Optimization of some packed array cases.

src/objects.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 10005 matching lines @@
       if (backing_store->IsDictionary()) {
         SeededNumberDictionary* dictionary =
             SeededNumberDictionary::cast(backing_store);
         *capacity = dictionary->Capacity();
         *used = dictionary->NumberOfElements();
         break;
       }
       // Fall through.
     case FAST_SMI_ELEMENTS:
     case FAST_ELEMENTS:
+      if (FLAG_packed_arrays && IsJSArray()) {

[Jakob Kummerow, 2012/06/12 12:50:44]

This flag check isn't necessary, as we can't have PACKED elements kinds without
the flag anyway. Same below.

[danno, 2012/06/12 15:38:14]

Done.

+        *capacity = backing_store_base->length();
+        *used = Smi::cast(JSArray::cast(this)->length())->value();
+        break;
+      }
+      // Fall through if packing is not guaranteed.
     case FAST_HOLEY_SMI_ELEMENTS:
     case FAST_HOLEY_ELEMENTS:
       backing_store = FixedArray::cast(backing_store_base);
       *capacity = backing_store->length();
       for (int i = 0; i < *capacity; ++i) {
         if (!backing_store->get(i)->IsTheHole()) ++(*used);
       }
       break;
     case DICTIONARY_ELEMENTS: {
       SeededNumberDictionary* dictionary =
           SeededNumberDictionary::cast(FixedArray::cast(elements()));
       *capacity = dictionary->Capacity();
       *used = dictionary->NumberOfElements();
       break;
     }
     case FAST_DOUBLE_ELEMENTS:
+      if (FLAG_packed_arrays && IsJSArray()) {
+        *capacity = backing_store_base->length();
+        *used = Smi::cast(JSArray::cast(this)->length())->value();
+        break;
+      }
+      // Fall through if packing is not guaranteed.
     case FAST_HOLEY_DOUBLE_ELEMENTS: {
       FixedDoubleArray* elms = FixedDoubleArray::cast(elements());
       *capacity = elms->length();
       for (int i = 0; i < *capacity; i++) {
         if (!elms->is_the_hole(i)) ++(*used);
       }
       break;
     }
     case EXTERNAL_BYTE_ELEMENTS:
     case EXTERNAL_UNSIGNED_BYTE_ELEMENTS:
@@ skipping 3132 matching lines @@
   set_year(Smi::FromInt(year), SKIP_WRITE_BARRIER);
   set_month(Smi::FromInt(month), SKIP_WRITE_BARRIER);
   set_day(Smi::FromInt(day), SKIP_WRITE_BARRIER);
   set_weekday(Smi::FromInt(weekday), SKIP_WRITE_BARRIER);
   set_hour(Smi::FromInt(hour), SKIP_WRITE_BARRIER);
   set_min(Smi::FromInt(min), SKIP_WRITE_BARRIER);
   set_sec(Smi::FromInt(sec), SKIP_WRITE_BARRIER);
 }
 
 } }  // namespace v8::internal