Add #[rustc_as_ptr] attribute

compiler/rustc_feature/src/builtin_attrs.rs

@@ -875,6 +875,11 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         lang, Normal, template!(NameValueStr: "name"), DuplicatesOk, EncodeCrossCrate::No, lang_items,
         "lang items are subject to change",
     ),
+    rustc_attr!(
+        rustc_as_ptr, Normal, template!(Word), ErrorFollowing,
+        EncodeCrossCrate::Yes,
+        "#[rustc_as_ptr] is used to mark functions returning pointers to their inner allocations."
+    ),
     rustc_attr!(
         rustc_pass_by_value, Normal, template!(Word), ErrorFollowing,
         EncodeCrossCrate::Yes,

compiler/rustc_passes/src/check_attr.rs

@@ -162,6 +162,9 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     self.check_rustc_std_internal_symbol(attr, span, target)
                 }
                 [sym::naked, ..] => self.check_naked(hir_id, attr, span, target, attrs),
+                [sym::rustc_as_ptr, ..] => {
+                    self.check_applied_to_fn_or_method(hir_id, attr, span, target)
+                }
                 [sym::rustc_never_returns_null_ptr, ..] => {
                     self.check_applied_to_fn_or_method(hir_id, attr, span, target)
                 }

compiler/rustc_span/src/symbol.rs

@@ -1652,6 +1652,7 @@ symbols! {
         rustc_allow_const_fn_unstable,
         rustc_allow_incoherent_impl,
         rustc_allowed_through_unstable_modules,
+        rustc_as_ptr,
         rustc_attrs,
         rustc_autodiff,
         rustc_box,