[postgresql] / src / backend / optimizer / plan / subselect.c

/*-------------------------------------------------------------------------
 *
 * subselect.c
 *        Planning routines for subselects and parameters.
 *
 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *        $PostgreSQL: pgsql/src/backend/optimizer/plan/subselect.c,v 1.133 2008/08/14 18:47:59 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/pg_operator.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/planmain.h"
#include "optimizer/planner.h"
#include "optimizer/prep.h"
#include "optimizer/subselect.h"
#include "optimizer/var.h"
#include "parser/parse_expr.h"
#include "parser/parse_relation.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteManip.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"


typedef struct convert_testexpr_context
{
        PlannerInfo *root;
        List       *subst_nodes;        /* Nodes to substitute for Params */
} convert_testexpr_context;

typedef struct process_sublinks_context
{
        PlannerInfo *root;
        bool            isTopQual;
} process_sublinks_context;

typedef struct finalize_primnode_context
{
        PlannerInfo *root;
        Bitmapset  *paramids;           /* Non-local PARAM_EXEC paramids found */
} finalize_primnode_context;


static List *generate_subquery_params(PlannerInfo *root, List *tlist,
                                                                          List **paramIds);
static List *generate_subquery_vars(PlannerInfo *root, List *tlist,
                                                                        Index varno);
static Node *convert_testexpr(PlannerInfo *root,
                                 Node *testexpr,
                                 List *subst_nodes);
static Node *convert_testexpr_mutator(Node *node,
                                                 convert_testexpr_context *context);
static bool subplan_is_hashable(SubLink *slink, SubPlan *node, Plan *plan);
static bool hash_ok_operator(OpExpr *expr);
static bool simplify_EXISTS_query(Query *query);
static Node *replace_correlation_vars_mutator(Node *node, PlannerInfo *root);
static Node *process_sublinks_mutator(Node *node,
                                                 process_sublinks_context *context);
static Bitmapset *finalize_plan(PlannerInfo *root,
                          Plan *plan,
                          Bitmapset *valid_params);
static bool finalize_primnode(Node *node, finalize_primnode_context *context);


/*
 * Generate a Param node to replace the given Var,
 * which is expected to have varlevelsup > 0 (ie, it is not local).
 */
static Param *
replace_outer_var(PlannerInfo *root, Var *var)
{
        Param      *retval;
        ListCell   *ppl;
        PlannerParamItem *pitem;
        Index           abslevel;
        int                     i;

        Assert(var->varlevelsup > 0 && var->varlevelsup < root->query_level);
        abslevel = root->query_level - var->varlevelsup;

        /*
         * If there's already a paramlist entry for this same Var, just use it.
         * NOTE: in sufficiently complex querytrees, it is possible for the same
         * varno/abslevel to refer to different RTEs in different parts of the
         * parsetree, so that different fields might end up sharing the same Param
         * number.      As long as we check the vartype as well, I believe that this
         * sort of aliasing will cause no trouble. The correct field should get
         * stored into the Param slot at execution in each part of the tree.
         *
         * We also need to demand a match on vartypmod.  This does not matter for
         * the Param itself, since those are not typmod-dependent, but it does
         * matter when make_subplan() instantiates a modified copy of the Var for
         * a subplan's args list.
         */
        i = 0;
        foreach(ppl, root->glob->paramlist)
        {
                pitem = (PlannerParamItem *) lfirst(ppl);
                if (pitem->abslevel == abslevel && IsA(pitem->item, Var))
                {
                        Var                *pvar = (Var *) pitem->item;

                        if (pvar->varno == var->varno &&
                                pvar->varattno == var->varattno &&
                                pvar->vartype == var->vartype &&
                                pvar->vartypmod == var->vartypmod)
                                break;
                }
                i++;
        }

        if (!ppl)
        {
                /* Nope, so make a new one */
                var = (Var *) copyObject(var);
                var->varlevelsup = 0;

                pitem = makeNode(PlannerParamItem);
                pitem->item = (Node *) var;
                pitem->abslevel = abslevel;

                root->glob->paramlist = lappend(root->glob->paramlist, pitem);
                /* i is already the correct index for the new item */
        }

        retval = makeNode(Param);
        retval->paramkind = PARAM_EXEC;
        retval->paramid = i;
        retval->paramtype = var->vartype;
        retval->paramtypmod = var->vartypmod;

        return retval;
}

/*
 * Generate a Param node to replace the given Aggref
 * which is expected to have agglevelsup > 0 (ie, it is not local).
 */
static Param *
replace_outer_agg(PlannerInfo *root, Aggref *agg)
{
        Param      *retval;
        PlannerParamItem *pitem;
        Index           abslevel;
        int                     i;

        Assert(agg->agglevelsup > 0 && agg->agglevelsup < root->query_level);
        abslevel = root->query_level - agg->agglevelsup;

        /*
         * It does not seem worthwhile to try to match duplicate outer aggs. Just
         * make a new slot every time.
         */
        agg = (Aggref *) copyObject(agg);
        IncrementVarSublevelsUp((Node *) agg, -((int) agg->agglevelsup), 0);
        Assert(agg->agglevelsup == 0);

        pitem = makeNode(PlannerParamItem);
        pitem->item = (Node *) agg;
        pitem->abslevel = abslevel;

        root->glob->paramlist = lappend(root->glob->paramlist, pitem);
        i = list_length(root->glob->paramlist) - 1;

        retval = makeNode(Param);
        retval->paramkind = PARAM_EXEC;
        retval->paramid = i;
        retval->paramtype = agg->aggtype;
        retval->paramtypmod = -1;

        return retval;
}

/*
 * Generate a new Param node that will not conflict with any other.
 *
 * This is used to allocate PARAM_EXEC slots for subplan outputs.
 */
static Param *
generate_new_param(PlannerInfo *root, Oid paramtype, int32 paramtypmod)
{
        Param      *retval;
        PlannerParamItem *pitem;

        retval = makeNode(Param);
        retval->paramkind = PARAM_EXEC;
        retval->paramid = list_length(root->glob->paramlist);
        retval->paramtype = paramtype;
        retval->paramtypmod = paramtypmod;

        pitem = makeNode(PlannerParamItem);
        pitem->item = (Node *) retval;
        pitem->abslevel = root->query_level;

        root->glob->paramlist = lappend(root->glob->paramlist, pitem);

        return retval;
}

/*
 * Get the datatype of the first column of the plan's output.
 *
 * This is stored for ARRAY_SUBLINK and for exprType(), which doesn't have any
 * way to get at the plan associated with a SubPlan node.  We really only need
 * the value for EXPR_SUBLINK and ARRAY_SUBLINK subplans, but for consistency
 * we set it always.
 */
static Oid
get_first_col_type(Plan *plan)
{
        /* In cases such as EXISTS, tlist might be empty; arbitrarily use VOID */
        if (plan->targetlist)
        {
                TargetEntry *tent = (TargetEntry *) linitial(plan->targetlist);

