clauses.c

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/*-------------------------------------------------------------------------
 *
 * clauses.c
 *    routines to manipulate qualification clauses
 *
 * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/optimizer/util/clauses.c
 *
 * HISTORY
 *    AUTHOR            DATE            MAJOR EVENT
 *    Andrew Yu         Nov 3, 1994     clause.c and clauses.c combined
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/htup_details.h"
#include "catalog/pg_aggregate.h"
#include "catalog/pg_class.h"
#include "catalog/pg_language.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "executor/executor.h"
#include "executor/functions.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/planmain.h"
#include "optimizer/prep.h"
#include "optimizer/var.h"
#include "parser/analyze.h"
#include "parser/parse_agg.h"
#include "parser/parse_coerce.h"
#include "parser/parse_func.h"
#include "rewrite/rewriteManip.h"
#include "tcop/tcopprot.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/fmgroids.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/syscache.h"
#include "utils/typcache.h"


typedef struct
{
    PlannerInfo *root;
    AggSplit    aggsplit;
    AggClauseCosts *costs;
} get_agg_clause_costs_context;

typedef struct
{
    ParamListInfo boundParams;
    PlannerInfo *root;
    List       *active_fns;
    Node       *case_val;
    bool        estimate;
} eval_const_expressions_context;

typedef struct
{
    int         nargs;
    List       *args;
    int        *usecounts;
} substitute_actual_parameters_context;

typedef struct
{
    int         nargs;
    List       *args;
    int         sublevels_up;
} substitute_actual_srf_parameters_context;

typedef struct
{
    char       *proname;
    char       *prosrc;
} inline_error_callback_arg;

typedef struct
{
    char        max_hazard;     /* worst proparallel hazard found so far */
    char        max_interesting;    /* worst proparallel hazard of interest */
    List       *safe_param_ids; /* PARAM_EXEC Param IDs to treat as safe */
} max_parallel_hazard_context;

static bool contain_agg_clause_walker(Node *node, void *context);
static bool get_agg_clause_costs_walker(Node *node,
                            get_agg_clause_costs_context *context);
static bool find_window_functions_walker(Node *node, WindowFuncLists *lists);
static bool contain_subplans_walker(Node *node, void *context);
static bool contain_mutable_functions_walker(Node *node, void *context);
static bool contain_volatile_functions_walker(Node *node, void *context);
static bool contain_volatile_functions_not_nextval_walker(Node *node, void *context);
static bool max_parallel_hazard_walker(Node *node,
                           max_parallel_hazard_context *context);
static bool contain_nonstrict_functions_walker(Node *node, void *context);
static bool contain_context_dependent_node(Node *clause);
static bool contain_context_dependent_node_walker(Node *node, int *flags);
static bool contain_leaked_vars_walker(Node *node, void *context);
static Relids find_nonnullable_rels_walker(Node *node, bool top_level);
static List *find_nonnullable_vars_walker(Node *node, bool top_level);
static bool is_strict_saop(ScalarArrayOpExpr *expr, bool falseOK);
static Node *eval_const_expressions_mutator(Node *node,
                               eval_const_expressions_context *context);
static bool contain_non_const_walker(Node *node, void *context);
static bool ece_function_is_safe(Oid funcid,
                     eval_const_expressions_context *context);
static List *simplify_or_arguments(List *args,
                      eval_const_expressions_context *context,
                      bool *haveNull, bool *forceTrue);
static List *simplify_and_arguments(List *args,
                       eval_const_expressions_context *context,
                       bool *haveNull, bool *forceFalse);
static Node *simplify_boolean_equality(Oid opno, List *args);
static Expr *simplify_function(Oid funcid,
                  Oid result_type, int32 result_typmod,
                  Oid result_collid, Oid input_collid, List **args_p,
                  bool funcvariadic, bool process_args, bool allow_non_const,
                  eval_const_expressions_context *context);
static List *reorder_function_arguments(List *args, HeapTuple func_tuple);
static List *add_function_defaults(List *args, HeapTuple func_tuple);
static List *fetch_function_defaults(HeapTuple func_tuple);
static void recheck_cast_function_args(List *args, Oid result_type,
                           HeapTuple func_tuple);
static Expr *evaluate_function(Oid funcid, Oid result_type, int32 result_typmod,
                  Oid result_collid, Oid input_collid, List *args,
                  bool funcvariadic,
                  HeapTuple func_tuple,
                  eval_const_expressions_context *context);
static Expr *inline_function(Oid funcid, Oid result_type, Oid result_collid,
                Oid input_collid, List *args,
                bool funcvariadic,
                HeapTuple func_tuple,
                eval_const_expressions_context *context);
static Node *substitute_actual_parameters(Node *expr, int nargs, List *args,
                             int *usecounts);
static Node *substitute_actual_parameters_mutator(Node *node,
                                     substitute_actual_parameters_context *context);
static void sql_inline_error_callback(void *arg);
static Expr *evaluate_expr(Expr *expr, Oid result_type, int32 result_typmod,
              Oid result_collation);
static Query *substitute_actual_srf_parameters(Query *expr,
                                 int nargs, List *args);
static Node *substitute_actual_srf_parameters_mutator(Node *node,
                                         substitute_actual_srf_parameters_context *context);
static bool tlist_matches_coltypelist(List *tlist, List *coltypelist);


/*****************************************************************************
 *      OPERATOR clause functions
 *****************************************************************************/

/*
 * make_opclause
 *    Creates an operator clause given its operator info, left operand
 *    and right operand (pass NULL to create single-operand clause),
 *    and collation info.
 */
Expr *
make_opclause(Oid opno, Oid opresulttype, bool opretset,
              Expr *leftop, Expr *rightop,
              Oid opcollid, Oid inputcollid)
{
    OpExpr     *expr = makeNode(OpExpr);

    expr->opno = opno;
    expr->opfuncid = InvalidOid;
    expr->opresulttype = opresulttype;
    expr->opretset = opretset;
    expr->opcollid = opcollid;
    expr->inputcollid = inputcollid;
    if (rightop)
        expr->args = list_make2(leftop, rightop);
    else
        expr->args = list_make1(leftop);
    expr->location = -1;
    return (Expr *) expr;
}

/*
 * get_leftop
 *
 * Returns the left operand of a clause of the form (op expr expr)
 *      or (op expr)
 */
Node *
get_leftop(const Expr *clause)
{
    const OpExpr *expr = (const OpExpr *) clause;

    if (expr->args != NIL)
        return linitial(expr->args);
    else
        return NULL;
}

/*
 * get_rightop
 *
 * Returns the right operand in a clause of the form (op expr expr).
 * NB: result will be NULL if applied to a unary op clause.
 */
Node *
get_rightop(const Expr *clause)
{
    const OpExpr *expr = (const OpExpr *) clause;

    if (list_length(expr->args) >= 2)
        return lsecond(expr->args);
    else
        return NULL;
}

/*****************************************************************************
 *      NOT clause functions
 *****************************************************************************/

