diff --git a/src/librustc_codegen_ssa/back/symbol_export.rs b/src/librustc_codegen_ssa/back/symbol_export.rs
index faf6809f35b1..4f2d592ffc6a 100644
--- a/src/librustc_codegen_ssa/back/symbol_export.rs
+++ b/src/librustc_codegen_ssa/back/symbol_export.rs
@@ -249,9 +249,9 @@ fn exported_symbols_provider_local(
             }
 
             match *mono_item {
-                MonoItem::Fn(Instance { def: InstanceDef::Item(def_id), substs }) => {
+                MonoItem::Fn(Instance { def: InstanceDef::Item(def), substs }) => {
                     if substs.non_erasable_generics().next().is_some() {
-                        let symbol = ExportedSymbol::Generic(def_id, substs);
+                        let symbol = ExportedSymbol::Generic(def.did, substs);
                         symbols.push((symbol, SymbolExportLevel::Rust));
                     }
                 }
diff --git a/src/librustc_middle/mir/mono.rs b/src/librustc_middle/mir/mono.rs
index c9e5a196f917..b7e3500ede42 100644
--- a/src/librustc_middle/mir/mono.rs
+++ b/src/librustc_middle/mir/mono.rs
@@ -346,8 +346,8 @@ impl<'tcx> CodegenUnit<'tcx> {
                             // instances into account. The others don't matter for
                             // the codegen tests and can even make item order
                             // unstable.
-                            InstanceDef::Item(def_id) => {
-                                def_id.as_local().map(|def_id| tcx.hir().as_local_hir_id(def_id))
+                            InstanceDef::Item(def) => {
+                                def.did.as_local().map(|def_id| tcx.hir().as_local_hir_id(def_id))
                             }
                             InstanceDef::VtableShim(..)
                             | InstanceDef::ReifyShim(..)
diff --git a/src/librustc_middle/ty/instance.rs b/src/librustc_middle/ty/instance.rs
index fef1f9a51e6b..4c96e1f965f7 100644
--- a/src/librustc_middle/ty/instance.rs
+++ b/src/librustc_middle/ty/instance.rs
@@ -29,7 +29,7 @@ pub enum InstanceDef<'tcx> {
     /// - `fn` items
     /// - closures
     /// - generators
-    Item(DefId),
+    Item(ty::WithOptParam<DefId>),
 
     /// An intrinsic `fn` item (with `"rust-intrinsic"` or `"platform-intrinsic"` ABI).
     ///
@@ -160,8 +160,8 @@ impl<'tcx> Instance<'tcx> {
         self.substs.non_erasable_generics().next()?;
 
         match self.def {
-            InstanceDef::Item(def_id) => tcx
-                .upstream_monomorphizations_for(def_id)
+            InstanceDef::Item(def) => tcx
+                .upstream_monomorphizations_for(def.did)
                 .and_then(|monos| monos.get(&self.substs).cloned()),
             InstanceDef::DropGlue(_, Some(_)) => tcx.upstream_drop_glue_for(self.substs),
             _ => None,
@@ -171,10 +171,10 @@ impl<'tcx> Instance<'tcx> {
 
 impl<'tcx> InstanceDef<'tcx> {
     #[inline]
-    pub fn def_id(&self) -> DefId {
-        match *self {
-            InstanceDef::Item(def_id)
-            | InstanceDef::VtableShim(def_id)
+    pub fn def_id(self) -> DefId {
+        match self {
+            InstanceDef::Item(def) => def.did,
+            InstanceDef::VtableShim(def_id)
             | InstanceDef::ReifyShim(def_id)
             | InstanceDef::FnPtrShim(def_id, _)
             | InstanceDef::Virtual(def_id, _)
@@ -185,6 +185,21 @@ impl<'tcx> InstanceDef<'tcx> {
         }
     }
 
