From d8e3986d4214612ce7992da2b9b3269785e3ea40 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Wed, 9 Aug 2023 20:00:07 +0000
Subject: [PATCH] Don't use type_of to determine if item has intrinsic shim

---
 compiler/rustc_ty_utils/src/instance.rs       | 65 +++++++++----------
 .../instance-doesnt-depend-on-type.rs         | 10 +++
 2 files changed, 40 insertions(+), 35 deletions(-)
 create mode 100644 tests/ui/inline-const/instance-doesnt-depend-on-type.rs

diff --git a/compiler/rustc_ty_utils/src/instance.rs b/compiler/rustc_ty_utils/src/instance.rs
index a21b5ef05e6..e1a15b5cf9f 100644
--- a/compiler/rustc_ty_utils/src/instance.rs
+++ b/compiler/rustc_ty_utils/src/instance.rs
@@ -1,4 +1,5 @@
 use rustc_errors::ErrorGuaranteed;
+use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::query::Providers;
@@ -15,54 +16,48 @@ fn resolve_instance<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::ParamEnvAnd<'tcx, (DefId, GenericArgsRef<'tcx>)>,
 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
-    let (param_env, (def, args)) = key.into_parts();
+    let (param_env, (def_id, args)) = key.into_parts();
 
-    let result = if let Some(trait_def_id) = tcx.trait_of_item(def) {
+    let result = if let Some(trait_def_id) = tcx.trait_of_item(def_id) {
         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
         resolve_associated_item(
             tcx,
-            def,
+            def_id,
             param_env,
             trait_def_id,
             tcx.normalize_erasing_regions(param_env, args),
         )
     } else {
-        let ty = tcx.type_of(def);
-        let item_type = tcx.subst_and_normalize_erasing_regions(args, param_env, ty);
+        let def = if matches!(tcx.def_kind(def_id), DefKind::Fn) && tcx.is_intrinsic(def_id) {
+            debug!(" => intrinsic");
+            ty::InstanceDef::Intrinsic(def_id)
+        } else if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
+            let ty = args.type_at(0);
 
-        let def = match *item_type.kind() {
-            ty::FnDef(def_id, ..) if tcx.is_intrinsic(def_id) => {
-                debug!(" => intrinsic");
-                ty::InstanceDef::Intrinsic(def)
-            }
-            ty::FnDef(def_id, args) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
-                let ty = args.type_at(0);
-
-                if ty.needs_drop(tcx, param_env) {
-                    debug!(" => nontrivial drop glue");
-                    match *ty.kind() {
-                        ty::Closure(..)
-                        | ty::Generator(..)
-                        | ty::Tuple(..)
-                        | ty::Adt(..)
-                        | ty::Dynamic(..)
-                        | ty::Array(..)
-                        | ty::Slice(..) => {}
-                        // Drop shims can only be built from ADTs.
-                        _ => return Ok(None),
-                    }
-
-                    ty::InstanceDef::DropGlue(def_id, Some(ty))
-                } else {
-                    debug!(" => trivial drop glue");
-                    ty::InstanceDef::DropGlue(def_id, None)
+            if ty.needs_drop(tcx, param_env) {
+                debug!(" => nontrivial drop glue");
+                match *ty.kind() {
+                    ty::Closure(..)
+                    | ty::Generator(..)
+                    | ty::Tuple(..)
+                    | ty::Adt(..)
+                    | ty::Dynamic(..)
+                    | ty::Array(..)
+                    | ty::Slice(..) => {}
+                    // Drop shims can only be built from ADTs.
+                    _ => return Ok(None),
                 }
+
+                ty::InstanceDef::DropGlue(def_id, Some(ty))
+            } else {
+                debug!(" => trivial drop glue");
+                ty::InstanceDef::DropGlue(def_id, None)
             }
-            _ => {
-                debug!(" => free item");
-                ty::InstanceDef::Item(def)
-            }
+        } else {
+            debug!(" => free item");
+            ty::InstanceDef::Item(def_id)
         };
+
         Ok(Some(Instance { def, args }))
     };
     debug!("inner_resolve_instance: result={:?}", result);
diff --git a/tests/ui/inline-const/instance-doesnt-depend-on-type.rs b/tests/ui/inline-const/instance-doesnt-depend-on-type.rs
new file mode 100644
index 00000000000..bc739785c8b
--- /dev/null
+++ b/tests/ui/inline-const/instance-doesnt-depend-on-type.rs
@@ -0,0 +1,10 @@
+// check-pass
+// issue: 114660
+
+#![feature(inline_const)]
+
+fn main() {
+    const { core::mem::transmute::<u8, u8> };
+    // Don't resolve the instance of this inline constant to be an intrinsic,
+    // even if the type of the constant is `extern "intrinsic" fn(u8) -> u8`.
+}