Always validate MIR after optimizing

src/librustc_mir/transform/mod.rs

@@ -191,6 +191,11 @@ pub fn run_passes(
     }
 
     body.phase = mir_phase;
+
+    if mir_phase == MirPhase::Optimized {
+        validate::Validator { when: format!("end of phase {:?}", mir_phase) }
+            .run_pass(tcx, source, body);
+    }
 }
 
 fn mir_const_qualif(tcx: TyCtxt<'_>, def_id: DefId) -> ConstQualifs {