/*
 * not_clause
 *
 * Returns t iff this is a 'not' clause: (NOT expr).
 */
bool
not_clause(Node *clause)
{
    return (clause != NULL &&
            IsA(clause, BoolExpr) &&
            ((BoolExpr *) clause)->boolop == NOT_EXPR);
}

/*
 * make_notclause
 *
 * Create a 'not' clause given the expression to be negated.
 */
Expr *
make_notclause(Expr *notclause)
{
    BoolExpr   *expr = makeNode(BoolExpr);

    expr->boolop = NOT_EXPR;
    expr->args = list_make1(notclause);
    expr->location = -1;
    return (Expr *) expr;
}

/*
 * get_notclausearg
 *
 * Retrieve the clause within a 'not' clause
 */
Expr *
get_notclausearg(Expr *notclause)
{
    return linitial(((BoolExpr *) notclause)->args);
}

/*****************************************************************************
 *      OR clause functions
 *****************************************************************************/

/*
 * or_clause
 *
 * Returns t iff the clause is an 'or' clause: (OR { expr }).
 */
bool
or_clause(Node *clause)
{
    return (clause != NULL &&
            IsA(clause, BoolExpr) &&
            ((BoolExpr *) clause)->boolop == OR_EXPR);
}

/*
 * make_orclause
 *
 * Creates an 'or' clause given a list of its subclauses.
 */
Expr *
make_orclause(List *orclauses)
{
    BoolExpr   *expr = makeNode(BoolExpr);

    expr->boolop = OR_EXPR;
    expr->args = orclauses;
    expr->location = -1;
    return (Expr *) expr;
}

/*****************************************************************************
 *      AND clause functions
 *****************************************************************************/


/*
 * and_clause
 *
 * Returns t iff its argument is an 'and' clause: (AND { expr }).
 */
bool
and_clause(Node *clause)
{
    return (clause != NULL &&
            IsA(clause, BoolExpr) &&
            ((BoolExpr *) clause)->boolop == AND_EXPR);
}

/*
 * make_andclause
 *
 * Creates an 'and' clause given a list of its subclauses.
 */
Expr *
make_andclause(List *andclauses)
{
    BoolExpr   *expr = makeNode(BoolExpr);

    expr->boolop = AND_EXPR;
    expr->args = andclauses;
    expr->location = -1;
    return (Expr *) expr;
}

/*
 * make_and_qual
 *
 * Variant of make_andclause for ANDing two qual conditions together.
 * Qual conditions have the property that a NULL nodetree is interpreted
 * as 'true'.
 *
 * NB: this makes no attempt to preserve AND/OR flatness; so it should not
 * be used on a qual that has already been run through prepqual.c.
 */
Node *
make_and_qual(Node *qual1, Node *qual2)
{
    if (qual1 == NULL)
        return qual2;
    if (qual2 == NULL)
        return qual1;
    return (Node *) make_andclause(list_make2(qual1, qual2));
}

/*
 * The planner frequently prefers to represent qualification expressions
 * as lists of boolean expressions with implicit AND semantics.
 *
 * These functions convert between an AND-semantics expression list and the
 * ordinary representation of a boolean expression.
 *
 * Note that an empty list is considered equivalent to TRUE.
 */
Expr *
make_ands_explicit(List *andclauses)
{
    if (andclauses == NIL)
        return (Expr *) makeBoolConst(true, false);
    else if (list_length(andclauses) == 1)
        return (Expr *) linitial(andclauses);
    else
        return make_andclause(andclauses);
}

List *
make_ands_implicit(Expr *clause)
{
    /*
     * NB: because the parser sets the qual field to NULL in a query that has
     * no WHERE clause, we must consider a NULL input clause as TRUE, even
     * though one might more reasonably think it FALSE.  Grumble. If this
     * causes trouble, consider changing the parser's behavior.
     */
    if (clause == NULL)
        return NIL;             /* NULL -> NIL list == TRUE */
    else if (and_clause((Node *) clause))
        return ((BoolExpr *) clause)->args;
    else if (IsA(clause, Const) &&
             !((Const *) clause)->constisnull &&
             DatumGetBool(((Const *) clause)->constvalue))
        return NIL;             /* constant TRUE input -> NIL list */
    else
        return list_make1(clause);
}


/*****************************************************************************
 *      Aggregate-function clause manipulation
 *****************************************************************************/

/*
 * contain_agg_clause
 *    Recursively search for Aggref/GroupingFunc nodes within a clause.
 *
 *    Returns true if any aggregate found.
 *
 * This does not descend into subqueries, and so should be used only after
 * reduction of sublinks to subplans, or in contexts where it's known there
 * are no subqueries.  There mustn't be outer-aggregate references either.
 *
 * (If you want something like this but able to deal with subqueries,
 * see rewriteManip.c's contain_aggs_of_level().)
 */
bool
contain_agg_clause(Node *clause)
{
    return contain_agg_clause_walker(clause, NULL);
}

static bool
contain_agg_clause_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Aggref))
    {
        Assert(((Aggref *) node)->agglevelsup == 0);
        return true;            /* abort the tree traversal and return true */
    }
    if (IsA(node, GroupingFunc))
    {
        Assert(((GroupingFunc *) node)->agglevelsup == 0);
        return true;            /* abort the tree traversal and return true */
    }
    Assert(!IsA(node, SubLink));
    return expression_tree_walker(node, contain_agg_clause_walker, context);
}

/*
 * get_agg_clause_costs
 *    Recursively find the Aggref nodes in an expression tree, and
 *    accumulate cost information about them.
 *
 * 'aggsplit' tells us the expected partial-aggregation mode, which affects
 * the cost estimates.
 *
 * NOTE that the counts/costs are ADDED to those already in *costs ... so
 * the caller is responsible for zeroing the struct initially.
 *
 * We count the nodes, estimate their execution costs, and estimate the total
 * space needed for their transition state values if all are evaluated in
 * parallel (as would be done in a HashAgg plan).  Also, we check whether
 * partial aggregation is feasible.  See AggClauseCosts for the exact set
 * of statistics collected.
 *
 * In addition, we mark Aggref nodes with the correct aggtranstype, so
 * that that doesn't need to be done repeatedly.  (That makes this function's
 * name a bit of a misnomer.)
 *
 * This does not descend into subqueries, and so should be used only after
 * reduction of sublinks to subplans, or in contexts where it's known there
 * are no subqueries.  There mustn't be outer-aggregate references either.
 */
void
get_agg_clause_costs(PlannerInfo *root, Node *clause, AggSplit aggsplit,
                     AggClauseCosts *costs)
{
    get_agg_clause_costs_context context;

    context.root = root;
    context.aggsplit = aggsplit;
    context.costs = costs;
    (void) get_agg_clause_costs_walker(clause, &context);
}

static bool
get_agg_clause_costs_walker(Node *node, get_agg_clause_costs_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Aggref))
    {
        Aggref     *aggref = (Aggref *) node;
        AggClauseCosts *costs = context->costs;
        HeapTuple   aggTuple;
        Form_pg_aggregate aggform;
        Oid         aggtransfn;
        Oid         aggfinalfn;
        Oid         aggcombinefn;
        Oid         aggserialfn;
        Oid         aggdeserialfn;
        Oid         aggtranstype;
        int32       aggtransspace;
        QualCost    argcosts;

