[Interpreter] Avoid allocating pairs array in VisitDeclarations.

test/unittests/interpreter/constant-array-builder-unittest.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/factory.h"
 #include "src/handles-inl.h"
 #include "src/interpreter/constant-array-builder.h"
 #include "src/isolate.h"
@@ skipping 265 matching lines @@
     Handle<Object> expected;
     if (i == 0 || i == 256 || i == 65536) {
       expected = isolate()->factory()->NewNumber(count++);
     } else {
       expected = isolate()->factory()->the_hole_value();
     }
     CHECK(constant_array->get(i)->SameValue(*expected));
   }
 }
 
+TEST_F(ConstantArrayBuilderTest, AllocateEntriesWithFixedReservations) {
+  ConstantArrayBuilder builder(isolate(), zone());
+  for (size_t i = 0; i < k16BitCapacity; i++) {
+    if ((i % 2) == 0) {
+      CHECK_EQ(i, builder.AllocateEntry());
+    } else {
+      builder.Insert(handle(Smi::FromInt(static_cast<int>(i)), isolate()));
+    }
+  }
+  CHECK_EQ(builder.size(), k16BitCapacity);
+
+  // Check values before reserved entries are inserted.
+  for (size_t i = 0; i < k16BitCapacity; i++) {
+    if ((i % 2) == 0) {
+      // Check reserved values are the hole.
+      Handle<Object> empty = builder.At(i);
+      CHECK(empty->SameValue(isolate()->heap()->the_hole_value()));
+    } else {
+      CHECK_EQ(Handle<Smi>::cast(builder.At(i))->value(), i);
+    }
+  }
+
+  // Insert reserved entries.
+  for (size_t i = 0; i < k16BitCapacity; i += 2) {
+    builder.InsertAllocatedEntry(
+        i, handle(Smi::FromInt(static_cast<int>(i)), isolate()));
+  }
+
+  // Check values after reserved entries are inserted.
+  for (size_t i = 0; i < k16BitCapacity; i++) {
+    CHECK_EQ(Handle<Smi>::cast(builder.At(i))->value(), i);
+  }
+}
+
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8