[GR-71015] Unset mark status of all objects in fixup phase.

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/CompactingOldGeneration.java

@@ -336,6 +336,17 @@ private void fixupReferencesBeforeCompaction(ChunkReleaser chunkReleaser, Timers
             oldFixupAlignedChunksTimer.stop();
         }
 
+        /*
+         * Check each unaligned object and fix its references if the object is marked. Add the chunk
+         * to the releaser's list in case the object is not marked and therefore won't survive.
+         */
+        Timer oldFixupUnalignedChunksTimer = timers.oldFixupUnalignedChunks.start();
+        try {
+            fixupUnalignedChunkReferences(chunkReleaser);
+        } finally {
+            oldFixupUnalignedChunksTimer.stop();
+        }
+
         Timer oldFixupImageHeapTimer = timers.oldFixupImageHeap.start();
         try {
             for (ImageHeapInfo info : HeapImpl.getImageHeapInfos()) {
@@ -374,17 +385,6 @@ private void fixupReferencesBeforeCompaction(ChunkReleaser chunkReleaser, Timers
             oldFixupStackTimer.stop();
         }
 
-        /*
-         * Check each unaligned object and fix its references if the object is marked. Add the chunk
-         * to the releaser's list in case the object is not marked and therefore won't survive.
-         */
-        Timer oldFixupUnalignedChunksTimer = timers.oldFixupUnalignedChunks.start();
-        try {
-            fixupUnalignedChunkReferences(chunkReleaser);
-        } finally {
-            oldFixupUnalignedChunksTimer.stop();
-        }
-
         Timer oldFixupRuntimeCodeCacheTimer = timers.oldFixupRuntimeCodeCache.start();
         try {
             if (RuntimeCompilation.isEnabled()) {

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/ReferenceObjectProcessing.java

@@ -246,6 +246,7 @@ private static boolean maybeUpdateForwardedReference(Reference<?> dr, Pointer re
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     private static boolean willSurviveThisCollection(Object obj) {
         if (SerialGCOptions.useCompactingOldGen() && GCImpl.getGCImpl().isCompleteCollection()) {
+            // Only for discovery, during processing for enqueuing mark status is already cleared
             return ObjectHeaderImpl.isMarked(obj);
         }
         HeapChunk.Header<?> chunk = HeapChunk.getEnclosingHeapChunk(obj);

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/ObjectMoveInfo.java

@@ -180,6 +180,7 @@ public static void walkObjectsForFixup(AlignedHeapChunk.AlignedHeader chunk, Obj
             while (p.notEqual(objSeqEnd)) {
                 assert p.belowThan(objSeqEnd);
                 Object obj = p.toObjectNonNull();
+                ObjectHeaderImpl.unsetMarkedAndKeepRememberedSetBit(obj);
                 UnsignedWord objSize = LayoutEncoding.getSizeFromObjectInlineInGC(obj);
 
                 /*

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/ObjectRefFixupVisitor.java

@@ -72,7 +72,7 @@ private static void visitObjectReference(Pointer objRef, boolean compressed, Obj
                             || holderObject == null // references from CodeInfo, invalidated or weak
                             || holderObject instanceof Reference<?>; // cleared referent
 
-            Object obj = newLocation.toObjectNonNull();
+            Object obj = newLocation.toObject();
             ReferenceAccess.singleton().writeObjectAt(objRef, obj, compressed);
         }
         // Note that image heap cards have already been cleaned and re-marked during the scan

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/PlanningVisitor.java

@@ -99,8 +99,6 @@ public boolean visitChunk(AlignedHeapChunk.AlignedHeader chunk) {
             }
 
             if (ObjectHeaderImpl.isMarkedHeader(header)) {
-                ObjectHeaderImpl.unsetMarkedAndKeepRememberedSetBit(p.toObjectNonNull());
-
                 /*
                  * Adding the optional identity hash field would increase an object's size, so we
                  * should have copied all objects that need one during marking instead.