[ftlopt] StructureSet::onlyStructure() should return nullptr if it's not a singleton (instead of asserting)

[Filip Pizlo]

Patch forthcoming.

[Filip Pizlo]

Created attachment 233385 [details]
the patch

[Ahmad Saleem]

This function is following:

https://searchfox.org/wubkat/rev/dc6a01c9fd207e1b1394a1cb8261b410a1909cf6/Source/JavaScriptCore/bytecode/StructureSet.h#52

    Structure* onlyStructure() const
    {
        return onlyEntry();
    }

While onlyEntry is:

    // Returns the only entry if the array has exactly one entry.
    T onlyEntry() const
    {
        if (isThin())
            return singleEntry();
        OutOfLineList* list = this->list();
        if (list->m_length != 1)
            return T();
        return list->list()[0];
    }

__

Which is similar to proposed patch, so I think it is fixed.

Marking this as 'RESOLVED CONFIGURATION CHANGED' and CCing - Alexey and Yusuke.