On MIPS, keeps Object::null() in a register.

runtime/vm/flow_graph_compiler_mips.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_MIPS.
 #if defined(TARGET_ARCH_MIPS)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "lib/error.h"
@@ skipping 767 matching lines @@
   // S4 : arguments descriptor array.
   __ BranchLink(&StubCode::CallNoSuchMethodFunctionLabel());
   // Emit descriptors in order to provide correct postion in stacktrace.
   AddCurrentDescriptor(PcDescriptors::kOther, -1, function.token_pos());
   if (is_optimizing()) {
     stackmap_table_builder_->AddEntry(assembler()->CodeSize(),
                                       empty_stack_bitmap,
                                       0);  // No registers.
   }
   // The noSuchMethod call may return.
-  __ LeaveDartFrame();
-  __ Ret();
+  __ LeaveDartFrameAndReturn();
 
   __ Bind(&all_arguments_processed);
   // Nullify originally passed arguments only after they have been copied and
   // checked, otherwise noSuchMethod would not see their original values.
   // This step can be skipped in case we decide that formal parameters are
   // implicitly final, since garbage collecting the unmodified value is not
   // an issue anymore.
 
   __ LoadImmediate(T0, reinterpret_cast<intptr_t>(Object::null()));
 
@@ skipping 192 matching lines @@
         // S4 : arguments descriptor array.
         __ BranchLink(&StubCode::CallNoSuchMethodFunctionLabel());
         // Emit descriptors in order to provide correct postion in stacktrace.
         AddCurrentDescriptor(PcDescriptors::kOther, -1, function.token_pos());
         if (is_optimizing()) {
           stackmap_table_builder_->AddEntry(assembler()->CodeSize(),
                                             empty_stack_bitmap,
                                             0);  // No registers.
         }
         // The noSuchMethod call may return.
-        __ LeaveDartFrame();
-        __ Ret();
+        __ LeaveDartFrameAndReturn();
       } else {
         __ Stop("Wrong number of arguments");
       }
       __ Bind(&correct_num_arguments);
     }
     // The arguments descriptor is never saved in the absence of optional
     // parameters, since any argument definition test would always yield true.
     ASSERT(saved_args_desc_var == NULL);
   } else {
     if (saved_args_desc_var != NULL) {
@@ skipping 556 matching lines @@
   __ AddImmediate(SP, kDoubleSize);
 }
 
 
 #undef __
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS