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

BUG=

Review-Url: https://codereview.chromium.org/2586513002
Cr-Commit-Position: refs/heads/master@{#42139}

src/interpreter/constant-array-builder.cc

@@ -132,13 +132,10 @@ 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;
-    }
     DCHECK(array_index == 0 ||
            base::bits::IsPowerOfTwo32(static_cast<uint32_t>(array_index)));
 #if DEBUG
@@ -151,15 +148,14 @@ 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.
+    size_t padding = slice->capacity() - slice->size();
+    if (static_cast<size_t>(fixed_array->length() - array_index) <= padding) {
+      break;
     }
+    array_index += padding;
   }
-  DCHECK_EQ(array_index, fixed_array->length());
+  DCHECK_GE(array_index, fixed_array->length());
   return fixed_array;
 }