Skip reveal_all if needs_subst.

src/librustc/mir/interpret/queries.rs

@@ -3,6 +3,7 @@ use super::{ConstEvalResult, ErrorHandled, GlobalId};
 use crate::mir;
 use crate::ty::subst::{InternalSubsts, SubstsRef};
 use crate::ty::{self, TyCtxt};
+use crate::ty::fold::TypeFoldable;
 use rustc_hir::def_id::DefId;
 use rustc_span::Span;
 
@@ -18,7 +19,13 @@ impl<'tcx> TyCtxt<'tcx> {
         let substs = InternalSubsts::identity_for_item(self, def_id);
         let instance = ty::Instance::new(def_id, substs);
         let cid = GlobalId { instance, promoted: None };
-        let param_env = self.param_env(def_id).with_reveal_all();
+        let needs_subst = instance.needs_subst();
+        let param_env = if needs_subst {
+            self.param_env(def_id)
+        } else {
+            self.param_env(def_id).with_reveal_all()
+        };
+        debug!("const_eval_poly: needs_subst = {:?}. param_env = {:?}", needs_subst, param_env);
         self.const_eval_global_id(param_env, cid, None)
     }
 

src/librustc_mir/interpret/place.rs

@@ -305,7 +305,9 @@ where
     ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
         let pointee_type =
             val.layout.ty.builtin_deref(true).expect("`ref_to_mplace` called on non-ptr type").ty;
-        let layout = self.layout_of(pointee_type)?;
+        let layout = self.layout_of(pointee_type);
+        debug!("ref_to_mplace: layout_of(pointee_type = {:?}) = {:?}", pointee_type, layout);
+        let layout = layout?;
         let (ptr, meta) = match *val {
             Immediate::Scalar(ptr) => (ptr.not_undef()?, MemPlaceMeta::None),
             Immediate::ScalarPair(ptr, meta) => {