        Assert(aggref->agglevelsup == 0);

        /*
         * Fetch info about aggregate from pg_aggregate.  Note it's correct to
         * ignore the moving-aggregate variant, since what we're concerned
         * with here is aggregates not window functions.
         */
        aggTuple = SearchSysCache1(AGGFNOID,
                                   ObjectIdGetDatum(aggref->aggfnoid));
        if (!HeapTupleIsValid(aggTuple))
            elog(ERROR, "cache lookup failed for aggregate %u",
                 aggref->aggfnoid);
        aggform = (Form_pg_aggregate) GETSTRUCT(aggTuple);
        aggtransfn = aggform->aggtransfn;
        aggfinalfn = aggform->aggfinalfn;
        aggcombinefn = aggform->aggcombinefn;
        aggserialfn = aggform->aggserialfn;
        aggdeserialfn = aggform->aggdeserialfn;
        aggtranstype = aggform->aggtranstype;
        aggtransspace = aggform->aggtransspace;
        ReleaseSysCache(aggTuple);

        /*
         * Resolve the possibly-polymorphic aggregate transition type, unless
         * already done in a previous pass over the expression.
         */
        if (OidIsValid(aggref->aggtranstype))
            aggtranstype = aggref->aggtranstype;
        else
        {
            Oid         inputTypes[FUNC_MAX_ARGS];
            int         numArguments;

            /* extract argument types (ignoring any ORDER BY expressions) */
            numArguments = get_aggregate_argtypes(aggref, inputTypes);

            /* resolve actual type of transition state, if polymorphic */
            aggtranstype = resolve_aggregate_transtype(aggref->aggfnoid,
                                                       aggtranstype,
                                                       inputTypes,
                                                       numArguments);
            aggref->aggtranstype = aggtranstype;
        }

        /*
         * Count it, and check for cases requiring ordered input.  Note that
         * ordered-set aggs always have nonempty aggorder.  Any ordered-input
         * case also defeats partial aggregation.
         */
        costs->numAggs++;
        if (aggref->aggorder != NIL || aggref->aggdistinct != NIL)
        {
            costs->numOrderedAggs++;
            costs->hasNonPartial = true;
        }

        /*
         * Check whether partial aggregation is feasible, unless we already
         * found out that we can't do it.
         */
        if (!costs->hasNonPartial)
        {
            /*
             * If there is no combine function, then partial aggregation is
             * not possible.
             */
            if (!OidIsValid(aggcombinefn))
                costs->hasNonPartial = true;

            /*
             * If we have any aggs with transtype INTERNAL then we must check
             * whether they have serialization/deserialization functions; if
             * not, we can't serialize partial-aggregation results.
             */
            else if (aggtranstype == INTERNALOID &&
                     (!OidIsValid(aggserialfn) || !OidIsValid(aggdeserialfn)))
                costs->hasNonSerial = true;
        }

        /*
         * Add the appropriate component function execution costs to
         * appropriate totals.
         */
        if (DO_AGGSPLIT_COMBINE(context->aggsplit))
        {
            /* charge for combining previously aggregated states */
            costs->transCost.per_tuple += get_func_cost(aggcombinefn) * cpu_operator_cost;
        }
        else
            costs->transCost.per_tuple += get_func_cost(aggtransfn) * cpu_operator_cost;
        if (DO_AGGSPLIT_DESERIALIZE(context->aggsplit) &&
            OidIsValid(aggdeserialfn))
            costs->transCost.per_tuple += get_func_cost(aggdeserialfn) * cpu_operator_cost;
        if (DO_AGGSPLIT_SERIALIZE(context->aggsplit) &&
            OidIsValid(aggserialfn))
            costs->finalCost += get_func_cost(aggserialfn) * cpu_operator_cost;
        if (!DO_AGGSPLIT_SKIPFINAL(context->aggsplit) &&
            OidIsValid(aggfinalfn))
            costs->finalCost += get_func_cost(aggfinalfn) * cpu_operator_cost;

        /*
         * These costs are incurred only by the initial aggregate node, so we
         * mustn't include them again at upper levels.
         */
        if (!DO_AGGSPLIT_COMBINE(context->aggsplit))
        {
            /* add the input expressions' cost to per-input-row costs */
            cost_qual_eval_node(&argcosts, (Node *) aggref->args, context->root);
            costs->transCost.startup += argcosts.startup;
            costs->transCost.per_tuple += argcosts.per_tuple;

            /*
             * Add any filter's cost to per-input-row costs.
             *
             * XXX Ideally we should reduce input expression costs according
             * to filter selectivity, but it's not clear it's worth the
             * trouble.
             */
            if (aggref->aggfilter)
            {
                cost_qual_eval_node(&argcosts, (Node *) aggref->aggfilter,
                                    context->root);
                costs->transCost.startup += argcosts.startup;
                costs->transCost.per_tuple += argcosts.per_tuple;
            }
        }

        /*
         * If there are direct arguments, treat their evaluation cost like the
         * cost of the finalfn.
         */
        if (aggref->aggdirectargs)
        {
            cost_qual_eval_node(&argcosts, (Node *) aggref->aggdirectargs,
                                context->root);
            costs->transCost.startup += argcosts.startup;
            costs->finalCost += argcosts.per_tuple;
        }

        /*
         * If the transition type is pass-by-value then it doesn't add
         * anything to the required size of the hashtable.  If it is
         * pass-by-reference then we have to add the estimated size of the
         * value itself, plus palloc overhead.
         */
        if (!get_typbyval(aggtranstype))
        {
            int32       avgwidth;

            /* Use average width if aggregate definition gave one */
            if (aggtransspace > 0)
                avgwidth = aggtransspace;
            else if (aggtransfn == F_ARRAY_APPEND)
            {
                /*
                 * If the transition function is array_append(), it'll use an
                 * expanded array as transvalue, which will occupy at least
                 * ALLOCSET_SMALL_INITSIZE and possibly more.  Use that as the
                 * estimate for lack of a better idea.
                 */
                avgwidth = ALLOCSET_SMALL_INITSIZE;
            }
            else
            {
                /*
                 * If transition state is of same type as first aggregated
                 * input, assume it's the same typmod (same width) as well.
                 * This works for cases like MAX/MIN and is probably somewhat
                 * reasonable otherwise.
                 */
                int32       aggtranstypmod = -1;

                if (aggref->args)
                {
                    TargetEntry *tle = (TargetEntry *) linitial(aggref->args);

                    if (aggtranstype == exprType((Node *) tle->expr))
                        aggtranstypmod = exprTypmod((Node *) tle->expr);
                }

                avgwidth = get_typavgwidth(aggtranstype, aggtranstypmod);
            }

            avgwidth = MAXALIGN(avgwidth);
            costs->transitionSpace += avgwidth + 2 * sizeof(void *);
        }
        else if (aggtranstype == INTERNALOID)
        {
            /*
             * INTERNAL transition type is a special case: although INTERNAL
             * is pass-by-value, it's almost certainly being used as a pointer
             * to some large data structure.  The aggregate definition can
             * provide an estimate of the size.  If it doesn't, then we assume
             * ALLOCSET_DEFAULT_INITSIZE, which is a good guess if the data is
             * being kept in a private memory context, as is done by
             * array_agg() for instance.
             */
            if (aggtransspace > 0)
                costs->transitionSpace += aggtransspace;
            else
                costs->transitionSpace += ALLOCSET_DEFAULT_INITSIZE;
        }

