[master] RFR: 8323192: [Lilliput] Implement new Serial Full GC

[Roman Kennke]

This implements a compressor-style compacting full-GC for the Serial GC, which does not require storing any forwarding pointers in object headers.

For a description of the algorithm, see the text block at the beginning of serialCompressor.hpp.

Notice that the algorithm uses extra memory: 1/64th of the heap-size is allocated for the marking bitmap and another 1/64th of the heap-size is allocated for the block-offset-table. On the other hand, it does not use storage for preserved-marks table, which is very unpredictable (often it is quite small, but if a workload churns locks or mass-i-hashes objects, it can become pretty large).

Performance:
I tested performance using the following program, which exxagerates the performance impact of the algorithm. Real-world workloads would be more dominated by the copying.


public class Retain {
        static final int RETAINED = Integer.getInteger("retained", 10_000_000);
        static final int GCS      = Integer.getInteger("gcs", 100);
        static Object[] OBJECTS = new Object[RETAINED];

        public static void main(String... args) {
                for (int t = 0; t < GCS; t++) {
                        for (int c = 0; c < RETAINED; c++) {
                                OBJECTS[c] = new Object();
                        }
                        System.gc();
                }
        }
}



The new algorithm can be tested by:
`java -XX:+UseSerialGC -XX:+UnlockExperimentalVMOptions -XX:+UseCompressorFullGC -Xlog:gc*:file=compressor.txt Retain
`

Average time for full-GCs on by machine:
 - baseline: 394.61ms
 - compressor: 411.61ms (+4.3%)

Testing:
 - [x] tier1 +UseSerialGC +UseFullGCCompressor x86_64
 - [x] tier1 +UseSerialGC +UseFullGCCompressor x86
 - [ ] tier1 +UseSerialGC +UseFullGCCompressor aarch64
 - [x] tier1 +UseSerialGC +UseCompactObjectHeaders x86_64
 - [x] tier1 +UseSerialGC +UseCompactObjectHeaders x86
 - [ ] tier1 +UseSerialGC +UseCompactObjectHeaders aarch64

-------------

Commit messages:
 - Add missing include
 - More cleanups and docs
 - Better space iteration, some docs, etc
 - Array chunking
 - Various stuff
 - Add missing fwd declaration
 - No tabs
 - Initial prototype

Changes: https://git.openjdk.org/lilliput/pull/122/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=122&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323192
  Stats: 871 lines in 11 files changed: 853 ins; 15 del; 3 mod
  Patch: https://git.openjdk.org/lilliput/pull/122.diff
  Fetch: git fetch https://git.openjdk.org/lilliput.git pull/122/head:pull/122

PR: https://git.openjdk.org/lilliput/pull/122