                Assert(IsA(tent, TargetEntry));
                if (!tent->resjunk)
                        return exprType((Node *) tent->expr);
        }
        return VOIDOID;
}

/*
 * Convert a SubLink (as created by the parser) into a SubPlan.
 *
 * We are given the original SubLink and the already-processed testexpr
 * (use this instead of the SubLink's own field).  We are also told if
 * this expression appears at top level of a WHERE/HAVING qual.
 *
 * The result is whatever we need to substitute in place of the SubLink
 * node in the executable expression.  This will be either the SubPlan
 * node (if we have to do the subplan as a subplan), or a Param node
 * representing the result of an InitPlan, or a row comparison expression
 * tree containing InitPlan Param nodes.
 */
static Node *
make_subplan(PlannerInfo *root, SubLink *slink, Node *testexpr, bool isTopQual)
{
        Query      *subquery = (Query *) (slink->subselect);
        double          tuple_fraction;
        SubPlan    *splan;
        Plan       *plan;
        PlannerInfo *subroot;
        bool            isInitPlan;
        Bitmapset  *tmpset;
        int                     paramid;
        Node       *result;

        /*
         * Copy the source Query node.  This is a quick and dirty kluge to resolve
         * the fact that the parser can generate trees with multiple links to the
         * same sub-Query node, but the planner wants to scribble on the Query.
         * Try to clean this up when we do querytree redesign...
         */
        subquery = (Query *) copyObject(subquery);

        /*
         * If it's an EXISTS subplan, we might be able to simplify it.
         */
        if (slink->subLinkType == EXISTS_SUBLINK)
                (void) simplify_EXISTS_query(subquery);

        /*
         * For an EXISTS subplan, tell lower-level planner to expect that only the
         * first tuple will be retrieved.  For ALL and ANY subplans, we will be
         * able to stop evaluating if the test condition fails, so very often not
         * all the tuples will be retrieved; for lack of a better idea, specify
         * 50% retrieval.  For EXPR and ROWCOMPARE subplans, use default behavior
         * (we're only expecting one row out, anyway).
         *
         * NOTE: if you change these numbers, also change cost_qual_eval_walker()
         * and get_initplan_cost() in path/costsize.c.
         *
         * XXX If an ALL/ANY subplan is uncorrelated, we may decide to hash or
         * materialize its result below.  In that case it would've been better to
         * specify full retrieval.      At present, however, we can only detect
         * correlation or lack of it after we've made the subplan :-(. Perhaps
         * detection of correlation should be done as a separate step. Meanwhile,
         * we don't want to be too optimistic about the percentage of tuples
         * retrieved, for fear of selecting a plan that's bad for the
         * materialization case.
         */
        if (slink->subLinkType == EXISTS_SUBLINK)
                tuple_fraction = 1.0;   /* just like a LIMIT 1 */
        else if (slink->subLinkType == ALL_SUBLINK ||
                         slink->subLinkType == ANY_SUBLINK)
                tuple_fraction = 0.5;   /* 50% */
        else
                tuple_fraction = 0.0;   /* default behavior */

        /*
         * Generate the plan for the subquery.
         */
        plan = subquery_planner(root->glob, subquery,
                                                        root->query_level + 1,
                                                        tuple_fraction,
                                                        &subroot);

        /*
         * Initialize the SubPlan node.  Note plan_id isn't set yet.
         */
        splan = makeNode(SubPlan);
        splan->subLinkType = slink->subLinkType;
        splan->testexpr = NULL;
        splan->paramIds = NIL;
        splan->firstColType = get_first_col_type(plan);
        splan->useHashTable = false;
        /* At top level of a qual, can treat UNKNOWN the same as FALSE */
        splan->unknownEqFalse = isTopQual;
        splan->setParam = NIL;
        splan->parParam = NIL;
        splan->args = NIL;

        /*
         * Make parParam list of params that current query level will pass to this
         * child plan.
         */
        tmpset = bms_copy(plan->extParam);
        while ((paramid = bms_first_member(tmpset)) >= 0)
        {
                PlannerParamItem *pitem = list_nth(root->glob->paramlist, paramid);

                if (pitem->abslevel == root->query_level)
                        splan->parParam = lappend_int(splan->parParam, paramid);
        }
        bms_free(tmpset);

        /*
         * Un-correlated or undirect correlated plans of EXISTS, EXPR, ARRAY, or
         * ROWCOMPARE types can be used as initPlans.  For EXISTS, EXPR, or ARRAY,
         * we just produce a Param referring to the result of evaluating the
         * initPlan.  For ROWCOMPARE, we must modify the testexpr tree to contain
         * PARAM_EXEC Params instead of the PARAM_SUBLINK Params emitted by the
         * parser.
         */
        if (splan->parParam == NIL && slink->subLinkType == EXISTS_SUBLINK)
        {
                Param      *prm;

                prm = generate_new_param(root, BOOLOID, -1);
                splan->setParam = list_make1_int(prm->paramid);
                isInitPlan = true;
                result = (Node *) prm;
        }
        else if (splan->parParam == NIL && slink->subLinkType == EXPR_SUBLINK)
        {
                TargetEntry *te = linitial(plan->targetlist);
                Param      *prm;

                Assert(!te->resjunk);
                prm = generate_new_param(root,
                                                                 exprType((Node *) te->expr),
                                                                 exprTypmod((Node *) te->expr));
                splan->setParam = list_make1_int(prm->paramid);
                isInitPlan = true;
                result = (Node *) prm;
        }
        else if (splan->parParam == NIL && slink->subLinkType == ARRAY_SUBLINK)
        {
                TargetEntry *te = linitial(plan->targetlist);
                Oid                     arraytype;
                Param      *prm;

                Assert(!te->resjunk);
                arraytype = get_array_type(exprType((Node *) te->expr));
                if (!OidIsValid(arraytype))
                        elog(ERROR, "could not find array type for datatype %s",
                                 format_type_be(exprType((Node *) te->expr)));
                prm = generate_new_param(root,
                                                                 arraytype,
                                                                 exprTypmod((Node *) te->expr));
                splan->setParam = list_make1_int(prm->paramid);
                isInitPlan = true;
                result = (Node *) prm;
        }
        else if (splan->parParam == NIL && slink->subLinkType == ROWCOMPARE_SUBLINK)
        {
                /* Adjust the Params */
                List       *params;

                params = generate_subquery_params(root,
                                                                                  plan->targetlist,
                                                                                  &splan->paramIds);
                result = convert_testexpr(root,
                                                                  testexpr,
                                                                  params);
                splan->setParam = list_copy(splan->paramIds);
                isInitPlan = true;

