[steveklabnik]

Yes, the latter was what I was thinking of:

  use std::cell::UnsafeCell;

  pub fn no_unTsafecell(x: &i32) {
    
  }

  pub fn unsafecell(x: &UnsafeCell<i32>) {
    
  }

gives

  define void @_ZN10playground14no_unTsafecell17hd5b10dbf031749b4E(i32* noalias nocapture readonly align 4 dereferenceable(4) %x) unnamed_addr #0 {

  define void @_ZN10playground10unsafecell17h3318292255a4201bE(i32* nocapture align 4 dereferenceable(4) %x) unnamed_addr #0 {

thanks :)