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Commit67b2cee

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Add for_each_from, to simplify loops starting from non-first list cells.
We have a dozen or so places that need to iterate over all but thefirst cell of a List. Prior to v13 this was typically written asfor_each_cell(lc, lnext(list_head(list)))Commit1cff1b9 changed these tofor_each_cell(lc, list, list_second_cell(list))This patch introduces a new macro for_each_from() which expressesthe start point as a list index, allowing these to be written asfor_each_from(lc, list, 1)This is marginally more efficient, since ForEachState.i can beinitialized directly instead of backing into it from a ListCelladdress. It also seems clearer and less typo-prone.Some of the remaining uses of for_each_cell() look like they couldprofitably be changed to for_each_from(), but here I confined myselfto changing uses of list_second_cell().Also, fix for_each_cell_setup() and for_both_cell_setup() toconst-ify their arguments; that's a simple oversight in1cff1b9.Back-patch into v13, on the grounds that (1) the const-ificationis a minor bug fix, and (2) it's better for back-patching purposesif we only have two ways to write these loops rather than three.In HEAD, also remove list_third_cell() and list_fourth_cell(),which were also introduced in1cff1b9, and are unused as ofcc99baa43. It seems unlikely that any third-party code wouldhave started to use them already; anyone who has can be directedto list_nth_cell instead.Discussion:https://postgr.es/m/CAApHDvpo1zj9KhEpU2cCRZfSM3Q6XGdhzuAS2v79PH7WJBkYVA@mail.gmail.com
1 parent61a78c7 commit67b2cee

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9 files changed

+42
-18
lines changed

9 files changed

+42
-18
lines changed

‎src/backend/commands/tablecmds.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -5732,7 +5732,7 @@ ATCheckPartitionsNotInUse(Relation rel, LOCKMODE lockmode)
57325732

57335733
inh = find_all_inheritors(RelationGetRelid(rel), lockmode, NULL);
57345734
/* first element is the parent rel; must ignore it */
5735-
for_each_cell(cell, inh,list_second_cell(inh))
5735+
for_each_from(cell, inh,1)
57365736
{
57375737
Relationchildrel;
57385738

‎src/backend/nodes/nodeFuncs.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -441,7 +441,7 @@ exprTypmod(const Node *expr)
441441
typmod=exprTypmod((Node*)linitial(cexpr->args));
442442
if (typmod<0)
443443
return-1;/* no point in trying harder */
444-
for_each_cell(arg,cexpr->args,list_second_cell(cexpr->args))
444+
for_each_from(arg,cexpr->args,1)
445445
{
446446
Node*e= (Node*)lfirst(arg);
447447

@@ -469,7 +469,7 @@ exprTypmod(const Node *expr)
469469
typmod=exprTypmod((Node*)linitial(mexpr->args));
470470
if (typmod<0)
471471
return-1;/* no point in trying harder */
472-
for_each_cell(arg,mexpr->args,list_second_cell(mexpr->args))
472+
for_each_from(arg,mexpr->args,1)
473473
{
474474
Node*e= (Node*)lfirst(arg);
475475

‎src/backend/optimizer/plan/createplan.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2259,7 +2259,7 @@ create_groupingsets_plan(PlannerInfo *root, GroupingSetsPath *best_path)
22592259
{
22602260
boolis_first_sort= ((RollupData*)linitial(rollups))->is_hashed;
22612261

2262-
for_each_cell(lc,rollups,list_second_cell(rollups))
2262+
for_each_from(lc,rollups,1)
22632263
{
22642264
RollupData*rollup=lfirst(lc);
22652265
AttrNumber*new_grpColIdx;

‎src/backend/optimizer/plan/planner.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -4431,7 +4431,7 @@ consider_groupingsets_paths(PlannerInfo *root,
44314431
* below, must use the same condition.
44324432
*/
44334433
i=0;
4434-
for_each_cell(lc,gd->rollups,list_second_cell(gd->rollups))
4434+
for_each_from(lc,gd->rollups,1)
44354435
{
44364436
RollupData*rollup=lfirst_node(RollupData,lc);
44374437

@@ -4465,7 +4465,7 @@ consider_groupingsets_paths(PlannerInfo *root,
44654465
rollups=list_make1(linitial(gd->rollups));
44664466

44674467
i=0;
4468-
for_each_cell(lc,gd->rollups,list_second_cell(gd->rollups))
4468+
for_each_from(lc,gd->rollups,1)
44694469
{
44704470
RollupData*rollup=lfirst_node(RollupData,lc);
44714471

‎src/backend/parser/parse_agg.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1083,7 +1083,7 @@ parseCheckAggregates(ParseState *pstate, Query *qry)
10831083

10841084
if (gset_common)
10851085
{
1086-
for_each_cell(l,gsets,list_second_cell(gsets))
1086+
for_each_from(l,gsets,1)
10871087
{
10881088
gset_common=list_intersection_int(gset_common,lfirst(l));
10891089
if (!gset_common)
@@ -1774,7 +1774,7 @@ expand_grouping_sets(List *groupingSets, int limit)
17741774
result=lappend(result,list_union_int(NIL, (List*)lfirst(lc)));
17751775
}
17761776