                /*
                 * The executable expression is returned to become part of the outer
                 * plan's expression tree; it is not kept in the initplan node.
                 */
        }
        else
        {
                List       *args;
                ListCell   *l;

                if (testexpr)
                {
                        List       *params;

                        /* Adjust the Params in the testexpr */
                        params = generate_subquery_params(root,
                                                                                          plan->targetlist,
                                                                                          &splan->paramIds);
                        splan->testexpr = convert_testexpr(root,
                                                                                           testexpr,
                                                                                           params);
                }

                /*
                 * We can't convert subplans of ALL_SUBLINK or ANY_SUBLINK types to
                 * initPlans, even when they are uncorrelated or undirect correlated,
                 * because we need to scan the output of the subplan for each outer
                 * tuple.  But if it's an IN (= ANY) test, we might be able to use a
                 * hashtable to avoid comparing all the tuples.
                 */
                if (subplan_is_hashable(slink, splan, plan))
                        splan->useHashTable = true;

                /*
                 * Otherwise, we have the option to tack a MATERIAL node onto the top
                 * of the subplan, to reduce the cost of reading it repeatedly.  This
                 * is pointless for a direct-correlated subplan, since we'd have to
                 * recompute its results each time anyway.      For uncorrelated/undirect
                 * correlated subplans, we add MATERIAL unless the subplan's top plan
                 * node would materialize its output anyway.
                 */
                else if (splan->parParam == NIL)
                {
                        bool            use_material;

                        switch (nodeTag(plan))
                        {
                                case T_Material:
                                case T_FunctionScan:
                                case T_Sort:
                                        use_material = false;
                                        break;
                                default:
                                        use_material = true;
                                        break;
                        }
                        if (use_material)
                                plan = materialize_finished_plan(plan);
                }

                /*
                 * Make splan->args from parParam.
                 */
                args = NIL;
                foreach(l, splan->parParam)
                {
                        PlannerParamItem *pitem = list_nth(root->glob->paramlist,
                                                                                           lfirst_int(l));

                        /*
                         * The Var or Aggref has already been adjusted to have the correct
                         * varlevelsup or agglevelsup.  We probably don't even need to
                         * copy it again, but be safe.
                         */
                        args = lappend(args, copyObject(pitem->item));
                }
                splan->args = args;

                result = (Node *) splan;
                isInitPlan = false;
        }

        /*
         * Add the subplan and its rtable to the global lists.
         */
        root->glob->subplans = lappend(root->glob->subplans,
                                                                   plan);
        root->glob->subrtables = lappend(root->glob->subrtables,
                                                                         subroot->parse->rtable);
        splan->plan_id = list_length(root->glob->subplans);

        if (isInitPlan)
                root->init_plans = lappend(root->init_plans, splan);

        /*
         * A parameterless subplan (not initplan) should be prepared to handle
         * REWIND efficiently.  If it has direct parameters then there's no point
         * since it'll be reset on each scan anyway; and if it's an initplan then
         * there's no point since it won't get re-run without parameter changes
         * anyway.      The input of a hashed subplan doesn't need REWIND either.
         */
        if (splan->parParam == NIL && !isInitPlan && !splan->useHashTable)
                root->glob->rewindPlanIDs = bms_add_member(root->glob->rewindPlanIDs,
                                                                                                   splan->plan_id);

        return result;
}

/*
 * generate_subquery_params: build a list of Params representing the output
 * columns of a sublink's sub-select, given the sub-select's targetlist.
 *
 * We also return an integer list of the paramids of the Params.
 */
static List *
generate_subquery_params(PlannerInfo *root, List *tlist, List **paramIds)
{
        List       *result;
        List       *ids;
        ListCell   *lc;

        result = ids = NIL;
        foreach(lc, tlist)
        {
                TargetEntry *tent = (TargetEntry *) lfirst(lc);
                Param      *param;

                if (tent->resjunk)
                        continue;

                param = generate_new_param(root,
                                                                   exprType((Node *) tent->expr),
                                                                   exprTypmod((Node *) tent->expr));
                result = lappend(result, param);
                ids = lappend_int(ids, param->paramid);
        }

        *paramIds = ids;
        return result;
}

/*
 * generate_subquery_vars: build a list of Vars representing the output
 * columns of a sublink's sub-select, given the sub-select's targetlist.
 * The Vars have the specified varno (RTE index).
 */
static List *
generate_subquery_vars(PlannerInfo *root, List *tlist, Index varno)
{
        List       *result;
        ListCell   *lc;

        result = NIL;
        foreach(lc, tlist)
        {
                TargetEntry *tent = (TargetEntry *) lfirst(lc);
                Var                *var;

                if (tent->resjunk)
                        continue;

                var = makeVar(varno,
                                          tent->resno,
                                          exprType((Node *) tent->expr),
                                          exprTypmod((Node *) tent->expr),
                                          0);
                result = lappend(result, var);
        }

        return result;
}

/*
 * convert_testexpr: convert the testexpr given by the parser into
 * actually executable form.  This entails replacing PARAM_SUBLINK Params
 * with Params or Vars representing the results of the sub-select.  The
 * nodes to be substituted are passed in as the List result from
 * generate_subquery_params or generate_subquery_vars.
 *
 * The given testexpr has already been recursively processed by
 * process_sublinks_mutator.  Hence it can no longer contain any
 * PARAM_SUBLINK Params for lower SubLink nodes; we can safely assume that
 * any we find are for our own level of SubLink.
 */
static Node *
convert_testexpr(PlannerInfo *root,
                                 Node *testexpr,
                                 List *subst_nodes)
{
        convert_testexpr_context context;

        context.root = root;
        context.subst_nodes = subst_nodes;
        return convert_testexpr_mutator(testexpr, &context);
}

static Node *
convert_testexpr_mutator(Node *node,
                                                 convert_testexpr_context *context)
{
        if (node == NULL)
                return NULL;
        if (IsA(node, Param))
        {
                Param      *param = (Param *) node;

                if (param->paramkind == PARAM_SUBLINK)
                {
                        if (param->paramid <= 0 ||
                                param->paramid > list_length(context->subst_nodes))
                                elog(ERROR, "unexpected PARAM_SUBLINK ID: %d", param->paramid);

                        /*
                         * We copy the list item to avoid having doubly-linked
                         * substructure in the modified parse tree.  This is probably
                         * unnecessary when it's a Param, but be safe.
                         */
                        return (Node *) copyObject(list_nth(context->subst_nodes,
                                                                                                param->paramid - 1));
                }
        }
        return expression_tree_mutator(node,
                                                                   convert_testexpr_mutator,
                                                                   (void *) context);
}

