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Remove lappend_cell...() family of List functions.

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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
This commit is contained in:
Tom Lane
2019-07-16 13:12:24 -04:00
parent 2f5b8eb5a2
commit c245776906
3 changed files with 6 additions and 62 deletions
Download Patch File Download Diff File Expand all files Collapse all files

17
src/backend/optimizer/geqo/geqo_eval.c
View File

@@ -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;
}