Implement argument definition test in the vm.

runtime/vm/flow_graph_compiler_ia32.cc

Index: runtime/vm/flow_graph_compiler_ia32.cc
===================================================================
--- runtime/vm/flow_graph_compiler_ia32.cc	(revision 11659)
+++ runtime/vm/flow_graph_compiler_ia32.cc	(working copy)
@@ -923,6 +923,8 @@
   // the presence of optional named parameters.
   // No such checking code is generated if only fixed parameters are declared,
   // unless we are debug mode or unless we are compiling a closure.
+  LocalVariable* saved_args_desc_var =
+      parsed_function().GetSavedArgumentsDescriptorVar();
   if (copied_parameter_count == 0) {
 #ifdef DEBUG
     const bool check_arguments = true;
@@ -947,12 +949,25 @@
       }
       __ Bind(&argc_in_range);
     }
+    // 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) {
+      __ Comment("Save arguments descriptor");
+      // The saved_args_desc_var is allocated one slot before the first local.
+      const intptr_t slot = parsed_function().first_stack_local_index() + 1;
+      // If the saved_args_desc_var is captured, it is first moved to the stack
+      // and later to the context, once the context is allocated.
+      ASSERT(saved_args_desc_var->is_captured() ||
+             (saved_args_desc_var->index() == slot));
+      __ movl(Address(EBP, slot * kWordSize), EDX);

[srdjan, 2012/08/30 22:15:59]

It would be nice to name the register that is used for argument descriptor
(EDX).

[regis, 2012/08/30 22:45:31]

For now, I named it locally (here and in the corresponding x64 location). We
would need to touch many files to be consistent and use global names for the
arguments descriptor, the name of the dynamic function, etc...

+    }
     CopyParameters();
   }
 
   // In unoptimized code, initialize (non-argument) stack allocated slots to
-  // null.
+  // null. This does not cover the saved_args_desc_var slot.
   if (!is_optimizing() && (local_count > 0)) {
     __ Comment("Initialize spill slots");
     const intptr_t slot_base = parsed_function().first_stack_local_index();