/*
 * subplan_is_hashable: decide whether we can implement a subplan by hashing
 *
 * Caution: the SubPlan node is not completely filled in yet.  We can rely
 * on its plan and parParam fields, however.
 */
static bool
subplan_is_hashable(SubLink *slink, SubPlan *node, Plan *plan)
{
        double          subquery_size;
        ListCell   *l;

        /*
         * The sublink type must be "= ANY" --- that is, an IN operator.  We
         * expect that the test expression will be either a single OpExpr, or an
         * AND-clause containing OpExprs.  (If it's anything else then the parser
         * must have determined that the operators have non-equality-like
         * semantics.  In the OpExpr case we can't be sure what the operator's
         * semantics are like, but the test below for hashability will reject
         * anything that's not equality.)
         */
        if (slink->subLinkType != ANY_SUBLINK)
                return false;
        if (slink->testexpr == NULL ||
                (!IsA(slink->testexpr, OpExpr) &&
                 !and_clause(slink->testexpr)))
                return false;

        /*
         * The subplan must not have any direct correlation vars --- else we'd
         * have to recompute its output each time, so that the hashtable wouldn't
         * gain anything.
         */
        if (node->parParam != NIL)
                return false;

        /*
         * The estimated size of the subquery result must fit in work_mem. (Note:
         * we use sizeof(HeapTupleHeaderData) here even though the tuples will
         * actually be stored as MinimalTuples; this provides some fudge factor
         * for hashtable overhead.)
         */
        subquery_size = plan->plan_rows *
                (MAXALIGN(plan->plan_width) + MAXALIGN(sizeof(HeapTupleHeaderData)));
        if (subquery_size > work_mem * 1024L)
                return false;

        /*
         * The combining operators must be hashable and strict. The need for
         * hashability is obvious, since we want to use hashing. Without
         * strictness, behavior in the presence of nulls is too unpredictable.  We
         * actually must assume even more than plain strictness: they can't yield
         * NULL for non-null inputs, either (see nodeSubplan.c).  However, hash
         * indexes and hash joins assume that too.
         */
        if (IsA(slink->testexpr, OpExpr))
        {
                if (!hash_ok_operator((OpExpr *) slink->testexpr))
                        return false;
        }
        else
        {
                foreach(l, ((BoolExpr *) slink->testexpr)->args)
                {
                        Node       *andarg = (Node *) lfirst(l);

                        if (!IsA(andarg, OpExpr))
                                return false;   /* probably can't happen */
                        if (!hash_ok_operator((OpExpr *) andarg))
                                return false;
                }
        }

        return true;
}

static bool
hash_ok_operator(OpExpr *expr)
{
        Oid                     opid = expr->opno;
        HeapTuple       tup;
        Form_pg_operator optup;

        tup = SearchSysCache(OPEROID,
                                                 ObjectIdGetDatum(opid),
                                                 0, 0, 0);
        if (!HeapTupleIsValid(tup))
                elog(ERROR, "cache lookup failed for operator %u", opid);
        optup = (Form_pg_operator) GETSTRUCT(tup);
        if (!optup->oprcanhash || !func_strict(optup->oprcode))
        {
                ReleaseSysCache(tup);
                return false;
        }
        ReleaseSysCache(tup);
        return true;
}

/*
 * convert_ANY_sublink_to_join: can we convert an ANY SubLink to a join?
 *
 * The caller has found an ANY SubLink at the top level of WHERE, but has not
 * checked the properties of the SubLink further.  Decide whether it is
 * appropriate to process this SubLink in join style.  If not, return NULL.
 * If so, build the qual clause(s) to replace the SubLink, and return them.
 * The qual clauses are wrapped in a FlattenedSubLink node to help later
 * processing place them properly.
 *
 * Side effects of a successful conversion include adding the SubLink's
 * subselect to the query's rangetable.
 */
Node *
convert_ANY_sublink_to_join(PlannerInfo *root, SubLink *sublink)
{
        Query      *parse = root->parse;
        Query      *subselect = (Query *) sublink->subselect;
        Relids          left_varnos;
        int                     rtindex;
        RangeTblEntry *rte;
        RangeTblRef *rtr;
        List       *subquery_vars;
        Expr       *quals;
        FlattenedSubLink *fslink;

        Assert(sublink->subLinkType == ANY_SUBLINK);

        /*
         * The sub-select must not refer to any Vars of the parent query. (Vars of
         * higher levels should be okay, though.)
         */
        if (contain_vars_of_level((Node *) subselect, 1))
                return NULL;

        /*
         * The test expression must contain some Vars of the current query,
         * else it's not gonna be a join.  (Note that it won't have Vars
         * referring to the subquery, rather Params.)
         */
        left_varnos = pull_varnos(sublink->testexpr);
        if (bms_is_empty(left_varnos))
                return NULL;

        /*
         * The combining operators and left-hand expressions mustn't be volatile.
         */
        if (contain_volatile_functions(sublink->testexpr))
                return NULL;

        /*
         * Okay, pull up the sub-select into top range table and jointree.
         *
         * We rely here on the assumption that the outer query has no references
         * to the inner (necessarily true, other than the Vars that we build
         * below). Therefore this is a lot easier than what pull_up_subqueries has
         * to go through.
         */
        rte = addRangeTableEntryForSubquery(NULL,
                                                                                subselect,
                                                                                makeAlias("ANY_subquery", NIL),
                                                                                false);
        parse->rtable = lappend(parse->rtable, rte);
        rtindex = list_length(parse->rtable);
        rtr = makeNode(RangeTblRef);
        rtr->rtindex = rtindex;

        /*
         * We assume it's okay to add the pulled-up subquery to the topmost FROM
         * list.  This should be all right for ANY clauses appearing in WHERE
         * or in upper-level plain JOIN/ON clauses.  ANYs appearing below any
         * outer joins couldn't be placed there, however.
         */
        parse->jointree->fromlist = lappend(parse->jointree->fromlist, rtr);

        /*
         * Build a list of Vars representing the subselect outputs.
         */
        subquery_vars = generate_subquery_vars(root,
                                                                                   subselect->targetList,
                                                                                   rtindex);

        /*
         * Build the result qual expression, replacing Params with these Vars.
         */
        quals = (Expr *) convert_testexpr(root,
                                                                          sublink->testexpr,
                                                                          subquery_vars);