        /*
         * We assume that the parser checked that there are no aggregates (of
         * this level anyway) in the aggregated arguments, direct arguments,
         * or filter clause.  Hence, we need not recurse into any of them.
         */
        return false;
    }
    Assert(!IsA(node, SubLink));
    return expression_tree_walker(node, get_agg_clause_costs_walker,
                                  (void *) context);
}


/*****************************************************************************
 *      Window-function clause manipulation
 *****************************************************************************/

/*
 * contain_window_function
 *    Recursively search for WindowFunc nodes within a clause.
 *
 * Since window functions don't have level fields, but are hard-wired to
 * be associated with the current query level, this is just the same as
 * rewriteManip.c's function.
 */
bool
contain_window_function(Node *clause)
{
    return contain_windowfuncs(clause);
}

/*
 * find_window_functions
 *    Locate all the WindowFunc nodes in an expression tree, and organize
 *    them by winref ID number.
 *
 * Caller must provide an upper bound on the winref IDs expected in the tree.
 */
WindowFuncLists *
find_window_functions(Node *clause, Index maxWinRef)
{
    WindowFuncLists *lists = palloc(sizeof(WindowFuncLists));

    lists->numWindowFuncs = 0;
    lists->maxWinRef = maxWinRef;
    lists->windowFuncs = (List **) palloc0((maxWinRef + 1) * sizeof(List *));
    (void) find_window_functions_walker(clause, lists);
    return lists;
}

static bool
find_window_functions_walker(Node *node, WindowFuncLists *lists)
{
    if (node == NULL)
        return false;
    if (IsA(node, WindowFunc))
    {
        WindowFunc *wfunc = (WindowFunc *) node;

        /* winref is unsigned, so one-sided test is OK */
        if (wfunc->winref > lists->maxWinRef)
            elog(ERROR, "WindowFunc contains out-of-range winref %u",
                 wfunc->winref);
        /* eliminate duplicates, so that we avoid repeated computation */
        if (!list_member(lists->windowFuncs[wfunc->winref], wfunc))
        {
            lists->windowFuncs[wfunc->winref] =
                lappend(lists->windowFuncs[wfunc->winref], wfunc);
            lists->numWindowFuncs++;
        }

        /*
         * We assume that the parser checked that there are no window
         * functions in the arguments or filter clause.  Hence, we need not
         * recurse into them.  (If either the parser or the planner screws up
         * on this point, the executor will still catch it; see ExecInitExpr.)
         */
        return false;
    }
    Assert(!IsA(node, SubLink));
    return expression_tree_walker(node, find_window_functions_walker,
                                  (void *) lists);
}


/*****************************************************************************
 *      Support for expressions returning sets
 *****************************************************************************/

/*
 * expression_returns_set_rows
 *    Estimate the number of rows returned by a set-returning expression.
 *    The result is 1 if it's not a set-returning expression.
 *
 * We should only examine the top-level function or operator; it used to be
 * appropriate to recurse, but not anymore.  (Even if there are more SRFs in
 * the function's inputs, their multipliers are accounted for separately.)
 *
 * Note: keep this in sync with expression_returns_set() in nodes/nodeFuncs.c.
 */
double
expression_returns_set_rows(Node *clause)
{
    if (clause == NULL)
        return 1.0;
    if (IsA(clause, FuncExpr))
    {
        FuncExpr   *expr = (FuncExpr *) clause;

        if (expr->funcretset)
            return clamp_row_est(get_func_rows(expr->funcid));
    }
    if (IsA(clause, OpExpr))
    {
        OpExpr     *expr = (OpExpr *) clause;

        if (expr->opretset)
        {
            set_opfuncid(expr);
            return clamp_row_est(get_func_rows(expr->opfuncid));
        }
    }
    return 1.0;
}


/*****************************************************************************
 *      Subplan clause manipulation
 *****************************************************************************/

/*
 * contain_subplans
 *    Recursively search for subplan nodes within a clause.
 *
 * If we see a SubLink node, we will return true.  This is only possible if
 * the expression tree hasn't yet been transformed by subselect.c.  We do not
 * know whether the node will produce a true subplan or just an initplan,
 * but we make the conservative assumption that it will be a subplan.
 *
 * Returns true if any subplan found.
 */
bool
contain_subplans(Node *clause)
{
    return contain_subplans_walker(clause, NULL);
}

static bool
contain_subplans_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, SubPlan) ||
        IsA(node, AlternativeSubPlan) ||
        IsA(node, SubLink))
        return true;            /* abort the tree traversal and return true */
    return expression_tree_walker(node, contain_subplans_walker, context);
}


/*****************************************************************************
 *      Check clauses for mutable functions
 *****************************************************************************/

/*
 * contain_mutable_functions
 *    Recursively search for mutable functions within a clause.
 *
 * Returns true if any mutable function (or operator implemented by a
 * mutable function) is found.  This test is needed so that we don't
 * mistakenly think that something like "WHERE random() < 0.5" can be treated
 * as a constant qualification.
 *
 * We will recursively look into Query nodes (i.e., SubLink sub-selects)
 * but not into SubPlans.  See comments for contain_volatile_functions().
 */
bool
contain_mutable_functions(Node *clause)
{
    return contain_mutable_functions_walker(clause, NULL);
}

static bool
contain_mutable_functions_checker(Oid func_id, void *context)
{
    return (func_volatile(func_id) != PROVOLATILE_IMMUTABLE);
}

static bool
contain_mutable_functions_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;
    /* Check for mutable functions in node itself */
    if (check_functions_in_node(node, contain_mutable_functions_checker,
                                context))
        return true;

    if (IsA(node, SQLValueFunction))
    {
        /* all variants of SQLValueFunction are stable */
        return true;
    }

    if (IsA(node, NextValueExpr))
    {
        /* NextValueExpr is volatile */
        return true;
    }

    /*
     * It should be safe to treat MinMaxExpr as immutable, because it will
     * depend on a non-cross-type btree comparison function, and those should
     * always be immutable.  Treating XmlExpr as immutable is more dubious,
     * and treating CoerceToDomain as immutable is outright dangerous.  But we
     * have done so historically, and changing this would probably cause more
     * problems than it would fix.  In practice, if you have a non-immutable
     * domain constraint you are in for pain anyhow.
     */

    /* Recurse to check arguments */
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        return query_tree_walker((Query *) node,
                                 contain_mutable_functions_walker,
                                 context, 0);
    }
    return expression_tree_walker(node, contain_mutable_functions_walker,
                                  context);
}


