Make const_eval_select a rustc_intrinsic

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -579,7 +579,7 @@ pub fn check_intrinsic_type(
 
             sym::is_val_statically_known => (1, 1, vec![param(0)], tcx.types.bool),
 
-            sym::const_eval_select => (4, 0, vec![param(0), param(1), param(2)], param(3)),
+            sym::const_eval_select => (4, 1, vec![param(0), param(1), param(2)], param(3)),
 
             sym::vtable_size | sym::vtable_align => {
                 (0, 0, vec![Ty::new_imm_ptr(tcx, Ty::new_unit(tcx))], tcx.types.usize)

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1704,12 +1704,14 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         {
             for &local_def_id in tcx.mir_keys(()) {
                 if let DefKind::AssocFn | DefKind::Fn = tcx.def_kind(local_def_id) {
+                    if tcx.intrinsic(local_def_id).map_or(true, |i| !i.must_be_overridden) {
                         record_array!(self.tables.deduced_param_attrs[local_def_id.to_def_id()] <-
                             self.tcx.deduced_param_attrs(local_def_id.to_def_id()));
                     }
                 }
             }
         }
+    }
 
     #[instrument(level = "debug", skip(self))]
     fn encode_stability(&mut self, def_id: DefId) {

compiler/rustc_middle/src/hir/map/mod.rs

@@ -1365,8 +1365,10 @@ impl<'hir> Visitor<'hir> for ItemCollector<'hir> {
 
     fn visit_impl_item(&mut self, item: &'hir ImplItem<'hir>) {
         if associated_body(Node::ImplItem(item)).is_some() {
+            if !self.tcx.has_attr(item.owner_id.def_id, sym::rustc_intrinsic_must_be_overridden) {
                 self.body_owners.push(item.owner_id.def_id);
             }
+        }
 
         self.impl_items.push(item.impl_item_id());
         intravisit::walk_impl_item(self, item)

library/core/src/intrinsics.rs

@@ -2508,6 +2508,19 @@ extern "rust-intrinsic" {
     #[rustc_nounwind]
     pub fn vtable_align(ptr: *const ()) -> usize;
 
+    #[cfg(bootstrap)]
+    #[rustc_const_unstable(feature = "const_eval_select", issue = "none")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
+    pub fn const_eval_select<ARG: Tuple, F, G, RET>(
+        arg: ARG,
+        called_in_const: F,
+        called_at_rt: G,
+    ) -> RET
+    where
+        G: FnOnce<ARG, Output = RET>,
+        F: FnOnce<ARG, Output = RET>;
+}
+
 /// Selects which function to call depending on the context.
 ///
 /// If this function is evaluated at compile-time, then a call to this
@@ -2565,15 +2578,20 @@ extern "rust-intrinsic" {
 /// Currently such an assertion would always succeed; until Rust decides
 /// otherwise, that principle should not be violated.
 #[rustc_const_unstable(feature = "const_eval_select", issue = "none")]
-    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
-    pub fn const_eval_select<ARG: Tuple, F, G, RET>(
-        arg: ARG,
-        called_in_const: F,
-        called_at_rt: G,
+#[unstable(feature = "core_intrinsics", issue = "none")]
+#[cfg(not(bootstrap))]
+#[rustc_intrinsic]
+#[rustc_intrinsic_must_be_overridden]
+pub const fn const_eval_select<ARG: Tuple, F, G, RET>(
+    _arg: ARG,
+    _called_in_const: F,
+    _called_at_rt: G,
 ) -> RET
 where
     G: FnOnce<ARG, Output = RET>,
-        F: FnOnce<ARG, Output = RET>;
+    F: FnOnce<ARG, Output = RET>,
+{
+    unreachable!()
 }
 
 /// Returns whether the argument's value is statically known at

tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs

@@ -509,17 +509,19 @@ trait StructuralPartialEq {}
 
 const fn drop<T: ~const Destruct>(_: T) {}
 
-extern "rust-intrinsic" {
 #[rustc_const_stable(feature = "const_eval_select", since = "1.0.0")]
-    #[rustc_safe_intrinsic]
-    fn const_eval_select<ARG: Tuple, F, G, RET>(
+#[rustc_intrinsic_must_be_overridden]
+#[rustc_intrinsic]
+const fn const_eval_select<ARG: Tuple, F, G, RET>(
     arg: ARG,
     called_in_const: F,
     called_at_rt: G,
 ) -> RET
 where
     F: const FnOnce<ARG, Output = RET>,
-        G: FnOnce<ARG, Output = RET>;
+    G: FnOnce<ARG, Output = RET>,
+{
+    loop {}
 }
 
 fn test_const_eval_select() {