        /*
         * Now build the FlattenedSubLink node.
         */
        fslink = makeNode(FlattenedSubLink);
        fslink->jointype = JOIN_SEMI;
        fslink->lefthand = left_varnos;
        fslink->righthand = bms_make_singleton(rtindex);
        fslink->quals = quals;

        return (Node *) fslink;
}

/*
 * simplify_EXISTS_query: remove any useless stuff in an EXISTS's subquery
 *
 * The only thing that matters about an EXISTS query is whether it returns
 * zero or more than zero rows.  Therefore, we can remove certain SQL features
 * that won't affect that.  The only part that is really likely to matter in
 * typical usage is simplifying the targetlist: it's a common habit to write
 * "SELECT * FROM" even though there is no need to evaluate any columns.
 *
 * Note: by suppressing the targetlist we could cause an observable behavioral
 * change, namely that any errors that might occur in evaluating the tlist
 * won't occur, nor will other side-effects of volatile functions.  This seems
 * unlikely to bother anyone in practice.
 *
 * Returns TRUE if was able to discard the targetlist, else FALSE.
 */
static bool
simplify_EXISTS_query(Query *query)
{
        /*
         * We don't try to simplify at all if the query uses set operations,
         * aggregates, HAVING, LIMIT/OFFSET, or FOR UPDATE/SHARE; none of these
         * seem likely in normal usage and their possible effects are complex.
         */
        if (query->commandType != CMD_SELECT ||
                query->intoClause ||
                query->setOperations ||
                query->hasAggs ||
                query->havingQual ||
                query->limitOffset ||
                query->limitCount ||
                query->rowMarks)
                return false;

        /*
         * Mustn't throw away the targetlist if it contains set-returning
         * functions; those could affect whether zero rows are returned!
         */
        if (expression_returns_set((Node *) query->targetList))
                return false;

        /*
         * Otherwise, we can throw away the targetlist, as well as any GROUP,
         * DISTINCT, and ORDER BY clauses; none of those clauses will change
         * a nonzero-rows result to zero rows or vice versa.  (Furthermore,
         * since our parsetree representation of these clauses depends on the
         * targetlist, we'd better throw them away if we drop the targetlist.)
         */
        query->targetList = NIL;
        query->groupClause = NIL;
        query->distinctClause = NIL;
        query->sortClause = NIL;
        query->hasDistinctOn = false;

        return true;
}

/*
 * convert_EXISTS_sublink_to_join: can we convert an EXISTS SubLink to a join?
 *
 * The caller has found an EXISTS SubLink at the top level of WHERE, or just
 * underneath a NOT, but has not checked the properties of the SubLink
 * further.  Decide whether it is appropriate to process this SubLink in join
 * style.  If not, return NULL.  If so, build the qual clause(s) to replace
 * the SubLink, and return them.  (In the NOT case, the returned clauses are
 * intended to replace the NOT as well.)  The qual clauses are wrapped in a
 * FlattenedSubLink node to help later processing place them properly.
 *
 * Side effects of a successful conversion include adding the SubLink's
 * subselect to the query's rangetable.
 */
Node *
convert_EXISTS_sublink_to_join(PlannerInfo *root, SubLink *sublink,
                                                           bool under_not)
{
        Query      *parse = root->parse;
        Query      *subselect = (Query *) sublink->subselect;
        Node       *whereClause;
        int                     rtoffset;
        int                     varno;
        Relids          clause_varnos;
        Relids          left_varnos;
        Relids          right_varnos;
        Relids          subselect_varnos;
        FlattenedSubLink *fslink;

        Assert(sublink->subLinkType == EXISTS_SUBLINK);

        /*
         * Copy the subquery so we can modify it safely (see comments in
         * make_subplan).
         */
        subselect = (Query *) copyObject(subselect);

        /*
         * See if the subquery can be simplified based on the knowledge that
         * it's being used in EXISTS().  If we aren't able to get rid of its
         * targetlist, we have to fail, because the pullup operation leaves
         * us with noplace to evaluate the targetlist.
         */
        if (!simplify_EXISTS_query(subselect))
                return NULL;

        /*
         * Separate out the WHERE clause.  (We could theoretically also remove
         * top-level plain JOIN/ON clauses, but it's probably not worth the
         * trouble.)
         */
        whereClause = subselect->jointree->quals;
        subselect->jointree->quals = NULL;

        /*
         * The rest of the sub-select must not refer to any Vars of the parent
         * query.  (Vars of higher levels should be okay, though.)
         */
        if (contain_vars_of_level((Node *) subselect, 1))
                return NULL;

        /*
         * On the other hand, the WHERE clause must contain some Vars of the
         * parent query, else it's not gonna be a join.
         */
        if (!contain_vars_of_level(whereClause, 1))
                return NULL;

        /*
         * We don't risk optimizing if the WHERE clause is volatile, either.
         */
        if (contain_volatile_functions(whereClause))
                return NULL;

        /*
         * Also disallow SubLinks within the WHERE clause.  (XXX this could
         * probably be supported, but it would complicate the transformation
         * below, and it doesn't seem worth worrying about in a first pass.)
         */
        if (contain_subplans(whereClause))
                return NULL;

        /*
         * Okay, pull up the sub-select into top range table and jointree.
         *
         * We rely here on the assumption that the outer query has no references
         * to the inner (necessarily true). Therefore this is a lot easier than
         * what pull_up_subqueries has to go through.
         *
         * In fact, it's even easier than what convert_ANY_sublink_to_join has
         * to do.  The machinations of simplify_EXISTS_query ensured that there
         * is nothing interesting in the subquery except an rtable and jointree,
         * and even the jointree FromExpr no longer has quals.  So we can just
         * append the rtable to our own and append the fromlist to our own.
         * But first, adjust all level-zero varnos in the subquery to account
         * for the rtable merger.
         */
        rtoffset = list_length(parse->rtable);
        OffsetVarNodes((Node *) subselect, rtoffset, 0);
        OffsetVarNodes(whereClause, rtoffset, 0);

        /*
         * Upper-level vars in subquery will now be one level closer to their
         * parent than before; in particular, anything that had been level 1
         * becomes level zero.
         */
        IncrementVarSublevelsUp((Node *) subselect, -1, 1);
        IncrementVarSublevelsUp(whereClause, -1, 1);

        /*
         * Now that the WHERE clause is adjusted to match the parent query
         * environment, we can easily identify all the level-zero rels it uses.
         * The ones <= rtoffset are "left rels" of the join we're forming,
         * and the ones > rtoffset are "right rels".
         */
        clause_varnos = pull_varnos(whereClause);
        left_varnos = right_varnos = NULL;
        while ((varno = bms_first_member(clause_varnos)) >= 0)
        {
                if (varno <= rtoffset)
                        left_varnos = bms_add_member(left_varnos, varno);
                else
                        right_varnos = bms_add_member(right_varnos, varno);
        }
        bms_free(clause_varnos);
        Assert(!bms_is_empty(left_varnos));