/*****************************************************************************
 *      Check clauses for volatile functions
 *****************************************************************************/

/*
 * contain_volatile_functions
 *    Recursively search for volatile functions within a clause.
 *
 * Returns true if any volatile function (or operator implemented by a
 * volatile function) is found. This test prevents, for example,
 * invalid conversions of volatile expressions into indexscan quals.
 *
 * We will recursively look into Query nodes (i.e., SubLink sub-selects)
 * but not into SubPlans.  This is a bit odd, but intentional.  If we are
 * looking at a SubLink, we are probably deciding whether a query tree
 * transformation is safe, and a contained sub-select should affect that;
 * for example, duplicating a sub-select containing a volatile function
 * would be bad.  However, once we've got to the stage of having SubPlans,
 * subsequent planning need not consider volatility within those, since
 * the executor won't change its evaluation rules for a SubPlan based on
 * volatility.
 */
bool
contain_volatile_functions(Node *clause)
{
    return contain_volatile_functions_walker(clause, NULL);
}

static bool
contain_volatile_functions_checker(Oid func_id, void *context)
{
    return (func_volatile(func_id) == PROVOLATILE_VOLATILE);
}

static bool
contain_volatile_functions_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;
    /* Check for volatile functions in node itself */
    if (check_functions_in_node(node, contain_volatile_functions_checker,
                                context))
        return true;

    if (IsA(node, NextValueExpr))
    {
        /* NextValueExpr is volatile */
        return true;
    }

    /*
     * See notes in contain_mutable_functions_walker about why we treat
     * MinMaxExpr, XmlExpr, and CoerceToDomain as immutable, while
     * SQLValueFunction is stable.  Hence, none of them are of interest here.
     */

    /* Recurse to check arguments */
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        return query_tree_walker((Query *) node,
                                 contain_volatile_functions_walker,
                                 context, 0);
    }
    return expression_tree_walker(node, contain_volatile_functions_walker,
                                  context);
}

/*
 * Special purpose version of contain_volatile_functions() for use in COPY:
 * ignore nextval(), but treat all other functions normally.
 */
bool
contain_volatile_functions_not_nextval(Node *clause)
{
    return contain_volatile_functions_not_nextval_walker(clause, NULL);
}

static bool
contain_volatile_functions_not_nextval_checker(Oid func_id, void *context)
{
    return (func_id != F_NEXTVAL_OID &&
            func_volatile(func_id) == PROVOLATILE_VOLATILE);
}

static bool
contain_volatile_functions_not_nextval_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;
    /* Check for volatile functions in node itself */
    if (check_functions_in_node(node,
                                contain_volatile_functions_not_nextval_checker,
                                context))
        return true;

    /*
     * See notes in contain_mutable_functions_walker about why we treat
     * MinMaxExpr, XmlExpr, and CoerceToDomain as immutable, while
     * SQLValueFunction is stable.  Hence, none of them are of interest here.
     * Also, since we're intentionally ignoring nextval(), presumably we
     * should ignore NextValueExpr.
     */

    /* Recurse to check arguments */
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        return query_tree_walker((Query *) node,
                                 contain_volatile_functions_not_nextval_walker,
                                 context, 0);
    }
    return expression_tree_walker(node,
                                  contain_volatile_functions_not_nextval_walker,
                                  context);
}


/*****************************************************************************
 *      Check queries for parallel unsafe and/or restricted constructs
 *****************************************************************************/

/*
 * max_parallel_hazard
 *      Find the worst parallel-hazard level in the given query
 *
 * Returns the worst function hazard property (the earliest in this list:
 * PROPARALLEL_UNSAFE, PROPARALLEL_RESTRICTED, PROPARALLEL_SAFE) that can
 * be found in the given parsetree.  We use this to find out whether the query
 * can be parallelized at all.  The caller will also save the result in
 * PlannerGlobal so as to short-circuit checks of portions of the querytree
 * later, in the common case where everything is SAFE.
 */
char
max_parallel_hazard(Query *parse)
{
    max_parallel_hazard_context context;

    context.max_hazard = PROPARALLEL_SAFE;
    context.max_interesting = PROPARALLEL_UNSAFE;
    context.safe_param_ids = NIL;
    (void) max_parallel_hazard_walker((Node *) parse, &context);
    return context.max_hazard;
}

/*
 * is_parallel_safe
 *      Detect whether the given expr contains only parallel-safe functions
 *
 * root->glob->maxParallelHazard must previously have been set to the
 * result of max_parallel_hazard() on the whole query.
 */
bool
is_parallel_safe(PlannerInfo *root, Node *node)
{
    max_parallel_hazard_context context;
    PlannerInfo *proot;
    ListCell   *l;

    /*
     * Even if the original querytree contained nothing unsafe, we need to
     * search the expression if we have generated any PARAM_EXEC Params while
     * planning, because those are parallel-restricted and there might be one
     * in this expression.  But otherwise we don't need to look.
     */
    if (root->glob->maxParallelHazard == PROPARALLEL_SAFE &&
        root->glob->paramExecTypes == NIL)
        return true;
    /* Else use max_parallel_hazard's search logic, but stop on RESTRICTED */
    context.max_hazard = PROPARALLEL_SAFE;
    context.max_interesting = PROPARALLEL_RESTRICTED;
    context.safe_param_ids = NIL;

    /*
     * The params that refer to the same or parent query level are considered
     * parallel-safe.  The idea is that we compute such params at Gather or
     * Gather Merge node and pass their value to workers.
     */
    for (proot = root; proot != NULL; proot = proot->parent_root)
    {
        foreach(l, proot->init_plans)
        {
            SubPlan    *initsubplan = (SubPlan *) lfirst(l);
            ListCell   *l2;

            foreach(l2, initsubplan->setParam)
                context.safe_param_ids = lcons_int(lfirst_int(l2),
                                                   context.safe_param_ids);
        }
    }

    return !max_parallel_hazard_walker(node, &context);
}

/* core logic for all parallel-hazard checks */
static bool
max_parallel_hazard_test(char proparallel, max_parallel_hazard_context *context)
{
    switch (proparallel)
    {
        case PROPARALLEL_SAFE:
            /* nothing to see here, move along */
            break;
        case PROPARALLEL_RESTRICTED:
            /* increase max_hazard to RESTRICTED */
            Assert(context->max_hazard != PROPARALLEL_UNSAFE);
            context->max_hazard = proparallel;
            /* done if we are not expecting any unsafe functions */
            if (context->max_interesting == proparallel)
                return true;
            break;
        case PROPARALLEL_UNSAFE:
            context->max_hazard = proparallel;
            /* we're always done at the first unsafe construct */
            return true;
        default:
            elog(ERROR, "unrecognized proparallel value \"%c\"", proparallel);
            break;
    }
    return false;
}

/* check_functions_in_node callback */
static bool
max_parallel_hazard_checker(Oid func_id, void *context)
{
    return max_parallel_hazard_test(func_parallel(func_id),
                                    (max_parallel_hazard_context *) context);
}

static bool
max_parallel_hazard_walker(Node *node, max_parallel_hazard_context *context)
{
    if (node == NULL)
        return false;

