Implement argument definition test in the vm.

runtime/vm/flow_graph_compiler_x64.cc

 // Copyright (c) 2012, 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_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "lib/error.h"
@@ skipping 914 matching lines @@
   if (is_optimizing()) {
     // Spill slots are allocated but not initialized.
     prologue_locs = new LocationSummary(0, 0, LocationSummary::kCall);
     prologue_locs->stack_bitmap()->SetLength(StackSize());
   }
 
   // We check the number of passed arguments when we have to copy them due to
   // 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;
 #else
     const bool check_arguments = function.IsClosureFunction();
 #endif
     if (check_arguments) {
       __ Comment("Check argument count");
       // Check that num_fixed <= argc <= num_params.
       Label argc_in_range;
       // Total number of args is the first Smi in args descriptor array (R10).
       __ movq(RAX, FieldAddress(R10, Array::data_offset()));
       __ cmpq(RAX, Immediate(Smi::RawValue(parameter_count)));
       __ j(EQUAL, &argc_in_range, Assembler::kNearJump);
       if (function.IsClosureFunction()) {
         GenerateCallRuntime(Isolate::kNoDeoptId,
                             function.token_pos(),
                             kClosureArgumentMismatchRuntimeEntry,
                             prologue_locs);
       } else {
         __ Stop("Wrong number of arguments");
       }
       __ 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");
+      const Register kArgumentsDescriptorReg = R10;
+      // 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));
+      __ movq(Address(RBP, slot * kWordSize), kArgumentsDescriptorReg);
+    }
     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();
     const Immediate raw_null =
         Immediate(reinterpret_cast<intptr_t>(Object::null()));
     __ movq(RAX, raw_null);
     for (intptr_t i = 0; i < local_count; ++i) {
       // Subtract index i (locals lie at lower addresses than RBP).
       __ movq(Address(RBP, (slot_base - i) * kWordSize), RAX);
     }
@@ skipping 318 matching lines @@
 void ParallelMoveResolver::Exchange(const Address& mem1, const Address& mem2) {
   __ Exchange(mem1, mem2);
 }
 
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64