With >= 64 non-string instance types, I removed an optimization

src/objects.h

 // 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 561 matching lines @@
 
 // We use the full 8 bits of the instance_type field to encode heap object
 // instance types.  The high-order bit (bit 7) is set if the object is not a
 // string, and cleared if it is a string.
 const uint32_t kIsNotStringMask = 0x80;
 const uint32_t kStringTag = 0x0;
 const uint32_t kNotStringTag = 0x80;
 
 // Bit 6 indicates that the object is an internalized string (if set) or not.
 // Bit 7 has to be clear as well.
-const uint32_t kIsInternalizedMask = 0x40;
-const uint32_t kNotInternalizedTag = 0x0;
-const uint32_t kInternalizedTag = 0x40;
+const uint32_t kIsNotInternalizedMask = 0x40;
+const uint32_t kNotInternalizedTag = 0x40;
+const uint32_t kInternalizedTag = 0x0;
 
 // If bit 7 is clear then bit 2 indicates whether the string consists of
 // two-byte characters or one-byte characters.
 const uint32_t kStringEncodingMask = 0x4;
 const uint32_t kTwoByteStringTag = 0x0;
 const uint32_t kOneByteStringTag = 0x4;
 
 // If bit 7 is clear, the low-order 2 bits indicate the representation
 // of the string.
 const uint32_t kStringRepresentationMask = 0x03;
@@ skipping 28 matching lines @@
 const uint32_t kShortExternalStringTag = 0x10;
 
 
 // A ConsString with an empty string as the right side is a candidate
 // for being shortcut by the garbage collector unless it is internalized.
 // It's not common to have non-flat internalized strings, so we do not
 // shortcut them thereby avoiding turning internalized strings into strings.
 // See heap.cc and mark-compact.cc.
 const uint32_t kShortcutTypeMask =
     kIsNotStringMask |
-    kIsInternalizedMask |
+    kIsNotInternalizedMask |
     kStringRepresentationMask;
-const uint32_t kShortcutTypeTag = kConsStringTag;
+const uint32_t kShortcutTypeTag = kConsStringTag | kNotInternalizedTag;
 
 
 enum InstanceType {
   // String types.
-  STRING_TYPE = kTwoByteStringTag | kSeqStringTag,
-  ASCII_STRING_TYPE = kOneByteStringTag | kSeqStringTag,
-  CONS_STRING_TYPE = kTwoByteStringTag | kConsStringTag,
-  CONS_ASCII_STRING_TYPE = kOneByteStringTag | kConsStringTag,
-  SLICED_STRING_TYPE = kTwoByteStringTag | kSlicedStringTag,
-  SLICED_ASCII_STRING_TYPE = kOneByteStringTag | kSlicedStringTag,
-  EXTERNAL_STRING_TYPE = kTwoByteStringTag | kExternalStringTag,
-  EXTERNAL_ASCII_STRING_TYPE = kOneByteStringTag | kExternalStringTag,
+  INTERNALIZED_STRING_TYPE = kTwoByteStringTag | kSeqStringTag,

[Yang, 2013/07/19 09:45:06]

I would prefer to have the kInternalizedTag added here as well, otherwise we are
implicating that kInternalizedTag == 0.

Same for all the other ones. It's a bit convoluted, but we only do it this once
here.

[mvstanton, 2013/07/19 11:07:42]

Done.

