Use immediate_backend_type

Author: saethlin

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -528,7 +528,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             PassMode::Direct(_) | PassMode::Pair(..) => {
                 let op = self.codegen_consume(bx, mir::Place::return_place().as_ref());
                 match op.val {
-                    Uninit => bx.const_undef(bx.backend_type(self.fn_abi.ret.layout)),
+                    Uninit => bx.const_undef(bx.immediate_backend_type(op.layout)),
                     Ref(place_val) => bx.load_from_place(bx.backend_type(op.layout), place_val),
                     _ => op.immediate_or_packed_pair(bx),
                 }