[printing] Fix DCHECK failure when printing FAST_HOLEY_DOUBLE_ELEMENTS

src/objects-printer.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/objects.h"
 
 #include <iomanip>
 #include <memory>
 
 #include "src/disasm.h"
@@ skipping 300 matching lines @@
           break;
       }
     }
   } else if (IsJSGlobalObject()) {
     global_dictionary()->Print(os);
   } else {
     property_dictionary()->Print(os);
   }
 }
 
+namespace {
+
+template <class T>
+double GetScalarElement(T* array, int index) {
+  return array->get_scalar(index);
+}
+
+double GetScalarElement(FixedDoubleArray* array, int index) {
+  if (array->is_the_hole(index)) return kHoleNanDouble;
+  return array->get_scalar(index);
+}
+
+bool is_the_hole(double maybe_hole) {
+  return bit_cast<uint64_t>(maybe_hole) == kHoleNanInt64;
+}
+
+}  // namespace
+
 template <class T, bool print_the_hole>
 static void DoPrintElements(std::ostream& os, Object* object) {  // NOLINT
   T* array = T::cast(object);
   if (array->length() == 0) return;
   int previous_index = 0;
-  double previous_value = array->get_scalar(0);
+  double previous_value = GetScalarElement(array, 0);
   double value = 0.0;
   int i;
   for (i = 1; i <= array->length(); i++) {
-    if (i < array->length()) value = array->get_scalar(i);
+    if (i < array->length()) value = GetScalarElement(array, i);
     bool values_are_nan = std::isnan(previous_value) && std::isnan(value);
     if ((previous_value == value || values_are_nan) && i != array->length()) {
-      continue;
+      // Values are not equal if only one of the is the hole.

[Jakob Kummerow, 2016/08/31 14:56:09]

nit: s/the/them/

+      if (!(is_the_hole(previous_value) ^ is_the_hole(value))) {

[Jakob Kummerow, 2016/08/31 14:56:09]

nit: !(a ^ b) === (a == b)

...and after that replacement I'd also fold it into the previous condition.

+        continue;
+      }
     }
     os << "\n";
     std::stringstream ss;
     ss << previous_index;
     if (previous_index != i - 1) {
       ss << '-' << (i - 1);
     }
     os << std::setw(12) << ss.str() << ": ";
-    if (print_the_hole &&
-        FixedDoubleArray::cast(object)->is_the_hole(previous_index)) {
+    if (print_the_hole && is_the_hole(previous_value)) {
       os << "<the_hole>";
     } else {
       os << previous_value;
     }
     previous_index = i;
     previous_value = value;
   }
 }
 
 
@@ skipping 1162 matching lines @@
     printf("Not a transition array\n");
   } else {
     reinterpret_cast<i::TransitionArray*>(object)->Print();
   }
 }
 
 extern void _v8_internal_Print_StackTrace() {
   i::Isolate* isolate = i::Isolate::Current();
   isolate->PrintStack(stdout);
 }