From c245776906b065fcd59831a25c3b24ad3ddcd849 Mon Sep 17 00:00:00 2001
From: Tom Lane
Date: Tue, 16 Jul 2019 13:12:24 -0400
Subject: Remove lappend_cell...() family of List functions.

It seems worth getting rid of these functions because they require the
caller to retain a ListCell pointer into a List that it's modifying,
which is a dangerous practice with the new List implementation.
(The only other List-modifying function that takes a ListCell pointer
as input is list_delete_cell, which nowadays is preferentially used
via the constrained API foreach_delete_current.)

There was only one remaining caller of these functions after commit
2f5b8eb5a, and that was some fairly ugly GEQO code that can be much
more clearly expressed using a list-index variable and list_insert_nth.
Hence, rewrite that code, and remove the functions.

Discussion: https://postgr.es/m/26193.1563228600@sss.pgh.pa.us
---
 src/backend/optimizer/geqo/geqo_eval.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

(limited to 'src/backend/optimizer')

diff --git a/src/backend/optimizer/geqo/geqo_eval.c b/src/backend/optimizer/geqo/geqo_eval.c
index 8a44ac8530d..7b67a29c88a 100644
--- a/src/backend/optimizer/geqo/geqo_eval.c
+++ b/src/backend/optimizer/geqo/geqo_eval.c
@@ -239,6 +239,7 @@ merge_clump(PlannerInfo *root, List *clumps, Clump *new_clump, int num_gene,
 			bool force)
 {
 	ListCell   *lc;
+	int			pos;
 
 	/* Look for a clump that new_clump can join to */
 	foreach(lc, clumps)
@@ -304,21 +305,15 @@ merge_clump(PlannerInfo *root, List *clumps, Clump *new_clump, int num_gene,
 	if (clumps == NIL || new_clump->size == 1)
 		return lappend(clumps, new_clump);
 
-	/* Check if it belongs at the front */
-	lc = list_head(clumps);
-	if (new_clump->size > ((Clump *) lfirst(lc))->size)
-		return lcons(new_clump, clumps);
-
 	/* Else search for the place to insert it */
-	for (;;)
+	for (pos = 0; pos < list_length(clumps); pos++)
 	{
-		ListCell   *nxt = lnext(clumps, lc);
+		Clump	   *old_clump = (Clump *) list_nth(clumps, pos);
 
-		if (nxt == NULL || new_clump->size > ((Clump *) lfirst(nxt))->size)
-			break;				/* it belongs after 'lc', before 'nxt' */
-		lc = nxt;
+		if (new_clump->size > old_clump->size)
+			break;				/* new_clump belongs before old_clump */
 	}
-	lappend_cell(clumps, lc, new_clump);
+	clumps = list_insert_nth(clumps, pos, new_clump);
 
 	return clumps;
 }
-- 
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