[turbofan] Reduce memory consumption of graph building

src/compiler/generic-node-inl.h

Index: src/compiler/generic-node-inl.h
diff --git a/src/compiler/generic-node-inl.h b/src/compiler/generic-node-inl.h
index 76313af514b644a0a96a44419317ee9034f7d3bc..30f8f680938125e19b5dcd7d1fd95732a4000cf9 100644
--- a/src/compiler/generic-node-inl.h
+++ b/src/compiler/generic-node-inl.h
@@ -16,13 +16,16 @@ namespace internal {
 namespace compiler {
 
 template <class B, class S>
-GenericNode<B, S>::GenericNode(GenericGraphBase* graph, int input_count)
+GenericNode<B, S>::GenericNode(GenericGraphBase* graph, int input_count,
+                               int reserve_input_count)
     : BaseClass(graph->zone()),
       input_count_(input_count),
+      reserve_input_count_(reserve_input_count),
       has_appendable_inputs_(false),
       use_count_(0),
       first_use_(NULL),
       last_use_(NULL) {
+  DCHECK(reserve_input_count <= kMaxReservedInputs);
   inputs_.static_ = reinterpret_cast<Input*>(this + 1);
   AssignUniqueID(graph);
 }
@@ -154,12 +157,18 @@ void GenericNode<B, S>::EnsureAppendableInputs(Zone* zone) {
 
 template <class B, class S>
 void GenericNode<B, S>::AppendInput(Zone* zone, GenericNode<B, S>* to_append) {
-  EnsureAppendableInputs(zone);
   Use* new_use = new (zone) Use;
   Input new_input;
   new_input.to = to_append;
   new_input.use = new_use;
-  inputs_.appendable_->push_back(new_input);
+  if (reserve_input_count_ > 0) {
+    DCHECK(!has_appendable_inputs_);
+    reserve_input_count_--;
+    inputs_.static_[input_count_] = new_input;
+  } else {
+    EnsureAppendableInputs(zone);
+    inputs_.appendable_->push_back(new_input);
+  }
   new_use->input_index = input_count_;
   new_use->from = this;
   to_append->AppendUse(new_use);
@@ -224,15 +233,17 @@ inline bool GenericNode<B, S>::OwnedBy(GenericNode* owner) const {
 }
 
 template <class B, class S>
-S* GenericNode<B, S>::New(GenericGraphBase* graph, int input_count,
-                          S** inputs) {
+S* GenericNode<B, S>::New(GenericGraphBase* graph, int input_count, S** inputs,
+                          bool has_extensible_inputs) {
   size_t node_size = sizeof(GenericNode);
-  size_t inputs_size = input_count * sizeof(Input);
+  size_t reserve_input_count =
+      has_extensible_inputs ? kDefaultReservedInputs : 0;
+  size_t inputs_size = (input_count + reserve_input_count) * sizeof(Input);
   size_t uses_size = input_count * sizeof(Use);
   int size = static_cast<int>(node_size + inputs_size + uses_size);
   Zone* zone = graph->zone();
   void* buffer = zone->New(size);
-  S* result = new (buffer) S(graph, input_count);
+  S* result = new (buffer) S(graph, input_count, reserve_input_count);
   Input* input =
       reinterpret_cast<Input*>(reinterpret_cast<char*>(buffer) + node_size);
   Use* use =