[Interpreter] Avoid allocating pairs array in VisitDeclarations.

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

Index: test/unittests/interpreter/constant-array-builder-unittest.cc
diff --git a/test/unittests/interpreter/constant-array-builder-unittest.cc b/test/unittests/interpreter/constant-array-builder-unittest.cc
index c48ac58738c18d8a1f4eb4bbdc1e1a82678c50fb..8bee2452da2466d60b1b838f3eaf1782353f0f33 100644
--- a/test/unittests/interpreter/constant-array-builder-unittest.cc
+++ b/test/unittests/interpreter/constant-array-builder-unittest.cc
@@ -283,6 +283,40 @@ TEST_F(ConstantArrayBuilderTest, ReservationsAtAllScales) {
   }
 }
 
+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