        /* Also identify all the rels syntactically within the subselect */
        subselect_varnos = get_relids_in_jointree((Node *) subselect->jointree);
        Assert(bms_is_subset(right_varnos, subselect_varnos));

        /* Now we can attach the modified subquery rtable to the parent */
        parse->rtable = list_concat(parse->rtable, subselect->rtable);

        /*
         * We assume it's okay to add the pulled-up subquery to the topmost FROM
         * list.  This should be all right for EXISTS clauses appearing in WHERE
         * or in upper-level plain JOIN/ON clauses.  EXISTS appearing below any
         * outer joins couldn't be placed there, however.
         */
        parse->jointree->fromlist = list_concat(parse->jointree->fromlist,
                                                                                        subselect->jointree->fromlist);

        /*
         * Now build the FlattenedSubLink node.
         */
        fslink = makeNode(FlattenedSubLink);
        fslink->jointype = under_not ? JOIN_ANTI : JOIN_SEMI;
        fslink->lefthand = left_varnos;
        fslink->righthand = subselect_varnos;
        fslink->quals = (Expr *) whereClause;

        return (Node *) fslink;
}

/*
 * Replace correlation vars (uplevel vars) with Params.
 *
 * Uplevel aggregates are replaced, too.
 *
 * Note: it is critical that this runs immediately after SS_process_sublinks.
 * Since we do not recurse into the arguments of uplevel aggregates, they will
 * get copied to the appropriate subplan args list in the parent query with
 * uplevel vars not replaced by Params, but only adjusted in level (see
 * replace_outer_agg).  That's exactly what we want for the vars of the parent
 * level --- but if an aggregate's argument contains any further-up variables,
 * they have to be replaced with Params in their turn.  That will happen when
 * the parent level runs SS_replace_correlation_vars.  Therefore it must do
 * so after expanding its sublinks to subplans.  And we don't want any steps
 * in between, else those steps would never get applied to the aggregate
 * argument expressions, either in the parent or the child level.
 */
Node *
SS_replace_correlation_vars(PlannerInfo *root, Node *expr)
{
        /* No setup needed for tree walk, so away we go */
        return replace_correlation_vars_mutator(expr, root);
}

static Node *
replace_correlation_vars_mutator(Node *node, PlannerInfo *root)
{
        if (node == NULL)
                return NULL;
        if (IsA(node, Var))
        {
                if (((Var *) node)->varlevelsup > 0)
                        return (Node *) replace_outer_var(root, (Var *) node);
        }
        if (IsA(node, Aggref))
        {
                if (((Aggref *) node)->agglevelsup > 0)
                        return (Node *) replace_outer_agg(root, (Aggref *) node);
        }
        return expression_tree_mutator(node,
                                                                   replace_correlation_vars_mutator,
                                                                   (void *) root);
}

/*
 * Expand SubLinks to SubPlans in the given expression.
 *
 * The isQual argument tells whether or not this expression is a WHERE/HAVING
 * qualifier expression.  If it is, any sublinks appearing at top level need
 * not distinguish FALSE from UNKNOWN return values.
 */
Node *
SS_process_sublinks(PlannerInfo *root, Node *expr, bool isQual)
{
        process_sublinks_context context;

        context.root = root;
        context.isTopQual = isQual;
        return process_sublinks_mutator(expr, &context);
}

static Node *
process_sublinks_mutator(Node *node, process_sublinks_context *context)
{
        process_sublinks_context locContext;

        locContext.root = context->root;

        if (node == NULL)
                return NULL;
        if (IsA(node, SubLink))
        {
                SubLink    *sublink = (SubLink *) node;
                Node       *testexpr;

                /*
                 * First, recursively process the lefthand-side expressions, if any.
                 * They're not top-level anymore.
                 */
                locContext.isTopQual = false;
                testexpr = process_sublinks_mutator(sublink->testexpr, &locContext);

                /*
                 * Now build the SubPlan node and make the expr to return.
                 */
                return make_subplan(context->root,
                                                        sublink,
                                                        testexpr,
                                                        context->isTopQual);
        }

        /*
         * We should never see a SubPlan expression in the input (since this is
         * the very routine that creates 'em to begin with).  We shouldn't find
         * ourselves invoked directly on a Query, either.
         */
        Assert(!is_subplan(node));
        Assert(!IsA(node, Query));

        /*
         * Because make_subplan() could return an AND or OR clause, we have to
         * take steps to preserve AND/OR flatness of a qual.  We assume the input
         * has been AND/OR flattened and so we need no recursion here.
         *
         * If we recurse down through anything other than an AND node, we are
         * definitely not at top qual level anymore.  (Due to the coding here, we
         * will not get called on the List subnodes of an AND, so no check is
         * needed for List.)
         */
        if (and_clause(node))
        {
                List       *newargs = NIL;
                ListCell   *l;

                /* Still at qual top-level */
                locContext.isTopQual = context->isTopQual;

                foreach(l, ((BoolExpr *) node)->args)
                {
                        Node       *newarg;

                        newarg = process_sublinks_mutator(lfirst(l), &locContext);
                        if (and_clause(newarg))
                                newargs = list_concat(newargs, ((BoolExpr *) newarg)->args);
                        else
                                newargs = lappend(newargs, newarg);
                }
                return (Node *) make_andclause(newargs);
        }

        /* otherwise not at qual top-level */
        locContext.isTopQual = false;

        if (or_clause(node))
        {
                List       *newargs = NIL;
                ListCell   *l;

                foreach(l, ((BoolExpr *) node)->args)
                {
                        Node       *newarg;

                        newarg = process_sublinks_mutator(lfirst(l), &locContext);
                        if (or_clause(newarg))
                                newargs = list_concat(newargs, ((BoolExpr *) newarg)->args);
                        else
                                newargs = lappend(newargs, newarg);
                }
                return (Node *) make_orclause(newargs);
        }

        return expression_tree_mutator(node,
                                                                   process_sublinks_mutator,
                                                                   (void *) &locContext);
}

/*
 * SS_finalize_plan - do final sublink processing for a completed Plan.
 *
 * This recursively computes the extParam and allParam sets for every Plan
 * node in the given plan tree.  It also optionally attaches any previously
 * generated InitPlans to the top plan node.  (Any InitPlans should already
 * have been put through SS_finalize_plan.)
 */
void
SS_finalize_plan(PlannerInfo *root, Plan *plan, bool attach_initplans)
{
        Bitmapset  *valid_params,
                           *initExtParam,
                           *initSetParam;
        Cost            initplan_cost;
        int                     paramid;
        ListCell   *l;

