[generators] Create the fixed array holding the registers only once.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index dbda987b4490c8af83752e2c7dada24c531067ee..2b0d5089d5123359b219524d698f347c1e94bfe9 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -2287,6 +2287,7 @@ bool Heap::CreateInitialMaps() {
     ALLOCATE_MAP(ODDBALL_TYPE, Oddball::kSize, exception);
     ALLOCATE_MAP(ODDBALL_TYPE, Oddball::kSize, termination_exception);
     ALLOCATE_MAP(ODDBALL_TYPE, Oddball::kSize, optimized_out);
+    ALLOCATE_MAP(ODDBALL_TYPE, Oddball::kSize, placeholder);
 
     for (unsigned i = 0; i < arraysize(string_type_table); i++) {
       const StringTypeTable& entry = string_type_table[i];
@@ -2661,6 +2662,11 @@ void Heap::CreateInitialObjects() {
                            handle(Smi::FromInt(-6), isolate()), false,
                            "undefined", Oddball::kOptimizedOut));
 
+  set_placeholder(
+      *factory->NewOddball(factory->placeholder_map(), "placeholder",
+                           handle(Smi::FromInt(-7), isolate()), false,
+                           "undefined", Oddball::kPlaceholder));
+
   for (unsigned i = 0; i < arraysize(constant_string_table); i++) {
     Handle<String> str =
         factory->InternalizeUtf8String(constant_string_table[i].contents);