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.

1 files changed, 2 insertions, 2 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index f087b9f7815..6f960ca44cd 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/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)