    /* Check for hazardous functions in node itself */
    if (check_functions_in_node(node, max_parallel_hazard_checker,
                                context))
        return true;

    /*
     * It should be OK to treat MinMaxExpr as parallel-safe, since btree
     * opclass support functions are generally parallel-safe.  XmlExpr is a
     * bit more dubious but we can probably get away with it.  We err on the
     * side of caution by treating CoerceToDomain as parallel-restricted.
     * (Note: in principle that's wrong because a domain constraint could
     * contain a parallel-unsafe function; but useful constraints probably
     * never would have such, and assuming they do would cripple use of
     * parallel query in the presence of domain types.)  SQLValueFunction
     * should be safe in all cases.  NextValueExpr is parallel-unsafe.
     */
    if (IsA(node, CoerceToDomain))
    {
        if (max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context))
            return true;
    }

    if (IsA(node, NextValueExpr))
    {
        if (max_parallel_hazard_test(PROPARALLEL_UNSAFE, context))
            return true;
    }

    /*
     * As a notational convenience for callers, look through RestrictInfo.
     */
    else if (IsA(node, RestrictInfo))
    {
        RestrictInfo *rinfo = (RestrictInfo *) node;

        return max_parallel_hazard_walker((Node *) rinfo->clause, context);
    }

    /*
     * Really we should not see SubLink during a max_interesting == restricted
     * scan, but if we do, return true.
     */
    else if (IsA(node, SubLink))
    {
        if (max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context))
            return true;
    }

    /*
     * Only parallel-safe SubPlans can be sent to workers.  Within the
     * testexpr of the SubPlan, Params representing the output columns of the
     * subplan can be treated as parallel-safe, so temporarily add their IDs
     * to the safe_param_ids list while examining the testexpr.
     */
    else if (IsA(node, SubPlan))
    {
        SubPlan    *subplan = (SubPlan *) node;
        List       *save_safe_param_ids;

        if (!subplan->parallel_safe &&
            max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context))
            return true;
        save_safe_param_ids = context->safe_param_ids;
        context->safe_param_ids = list_concat(list_copy(subplan->paramIds),
                                              context->safe_param_ids);
        if (max_parallel_hazard_walker(subplan->testexpr, context))
            return true;        /* no need to restore safe_param_ids */
        context->safe_param_ids = save_safe_param_ids;
        /* we must also check args, but no special Param treatment there */
        if (max_parallel_hazard_walker((Node *) subplan->args, context))
            return true;
        /* don't want to recurse normally, so we're done */
        return false;
    }

    /*
     * We can't pass Params to workers at the moment either, so they are also
     * parallel-restricted, unless they are PARAM_EXTERN Params or are
     * PARAM_EXEC Params listed in safe_param_ids, meaning they could be
     * either generated within the worker or can be computed in master and
     * then their value can be passed to the worker.
     */
    else if (IsA(node, Param))
    {
        Param      *param = (Param *) node;

        if (param->paramkind == PARAM_EXTERN)
            return false;

        if (param->paramkind != PARAM_EXEC ||
            !list_member_int(context->safe_param_ids, param->paramid))
        {
            if (max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context))
                return true;
        }
        return false;           /* nothing to recurse to */
    }

    /*
     * When we're first invoked on a completely unplanned tree, we must
     * recurse into subqueries so to as to locate parallel-unsafe constructs
     * anywhere in the tree.
     */
    else if (IsA(node, Query))
    {
        Query      *query = (Query *) node;

        /* SELECT FOR UPDATE/SHARE must be treated as unsafe */
        if (query->rowMarks != NULL)
        {
            context->max_hazard = PROPARALLEL_UNSAFE;
            return true;
        }

        /* Recurse into subselects */
        return query_tree_walker(query,
                                 max_parallel_hazard_walker,
                                 context, 0);
    }

    /* Recurse to check arguments */
    return expression_tree_walker(node,
                                  max_parallel_hazard_walker,
                                  context);
}


/*****************************************************************************
 *      Check clauses for nonstrict functions
 *****************************************************************************/

/*
 * contain_nonstrict_functions
 *    Recursively search for nonstrict functions within a clause.
 *
 * Returns true if any nonstrict construct is found --- ie, anything that
 * could produce non-NULL output with a NULL input.
 *
 * The idea here is that the caller has verified that the expression contains
 * one or more Var or Param nodes (as appropriate for the caller's need), and
 * now wishes to prove that the expression result will be NULL if any of these
 * inputs is NULL.  If we return false, then the proof succeeded.
 */
bool
contain_nonstrict_functions(Node *clause)
{
    return contain_nonstrict_functions_walker(clause, NULL);
}

static bool
contain_nonstrict_functions_checker(Oid func_id, void *context)
{
    return !func_strict(func_id);
}

static bool
contain_nonstrict_functions_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Aggref))
    {
        /* an aggregate could return non-null with null input */
        return true;
    }
    if (IsA(node, GroupingFunc))
    {
        /*
         * A GroupingFunc doesn't evaluate its arguments, and therefore must
         * be treated as nonstrict.
         */
        return true;
    }
    if (IsA(node, WindowFunc))
    {
        /* a window function could return non-null with null input */
        return true;
    }
    if (IsA(node, ArrayRef))
    {
        /* array assignment is nonstrict, but subscripting is strict */
        if (((ArrayRef *) node)->refassgnexpr != NULL)
            return true;
        /* else fall through to check args */
    }
    if (IsA(node, DistinctExpr))
    {
        /* IS DISTINCT FROM is inherently non-strict */
        return true;
    }
    if (IsA(node, NullIfExpr))
    {
        /* NULLIF is inherently non-strict */
        return true;
    }
    if (IsA(node, BoolExpr))
    {
        BoolExpr   *expr = (BoolExpr *) node;

        switch (expr->boolop)
        {
            case AND_EXPR:
            case OR_EXPR:
                /* AND, OR are inherently non-strict */
                return true;
            default:
                break;
        }
    }
    if (IsA(node, SubLink))
    {
        /* In some cases a sublink might be strict, but in general not */
        return true;
    }
    if (IsA(node, SubPlan))
        return true;
    if (IsA(node, AlternativeSubPlan))
        return true;
    if (IsA(node, FieldStore))
        return true;
    if (IsA(node, ArrayCoerceExpr))
    {
        /*
         * ArrayCoerceExpr is strict at the array level, regardless of what
         * the per-element expression is; so we should ignore elemexpr and
         * recurse only into the arg.
         */
        return expression_tree_walker((Node *) ((ArrayCoerceExpr *) node)->arg,
                                      contain_nonstrict_functions_walker,
                                      context);
    }
    if (IsA(node, CaseExpr))
        return true;
    if (IsA(node, ArrayExpr))
        return true;
    if (IsA(node, RowExpr))
        return true;
    if (IsA(node, RowCompareExpr))
        return true;
    if (IsA(node, CoalesceExpr))
        return true;
    if (IsA(node, MinMaxExpr))
        return true;
    if (IsA(node, XmlExpr))
        return true;
    if (IsA(node, NullTest))
        return true;
    if (IsA(node, BooleanTest))
        return true;

