From 7025d85048468134823cfeec1c84559bb2607634 Mon Sep 17 00:00:00 2001
From: Yuya Watari <watari.yuya@gmail.com>
Date: Mon, 12 Jun 2023 07:33:04 +0900
Subject: [PATCH v2 4/4] Fix a bug where the necessary truncation was missing

---
 src/backend/nodes/bitmapset.c | 53 +++++++++++++++--------------------
 1 file changed, 22 insertions(+), 31 deletions(-)

diff --git a/src/backend/nodes/bitmapset.c b/src/backend/nodes/bitmapset.c
index 1839292d4b..fd59826c00 100644
--- a/src/backend/nodes/bitmapset.c
+++ b/src/backend/nodes/bitmapset.c
@@ -72,8 +72,6 @@
 #error "invalid BITS_PER_BITMAPWORD"
 #endif
 
-static bool bms_is_empty_internal(const Bitmapset *a);
-
 
 /*
  * bms_copy - make a palloc'd copy of a bitmapset
@@ -689,30 +687,6 @@ bms_membership(const Bitmapset *a)
 	return result;
 }
 
-/*
- * bms_is_empty_internal - is a set empty?
- *
- * This is now used only locally, to detect cases where a function has
- * computed an empty set that we must now get rid of.  Hence, we can
- * assume the input isn't NULL.
- */
-static bool
-bms_is_empty_internal(const Bitmapset *a)
-{
-	int			nwords;
-	int			wordnum;
-
-	nwords = a->nwords;
-	wordnum = 0;
-	do {
-		bitmapword	w = a->words[wordnum];
-
-		if (w != 0)
-			return false;
-	} while (++wordnum < nwords);
-	return true;
-}
-
 
 /*
  * These operations all "recycle" their non-const inputs, ie, either
@@ -781,12 +755,29 @@ bms_del_member(Bitmapset *a, int x)
 	wordnum = WORDNUM(x);
 	bitnum = BITNUM(x);
 	if (wordnum < a->nwords)
-		a->words[wordnum] &= ~((bitmapword) 1 << bitnum);
-	/* If we computed an empty result, we must return NULL */
-	if (bms_is_empty_internal(a))
 	{
-		pfree(a);
-		return NULL;
+		a->words[wordnum] &= ~((bitmapword) 1 << bitnum);
+
+		if (a->words[wordnum] == 0)
+		{
+			int		lastnonzero;
+
+			/* If this word became zero, we may have to truncate the result */
+			lastnonzero = a->nwords - 1;
+			do
+			{
+				if (a->words[lastnonzero] != 0)
+					break;
+			} while (--lastnonzero >= 0);
+			/* If we computed an empty result, we must return NULL */
+			if (lastnonzero == -1)
+			{
+				pfree(a);
+				return NULL;
+			}
+			/* get rid of trailing zero words */
+			a->nwords = lastnonzero + 1;
+		}
 	}
 	return a;
 }
-- 
2.41.0.windows.1