The code generator doesn't need to put the argument count in eax for...

src/codegen-arm.cc

 // Copyright 2006-2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3438 matching lines @@
   if (CheckForInlineRuntimeCall(node)) {
     ASSERT((has_cc() && frame_->height() == original_height) ||
            (!has_cc() && frame_->height() == original_height + 1));
     return;
   }
 
   ZoneList<Expression*>* args = node->arguments();
   Comment cmnt(masm_, "[ CallRuntime");
   Runtime::Function* function = node->function();
 
-  if (function != NULL) {
-    // Push the arguments ("left-to-right").
-    int arg_count = args->length();
-    for (int i = 0; i < arg_count; i++) {
-      LoadAndSpill(args->at(i));
-    }
-
-    // Call the C runtime function.
-    frame_->CallRuntime(function, arg_count);
-    frame_->EmitPush(r0);
-
-  } else {
+  if (function == NULL) {
     // Prepare stack for calling JS runtime function.
     __ mov(r0, Operand(node->name()));
     frame_->EmitPush(r0);
     // Push the builtins object found in the current global object.
     __ ldr(r1, GlobalObject());
     __ ldr(r0, FieldMemOperand(r1, GlobalObject::kBuiltinsOffset));
     frame_->EmitPush(r0);
+  }
 
-    int arg_count = args->length();
-    for (int i = 0; i < arg_count; i++) {
-      LoadAndSpill(args->at(i));
-    }
+  // Push the arguments ("left-to-right").
+  int arg_count = args->length();
+  for (int i = 0; i < arg_count; i++) {
+    LoadAndSpill(args->at(i));
+  }
 
+  if (function == NULL) {
     // Call the JS runtime function.
-    Handle<Code> stub = ComputeCallInitialize(args->length());
+    Handle<Code> stub = ComputeCallInitialize(arg_count);
     frame_->CallCodeObject(stub, RelocInfo::CODE_TARGET, arg_count + 1);
     __ ldr(cp, frame_->Context());
     frame_->Drop();
     frame_->EmitPush(r0);
+  } else {
+    // Call the C runtime function.
+    frame_->CallRuntime(function, arg_count);
+    frame_->EmitPush(r0);
   }
   ASSERT(frame_->height() == original_height + 1);
 }
 
 
 void CodeGenerator::VisitUnaryOperation(UnaryOperation* node) {
 #ifdef DEBUG
   int original_height = frame_->height();
 #endif
   VirtualFrame::SpilledScope spilled_scope(this);
@@ skipping 1724 matching lines @@
   __ mov(r2, Operand(0));
   __ GetBuiltinEntry(r3, Builtins::CALL_NON_FUNCTION);
   __ Jump(Handle<Code>(Builtins::builtin(Builtins::ArgumentsAdaptorTrampoline)),
           RelocInfo::CODE_TARGET);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal