Simplify maybe_record_as_seed.

Author: cjgillot

compiler/rustc_passes/src/dead.rs

@@ -745,8 +745,8 @@ fn maybe_record_as_seed<'tcx>(
 
     match tcx.def_kind(owner_id) {
         DefKind::Enum => {
-            let adt = tcx.adt_def(owner_id);
             if let Some(comes_from_allow) = allow_dead_code {
+                let adt = tcx.adt_def(owner_id);
                 worklist.extend(
                     adt.variants()
                         .iter()
@@ -771,8 +771,8 @@ fn maybe_record_as_seed<'tcx>(
                 }
             }
         }
-        DefKind::Impl { of_trait } => {
-            if allow_dead_code.is_none() && of_trait {
+        DefKind::Impl { of_trait: true } => {
+            if allow_dead_code.is_none() {
                 unsolved_items.push(owner_id.def_id);
             }
         }

compiler/rustc_passes/src/lib.rs

@@ -8,6 +8,7 @@
 #![allow(internal_features)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
+#![feature(if_let_guard)]
 #![feature(map_try_insert)]
 #![feature(rustdoc_internals)]
 // tidy-alphabetical-end