        /*
         * Examine any initPlans to determine the set of external params they
         * reference, the set of output params they supply, and their total cost.
         * We'll use at least some of this info below.  (Note we are assuming that
         * finalize_plan doesn't touch the initPlans.)
         *
         * In the case where attach_initplans is false, we are assuming that the
         * existing initPlans are siblings that might supply params needed by the
         * current plan.
         */
        initExtParam = initSetParam = NULL;
        initplan_cost = 0;
        foreach(l, root->init_plans)
        {
                SubPlan    *initsubplan = (SubPlan *) lfirst(l);
                Plan       *initplan = planner_subplan_get_plan(root, initsubplan);
                ListCell   *l2;

                initExtParam = bms_add_members(initExtParam, initplan->extParam);
                foreach(l2, initsubplan->setParam)
                {
                        initSetParam = bms_add_member(initSetParam, lfirst_int(l2));
                }
                initplan_cost += get_initplan_cost(root, initsubplan);
        }

        /*
         * Now determine the set of params that are validly referenceable in this
         * query level; to wit, those available from outer query levels plus the
         * output parameters of any initPlans.  (We do not include output
         * parameters of regular subplans.  Those should only appear within the
         * testexpr of SubPlan nodes, and are taken care of locally within
         * finalize_primnode.)
         *
         * Note: this is a bit overly generous since some parameters of upper
         * query levels might belong to query subtrees that don't include this
         * query.  However, valid_params is only a debugging crosscheck, so it
         * doesn't seem worth expending lots of cycles to try to be exact.
         */
        valid_params = bms_copy(initSetParam);
        paramid = 0;
        foreach(l, root->glob->paramlist)
        {
                PlannerParamItem *pitem = (PlannerParamItem *) lfirst(l);

                if (pitem->abslevel < root->query_level)
                {
                        /* valid outer-level parameter */
                        valid_params = bms_add_member(valid_params, paramid);
                }

                paramid++;
        }

        /*
         * Now recurse through plan tree.
         */
        (void) finalize_plan(root, plan, valid_params);

        bms_free(valid_params);

        /*
         * Finally, attach any initPlans to the topmost plan node, and add their
         * extParams to the topmost node's, too.  However, any setParams of the
         * initPlans should not be present in the topmost node's extParams, only
         * in its allParams.  (As of PG 8.1, it's possible that some initPlans
         * have extParams that are setParams of other initPlans, so we have to
         * take care of this situation explicitly.)
         *
         * We also add the eval cost of each initPlan to the startup cost of the
         * top node.  This is a conservative overestimate, since in fact each
         * initPlan might be executed later than plan startup, or even not at all.
         */
        if (attach_initplans)
        {
                plan->initPlan = root->init_plans;
                root->init_plans = NIL;         /* make sure they're not attached twice */

                /* allParam must include all these params */
                plan->allParam = bms_add_members(plan->allParam, initExtParam);
                plan->allParam = bms_add_members(plan->allParam, initSetParam);
                /* extParam must include any child extParam */
                plan->extParam = bms_add_members(plan->extParam, initExtParam);
                /* but extParam shouldn't include any setParams */
                plan->extParam = bms_del_members(plan->extParam, initSetParam);
                /* ensure extParam is exactly NULL if it's empty */
                if (bms_is_empty(plan->extParam))
                        plan->extParam = NULL;

                plan->startup_cost += initplan_cost;
                plan->total_cost += initplan_cost;
        }
}

/*
 * Recursive processing of all nodes in the plan tree
 *
 * The return value is the computed allParam set for the given Plan node.
 * This is just an internal notational convenience.
 */
static Bitmapset *
finalize_plan(PlannerInfo *root, Plan *plan, Bitmapset *valid_params)
{
        finalize_primnode_context context;

        if (plan == NULL)
                return NULL;

        context.root = root;
        context.paramids = NULL;        /* initialize set to empty */

        /*
         * When we call finalize_primnode, context.paramids sets are automatically
         * merged together.  But when recursing to self, we have to do it the hard
         * way.  We want the paramids set to include params in subplans as well as
         * at this level.
         */

        /* Find params in targetlist and qual */
        finalize_primnode((Node *) plan->targetlist, &context);
        finalize_primnode((Node *) plan->qual, &context);

        /* Check additional node-type-specific fields */
        switch (nodeTag(plan))
        {
                case T_Result:
                        finalize_primnode(((Result *) plan)->resconstantqual,
                                                          &context);
                        break;

                case T_IndexScan:
                        finalize_primnode((Node *) ((IndexScan *) plan)->indexqual,
                                                          &context);

                        /*
                         * we need not look at indexqualorig, since it will have the same
                         * param references as indexqual.
                         */
                        break;

                case T_BitmapIndexScan:
                        finalize_primnode((Node *) ((BitmapIndexScan *) plan)->indexqual,
                                                          &context);

                        /*
                         * we need not look at indexqualorig, since it will have the same
                         * param references as indexqual.
                         */
                        break;

                case T_BitmapHeapScan:
                        finalize_primnode((Node *) ((BitmapHeapScan *) plan)->bitmapqualorig,
                                                          &context);
                        break;

                case T_TidScan:
                        finalize_primnode((Node *) ((TidScan *) plan)->tidquals,
                                                          &context);
                        break;

                case T_SubqueryScan:

                        /*
                         * In a SubqueryScan, SS_finalize_plan has already been run on the
                         * subplan by the inner invocation of subquery_planner, so there's
                         * no need to do it again.      Instead, just pull out the subplan's
                         * extParams list, which represents the params it needs from my
                         * level and higher levels.
                         */
                        context.paramids = bms_add_members(context.paramids,
                                                                 ((SubqueryScan *) plan)->subplan->extParam);
                        break;

                case T_FunctionScan:
                        finalize_primnode(((FunctionScan *) plan)->funcexpr,
                                                          &context);
                        break;

                case T_ValuesScan:
                        finalize_primnode((Node *) ((ValuesScan *) plan)->values_lists,
                                                          &context);
                        break;

                case T_Append:
                        {
                                ListCell   *l;

                                foreach(l, ((Append *) plan)->appendplans)
                                {
                                        context.paramids =
                                                bms_add_members(context.paramids,
                                                                                finalize_plan(root,
                                                                                                          (Plan *) lfirst(l),
                                                                                                          valid_params));
                                }
                        }
                        break;

                case T_BitmapAnd:
                        {
                                ListCell   *l;

                                foreach(l, ((BitmapAnd *) plan)->bitmapplans)
                                {
                                        context.paramids =
                                                bms_add_members(context.paramids,
                                                                                finalize_plan(root,
                                                                                                          (Plan *) lfirst(l),
                                                                                                          valid_params));
                                }
                        }
                        break;

                case T_BitmapOr:
                        {
                                ListCell   *l;