+    #[inline]
+    pub fn with_opt_param(self) -> ty::WithOptParam<DefId> {
+        match self {
+            InstanceDef::Item(def) => def,
+            InstanceDef::VtableShim(def_id)
+            | InstanceDef::ReifyShim(def_id)
+            | InstanceDef::FnPtrShim(def_id, _)
+            | InstanceDef::Virtual(def_id, _)
+            | InstanceDef::Intrinsic(def_id)
+            | InstanceDef::ClosureOnceShim { call_once: def_id }
+            | InstanceDef::DropGlue(def_id, _)
+            | InstanceDef::CloneShim(def_id, _) => ty::WithOptParam::dummy(def_id),
+        }
+    }
+
     #[inline]
     pub fn attrs(&self, tcx: TyCtxt<'tcx>) -> ty::Attributes<'tcx> {
         tcx.get_attrs(self.def_id())
@@ -198,7 +213,7 @@ impl<'tcx> InstanceDef<'tcx> {
     pub fn requires_inline(&self, tcx: TyCtxt<'tcx>) -> bool {
         use rustc_hir::definitions::DefPathData;
         let def_id = match *self {
-            ty::InstanceDef::Item(def_id) => def_id,
+            ty::InstanceDef::Item(def) => def.did,
             ty::InstanceDef::DropGlue(_, Some(_)) => return false,
             _ => return true,
         };
@@ -244,8 +259,8 @@ impl<'tcx> InstanceDef<'tcx> {
 
     pub fn requires_caller_location(&self, tcx: TyCtxt<'_>) -> bool {
         match *self {
-            InstanceDef::Item(def_id) => {
-                tcx.codegen_fn_attrs(def_id).flags.contains(CodegenFnAttrFlags::TRACK_CALLER)
+            InstanceDef::Item(def) => {
+                tcx.codegen_fn_attrs(def.did).flags.contains(CodegenFnAttrFlags::TRACK_CALLER)
             }
             _ => false,
         }
@@ -283,7 +298,7 @@ impl<'tcx> Instance<'tcx> {
             def_id,
             substs
         );
-        Instance { def: InstanceDef::Item(def_id), substs }
+        Instance { def: InstanceDef::Item(ty::WithOptParam::dummy(def_id)), substs }
     }
 
