Store a DefId instead of an AdtDef in AggregateKind::Adt

The `AggregateKind` enum ends up in the final mir `Body`. Currently,
any changes to `AdtDef` (regardless of how significant they are)
will legitimately cause the overall result of `optimized_mir` to change,
invalidating any codegen re-use involving that mir.

This will get worse once we start hashing the `Span` inside `FieldDef`
(which is itself contained in `AdtDef`).

To try to reduce these kinds of invalidations, this commit changes
`AggregateKind::Adt` to store just the `DefId`, instead of the full
`AdtDef`. This allows the result of `optimized_mir` to be unchanged
if the `AdtDef` changes in a way that doesn't actually affect any
of the MIR we build.

Author: Aaron1011

Diff for: compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1916,7 +1916,8 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         let tcx = self.tcx();
 
         match *ak {
-            AggregateKind::Adt(def, variant_index, substs, _, active_field_index) => {
+            AggregateKind::Adt(adt_did, variant_index, substs, _, active_field_index) => {
+                let def = tcx.adt_def(adt_did);
                 let variant = &def.variants[variant_index];
                 let adj_field_index = active_field_index.unwrap_or(field_index);
                 if let Some(field) = variant.fields.get(adj_field_index) {
@@ -2621,8 +2622,8 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         );
 
         let (def_id, instantiated_predicates) = match aggregate_kind {
-            AggregateKind::Adt(def, _, substs, _, _) => {
-                (def.did, tcx.predicates_of(def.did).instantiate(tcx, substs))
+            AggregateKind::Adt(adt_did, _, substs, _, _) => {
+                (*adt_did, tcx.predicates_of(*adt_did).instantiate(tcx, substs))
             }
 
             // For closures, we have some **extra requirements** we

Diff for: compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -112,9 +112,9 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
             mir::Rvalue::Aggregate(ref kind, ref operands) => {
                 let (dest, active_field_index) = match **kind {
-                    mir::AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
+                    mir::AggregateKind::Adt(adt_did, variant_index, _, _, active_field_index) => {
                         dest.codegen_set_discr(&mut bx, variant_index);
-                        if adt_def.is_enum() {
+                        if bx.tcx().adt_def(adt_did).is_enum() {
                             (dest.project_downcast(&mut bx, variant_index), active_field_index)
                         } else {
                             (dest, active_field_index)

Diff for: compiler/rustc_const_eval/src/interpret/step.rs

@@ -199,9 +199,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             Aggregate(ref kind, ref operands) => {
                 // active_field_index is for union initialization.
                 let (dest, active_field_index) = match **kind {
-                    mir::AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
+                    mir::AggregateKind::Adt(adt_did, variant_index, _, _, active_field_index) => {
                         self.write_discriminant(variant_index, &dest)?;
-                        if adt_def.is_enum() {
+                        if self.tcx.adt_def(adt_did).is_enum() {
                             assert!(active_field_index.is_none());
                             (self.place_downcast(&dest, variant_index)?, None)
                         } else {

Diff for: compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs

@@ -270,7 +270,8 @@ where
         Rvalue::Aggregate(kind, operands) => {
             // Return early if we know that the struct or enum being constructed is always
             // qualified.
-            if let AggregateKind::Adt(def, _, substs, ..) = **kind {
+            if let AggregateKind::Adt(adt_did, _, substs, ..) = **kind {
+                let def = cx.tcx.adt_def(adt_did);
                 if Q::in_adt_inherently(cx, def, substs) {
                     return true;
                 }

Diff for: compiler/rustc_const_eval/src/util/aggregate.rs

@@ -22,7 +22,8 @@ pub fn expand_aggregate<'tcx>(
 ) -> impl Iterator<Item = Statement<'tcx>> + TrustedLen {
     let mut set_discriminant = None;
     let active_field_index = match kind {
-        AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
+        AggregateKind::Adt(adt_did, variant_index, _, _, active_field_index) => {
+            let adt_def = tcx.adt_def(adt_did);
             if adt_def.is_enum() {
                 set_discriminant = Some(Statement {
                     kind: StatementKind::SetDiscriminant { place: Box::new(lhs), variant_index },

Diff for: compiler/rustc_middle/src/mir/mod.rs

@@ -2268,7 +2268,7 @@ pub enum AggregateKind<'tcx> {
     /// active field number and is present only for union expressions
     /// -- e.g., for a union expression `SomeUnion { c: .. }`, the
     /// active field index would identity the field `c`
-    Adt(&'tcx AdtDef, VariantIdx, SubstsRef<'tcx>, Option<UserTypeAnnotationIndex>, Option<usize>),
+    Adt(DefId, VariantIdx, SubstsRef<'tcx>, Option<UserTypeAnnotationIndex>, Option<usize>),
 