                                foreach(l, ((BitmapOr *) plan)->bitmapplans)
                                {
                                        context.paramids =
                                                bms_add_members(context.paramids,
                                                                                finalize_plan(root,
                                                                                                          (Plan *) lfirst(l),
                                                                                                          valid_params));
                                }
                        }
                        break;

                case T_NestLoop:
                        finalize_primnode((Node *) ((Join *) plan)->joinqual,
                                                          &context);
                        break;

                case T_MergeJoin:
                        finalize_primnode((Node *) ((Join *) plan)->joinqual,
                                                          &context);
                        finalize_primnode((Node *) ((MergeJoin *) plan)->mergeclauses,
                                                          &context);
                        break;

                case T_HashJoin:
                        finalize_primnode((Node *) ((Join *) plan)->joinqual,
                                                          &context);
                        finalize_primnode((Node *) ((HashJoin *) plan)->hashclauses,
                                                          &context);
                        break;

                case T_Limit:
                        finalize_primnode(((Limit *) plan)->limitOffset,
                                                          &context);
                        finalize_primnode(((Limit *) plan)->limitCount,
                                                          &context);
                        break;

                case T_Hash:
                case T_Agg:
                case T_SeqScan:
                case T_Material:
                case T_Sort:
                case T_Unique:
                case T_SetOp:
                case T_Group:
                        break;

                default:
                        elog(ERROR, "unrecognized node type: %d",
                                 (int) nodeTag(plan));
        }

        /* Process left and right child plans, if any */
        context.paramids = bms_add_members(context.paramids,
                                                                           finalize_plan(root,
                                                                                                         plan->lefttree,
                                                                                                         valid_params));

        context.paramids = bms_add_members(context.paramids,
                                                                           finalize_plan(root,
                                                                                                         plan->righttree,
                                                                                                         valid_params));

        /* Now we have all the paramids */

        if (!bms_is_subset(context.paramids, valid_params))
                elog(ERROR, "plan should not reference subplan's variable");

        /*
         * Note: by definition, extParam and allParam should have the same value
         * in any plan node that doesn't have child initPlans.  We set them
         * equal here, and later SS_finalize_plan will update them properly
         * in node(s) that it attaches initPlans to.
         *
         * For speed at execution time, make sure extParam/allParam are actually
         * NULL if they are empty sets.
         */
        if (bms_is_empty(context.paramids))
        {
                plan->extParam = NULL;
                plan->allParam = NULL;
        }
        else
        {
                plan->extParam = context.paramids;
                plan->allParam = bms_copy(context.paramids);
        }

        return plan->allParam;
}

/*
 * finalize_primnode: add IDs of all PARAM_EXEC params appearing in the given
 * expression tree to the result set.
 */
static bool
finalize_primnode(Node *node, finalize_primnode_context *context)
{
        if (node == NULL)
                return false;
        if (IsA(node, Param))
        {
                if (((Param *) node)->paramkind == PARAM_EXEC)
                {
                        int                     paramid = ((Param *) node)->paramid;

                        context->paramids = bms_add_member(context->paramids, paramid);
                }
                return false;                   /* no more to do here */
        }
        if (is_subplan(node))
        {
                SubPlan    *subplan = (SubPlan *) node;
                Plan       *plan = planner_subplan_get_plan(context->root, subplan);
                ListCell   *lc;
                Bitmapset  *subparamids;

                /* Recurse into the testexpr, but not into the Plan */
                finalize_primnode(subplan->testexpr, context);

                /*
                 * Remove any param IDs of output parameters of the subplan that were
                 * referenced in the testexpr.  These are not interesting for
                 * parameter change signaling since we always re-evaluate the subplan.
                 * Note that this wouldn't work too well if there might be uses of the
                 * same param IDs elsewhere in the plan, but that can't happen because
                 * generate_new_param never tries to merge params.
                 */
                foreach(lc, subplan->paramIds)
                {
                        context->paramids = bms_del_member(context->paramids,
                                                                                           lfirst_int(lc));
                }

                /* Also examine args list */
                finalize_primnode((Node *) subplan->args, context);

                /*
                 * Add params needed by the subplan to paramids, but excluding those
                 * we will pass down to it.
                 */
                subparamids = bms_copy(plan->extParam);
                foreach(lc, subplan->parParam)
                {
                        subparamids = bms_del_member(subparamids, lfirst_int(lc));
                }
                context->paramids = bms_join(context->paramids, subparamids);

                return false;                   /* no more to do here */
        }
        return expression_tree_walker(node, finalize_primnode,
                                                                  (void *) context);
}

/*
 * SS_make_initplan_from_plan - given a plan tree, make it an InitPlan
 *
 * The plan is expected to return a scalar value of the indicated type.
 * We build an EXPR_SUBLINK SubPlan node and put it into the initplan
 * list for the current query level.  A Param that represents the initplan's
 * output is returned.
 *
 * We assume the plan hasn't been put through SS_finalize_plan.
 */
Param *
SS_make_initplan_from_plan(PlannerInfo *root, Plan *plan,
                                                   Oid resulttype, int32 resulttypmod)
{
        SubPlan    *node;
        Param      *prm;

        /*
         * We must run SS_finalize_plan(), since that's normally done before a
         * subplan gets put into the initplan list.  Tell it not to attach any
         * pre-existing initplans to this one, since they are siblings not
         * children of this initplan.  (This is something else that could perhaps
         * be cleaner if we did extParam/allParam processing in setrefs.c instead
         * of here?  See notes for materialize_finished_plan.)
         */

        /*
         * Build extParam/allParam sets for plan nodes.
         */
        SS_finalize_plan(root, plan, false);

        /*
         * Add the subplan and its rtable to the global lists.
         */
        root->glob->subplans = lappend(root->glob->subplans,
                                                                   plan);
        root->glob->subrtables = lappend(root->glob->subrtables,
                                                                         root->parse->rtable);

        /*
         * Create a SubPlan node and add it to the outer list of InitPlans.
         * Note it has to appear after any other InitPlans it might depend on
         * (see comments in ExecReScan).
         */
        node = makeNode(SubPlan);
        node->subLinkType = EXPR_SUBLINK;
        node->firstColType = get_first_col_type(plan);
        node->plan_id = list_length(root->glob->subplans);

        root->init_plans = lappend(root->init_plans, node);

        /*
         * The node can't have any inputs (since it's an initplan), so the
         * parParam and args lists remain empty.
         */

        /*
         * Make a Param that will be the subplan's output.
         */
        prm = generate_new_param(root, resulttype, resulttypmod);
        node->setParam = list_make1_int(prm->paramid);

        return prm;
}