     pub fn mono(tcx: TyCtxt<'tcx>, def_id: DefId) -> Instance<'tcx> {
@@ -356,9 +371,9 @@ impl<'tcx> Instance<'tcx> {
         debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
         Instance::resolve(tcx, param_env, def_id, substs).ok().flatten().map(|mut resolved| {
             match resolved.def {
-                InstanceDef::Item(def_id) if resolved.def.requires_caller_location(tcx) => {
+                InstanceDef::Item(def) if resolved.def.requires_caller_location(tcx) => {
                     debug!(" => fn pointer created for function with #[track_caller]");
-                    resolved.def = InstanceDef::ReifyShim(def_id);
+                    resolved.def = InstanceDef::ReifyShim(def.did);
                 }
                 InstanceDef::Virtual(def_id, _) => {
                     debug!(" => fn pointer created for virtual call");
diff --git a/src/librustc_middle/ty/mod.rs b/src/librustc_middle/ty/mod.rs
index bc55c1b2fe8c..ce76a3bef832 100644
--- a/src/librustc_middle/ty/mod.rs
+++ b/src/librustc_middle/ty/mod.rs
@@ -2880,7 +2880,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// Returns the possibly-auto-generated MIR of a `(DefId, Subst)` pair.
     pub fn instance_mir(self, instance: ty::InstanceDef<'tcx>) -> &'tcx Body<'tcx> {
         match instance {
-            ty::InstanceDef::Item(did) => self.optimized_mir(did),
+            ty::InstanceDef::Item(def) => self.optimized_mir(def.did),
             ty::InstanceDef::VtableShim(..)
             | ty::InstanceDef::ReifyShim(..)
             | ty::InstanceDef::Intrinsic(..)
diff --git a/src/librustc_middle/ty/structural_impls.rs b/src/librustc_middle/ty/structural_impls.rs
index 159af277d240..67d0030dea8f 100644
--- a/src/librustc_middle/ty/structural_impls.rs
+++ b/src/librustc_middle/ty/structural_impls.rs
@@ -838,7 +838,7 @@ impl<'tcx> TypeFoldable<'tcx> for ty::instance::Instance<'tcx> {
         Self {
             substs: self.substs.fold_with(folder),
             def: match self.def {
-                Item(did) => Item(did.fold_with(folder)),
+                Item(def) => Item(def.fold_with(folder)),
                 VtableShim(did) => VtableShim(did.fold_with(folder)),
                 ReifyShim(did) => ReifyShim(did.fold_with(folder)),
                 Intrinsic(did) => Intrinsic(did.fold_with(folder)),
@@ -857,7 +857,8 @@ impl<'tcx> TypeFoldable<'tcx> for ty::instance::Instance<'tcx> {
         use crate::ty::InstanceDef::*;
         self.substs.visit_with(visitor)
             || match self.def {
-                Item(did) | VtableShim(did) | ReifyShim(did) | Intrinsic(did) | Virtual(did, _) => {
+                Item(def) => def.visit_with(visitor),
+                VtableShim(did) | ReifyShim(did) | Intrinsic(did) | Virtual(did, _) => {
                     did.visit_with(visitor)
                 }
                 FnPtrShim(did, ty) | CloneShim(did, ty) => {
diff --git a/src/librustc_mir/const_eval/eval_queries.rs b/src/librustc_mir/const_eval/eval_queries.rs
index 24a0107ab968..a8f0de68f22f 100644
--- a/src/librustc_mir/const_eval/eval_queries.rs
+++ b/src/librustc_mir/const_eval/eval_queries.rs
@@ -288,21 +288,21 @@ pub fn const_eval_raw_provider<'tcx>(
     }
 
     let cid = key.value;
-    let def_id = cid.instance.def.def_id();
+    let def = cid.instance.def.with_opt_param();
 
-    if let Some(def_id) = def_id.as_local() {
-        if tcx.has_typeck_tables(def_id) {
-            if let Some(error_reported) = tcx.typeck_tables_of(def_id).tainted_by_errors {
+    if let Some(def) = def.as_local() {
+        if tcx.has_typeck_tables(def.did) {
+            if let Some(error_reported) = tcx.typeck_tables_of_const_arg(def).tainted_by_errors {
                 return Err(ErrorHandled::Reported(error_reported));
             }
         }
     }
 
-    let is_static = tcx.is_static(def_id);
+    let is_static = tcx.is_static(def.did);
 
     let mut ecx = InterpCx::new(
         tcx,
-        tcx.def_span(cid.instance.def_id()),
+        tcx.def_span(def.did),
         key.param_env,
         CompileTimeInterpreter::new(tcx.sess.const_eval_limit()),
         MemoryExtra { can_access_statics: is_static },
@@ -334,9 +334,9 @@ pub fn const_eval_raw_provider<'tcx>(
                 }
 
