Applies on top of v2 and nocfbot-0001.  Not for the CF bot.
Ask the clog only: TransactionIdDidAbort() on xmax.

diff --git a/src/backend/access/heap/heapam_visibility.c b/src/backend/access/heap/heapam_visibility.c
--- a/src/backend/access/heap/heapam_visibility.c
+++ b/src/backend/access/heap/heapam_visibility.c
@@ -1197,10 +1197,15 @@ HeapTupleSatisfiesVacuumHorizon(HeapTuple htup, Buffer buffer, TransactionId *de
 			{
 				TransactionId xmax = HeapTupleHeaderGetUpdateXid(tuple);
 
-				/* xmax == xmin: xmax is in progress too, nothing to do */
+				/*
+				 * xmin is in progress, so xmax is in the inserter's
+				 * transaction tree.  If xmax == xmin, it is in progress
+				 * too.  Otherwise it is running or it is a subtransaction
+				 * that aborted, and the abort reaches the clog before the
+				 * subtransaction leaves the proc array: the clog tells.
+				 */
 				if (!TransactionIdEquals(xmax, HeapTupleHeaderGetRawXmin(tuple)) &&
-					!TransactionIdIsInProgress(xmax) &&
-					!TransactionIdDidCommit(xmax))
+					TransactionIdDidAbort(xmax))
 					SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
 								InvalidTransactionId);
 			}