Compiling an array literal should be context-independent.

src/ast/ast.cc

 // Copyright 2012 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/ast/ast.h"
 
 #include <cmath>  // For isfinite.
 
 #include "src/ast/compile-time-value.h"
 #include "src/ast/prettyprinter.h"
@@ skipping 562 matching lines @@
   set_depth(depth_acc);
 }
 
 
 void ArrayLiteral::BuildConstantElements(Isolate* isolate) {
   DCHECK_LT(first_spread_index_, 0);
 
   if (!constant_elements_.is_null()) return;
 
   int constants_length = values()->length();
-
-  // Allocate a fixed array to hold all the object literals.
-  Handle<JSArray> array = isolate->factory()->NewJSArray(
-      FAST_HOLEY_SMI_ELEMENTS, constants_length, constants_length,
-      INITIALIZE_ARRAY_ELEMENTS_WITH_HOLE);
+  ElementsKind kind = FAST_SMI_ELEMENTS;

[Toon Verwaest, 2016/11/08 10:18:02]

FIRST_FAST_ELEMENTS_KIND?

[Yang, 2016/11/09 07:32:23]

Done.

+  Handle<FixedArray> fixed_array =
+      isolate->factory()->NewFixedArrayWithHoles(constants_length);
 
   // Fill in the literals.
   bool is_simple = true;
   int depth_acc = 1;
   bool is_holey = false;
   int array_index = 0;
   for (; array_index < constants_length; array_index++) {
     Expression* element = values()->at(array_index);
     DCHECK(!element->IsSpread());
     MaterializedLiteral* m_literal = element->AsMaterializedLiteral();
     if (m_literal != NULL) {
       m_literal->BuildConstants(isolate);
       if (m_literal->depth() + 1 > depth_acc) {
         depth_acc = m_literal->depth() + 1;
       }
     }
 
     // New handle scope here, needs to be after BuildContants().
     HandleScope scope(isolate);
     Handle<Object> boilerplate_value = GetBoilerplateValue(element, isolate);
     if (boilerplate_value->IsTheHole(isolate)) {
       is_holey = true;

[Toon Verwaest, 2016/11/08 10:16:54]

if you already do kind = GetHoleyElementsKind(kind) here, you can drop the
is_holey flag and additional branch below.

[Yang, 2016/11/09 07:32:23]

Unfortunately this does not work due to how GetMoreGeneralElementsKind works. We
could go from FAST_SMI_ELEMENTS to FAST_HOLEY_SMI_ELEMENTS, and then upon seeing
a double, go to FAST_DOUBLE_ELEMENTS, but we should have gone to
FAST_HOLEY_DOUBLE_ELEMENTS.

Is this something that needs to be addressed elsewhere?

       continue;
     }
 
     if (boilerplate_value->IsUninitialized(isolate)) {
       boilerplate_value = handle(Smi::kZero, isolate);
       is_simple = false;
     }
 
-    JSObject::AddDataElement(array, array_index, boilerplate_value, NONE)
-        .Assert();
+    kind = GetMoreGeneralElementsKind(kind,
+                                      boilerplate_value->OptimalElementsKind());
+    fixed_array->set(array_index, *boilerplate_value);
   }
 
-  JSObject::ValidateElements(array);
-  Handle<FixedArrayBase> element_values(array->elements());
-
   // Simple and shallow arrays can be lazily copied, we transform the
   // elements array to a copy-on-write array.
   if (is_simple && depth_acc == 1 && array_index > 0 &&
-      array->HasFastSmiOrObjectElements()) {
-    element_values->set_map(isolate->heap()->fixed_cow_array_map());
+      IsFastSmiOrObjectElementsKind(kind)) {
+    fixed_array->set_map(isolate->heap()->fixed_cow_array_map());
   }
 
+  Handle<FixedArrayBase> elements = fixed_array;
+
+  // In case of only double elements, copy over into a FixedDoubleArray.
+  if (IsFastDoubleElementsKind(kind)) {
+    Handle<FixedDoubleArray> fixed_double_array =
+        Handle<FixedDoubleArray>::cast(
+            isolate->factory()->NewFixedDoubleArray(constants_length));
+    for (int i = 0; i < constants_length; i++) {
+      Object* element = fixed_array->get(i);
+      if (element->IsTheHole(isolate)) {
+        DCHECK(is_holey);
+        fixed_double_array->set_the_hole(i);
+      } else {
+        fixed_double_array->set(i, element->Number());

[Toon Verwaest, 2016/11/08 10:16:54]

What about having a CopyElements on the elements accessor that doesn't take a
JSObject* from_holder but FixedArrayBase* from, that way we can use the regular
CopySmiToDoubleElements here. It would look like

if (IsFastDoubleElementsKind(kind)) {
  ElementsAccessor* accessor = ElementsAccessor::ForKind(kind);
  elements = isolate->factory()->NewFixedDoubleArray(constants_length);
  accessor->CopyElements(fixed_array, elements);
}

[Yang, 2016/11/09 07:32:23]

Done.

+      }
+    }
+    elements = fixed_double_array;
+  }
+
+  if (is_holey) kind = GetHoleyElementsKind(kind);
+
   // Remember both the literal's constant values as well as the ElementsKind
   // in a 2-element FixedArray.
   Handle<FixedArray> literals = isolate->factory()->NewFixedArray(2, TENURED);
-
-  ElementsKind kind = array->GetElementsKind();
-  kind = is_holey ? GetHoleyElementsKind(kind) : GetPackedElementsKind(kind);
-
   literals->set(0, Smi::FromInt(kind));
-  literals->set(1, *element_values);
+  literals->set(1, *elements);
 
   constant_elements_ = literals;
   set_is_simple(is_simple);
   set_depth(depth_acc);
 }
 
 
 void ArrayLiteral::AssignFeedbackVectorSlots(Isolate* isolate,
                                              FeedbackVectorSpec* spec,
                                              FeedbackVectorSlotCache* cache) {
@@ skipping 292 matching lines @@
 // static
 bool Literal::Match(void* literal1, void* literal2) {
   const AstValue* x = static_cast<Literal*>(literal1)->raw_value();
   const AstValue* y = static_cast<Literal*>(literal2)->raw_value();
   return (x->IsString() && y->IsString() && x->AsString() == y->AsString()) ||
          (x->IsNumber() && y->IsNumber() && x->AsNumber() == y->AsNumber());
 }
 
 }  // namespace internal
 }  // namespace v8