ChangeLog

112012-03-23 Mark Hahnenberg <mhahnenberg@apple.com>

22

        tryReallocate could break the zero-ed memory invariant of CopiedBlocks

        https://bugs.webkit.org/show_bug.cgi?id=82087

        Reviewed by NOBODY (OOPS!).

        Removing this optimization turned out to be ~1% regression on kraken, so I simply 

        undid the modification to the current block if we fail.

        * heap/CopiedSpace.cpp:

        (JSC::CopiedSpace::tryReallocate): Undid the reset in the CopiedAllocator if we fail 

        to reallocate from the current block.

2012-03-23  Mark Hahnenberg  <mhahnenberg@apple.com>

        Simplify memory usage tracking in CopiedSpace

        https://bugs.webkit.org/show_bug.cgi?id=80705

Source/JavaScriptCore/heap/CopiedAllocator.h

@@public:

    bool wasLastAllocation(void*, size_t);

    void startedCopying();

    void resetCurrentBlock(CopiedBlock*);

42 void resetLastAllocation(void*);

    size_t currentCapacity();

private:

@@inline size_t CopiedAllocator::currentCapacity()

    return m_currentBlock->capacity();

}

inline void CopiedAllocator::resetLastAllocation(void* ptr)

{

    m_currentOffset = static_cast<char*>(ptr);

}

} // namespace JSC

#endif

Source/JavaScriptCore/heap/CopiedSpace.cpp

@@CheckedBoolean CopiedSpace::tryReallocate(void** ptr, size_t oldSize, size_t new

        return tryReallocateOversize(ptr, oldSize, newSize);

    if (m_allocator.wasLastAllocation(oldPtr, oldSize)) {

        m_allocator.resetLastAllocation(oldPtr);

        if (m_allocator.fitsInCurrentBlock(newSize))

            return m_allocator.allocate(newSize);

        size_t delta = newSize - oldSize;

        if (m_allocator.fitsInCurrentBlock(delta)) {

            (void)m_allocator.allocate(delta);

            return true;

        }

    }

    void* result = 0;