Clean up special function const checks

Mark them as const and `#[rustc_do_not_const_check]` instead of hard-coding
them in const-eval checks.

1 files changed, 20 insertions, 32 deletions

diff --git a/compiler/rustc_const_eval/src/const_eval/machine.rs b/compiler/rustc_const_eval/src/const_eval/machine.rs
index 8efe3eb868b..e01466f8fe2 100644
--- a/compiler/rustc_const_eval/src/const_eval/machine.rs
+++ b/compiler/rustc_const_eval/src/const_eval/machine.rs
@@ -30,34 +30,25 @@ impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>> {
         &mut self,
         instance: ty::Instance<'tcx>,
         args: &[OpTy<'tcx>],
-        is_const_fn: bool,
     ) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
-        // The list of functions we handle here must be in sync with
-        // `is_lang_special_const_fn` in `transform/check_consts/mod.rs`.
+        // All `#[rustc_do_not_const_check]` functions should be hooked here.
         let def_id = instance.def_id();
 
-        if is_const_fn {
-            if Some(def_id) == self.tcx.lang_items().const_eval_select() {
-                // redirect to const_eval_select_ct
-                if let Some(const_eval_select) = self.tcx.lang_items().const_eval_select_ct() {
-                    return Ok(Some(
-                        ty::Instance::resolve(
-                            *self.tcx,
-                            ty::ParamEnv::reveal_all(),
-                            const_eval_select,
-                            instance.substs,
-                        )
-                        .unwrap()
-                        .unwrap(),
-                    ));
-                }
+        if Some(def_id) == self.tcx.lang_items().const_eval_select() {
+            // redirect to const_eval_select_ct
+            if let Some(const_eval_select) = self.tcx.lang_items().const_eval_select_ct() {
+                return Ok(Some(
+                    ty::Instance::resolve(
+                        *self.tcx,
+                        ty::ParamEnv::reveal_all(),
+                        const_eval_select,
+                        instance.substs,
+                    )
+                    .unwrap()
+                    .unwrap(),
+                ));
             }
-            return Ok(None);
-        }
-
-        if Some(def_id) == self.tcx.lang_items().panic_fn()
-            || Some(def_id) == self.tcx.lang_items().panic_str()
-            || Some(def_id) == self.tcx.lang_items().panic_display()
+        } else if Some(def_id) == self.tcx.lang_items().panic_display()
             || Some(def_id) == self.tcx.lang_items().begin_panic_fn()
         {
             // &str or &&str
@@ -286,19 +277,16 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
                 }
             }
 
-            // Some functions we support even if they are non-const -- but avoid testing
-            // that for const fn!
-            // `const_eval_select` is a const fn because it must use const trait bounds.
-            if let Some(new_instance) = ecx.hook_special_const_fn(instance, args, is_const_fn)? {
-                // We call another const fn instead.
-                return Self::find_mir_or_eval_fn(ecx, new_instance, _abi, args, _ret, _unwind);
-            }
-
             if !is_const_fn {
                 // We certainly do *not* want to actually call the fn
                 // though, so be sure we return here.
                 throw_unsup_format!("calling non-const function `{}`", instance)
             }
+
+            if let Some(new_instance) = ecx.hook_special_const_fn(instance, args)? {
+                // We call another const fn instead.
+                return Self::find_mir_or_eval_fn(ecx, new_instance, _abi, args, _ret, _unwind);
+            }
         }
         // This is a const fn. Call it.
         Ok(Some(ecx.load_mir(instance.def, None)?))