[ignition] Prefill the constant array with holes to avoid needing to write padding holes

src/interpreter/constant-array-builder.cc

Index: src/interpreter/constant-array-builder.cc
diff --git a/src/interpreter/constant-array-builder.cc b/src/interpreter/constant-array-builder.cc
index d2b799562383dd87c5210509bff00061436d6573..ba79a5b00a12313b14e0aea48262c4b59dcdc0da 100644
--- a/src/interpreter/constant-array-builder.cc
+++ b/src/interpreter/constant-array-builder.cc
@@ -126,13 +126,12 @@ Handle<FixedArray> ConstantArrayBuilder::ToFixedArray(Isolate* isolate) {
                          handle(reserved_smi.first, isolate));
   }
 
-  Handle<FixedArray> fixed_array = isolate->factory()->NewFixedArray(
+  Handle<FixedArray> fixed_array = isolate->factory()->NewFixedArrayWithHoles(
       static_cast<int>(size()), PretenureFlag::TENURED);
   int array_index = 0;
   for (const ConstantArraySlice* slice : idx_slice_) {
-    if (array_index == fixed_array->length()) {
-      break;
-    }
+    if (array_index >= fixed_array->length()) break;
+
     DCHECK(array_index == 0 ||
            base::bits::IsPowerOfTwo32(static_cast<uint32_t>(array_index)));
     // Different slices might contain the same element due to reservations, but
@@ -143,15 +142,9 @@ Handle<FixedArray> ConstantArrayBuilder::ToFixedArray(Isolate* isolate) {
     for (size_t i = 0; i < slice->size(); ++i) {
       fixed_array->set(array_index++, *slice->At(slice->start_index() + i));
     }
-    // Insert holes where reservations led to unused slots.
-    size_t padding =
-        std::min(static_cast<size_t>(fixed_array->length() - array_index),
-                 slice->capacity() - slice->size());
-    for (size_t i = 0; i < padding; i++) {
-      fixed_array->set(array_index++, *the_hole_value());
-    }
+    // Leave holes where reservations led to unused slots.
+    array_index += slice->capacity() - slice->size();
   }
-  DCHECK_EQ(array_index, fixed_array->length());

[Leszek Swirski, 2016/12/16 16:50:54]

I would keep this check, as a DCHECK_GE

   return fixed_array;
 }