Make stack_parameter_count a plain register.

src/deoptimizer.cc

 // Copyright 2013 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 1476 matching lines @@
   value = reinterpret_cast<intptr_t>(
       Smi::FromInt(StackFrame::STUB_FAILURE_TRAMPOLINE));
   output_frame->SetFrameSlot(output_frame_offset, value);
   if (trace_) {
     PrintF("    0x%08" V8PRIxPTR ": [top + %d] <- 0x%08"
            V8PRIxPTR " ; function (stub failure sentinel)\n",
            top_address + output_frame_offset, output_frame_offset, value);
   }
 
   intptr_t caller_arg_count = 0;
-  bool arg_count_known = descriptor->stack_parameter_count_ == NULL;
+  bool arg_count_known = !descriptor->stack_parameter_count_.is_valid();
 
   // Build the Arguments object for the caller's parameters and a pointer to it.
   output_frame_offset -= kPointerSize;
   int args_arguments_offset = output_frame_offset;
   intptr_t the_hole = reinterpret_cast<intptr_t>(
       isolate_->heap()->the_hole_value());
   if (arg_count_known) {
     value = frame_ptr + StandardFrameConstants::kCallerSPOffset +
         (caller_arg_count - 1) * kPointerSize;
   } else {
@@ skipping 1437 matching lines @@
 
 void DeoptimizedFrameInfo::Iterate(ObjectVisitor* v) {
   v->VisitPointer(BitCast<Object**>(&function_));
   v->VisitPointers(parameters_, parameters_ + parameters_count_);
   v->VisitPointers(expression_stack_, expression_stack_ + expression_count_);
 }
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal