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

src/virtual-frame.cc

 // Copyright 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 161 matching lines @@
 }
 
 
 void VirtualFrame::Spill(Register target) {
   if (is_used(target)) {
     SpillElementAt(register_index(target));
   }
 }
 
 
-// Spill any register if possible, making its external reference count zero.
+// If there are any registers referenced only by the frame, spill one.
 Register VirtualFrame::SpillAnyRegister() {
-  // Find the leftmost (ordered by register code), least
-  // internally-referenced register whose internal reference count matches
-  // its external reference count (so that spilling it from the frame frees
-  // it for use).
+  // Find the leftmost (ordered by register code) register whose only
+  // reference is in the frame.
   for (int i = 0; i < kNumRegisters; i++) {
     if (is_used(i) && cgen_->allocator()->count(i) == 1) {
       Register result = { i };
       Spill(result);
       ASSERT(!cgen_->allocator()->is_used(result));
       return result;
     }
   }
   return no_reg;
 }
@@ skipping 347 matching lines @@
 #endif
   if (stack_pointer_ != other->stack_pointer_) return false;
   for (int i = 0; i < elements_.length(); i++) {
     if (!elements_[i].Equals(other->elements_[i])) return false;
   }
 
   return true;
 }
 
 } }  // namespace v8::internal