8346011: [Lilliput] Compact Full-GC Forwarding

[rkennke]

The current forwarding scheme that is used during full-GC overrides much of the mark-word. This is a problem for current compact headers when the heap is larger than 8TB (in which case we currently disable compact headers altogether) and becomes a much worse issue with 4-byte-compact-headers, because it would override the compressed class-pointer in the upper header bits.

This implementation uses a side-table (currently 1/512th of the heap size) to store part of the target addresses, and 9 bits in the header for the rest of it. For the full description of the algorithm, see top of fullGCForwarding.hpp.

Testing:

• hotspot_gc
• tier1
• tier1 +UseSerialGC
• tier1 +UseParallelGC
• tier1 +UseShenandoahGC

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Issue

• JDK-8346011: [Lilliput] Compact Full-GC Forwarding (Enhancement - P4)

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