                 v
-            } else if let Some(def_id) = def_id.as_local() {
+            } else if let Some(def) = def.as_local() {
                 // constant defined in this crate, we can figure out a lint level!
-                match tcx.def_kind(def_id.to_def_id()) {
+                match tcx.def_kind(def.did.to_def_id()) {
                     // constants never produce a hard error at the definition site. Anything else is
                     // a backwards compatibility hazard (and will break old versions of winapi for
                     // sure)
@@ -346,9 +346,9 @@ pub fn const_eval_raw_provider<'tcx>(
                     // validation thus preventing such a hard error from being a backwards
                     // compatibility hazard
                     DefKind::Const | DefKind::AssocConst => {
-                        let hir_id = tcx.hir().as_local_hir_id(def_id);
+                        let hir_id = tcx.hir().as_local_hir_id(def.did);
                         err.report_as_lint(
-                            tcx.at(tcx.def_span(def_id)),
+                            tcx.at(tcx.def_span(def.did)),
                             "any use of this value will cause an error",
                             hir_id,
                             Some(err.span),
@@ -359,7 +359,7 @@ pub fn const_eval_raw_provider<'tcx>(
                     // deny-by-default lint
                     _ => {
                         if let Some(p) = cid.promoted {
-                            let span = tcx.promoted_mir(def_id)[p].span;
+                            let span = tcx.promoted_mir(def.did)[p].span;
                             if let err_inval!(ReferencedConstant) = err.error {
                                 err.report_as_error(
                                     tcx.at(span),
@@ -369,7 +369,7 @@ pub fn const_eval_raw_provider<'tcx>(
                                 err.report_as_lint(
                                     tcx.at(span),
                                     "reaching this expression at runtime will panic or abort",
-                                    tcx.hir().as_local_hir_id(def_id),
+                                    tcx.hir().as_local_hir_id(def.did),
                                     Some(err.span),
                                 )
                             }
diff --git a/src/librustc_mir/const_eval/machine.rs b/src/librustc_mir/const_eval/machine.rs
index 8be0ab9019fe..6453630bb92b 100644
--- a/src/librustc_mir/const_eval/machine.rs
+++ b/src/librustc_mir/const_eval/machine.rs
@@ -191,11 +191,11 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         debug!("find_mir_or_eval_fn: {:?}", instance);
 
         // Only check non-glue functions
-        if let ty::InstanceDef::Item(def_id) = instance.def {
+        if let ty::InstanceDef::Item(def) = instance.def {
             // Execution might have wandered off into other crates, so we cannot do a stability-
             // sensitive check here.  But we can at least rule out functions that are not const
             // at all.
-            if ecx.tcx.is_const_fn_raw(def_id) {
+            if ecx.tcx.is_const_fn_raw(def.did) {
                 // If this function is a `const fn` then under certain circumstances we
                 // can evaluate call via the query system, thus memoizing all future calls.
                 if ecx.try_eval_const_fn_call(instance, ret, args)? {
diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index 602876e3de16..641b8cce5e41 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -394,24 +394,26 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         promoted: Option<mir::Promoted>,
     ) -> InterpResult<'tcx, &'tcx mir::Body<'tcx>> {
         // do not continue if typeck errors occurred (can only occur in local crate)
-        let did = instance.def_id();
-        if let Some(did) = did.as_local() {
-            if self.tcx.has_typeck_tables(did) {
-                if let Some(error_reported) = self.tcx.typeck_tables_of(did).tainted_by_errors {
+        let def = instance.with_opt_param();
+        if let Some(def) = def.as_local() {
+            if self.tcx.has_typeck_tables(def.did) {
+                if let Some(error_reported) =
+                    self.tcx.typeck_tables_of_const_arg(def).tainted_by_errors
+                {
                     throw_inval!(TypeckError(error_reported))
                 }
             }
         }
         trace!("load mir(instance={:?}, promoted={:?})", instance, promoted);
         if let Some(promoted) = promoted {
-            return Ok(&self.tcx.promoted_mir(did)[promoted]);
+            return Ok(&self.tcx.promoted_mir(def.did)[promoted]);
         }
         match instance {
-            ty::InstanceDef::Item(def_id) => {
-                if self.tcx.is_mir_available(did) {
-                    Ok(self.tcx.optimized_mir(did))
+            ty::InstanceDef::Item(def) => {
+                if self.tcx.is_mir_available(def.did) {
+                    Ok(self.tcx.optimized_mir(def.did))
                 } else {
-                    throw_unsup!(NoMirFor(def_id))
+                    throw_unsup!(NoMirFor(def.did))
                 }
             }
             _ => Ok(self.tcx.instance_mir(instance)),
diff --git a/src/librustc_mir/monomorphize/collector.rs b/src/librustc_mir/monomorphize/collector.rs
index a927df02cdcf..35fb950ce66b 100644
--- a/src/librustc_mir/monomorphize/collector.rs
+++ b/src/librustc_mir/monomorphize/collector.rs
@@ -768,8 +768,8 @@ fn visit_instance_use<'tcx>(
 // need a mono item.
 fn should_monomorphize_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: &Instance<'tcx>) -> bool {
     let def_id = match instance.def {
-        ty::InstanceDef::Item(def_id) | ty::InstanceDef::DropGlue(def_id, Some(_)) => def_id,
-
+        ty::InstanceDef::Item(def) => def.did,
+        ty::InstanceDef::DropGlue(def_id, Some(_)) => def_id,
         ty::InstanceDef::VtableShim(..)
         | ty::InstanceDef::ReifyShim(..)
         | ty::InstanceDef::ClosureOnceShim { .. }
diff --git a/src/librustc_mir/monomorphize/partitioning.rs b/src/librustc_mir/monomorphize/partitioning.rs
index ebea65c8f96f..208d28205813 100644
--- a/src/librustc_mir/monomorphize/partitioning.rs
+++ b/src/librustc_mir/monomorphize/partitioning.rs
@@ -314,7 +314,8 @@ fn mono_item_visibility(
     };
 