    /* Check other function-containing nodes */
    if (check_functions_in_node(node, contain_nonstrict_functions_checker,
                                context))
        return true;

    return expression_tree_walker(node, contain_nonstrict_functions_walker,
                                  context);
}

/*****************************************************************************
 *      Check clauses for context-dependent nodes
 *****************************************************************************/

/*
 * contain_context_dependent_node
 *    Recursively search for context-dependent nodes within a clause.
 *
 * CaseTestExpr nodes must appear directly within the corresponding CaseExpr,
 * not nested within another one, or they'll see the wrong test value.  If one
 * appears "bare" in the arguments of a SQL function, then we can't inline the
 * SQL function for fear of creating such a situation.
 *
 * CoerceToDomainValue would have the same issue if domain CHECK expressions
 * could get inlined into larger expressions, but presently that's impossible.
 * Still, it might be allowed in future, or other node types with similar
 * issues might get invented.  So give this function a generic name, and set
 * up the recursion state to allow multiple flag bits.
 */
static bool
contain_context_dependent_node(Node *clause)
{
    int         flags = 0;

    return contain_context_dependent_node_walker(clause, &flags);
}

#define CCDN_IN_CASEEXPR    0x0001  /* CaseTestExpr okay here? */

static bool
contain_context_dependent_node_walker(Node *node, int *flags)
{
    if (node == NULL)
        return false;
    if (IsA(node, CaseTestExpr))
        return !(*flags & CCDN_IN_CASEEXPR);
    if (IsA(node, CaseExpr))
    {
        CaseExpr   *caseexpr = (CaseExpr *) node;

        /*
         * If this CASE doesn't have a test expression, then it doesn't create
         * a context in which CaseTestExprs should appear, so just fall
         * through and treat it as a generic expression node.
         */
        if (caseexpr->arg)
        {
            int         save_flags = *flags;
            bool        res;

            /*
             * Note: in principle, we could distinguish the various sub-parts
             * of a CASE construct and set the flag bit only for some of them,
             * since we are only expecting CaseTestExprs to appear in the
             * "expr" subtree of the CaseWhen nodes.  But it doesn't really
             * seem worth any extra code.  If there are any bare CaseTestExprs
             * elsewhere in the CASE, something's wrong already.
             */
            *flags |= CCDN_IN_CASEEXPR;
            res = expression_tree_walker(node,
                                         contain_context_dependent_node_walker,
                                         (void *) flags);
            *flags = save_flags;
            return res;
        }
    }
    return expression_tree_walker(node, contain_context_dependent_node_walker,
                                  (void *) flags);
}

/*****************************************************************************
 *        Check clauses for Vars passed to non-leakproof functions
 *****************************************************************************/

/*
 * contain_leaked_vars
 *      Recursively scan a clause to discover whether it contains any Var
 *      nodes (of the current query level) that are passed as arguments to
 *      leaky functions.
 *
 * Returns true if the clause contains any non-leakproof functions that are
 * passed Var nodes of the current query level, and which might therefore leak
 * data.  Such clauses must be applied after any lower-level security barrier
 * clauses.
 */
bool
contain_leaked_vars(Node *clause)
{
    return contain_leaked_vars_walker(clause, NULL);
}

static bool
contain_leaked_vars_checker(Oid func_id, void *context)
{
    return !get_func_leakproof(func_id);
}

static bool
contain_leaked_vars_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;

    switch (nodeTag(node))
    {
        case T_Var:
        case T_Const:
        case T_Param:
        case T_ArrayRef:
        case T_ArrayExpr:
        case T_FieldSelect:
        case T_FieldStore:
        case T_NamedArgExpr:
        case T_BoolExpr:
        case T_RelabelType:
        case T_CollateExpr:
        case T_CaseExpr:
        case T_CaseTestExpr:
        case T_RowExpr:
        case T_MinMaxExpr:
        case T_SQLValueFunction:
        case T_NullTest:
        case T_BooleanTest:
        case T_NextValueExpr:
        case T_List:

            /*
             * We know these node types don't contain function calls; but
             * something further down in the node tree might.
             */
            break;

        case T_FuncExpr:
        case T_OpExpr:
        case T_DistinctExpr:
        case T_NullIfExpr:
        case T_ScalarArrayOpExpr:
        case T_CoerceViaIO:
        case T_ArrayCoerceExpr:

            /*
             * If node contains a leaky function call, and there's any Var
             * underneath it, reject.
             */
            if (check_functions_in_node(node, contain_leaked_vars_checker,
                                        context) &&
                contain_var_clause(node))
                return true;
            break;

        case T_RowCompareExpr:
            {
                /*
                 * It's worth special-casing this because a leaky comparison
                 * function only compromises one pair of row elements, which
                 * might not contain Vars while others do.
                 */
                RowCompareExpr *rcexpr = (RowCompareExpr *) node;
                ListCell   *opid;
                ListCell   *larg;
                ListCell   *rarg;

                forthree(opid, rcexpr->opnos,
                         larg, rcexpr->largs,
                         rarg, rcexpr->rargs)
                {
                    Oid         funcid = get_opcode(lfirst_oid(opid));

                    if (!get_func_leakproof(funcid) &&
                        (contain_var_clause((Node *) lfirst(larg)) ||
                         contain_var_clause((Node *) lfirst(rarg))))
                        return true;
                }
            }
            break;

        case T_CurrentOfExpr:

            /*
             * WHERE CURRENT OF doesn't contain leaky function calls.
             * Moreover, it is essential that this is considered non-leaky,
             * since the planner must always generate a TID scan when CURRENT
             * OF is present -- cf. cost_tidscan.
             */
            return false;

        default:

            /*
             * If we don't recognize the node tag, assume it might be leaky.
             * This prevents an unexpected security hole if someone adds a new
             * node type that can call a function.
             */
            return true;
    }
    return expression_tree_walker(node, contain_leaked_vars_walker,
                                  context);
}

/*
 * find_nonnullable_rels
 *      Determine which base rels are forced nonnullable by given clause.
 *
 * Returns the set of all Relids that are referenced in the clause in such
 * a way that the clause cannot possibly return TRUE if any of these Relids
 * is an all-NULL row.  (It is OK to err on the side of conservatism; hence
 * the analysis here is simplistic.)
 *
 * The semantics here are subtly different from contain_nonstrict_functions:
 * that function is concerned with NULL results from arbitrary expressions,
 * but here we assume that the input is a Boolean expression, and wish to
 * see if NULL inputs will provably cause a FALSE-or-NULL result.  We expect
 * the expression to have been AND/OR flattened and converted to implicit-AND
 * format.
 *
 * Note: this function is largely duplicative of find_nonnullable_vars().
 * The reason not to simplify this function into a thin wrapper around
 * find_nonnullable_vars() is that the tested conditions really are different:
 * a clause like "t1.v1 IS NOT NULL OR t1.v2 IS NOT NULL" does not prove
 * that either v1 or v2 can't be NULL, but it does prove that the t1 row
 * as a whole can't be all-NULL.
 *
 * top_level is true while scanning top-level AND/OR structure; here, showing
 * the result is either FALSE or NULL is good enough.  top_level is false when
 * we have descended below a NOT or a strict function: now we must be able to
 * prove that the subexpression goes to NULL.
 *
 * We don't use expression_tree_walker here because we don't want to descend
 * through very many kinds of nodes; only the ones we can be sure are strict.
 */
Relids
find_nonnullable_rels(Node *clause)
{
    return find_nonnullable_rels_walker(clause, true);
}

