add FIXME's for a later refactoring

compiler/rustc_codegen_ssa/src/mir/locals.rs

@@ -61,6 +61,7 @@ pub(super) fn overwrite_local(
             LocalRef::Operand(ref mut op) => {
                 let local_ty = self.monomorphize(self.mir.local_decls[local].ty);
                 if local_ty != op.layout.ty {
+                    // FIXME(#112651): This can be changed to an ICE afterwards.
                     debug!("updating type of operand due to subtyping");
                     with_no_trimmed_paths!(debug!(?op.layout.ty));
                     with_no_trimmed_paths!(debug!(?local_ty));

compiler/rustc_mir_transform/src/dest_prop.rs

@@ -768,16 +768,18 @@ fn visit_statement(&mut self, statement: &Statement<'tcx>, _: Location) {
                 return;
             };
 
-            // As described at the top of the file, we do not go near things that have their address
-            // taken.
+            // As described at the top of the file, we do not go near things that have
+            // their address taken.
             if self.borrowed.contains(src) || self.borrowed.contains(dest) {
                 return;
             }
 
-            // As described at the top of this file, we do not touch locals which have different types.
+            // As described at the top of this file, we do not touch locals which have
+            // different types.
             let src_ty = self.body.local_decls()[src].ty;
             let dest_ty = self.body.local_decls()[dest].ty;
             if src_ty != dest_ty {
+                // FIXME(#112651): This can be removed afterwards. Also update the module description.
                 trace!("skipped `{src:?} = {dest:?}` due to subtyping: {src_ty} != {dest_ty}");
                 return;
             }

compiler/rustc_mir_transform/src/ssa.rs

@@ -274,6 +274,7 @@ fn compute_copy_classes(ssa: &mut SsaLocals, body: &Body<'_>) {
         let local_ty = body.local_decls()[local].ty;
         let rhs_ty = body.local_decls()[rhs].ty;
         if local_ty != rhs_ty {
+            // FIXME(#112651): This can be removed afterwards.
             trace!("skipped `{local:?} = {rhs:?}` due to subtyping: {local_ty} != {rhs_ty}");
             continue;
         }