+  ASCII_INTERNALIZED_STRING_TYPE = kOneByteStringTag | kSeqStringTag,
+  CONS_INTERNALIZED_STRING_TYPE = kTwoByteStringTag | kConsStringTag,
+  CONS_ASCII_INTERNALIZED_STRING_TYPE = kOneByteStringTag | kConsStringTag,
+  EXTERNAL_INTERNALIZED_STRING_TYPE = kTwoByteStringTag | kExternalStringTag,
+  EXTERNAL_ASCII_INTERNALIZED_STRING_TYPE = kOneByteStringTag
+      | kExternalStringTag,
+  EXTERNAL_INTERNALIZED_STRING_WITH_ONE_BYTE_DATA_TYPE =
+      EXTERNAL_INTERNALIZED_STRING_TYPE | kOneByteDataHintTag,
+  SHORT_EXTERNAL_INTERNALIZED_STRING_TYPE =
+      EXTERNAL_INTERNALIZED_STRING_TYPE | kShortExternalStringTag,
+  SHORT_EXTERNAL_ASCII_INTERNALIZED_STRING_TYPE =
+      EXTERNAL_ASCII_INTERNALIZED_STRING_TYPE | kShortExternalStringTag,
+  SHORT_EXTERNAL_INTERNALIZED_STRING_WITH_ONE_BYTE_DATA_TYPE =
+      EXTERNAL_INTERNALIZED_STRING_WITH_ONE_BYTE_DATA_TYPE
+      | kShortExternalStringTag,
+
+  STRING_TYPE = INTERNALIZED_STRING_TYPE | kNotInternalizedTag,
+  ASCII_STRING_TYPE = ASCII_INTERNALIZED_STRING_TYPE | kNotInternalizedTag,
+  CONS_STRING_TYPE = CONS_INTERNALIZED_STRING_TYPE | kNotInternalizedTag,
+  CONS_ASCII_STRING_TYPE =
+      CONS_ASCII_INTERNALIZED_STRING_TYPE | kNotInternalizedTag,
+
+  SLICED_STRING_TYPE =
+      kTwoByteStringTag | kSlicedStringTag | kNotInternalizedTag,
+  SLICED_ASCII_STRING_TYPE =
+      kOneByteStringTag | kSlicedStringTag | kNotInternalizedTag,
+  EXTERNAL_STRING_TYPE =
+  EXTERNAL_INTERNALIZED_STRING_TYPE | kNotInternalizedTag,
+  EXTERNAL_ASCII_STRING_TYPE =
+  EXTERNAL_ASCII_INTERNALIZED_STRING_TYPE | kNotInternalizedTag,
   EXTERNAL_STRING_WITH_ONE_BYTE_DATA_TYPE =
-      EXTERNAL_STRING_TYPE | kOneByteDataHintTag,
-  SHORT_EXTERNAL_STRING_TYPE = EXTERNAL_STRING_TYPE | kShortExternalStringTag,
+      EXTERNAL_INTERNALIZED_STRING_WITH_ONE_BYTE_DATA_TYPE
+      | kNotInternalizedTag,
+  SHORT_EXTERNAL_STRING_TYPE =
+      SHORT_EXTERNAL_INTERNALIZED_STRING_TYPE | kNotInternalizedTag,
   SHORT_EXTERNAL_ASCII_STRING_TYPE =
-      EXTERNAL_ASCII_STRING_TYPE | kShortExternalStringTag,
+      SHORT_EXTERNAL_ASCII_INTERNALIZED_STRING_TYPE | kNotInternalizedTag,
   SHORT_EXTERNAL_STRING_WITH_ONE_BYTE_DATA_TYPE =
-      EXTERNAL_STRING_WITH_ONE_BYTE_DATA_TYPE | kShortExternalStringTag,
-
-  INTERNALIZED_STRING_TYPE = STRING_TYPE | kInternalizedTag,
-  ASCII_INTERNALIZED_STRING_TYPE = ASCII_STRING_TYPE | kInternalizedTag,
-  CONS_INTERNALIZED_STRING_TYPE = CONS_STRING_TYPE | kInternalizedTag,
-  CONS_ASCII_INTERNALIZED_STRING_TYPE =
-      CONS_ASCII_STRING_TYPE | kInternalizedTag,
-  EXTERNAL_INTERNALIZED_STRING_TYPE = EXTERNAL_STRING_TYPE | kInternalizedTag,
-  EXTERNAL_ASCII_INTERNALIZED_STRING_TYPE =
-      EXTERNAL_ASCII_STRING_TYPE | kInternalizedTag,
-  EXTERNAL_INTERNALIZED_STRING_WITH_ONE_BYTE_DATA_TYPE =
-      EXTERNAL_STRING_WITH_ONE_BYTE_DATA_TYPE | kInternalizedTag,
-  SHORT_EXTERNAL_INTERNALIZED_STRING_TYPE =
-      SHORT_EXTERNAL_STRING_TYPE | kInternalizedTag,
-  SHORT_EXTERNAL_ASCII_INTERNALIZED_STRING_TYPE =
-      SHORT_EXTERNAL_ASCII_STRING_TYPE | kInternalizedTag,
-  SHORT_EXTERNAL_INTERNALIZED_STRING_WITH_ONE_BYTE_DATA_TYPE =
-      SHORT_EXTERNAL_STRING_WITH_ONE_BYTE_DATA_TYPE | kInternalizedTag,
+      SHORT_EXTERNAL_INTERNALIZED_STRING_WITH_ONE_BYTE_DATA_TYPE
+      | kNotInternalizedTag,
 
   // Non-string names
   SYMBOL_TYPE = kNotStringTag,  // LAST_NAME_TYPE, FIRST_NONSTRING_TYPE
 
   // Objects allocated in their own spaces (never in new space).
   MAP_TYPE,
   CODE_TYPE,
   ODDBALL_TYPE,
   CELL_TYPE,
   PROPERTY_CELL_TYPE,
@@ skipping 9153 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_