Simplify Hydrogen code stubs with variable argument count

src/code-stubs-hydrogen.cc

 // Copyright 2012 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 132 matching lines @@
     isolate()->GetHTracer()->TraceCompilation(&info_);
   }
 
   int param_count = descriptor_->register_param_count_;
   HEnvironment* start_environment = graph()->start_environment();
   HBasicBlock* next_block = CreateBasicBlock(start_environment);
   Goto(next_block);
   next_block->SetJoinId(BailoutId::StubEntry());
   set_current_block(next_block);
 
+  bool runtime_stack_params = descriptor_->stack_parameter_count_.is_valid();
+  HInstruction* stack_parameter_count = NULL;
   for (int i = 0; i < param_count; ++i) {
-    HParameter* param =
-        Add<HParameter>(i, HParameter::REGISTER_PARAMETER);
+    Representation r = descriptor_->IsParameterCountRegister(i)
+        ? Representation::Integer32()
+        : Representation::Tagged();
+    HParameter* param = Add<HParameter>(i, HParameter::REGISTER_PARAMETER, r);
     start_environment->Bind(i, param);
     parameters_[i] = param;
+    if (descriptor_->IsParameterCountRegister(i)) {
+      param->set_type(HType::Smi());
+      stack_parameter_count = param;
+      arguments_length_ = stack_parameter_count;
+    }
   }
 
-  HInstruction* stack_parameter_count;
-  if (descriptor_->stack_parameter_count_.is_valid()) {
-    ASSERT(descriptor_->environment_length() == (param_count + 1));
-    stack_parameter_count = New<HParameter>(param_count,
-                                            HParameter::REGISTER_PARAMETER,
-                                            Representation::Integer32());
-    stack_parameter_count->set_type(HType::Smi());
-    // It's essential to bind this value to the environment in case of deopt.
-    AddInstruction(stack_parameter_count);
-    start_environment->Bind(param_count, stack_parameter_count);
-    arguments_length_ = stack_parameter_count;
-  } else {
-    ASSERT(descriptor_->environment_length() == param_count);
+  ASSERT(!runtime_stack_params || arguments_length_ != NULL);
+  if (!runtime_stack_params) {
     stack_parameter_count = graph()->GetConstantMinus1();
     arguments_length_ = graph()->GetConstant0();
   }
 
   context_ = Add<HContext>();
   start_environment->BindContext(context_);
 
   Add<HSimulate>(BailoutId::StubEntry());
 
   NoObservableSideEffectsScope no_effects(this);
 
   HValue* return_value = BuildCodeStub();
 
   // We might have extra expressions to pop from the stack in addition to the
   // arguments above.
   HInstruction* stack_pop_count = stack_parameter_count;
   if (descriptor_->function_mode_ == JS_FUNCTION_STUB_MODE) {
     if (!stack_parameter_count->IsConstant() &&
         descriptor_->hint_stack_parameter_count_ < 0) {
-      HInstruction* amount = graph()->GetConstant1();
-      stack_pop_count = Add<HAdd>(stack_parameter_count, amount);
-      stack_pop_count->ChangeRepresentation(Representation::Integer32());
+      HInstruction* constant_one = graph()->GetConstant1();
+      stack_pop_count = Add<HAdd>(stack_parameter_count, constant_one);
       stack_pop_count->ClearFlag(HValue::kCanOverflow);
+      // TODO(mvstanton): verify that stack_parameter_count+1 really fits in a
+      // smi.
     } else {
       int count = descriptor_->hint_stack_parameter_count_;
       stack_pop_count = Add<HConstant>(count);
     }
   }
 
   if (current_block() != NULL) {
     HReturn* hreturn_instruction = New<HReturn>(return_value,
                                                 stack_pop_count);
     FinishCurrentBlock(hreturn_instruction);
@@ skipping 1081 matching lines @@
   return js_function;
 }
 
 
 Handle<Code> FastNewClosureStub::GenerateCode(Isolate* isolate) {
   return DoGenerateCode(isolate, this);
 }
 
 
 } }  // namespace v8::internal