Clear all side forwarding bits #974
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This reverts an optimization which was intended to reduce the number of side forwarding bits cleared for ImmixSpace by clearing the forwarding bits metadata of defrag sources, only. This approach does not work for StickyImmix because it may move young objects, which is not "defrag". Now ImmixSpace clears the on-the-side forwarding bits for all chunks just like how it clears the on-the-side marking bits.
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This reverts an optimization which was intended to reduce the number of side forwarding bits cleared for ImmixSpace by clearing the forwarding bits metadata of defrag sources, only. This approach does not work for StickyImmix because it may move young objects, which is not "defrag".
Now ImmixSpace clears the on-the-side forwarding bits for all chunks just like how it clears the on-the-side marking bits.
This PR prefers correctness over performance, and may degrade the performance of VMs that use on-the-side forwarding bits. Currently it only affects the Ruby binding, but we plan to let the Ruby binding use in-header forwarding states, too. The performance of VMs that use in-header forwarding bits is not affected by this PR.
Fixes: #972