     let def_id = match instance.def {
-        InstanceDef::Item(def_id) | InstanceDef::DropGlue(def_id, Some(_)) => def_id,
+        InstanceDef::Item(def) => def.did,
+        InstanceDef::DropGlue(def_id, Some(_)) => def_id,
 
         // These are all compiler glue and such, never exported, always hidden.
         InstanceDef::VtableShim(..)
@@ -704,7 +705,7 @@ fn characteristic_def_id_of_mono_item<'tcx>(
     match mono_item {
         MonoItem::Fn(instance) => {
             let def_id = match instance.def {
-                ty::InstanceDef::Item(def_id) => def_id,
+                ty::InstanceDef::Item(def) => def.did,
                 ty::InstanceDef::VtableShim(..)
                 | ty::InstanceDef::ReifyShim(..)
                 | ty::InstanceDef::FnPtrShim(..)
diff --git a/src/librustc_mir/transform/check_consts/validation.rs b/src/librustc_mir/transform/check_consts/validation.rs
index 5cb161ebcfb5..f64c72e7b362 100644
--- a/src/librustc_mir/transform/check_consts/validation.rs
+++ b/src/librustc_mir/transform/check_consts/validation.rs
@@ -520,8 +520,8 @@ impl Visitor<'tcx> for Validator<'mir, 'tcx> {
                     let instance = Instance::resolve(self.tcx, self.param_env, def_id, substs);
                     debug!("Resolving ({:?}) -> {:?}", def_id, instance);
                     if let Ok(Some(func)) = instance {
-                        if let InstanceDef::Item(def_id) = func.def {
-                            if is_const_fn(self.tcx, def_id) {
+                        if let InstanceDef::Item(def) = func.def {
+                            if is_const_fn(self.tcx, def.did) {
                                 return;
                             }
                         }
diff --git a/src/librustc_mir/transform/mod.rs b/src/librustc_mir/transform/mod.rs
index 816cf08a6da4..e5d6ff4a3fb9 100644
--- a/src/librustc_mir/transform/mod.rs
+++ b/src/librustc_mir/transform/mod.rs
@@ -9,7 +9,7 @@ use rustc_middle::mir::visit::Visitor as _;
 use rustc_middle::mir::{traversal, Body, ConstQualifs, MirPhase, Promoted};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::steal::Steal;
-use rustc_middle::ty::{InstanceDef, TyCtxt, TypeFoldable};
+use rustc_middle::ty::{self, InstanceDef, TyCtxt, TypeFoldable};
 use rustc_span::{Span, Symbol};
 use std::borrow::Cow;
 
