Further robustify the keyed lookup cache against unlucky hash

src/heap.cc

Index: src/heap.cc
===================================================================
--- src/heap.cc	(revision 10474)
+++ src/heap.cc	(working copy)
@@ -6523,16 +6523,12 @@
 
 int KeyedLookupCache::Lookup(Map* map, String* name) {
   int index = (Hash(map, name) & kHashMask);
-  Key& key = keys_[index];
-  if ((key.map == map) && key.name->Equals(name)) {
-    return field_offsets_[index];
+  for (int i = 0; i < kEntriesPerBucket; i++) {
+    Key& key = keys_[index + i];
+    if ((key.map == map) && key.name->Equals(name)) {
+      return field_offsets_[index + i];
+    }
   }
-  ASSERT(kEntriesPerBucket == 2);  // There are two entries to check.
-  // First entry in the bucket missed, check the second.
-  Key& key2 = keys_[index + 1];
-  if ((key2.map == map) && key2.name->Equals(name)) {
-    return field_offsets_[index + 1];
-  }
   return kNotFound;
 }
 
@@ -6541,13 +6537,29 @@
   String* symbol;
   if (HEAP->LookupSymbolIfExists(name, &symbol)) {
     int index = (Hash(map, symbol) & kHashMask);
+    // After a GC there will be free slots, so we use them in order (this may
+    // help to get the most frequently used one in position 0).
+    for (int i = 0; i< kEntriesPerBucket; i++) {
+      Key& key = keys_[index];
+      Object* free_entry_indicator = NULL;
+      if (key.map == free_entry_indicator) {
+        key.map = map;
+        key.name = symbol;
+        field_offsets_[index + i] = field_offset;
+        return;
+      }
+    }
+    // No free entry found in this bucket, so we move them all down one and
+    // put the new entry at position zero.
+    for (int i = kEntriesPerBucket - 1; i > 0; i--) {
+      Key& key = keys_[index + i];
+      Key& key2 = keys_[index + i - 1];
+      key = key2;
+      field_offsets_[index + i] = field_offsets_[index + i - 1];
+    }
+
+    // Write the new first entry.
     Key& key = keys_[index];
-    Key& key2 = keys_[index + 1];  // Second entry in the bucket.
-    // Demote the first entry to the second in the bucket.
-    key2.map = key.map;
-    key2.name = key.name;
-    field_offsets_[index + 1] = field_offsets_[index];
-    // Write the new first entry.
     key.map = map;
     key.name = symbol;
     field_offsets_[index] = field_offset;