NonNull;
 use std::str;
 
-// from https://internals.rust-lang.org/t/discussion-on-offset-of/7440/2
-macro_rules! offset_of {
-    ($Struct:path, $field:ident) => {{
-        // Using a separate function to minimize unhygienic hazards
-        // (e.g. unsafety of #[repr(packed)] field borrows).
-        // Uncomment `const` when `const fn`s can juggle pointers.
-
-        // const
-        fn offset() -> usize {
-            let u = std::mem::MaybeUninit::<$Struct>::uninit();
-            // Use pattern-matching to avoid accidentally going through Deref.
-            let &$Struct { $field: ref f, .. } = unsafe { &*u.as_ptr() };
-            let o =
-                (f as *const _ as usize).wrapping_sub(&u as *const _ as usize);
-            // Triple check that we are within `u` still.
-            assert!((0..=std::mem::size_of_val(&u)).contains(&o));
-            o
-        }
-        offset()
-    }};
-}
-
 pub struct ExecListIter<'a, T> {
     n: &'a exec_node,
     offset: usize,