Simplify partitionReallocGeneric() implementation

Source/wtf/PartitionAlloc.cpp

 /*
  * Copyright (C) 2013 Google Inc. 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
@@ skipping 757 matching lines @@
 #if defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
     return realloc(ptr, newSize);
 #else
     if (UNLIKELY(!ptr))
         return partitionAllocGeneric(root, newSize);
     if (UNLIKELY(!newSize)) {
         partitionFreeGeneric(root, ptr);
         return 0;
     }
 
+    ASSERT(partitionPointerIsValid(partitionCookieFreePointerAdjust(ptr)));
+
+    size_t actualNewSize = partitionAllocActualSize(root, newSize);
+    size_t actualOldSize = partitionAllocGetSize(ptr);
+
     // TODO: note that tcmalloc will "ignore" a downsizing realloc() unless the
     // new size is a significant percentage smaller. We could do the same if we
     // determine it is a win.
-    void* realPtr = partitionCookieFreePointerAdjust(ptr);
-    ASSERT(partitionPointerIsValid(realPtr));
-    PartitionPage* oldPage = partitionPointerToPage(realPtr);
-    PartitionBucket* oldBucket = oldPage->bucket;
-
-    size_t allocSize = partitionCookieSizeAdjustAdd(newSize);
-    PartitionBucket* newBucket = partitionGenericSizeToBucket(root, allocSize);
-
-    // TODO: for a downsize on a direct mapped allocation, we really should
-    // just de-commit the correct number of pages off the end.
-    if (oldBucket == newBucket)
+    if (actualNewSize == actualOldSize) {
+        // Trying to allocate a block of size newSize would give us a block of
+        // the same size as the one we've already got, so no point in doing
+        // anything here.
+        // TODO: for an upsize or downsize on a direct mapped allocation, we
+        // should really try and resize it in-place.
         return ptr;
+    }
 
     // This realloc cannot be resized in-place. Sadness.
     void* ret = partitionAllocGeneric(root, newSize);
-    size_t copySize = oldPage->bucket->slotSize;
-    copySize = partitionCookieSizeAdjustSubtract(copySize);
+    size_t copySize = actualOldSize;
     if (newSize < copySize)
         copySize = newSize;
 
     memcpy(ret, ptr, copySize);
     partitionFreeGeneric(root, ptr);
     return ret;
 #endif
 }
 
 #ifndef NDEBUG
@@ skipping 47 matching lines @@
     printf("total live: %zu bytes\n", totalLive);
     printf("total resident: %zu bytes\n", totalResident);
     printf("total freeable: %zu bytes\n", totalFreeable);
     fflush(stdout);
 }
 
 #endif // !NDEBUG
 
 } // namespace WTF