remove box derefs from codgen

compiler/rustc_mir_transform/src/lib.rs

@@ -57,6 +57,7 @@ mod deref_separator;
 mod dest_prop;
 pub mod dump_mir;
 mod early_otherwise_branch;
+mod elaborate_box_derefs;
 mod elaborate_drops;
 mod function_item_references;
 mod generator;
@@ -427,6 +428,7 @@ fn run_post_borrowck_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tc
         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
         // but before optimizations begin.
         &deref_separator::Derefer,
+        &elaborate_box_derefs::ElaborateBoxDerefs,
         &add_retag::AddRetag,
         &lower_intrinsics::LowerIntrinsics,
         &simplify::SimplifyCfg::new("elaborate-drops"),