message: Remove NullOp::Box
diff: @@ -708,30 +708,6 @@ fn is_fat_ptr<'tcx>(fx: &FunctionCx<'_, '_, 'tcx>, ty: Ty<'tcx>) -> bool {
  let operand = operand.load_scalar(fx);
  lval.write_cvalue(fx, CValue::by_val(operand, box_layout));
  }
  - Rvalue::NullaryOp(NullOp::Box, content_ty) => {
  - let usize_type = fx.clif_type(fx.tcx.types.usize).unwrap();
  - let content_ty = fx.monomorphize(content_ty);
  - let layout = fx.layout_of(content_ty);
  - let llsize = fx.bcx.ins().iconst(usize_type, layout.size.bytes() as i64);
  - let llalign = fx.bcx.ins().iconst(usize_type, layout.align.abi.bytes() as i64);
  - let box_layout = fx.layout_of(fx.tcx.mk_box(content_ty));
  -
  - // Allocate space:
  - let def_id =
  - match fx.tcx.lang_items().require(rustc_hir::LangItem::ExchangeMalloc) {
  - Ok(id) => id,
  - Err(s) => {
  - fx.tcx
  - .sess
  - .fatal(&format!("allocation of `{}` {}", box_layout.ty, s));
  - }
  - };
  - let instance = ty::Instance::mono(fx.tcx, def_id).polymorphize(fx.tcx);
  - let func_ref = fx.get_function_ref(instance);
  - let call = fx.bcx.ins().call(func_ref, &[llsize, llalign]);
  - let ptr = fx.bcx.inst_results(call)[0];
  - lval.write_cvalue(fx, CValue::by_val(ptr, box_layout));
  - }
  Rvalue::NullaryOp(null_op, ty) => {
  assert!(
  lval.layout()
  @@ -742,7 +718,6 @@ fn is_fat_ptr<'tcx>(fx: &FunctionCx<'_, '_, 'tcx>, ty: Ty<'tcx>) -> bool {
  let val = match null_op {
  NullOp::SizeOf => layout.size.bytes(),
  NullOp::AlignOf => layout.align.abi.bytes(),
  - NullOp::Box => unreachable!(),
  };
  let val =
  CValue::const_val(fx, fx.layout_of(fx.tcx.types.usize), val.into());
  