Improve AdtDef interning.

This commit makes `AdtDef` use `Interned`. Much the commit is tedious
changes to introduce getter functions. The interesting changes are in
`compiler/rustc_middle/src/ty/adt.rs`.

Author: nnethercote

src/common.rs

@@ -67,7 +67,7 @@ fn clif_type_from_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<types::Typ
                 pointer_ty(tcx)
             }
         }
-        ty::Adt(adt_def, _) if adt_def.repr.simd() => {
+        ty::Adt(adt_def, _) if adt_def.repr().simd() => {
             let (element, count) = match &tcx.layout_of(ParamEnv::reveal_all().and(ty)).unwrap().abi
             {
                 Abi::Vector { element, count } => (element.clone(), *count),

src/unsize.rs

@@ -127,7 +127,7 @@ pub(crate) fn coerce_unsized_into<'tcx>(
         (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
             assert_eq!(def_a, def_b);
 
-            for i in 0..def_a.variants[VariantIdx::new(0)].fields.len() {
+            for i in 0..def_a.variant(VariantIdx::new(0)).fields.len() {
                 let src_f = src.value_field(fx, mir::Field::new(i));
                 let dst_f = dst.place_field(fx, mir::Field::new(i));
 
@@ -200,7 +200,7 @@ pub(crate) fn size_and_align_of_dst<'tcx>(
 
             // Packed types ignore the alignment of their fields.
             if let ty::Adt(def, _) = layout.ty.kind() {
-                if def.repr.packed() {
+                if def.repr().packed() {
                     unsized_align = sized_align;
                 }
             }

src/value_and_place.rs

@@ -24,7 +24,7 @@ fn codegen_field<'tcx>(
         }
         match field_layout.ty.kind() {
             ty::Slice(..) | ty::Str | ty::Foreign(..) => simple(fx),
-            ty::Adt(def, _) if def.repr.packed() => {
+            ty::Adt(def, _) if def.repr().packed() => {
                 assert_eq!(layout.align.abi.bytes(), 1);
                 simple(fx)
             }
@@ -816,7 +816,7 @@ pub(crate) fn assert_assignable<'tcx>(
             // dyn for<'r> Trait<'r> -> dyn Trait<'_> is allowed
         }
         (&ty::Adt(adt_def_a, substs_a), &ty::Adt(adt_def_b, substs_b))
-            if adt_def_a.did == adt_def_b.did =>
+            if adt_def_a.did() == adt_def_b.did() =>
         {
             let mut types_a = substs_a.types();
             let mut types_b = substs_b.types();