Remove bms_first_member().

This function has been semi-deprecated ever since we invented
bms_next_member().  Its habit of scribbling on the input bitmapset
isn't great, plus for sufficiently large bitmapsets it would take
O(N^2) time to complete a loop.  Now we have the additional problem
that reducing the input to empty while leaving it still accessible
would violate a planned invariant.  So let's just get rid of it,
after updating the few extant callers to use bms_next_member().

Patch by me; thanks to Nathan Bossart and Richard Guo for review.

Discussion: https://postgr.es/m/1159933.1677621588@sss.pgh.pa.us

contrib/file_fdw/file_fdw.c

@@ -858,7 +858,7 @@ check_selective_binary_conversion(RelOptInfo *baserel,
 	ListCell   *lc;
 	Relation	rel;
 	TupleDesc	tupleDesc;
-	AttrNumber	attnum;
+	int			attidx;
 	Bitmapset  *attrs_used = NULL;
 	bool		has_wholerow = false;
 	int			numattrs;
@@ -901,10 +901,11 @@ check_selective_binary_conversion(RelOptInfo *baserel,
 	rel = table_open(foreigntableid, AccessShareLock);
 	tupleDesc = RelationGetDescr(rel);
 
-	while ((attnum = bms_first_member(attrs_used)) >= 0)
+	attidx = -1;
+	while ((attidx = bms_next_member(attrs_used, attidx)) >= 0)
 	{
-		/* Adjust for system attributes. */
+		/* attidx is zero-based, attnum is the normal attribute number */
-		attnum += FirstLowInvalidHeapAttributeNumber;
+		AttrNumber	attnum = attidx + FirstLowInvalidHeapAttributeNumber;
 
 		if (attnum == 0)
 		{

contrib/sepgsql/dml.c

@@ -231,7 +231,8 @@ check_relation_privileges(Oid relOid,
 	updated = fixup_whole_row_references(relOid, updated);
 	columns = bms_union(selected, bms_union(inserted, updated));
 
-	while ((index = bms_first_member(columns)) >= 0)
+	index = -1;
+	while ((index = bms_next_member(columns, index)) >= 0)
 	{
 		AttrNumber	attnum;
 		uint32		column_perms = 0;

src/backend/access/heap/heapam.c

@@ -3859,9 +3859,6 @@ heap_attr_equals(TupleDesc tupdesc, int attrnum, Datum value1, Datum value2,
  * has_external indicates if any of the unmodified attributes (from those
  * listed as interesting) of the old tuple is a member of external_cols and is
  * stored externally.
- *
- * The input interesting_cols bitmapset is destructively modified; that is OK
- * since this is invoked at most once in heap_update.
  */
 static Bitmapset *
 HeapDetermineColumnsInfo(Relation relation,
@@ -3870,19 +3867,20 @@ HeapDetermineColumnsInfo(Relation relation,
 						 HeapTuple oldtup, HeapTuple newtup,
 						 bool *has_external)
 {
-	int			attrnum;
+	int			attidx;
 	Bitmapset  *modified = NULL;
 	TupleDesc	tupdesc = RelationGetDescr(relation);
 
-	while ((attrnum = bms_first_member(interesting_cols)) >= 0)
+	attidx = -1;
+	while ((attidx = bms_next_member(interesting_cols, attidx)) >= 0)
 	{
+		/* attidx is zero-based, attrnum is the normal attribute number */
+		AttrNumber	attrnum = attidx + FirstLowInvalidHeapAttributeNumber;
 		Datum		value1,
 					value2;
 		bool		isnull1,
 					isnull2;
 
-		attrnum += FirstLowInvalidHeapAttributeNumber;
-
 		/*
 		 * If it's a whole-tuple reference, say "not equal".  It's not really
 		 * worth supporting this case, since it could only succeed after a
@@ -3890,9 +3888,7 @@ HeapDetermineColumnsInfo(Relation relation,
 		 */
 		if (attrnum == 0)
 		{
-			modified = bms_add_member(modified,
+			modified = bms_add_member(modified, attidx);
-									  attrnum -
-									  FirstLowInvalidHeapAttributeNumber);
 			continue;
 		}
 
@@ -3905,9 +3901,7 @@ HeapDetermineColumnsInfo(Relation relation,
 		{
 			if (attrnum != TableOidAttributeNumber)
 			{
-				modified = bms_add_member(modified,
+				modified = bms_add_member(modified, attidx);
-										  attrnum -
-										  FirstLowInvalidHeapAttributeNumber);
 				continue;
 			}
 		}
@@ -3924,9 +3918,7 @@ HeapDetermineColumnsInfo(Relation relation,
 		if (!heap_attr_equals(tupdesc, attrnum, value1,
 							  value2, isnull1, isnull2))
 		{
-			modified = bms_add_member(modified,
+			modified = bms_add_member(modified, attidx);
-									  attrnum -
-									  FirstLowInvalidHeapAttributeNumber);
 			continue;
 		}
 
