Change BitmapAdjustPrefetchIterator to accept BlockNumber

BitmapAdjustPrefetchIterator() only used the blockno member of the
passed in TBMIterateResult to ensure that the prefetch iterator and
regular iterator stay in sync. Pass it the BlockNumber only, so that we
can move away from using the TBMIterateResult outside of table AM
specific code.

Author: Melanie Plageman
Reviewed-by: Tomas Vondra, Andres Freund, Heikki Linnakangas
Discussion: https://postgr.es/m/CAAKRu_ZwCwWFeL_H3ia26bP2e7HiKLWt0ZmGXPVwPO6uXq0vaA%40mail.gmail.com

Author: tvondra

src/backend/executor/nodeBitmapHeapscan.c

@@ -52,7 +52,7 @@
 static TupleTableSlot *BitmapHeapNext(BitmapHeapScanState *node);
 static inline void BitmapDoneInitializingSharedState(ParallelBitmapHeapState *pstate);
 static inline void BitmapAdjustPrefetchIterator(BitmapHeapScanState *node,
-												TBMIterateResult *tbmres);
+												BlockNumber blockno);
 static inline void BitmapAdjustPrefetchTarget(BitmapHeapScanState *node);
 static inline void BitmapPrefetch(BitmapHeapScanState *node,
 								  TableScanDesc scan);
@@ -231,7 +231,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
 				break;
 			}
 
-			BitmapAdjustPrefetchIterator(node, tbmres);
+			BitmapAdjustPrefetchIterator(node, tbmres->blockno);
 
 			valid_block = table_scan_bitmap_next_block(scan, tbmres);
 
@@ -342,7 +342,7 @@ BitmapDoneInitializingSharedState(ParallelBitmapHeapState *pstate)
  */
 static inline void
 BitmapAdjustPrefetchIterator(BitmapHeapScanState *node,
-							 TBMIterateResult *tbmres)
+							 BlockNumber blockno)
 {
 #ifdef USE_PREFETCH
 	ParallelBitmapHeapState *pstate = node->pstate;
@@ -361,7 +361,7 @@ BitmapAdjustPrefetchIterator(BitmapHeapScanState *node,
 			/* Do not let the prefetch iterator get behind the main one */
 			TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);
 
-			if (tbmpre == NULL || tbmpre->blockno != tbmres->blockno)
+			if (tbmpre == NULL || tbmpre->blockno != blockno)
 				elog(ERROR, "prefetch and main iterators are out of sync");
 		}
 		return;