1777-
for_each_cell(lc,expanded_groups,list_second_cell(expanded_groups))
1777+
for_each_from(lc,expanded_groups,1)
17781778
{
17791779
List*p=lfirst(lc);
17801780
List*new_result=NIL;

‎src/backend/utils/adt/jsonpath_gram.y

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -441,7 +441,7 @@ makeItemList(List *list)
441441
while (end->next)
442442
end = end->next;
443443

444-
for_each_cell(cell, list,list_second_cell(list))
444+
for_each_from(cell, list,1)
445445
{
446446
JsonPathParseItem *c = (JsonPathParseItem *)lfirst(cell);
447447

‎src/backend/utils/adt/ruleutils.c

Lines changed: 3 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -8123,7 +8123,7 @@ get_rule_expr(Node *node, deparse_context *context,
81238123
{
81248124
BoolExpr*expr= (BoolExpr*)node;
81258125
Node*first_arg=linitial(expr->args);
8126-
ListCell*arg=list_second_cell(expr->args);
8126+
ListCell*arg;
81278127

81288128
switch (expr->boolop)
81298129
{
@@ -8132,12 +8132,11 @@ get_rule_expr(Node *node, deparse_context *context,
81328132
appendStringInfoChar(buf,'(');
81338133
get_rule_expr_paren(first_arg,context,
81348134
false,node);
8135-
while(arg)
8135+
for_each_from(arg,expr->args,1)
81368136
{
81378137
appendStringInfoString(buf," AND ");
81388138
get_rule_expr_paren((Node*)lfirst(arg),context,
81398139
false,node);
8140-
arg=lnext(expr->args,arg);
81418140
}
81428141
if (!PRETTY_PAREN(context))
81438142
appendStringInfoChar(buf,')');
@@ -8148,12 +8147,11 @@ get_rule_expr(Node *node, deparse_context *context,
81488147
appendStringInfoChar(buf,'(');
81498148
get_rule_expr_paren(first_arg,context,
81508149
false,node);
8151-
while(arg)
8150+
for_each_from(arg,expr->args,1)
81528151
{
81538152
appendStringInfoString(buf," OR ");
81548153
get_rule_expr_paren((Node*)lfirst(arg),context,
81558154
false,node);
8156-
arg=lnext(expr->args,arg);
81578155
}
81588156
if (!PRETTY_PAREN(context))
81598157
appendStringInfoChar(buf,')');

‎src/backend/utils/adt/selfuncs.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3519,7 +3519,7 @@ estimate_num_groups(PlannerInfo *root, List *groupExprs, double input_rows,
35193519
* for remaining Vars on other rels.
35203520
*/
35213521
relvarinfos=lappend(relvarinfos,varinfo1);
3522-
for_each_cell(l,varinfos,list_second_cell(varinfos))
3522+
for_each_from(l,varinfos,1)
35233523
{
35243524
GroupVarInfo*varinfo2= (GroupVarInfo*)lfirst(l);
35253525

‎src/include/nodes/pg_list.h

Lines changed: 29 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -380,6 +380,32 @@ lnext(const List *l, const ListCell *c)
380380
*/
381381
#defineforeach_current_index(cell) (cell##__state.i)
382382

383+
/*
384+
* for_each_from -
385+
* Like foreach(), but start from the N'th (zero-based) list element,
386+
* not necessarily the first one.
387+
*
388+
* It's okay for N to exceed the list length, but not for it to be negative.
389+
*
390+
* The caveats for foreach() apply equally here.
391+
*/
392+
#definefor_each_from(cell,lst,N)\
393+
for (ForEachState cell##__state = for_each_from_setup(lst, N); \
394+
(cell##__state.l != NIL && \
395+
cell##__state.i < cell##__state.l->length) ? \
396+
(cell = &cell##__state.l->elements[cell##__state.i], true) : \
397+
(cell = NULL, false); \
398+
cell##__state.i++)
399+
400+
staticinlineForEachState
401+
for_each_from_setup(constList*lst,intN)
402+
{
403+
ForEachStater= {lst,N};
404+
405+
Assert(N >=0);
406+
returnr;
407+
}
408+
383409
/*
384410
* for_each_cell -
385411
* a convenience macro which loops through a list starting from a
@@ -396,7 +422,7 @@ lnext(const List *l, const ListCell *c)
396422
cell##__state.i++)
397423

398424
staticinlineForEachState
399-
for_each_cell_setup(List*lst,ListCell*initcell)
425+
for_each_cell_setup(constList*lst,constListCell*initcell)
400426
{
401427
ForEachStater= {lst,
402428
initcell ?list_cell_number(lst,initcell) :list_length(lst)};
@@ -447,8 +473,8 @@ for_each_cell_setup(List *lst, ListCell *initcell)
447473
cell1##__state.i1++, cell1##__state.i2++)
448474

449475
staticinlineForBothCellState
450-
for_both_cell_setup(List*list1,ListCell*initcell1,
451-
List*list2,ListCell*initcell2)
476+
for_both_cell_setup(constList*list1,constListCell*initcell1,
477+
constList*list2,constListCell*initcell2)
452478
{
453479
ForBothCellStater= {list1,list2,
454480
initcell1 ?list_cell_number(list1,initcell1) :list_length(list1),

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