     Closure(DefId, SubstsRef<'tcx>),
     Generator(DefId, SubstsRef<'tcx>, hir::Movability),
@@ -2427,28 +2427,26 @@ impl<'tcx> Debug for Rvalue<'tcx> {
                         }
                     }
 
-                    AggregateKind::Adt(adt_def, variant, substs, _user_ty, _) => {
-                        let variant_def = &adt_def.variants[variant];
-
-                        let name = ty::tls::with(|tcx| {
+                    AggregateKind::Adt(adt_did, variant, substs, _user_ty, _) => {
+                        ty::tls::with(|tcx| {
                             let mut name = String::new();
+                            let variant_def = &tcx.adt_def(adt_did).variants[variant];
                             let substs = tcx.lift(substs).expect("could not lift for printing");
                             FmtPrinter::new(tcx, &mut name, Namespace::ValueNS)
                                 .print_def_path(variant_def.def_id, substs)?;
-                            Ok(name)
-                        })?;
-
-                        match variant_def.ctor_kind {
-                            CtorKind::Const => fmt.write_str(&name),
-                            CtorKind::Fn => fmt_tuple(fmt, &name),
-                            CtorKind::Fictive => {
-                                let mut struct_fmt = fmt.debug_struct(&name);
-                                for (field, place) in iter::zip(&variant_def.fields, places) {
-                                    struct_fmt.field(field.ident.as_str(), place);
+
+                            match variant_def.ctor_kind {
+                                CtorKind::Const => fmt.write_str(&name),
+                                CtorKind::Fn => fmt_tuple(fmt, &name),
+                                CtorKind::Fictive => {
+                                    let mut struct_fmt = fmt.debug_struct(&name);
+                                    for (field, place) in iter::zip(&variant_def.fields, places) {
+                                        struct_fmt.field(field.ident.as_str(), place);
+                                    }
+                                    struct_fmt.finish()
                                 }
-                                struct_fmt.finish()
                             }
-                        }
+                        })
                     }
 
                     AggregateKind::Closure(def_id, substs) => ty::tls::with(|tcx| {

Diff for: compiler/rustc_middle/src/mir/tcx.rs

@@ -200,7 +200,7 @@ impl<'tcx> Rvalue<'tcx> {
             Rvalue::Aggregate(ref ak, ref ops) => match **ak {
                 AggregateKind::Array(ty) => tcx.mk_array(ty, ops.len() as u64),
                 AggregateKind::Tuple => tcx.mk_tup(ops.iter().map(|op| op.ty(local_decls, tcx))),
-                AggregateKind::Adt(def, _, substs, _, _) => tcx.type_of(def.did).subst(tcx, substs),
+                AggregateKind::Adt(did, _, substs, _, _) => tcx.type_of(did).subst(tcx, substs),
                 AggregateKind::Closure(did, substs) => tcx.mk_closure(did, substs),
                 AggregateKind::Generator(did, substs, movability) => {
                     tcx.mk_generator(did, substs, movability)

Diff for: compiler/rustc_mir_build/src/build/expr/into.rs

@@ -377,7 +377,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     })
                 });
                 let adt = Box::new(AggregateKind::Adt(
-                    adt_def,
+                    adt_def.did,
                     variant_index,
                     substs,
                     user_ty,

Diff for: compiler/rustc_mir_transform/src/check_unsafety.rs

@@ -117,8 +117,8 @@ impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
         match rvalue {
             Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
                 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
-                &AggregateKind::Adt(ref def, ..) => {
-                    match self.tcx.layout_scalar_valid_range(def.did) {
+                &AggregateKind::Adt(adt_did, ..) => {
+                    match self.tcx.layout_scalar_valid_range(adt_did) {
                         (Bound::Unbounded, Bound::Unbounded) => {}
                         _ => self.require_unsafe(
                             UnsafetyViolationKind::General,

Diff for: compiler/rustc_mir_transform/src/generator.rs

@@ -243,7 +243,7 @@ impl<'tcx> TransformVisitor<'tcx> {
         val: Operand<'tcx>,
         source_info: SourceInfo,
     ) -> impl Iterator<Item = Statement<'tcx>> {
-        let kind = AggregateKind::Adt(self.state_adt_ref, idx, self.state_substs, None, None);
+        let kind = AggregateKind::Adt(self.state_adt_ref.did, idx, self.state_substs, None, None);
         assert_eq!(self.state_adt_ref.variants[idx].fields.len(), 1);
         let ty = self
             .tcx

Diff for: compiler/rustc_mir_transform/src/shim.rs

@@ -777,7 +777,7 @@ pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> Body<'_> {
         adt_def.variants[variant_index].fields.iter().enumerate().map(|(idx, field_def)| {
             (Operand::Move(Place::from(Local::new(idx + 1))), field_def.ty(tcx, substs))
         }),
-        AggregateKind::Adt(adt_def, variant_index, substs, None, None),
+        AggregateKind::Adt(adt_def.did, variant_index, substs, None, None),
         source_info,
         tcx,
     )