@@ -3943,8 +3935,7 @@ HeapDetermineColumnsInfo(Relation relation,
 		 * member of external_cols.
 		 */
 		if (VARATT_IS_EXTERNAL((struct varlena *) DatumGetPointer(value1)) &&
-			bms_is_member(attrnum - FirstLowInvalidHeapAttributeNumber,
+			bms_is_member(attidx, external_cols))
-						  external_cols))
 			*has_external = true;
 	}
 

src/backend/executor/nodeAgg.c

@@ -1646,7 +1646,8 @@ find_hash_columns(AggState *aggstate)
 		}
 
 		/* and add the remaining columns */
-		while ((i = bms_first_member(colnos)) >= 0)
+		i = -1;
+		while ((i = bms_next_member(colnos, i)) >= 0)
 		{
 			perhash->hashGrpColIdxInput[perhash->numhashGrpCols] = i;
 			perhash->numhashGrpCols++;

src/backend/nodes/bitmapset.c

@@ -982,48 +982,6 @@ bms_join(Bitmapset *a, Bitmapset *b)
 	return result;
 }
 
-/*
- * bms_first_member - find and remove first member of a set
- *
- * Returns -1 if set is empty.  NB: set is destructively modified!
- *
- * This is intended as support for iterating through the members of a set.
- * The typical pattern is
- *
- *			while ((x = bms_first_member(inputset)) >= 0)
- *				process member x;
- *
- * CAUTION: this destroys the content of "inputset".  If the set must
- * not be modified, use bms_next_member instead.
- */
-int
-bms_first_member(Bitmapset *a)
-{
-	int			nwords;
-	int			wordnum;
-
-	if (a == NULL)
-		return -1;
-	nwords = a->nwords;
-	for (wordnum = 0; wordnum < nwords; wordnum++)
-	{
-		bitmapword	w = a->words[wordnum];
-
-		if (w != 0)
-		{
-			int			result;
-
-			w = RIGHTMOST_ONE(w);
-			a->words[wordnum] &= ~w;
-
-			result = wordnum * BITS_PER_BITMAPWORD;
-			result += bmw_rightmost_one_pos(w);
-			return result;
-		}
-	}
-	return -1;
-}
-
 /*
  * bms_next_member - find next member of a set
  *

src/backend/optimizer/plan/subselect.c

@@ -1481,7 +1481,8 @@ convert_EXISTS_sublink_to_join(PlannerInfo *root, SubLink *sublink,
 	 */
 	clause_varnos = pull_varnos(root, whereClause);
 	upper_varnos = NULL;
-	while ((varno = bms_first_member(clause_varnos)) >= 0)
+	varno = -1;
+	while ((varno = bms_next_member(clause_varnos, varno)) >= 0)
 	{
 		if (varno <= rtoffset)
 			upper_varnos = bms_add_member(upper_varnos, varno);

src/backend/parser/parse_expr.c

@@ -2759,7 +2759,7 @@ make_row_comparison_op(ParseState *pstate, List *opname,
 	 * them ... this coding arbitrarily picks the lowest btree strategy
 	 * number.
 	 */
-	i = bms_first_member(strats);
+	i = bms_next_member(strats, -1);
 	if (i < 0)
 	{
 		/* No common interpretation, so fail */

src/backend/replication/logical/relation.c

@@ -227,7 +227,8 @@ logicalrep_report_missing_attrs(LogicalRepRelation *remoterel,
 
 		initStringInfo(&missingattsbuf);
 
-		while ((i = bms_first_member(missingatts)) >= 0)
+		i = -1;
+		while ((i = bms_next_member(missingatts, i)) >= 0)
 		{
 			missingattcnt++;
 			if (missingattcnt == 1)

src/include/nodes/bitmapset.h

@@ -115,7 +115,6 @@ extern Bitmapset *bms_del_members(Bitmapset *a, const Bitmapset *b);
 extern Bitmapset *bms_join(Bitmapset *a, Bitmapset *b);
 
 /* support for iterating through the integer elements of a set: */
-extern int	bms_first_member(Bitmapset *a);
 extern int	bms_next_member(const Bitmapset *a, int prevbit);
 extern int	bms_prev_member(const Bitmapset *a, int prevbit);