@@ -116,7 +116,7 @@ pub struct MirSource<'tcx> {
 
 impl<'tcx> MirSource<'tcx> {
     pub fn item(def_id: DefId) -> Self {
-        MirSource { instance: InstanceDef::Item(def_id), promoted: None }
+        MirSource { instance: InstanceDef::Item(ty::WithOptParam::dummy(def_id)), promoted: None }
     }
 
     #[inline]
@@ -249,7 +249,7 @@ fn mir_const(tcx: TyCtxt<'_>, def_id: DefId) -> Steal<Body<'_>> {
     run_passes(
         tcx,
         &mut body,
-        InstanceDef::Item(def_id.to_def_id()),
+        InstanceDef::Item(ty::WithOptParam::dummy(def_id.to_def_id())),
         None,
         MirPhase::Const,
         &[&[
@@ -284,7 +284,7 @@ fn mir_validated(
     run_passes(
         tcx,
         &mut body,
-        InstanceDef::Item(def_id.to_def_id()),
+        InstanceDef::Item(ty::WithOptParam::dummy(def_id.to_def_id())),
         None,
         MirPhase::Validated,
         &[&[
@@ -350,7 +350,7 @@ fn run_post_borrowck_cleanup_passes<'tcx>(
     run_passes(
         tcx,
         body,
-        InstanceDef::Item(def_id.to_def_id()),
+        InstanceDef::Item(ty::WithOptParam::dummy(def_id.to_def_id())),
         promoted,
         MirPhase::DropElab,
         &[post_borrowck_cleanup],
@@ -414,7 +414,7 @@ fn run_optimization_passes<'tcx>(
     run_passes(
         tcx,
         body,
-        InstanceDef::Item(def_id.to_def_id()),
+        InstanceDef::Item(ty::WithOptParam::dummy(def_id.to_def_id())),
         promoted,
         MirPhase::Optimized,
         &[
diff --git a/src/librustc_mir/util/pretty.rs b/src/librustc_mir/util/pretty.rs
index db45481e4fd2..9b6dd2dc268a 100644
--- a/src/librustc_mir/util/pretty.rs
+++ b/src/librustc_mir/util/pretty.rs
@@ -248,7 +248,10 @@ pub fn write_mir_pretty<'tcx>(
 
         for (i, body) in tcx.promoted_mir(def_id).iter_enumerated() {
             writeln!(w)?;
-            let src = MirSource { instance: ty::InstanceDef::Item(def_id), promoted: Some(i) };
+            let src = MirSource {
+                instance: ty::InstanceDef::Item(ty::WithOptParam::dummy(def_id)),
+                promoted: Some(i),
+            };
             write_mir_fn(tcx, src, body, &mut |_, _| Ok(()), w)?;
         }
     }
diff --git a/src/librustc_ty/instance.rs b/src/librustc_ty/instance.rs
index d5c848817582..7c58963fccc8 100644
--- a/src/librustc_ty/instance.rs
+++ b/src/librustc_ty/instance.rs
@@ -86,7 +86,7 @@ fn inner_resolve_instance<'tcx>(
             }
             _ => {
                 debug!(" => free item");
-                ty::InstanceDef::Item(def.did)
+                ty::InstanceDef::Item(def)
             }
         };
         Ok(Some(Instance { def, substs }))
@@ -215,7 +215,7 @@ fn resolve_associated_item<'tcx>(
             Some(ty::Instance::new(leaf_def.item.def_id, substs))
         }
         traits::ImplSourceGenerator(generator_data) => Some(Instance {
-            def: ty::InstanceDef::Item(generator_data.generator_def_id),
+            def: ty::InstanceDef::Item(ty::WithOptParam::dummy(generator_data.generator_def_id)),
             substs: generator_data.substs,
         }),
         traits::ImplSourceClosure(closure_data) => {