static Relids
find_nonnullable_rels_walker(Node *node, bool top_level)
{
    Relids      result = NULL;
    ListCell   *l;

    if (node == NULL)
        return NULL;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;

        if (var->varlevelsup == 0)
            result = bms_make_singleton(var->varno);
    }
    else if (IsA(node, List))
    {
        /*
         * At top level, we are examining an implicit-AND list: if any of the
         * arms produces FALSE-or-NULL then the result is FALSE-or-NULL. If
         * not at top level, we are examining the arguments of a strict
         * function: if any of them produce NULL then the result of the
         * function must be NULL.  So in both cases, the set of nonnullable
         * rels is the union of those found in the arms, and we pass down the
         * top_level flag unmodified.
         */
        foreach(l, (List *) node)
        {
            result = bms_join(result,
                              find_nonnullable_rels_walker(lfirst(l),
                                                           top_level));
        }
    }
    else if (IsA(node, FuncExpr))
    {
        FuncExpr   *expr = (FuncExpr *) node;

        if (func_strict(expr->funcid))
            result = find_nonnullable_rels_walker((Node *) expr->args, false);
    }
    else if (IsA(node, OpExpr))
    {
        OpExpr     *expr = (OpExpr *) node;

        set_opfuncid(expr);
        if (func_strict(expr->opfuncid))
            result = find_nonnullable_rels_walker((Node *) expr->args, false);
    }
    else if (IsA(node, ScalarArrayOpExpr))
    {
        ScalarArrayOpExpr *expr = (ScalarArrayOpExpr *) node;

        if (is_strict_saop(expr, true))
            result = find_nonnullable_rels_walker((Node *) expr->args, false);
    }
    else if (IsA(node, BoolExpr))
    {
        BoolExpr   *expr = (BoolExpr *) node;

        switch (expr->boolop)
        {
            case AND_EXPR:
                /* At top level we can just recurse (to the List case) */
                if (top_level)
                {
                    result = find_nonnullable_rels_walker((Node *) expr->args,
                                                          top_level);
                    break;
                }

                /*
                 * Below top level, even if one arm produces NULL, the result
                 * could be FALSE (hence not NULL).  However, if *all* the
                 * arms produce NULL then the result is NULL, so we can take
                 * the intersection of the sets of nonnullable rels, just as
                 * for OR.  Fall through to share code.
                 */
                /* FALL THRU */
            case OR_EXPR:

                /*
                 * OR is strict if all of its arms are, so we can take the
                 * intersection of the sets of nonnullable rels for each arm.
                 * This works for both values of top_level.
                 */
                foreach(l, expr->args)
                {
                    Relids      subresult;

                    subresult = find_nonnullable_rels_walker(lfirst(l),
                                                             top_level);
                    if (result == NULL) /* first subresult? */
                        result = subresult;
                    else
                        result = bms_int_members(result, subresult);

                    /*
                     * If the intersection is empty, we can stop looking. This
                     * also justifies the test for first-subresult above.
                     */
                    if (bms_is_empty(result))
                        break;
                }
                break;
            case NOT_EXPR:
                /* NOT will return null if its arg is null */
                result = find_nonnullable_rels_walker((Node *) expr->args,
                                                      false);
                break;
            default:
                elog(ERROR, "unrecognized boolop: %d", (int) expr->boolop);
                break;
        }
    }
    else if (IsA(node, RelabelType))
    {
        RelabelType *expr = (RelabelType *) node;

        result = find_nonnullable_rels_walker((Node *) expr->arg, top_level);
    }
    else if (IsA(node, CoerceViaIO))
    {
        /* not clear this is useful, but it can't hurt */
        CoerceViaIO *expr = (CoerceViaIO *) node;

        result = find_nonnullable_rels_walker((Node *) expr->arg, top_level);
    }
    else if (IsA(node, ArrayCoerceExpr))
    {
        /* ArrayCoerceExpr is strict at the array level; ignore elemexpr */
        ArrayCoerceExpr *expr = (ArrayCoerceExpr *) node;

        result = find_nonnullable_rels_walker((Node *) expr->arg, top_level);
    }
    else if (IsA(node, ConvertRowtypeExpr))
    {
        /* not clear this is useful, but it can't hurt */
        ConvertRowtypeExpr *expr = (ConvertRowtypeExpr *) node;

        result = find_nonnullable_rels_walker((Node *) expr->arg, top_level);
    }
    else if (IsA(node, CollateExpr))
    {
        CollateExpr *expr = (CollateExpr *) node;

        result = find_nonnullable_rels_walker((Node *) expr->arg, top_level);
    }
    else if (IsA(node, NullTest))
    {
        /* IS NOT NULL can be considered strict, but only at top level */
        NullTest   *expr = (NullTest *) node;

        if (top_level && expr->nulltesttype == IS_NOT_NULL && !expr->argisrow)
            result = find_nonnullable_rels_walker((Node *) expr->arg, false);
    }
    else if (IsA(node, BooleanTest))
    {
        /* Boolean tests that reject NULL are strict at top level */
        BooleanTest *expr = (BooleanTest *) node;

        if (top_level &&
            (expr->booltesttype == IS_TRUE ||
             expr->booltesttype == IS_FALSE ||
             expr->booltesttype == IS_NOT_UNKNOWN))
            result = find_nonnullable_rels_walker((Node *) expr->arg, false);
    }
    else if (IsA(node, PlaceHolderVar))
    {
        PlaceHolderVar *phv = (PlaceHolderVar *) node;

        result = find_nonnullable_rels_walker((Node *) phv->phexpr, top_level);
    }
    return result;
}

/*
 * find_nonnullable_vars
 *      Determine which Vars are forced nonnullable by given clause.
 *
 * Returns a list of all level-zero Vars that are referenced in the clause in
 * such a way that the clause cannot possibly return TRUE if any of these Vars
 * is NULL.  (It is OK to err on the side of conservatism; hence the analysis
 * here is simplistic.)
 *
 * The semantics here are subtly different from contain_nonstrict_functions:
 * that function is concerned with NULL results from arbitrary expressions,
 * but here we assume that the input is a Boolean expression, and wish to
 * see if NULL inputs will provably cause a FALSE-or-NULL result.  We expect
 * the expression to have been AND/OR flattened and converted to implicit-AND
 * format.
 *
 * The result is a palloc'd List, but we have not copied the member Var nodes.
 * Also, we don't bother trying to eliminate duplicate entries.
 *
 * top_level is true while scanning top-level AND/OR structure; here, showing
 * the result is either FALSE or NULL is good enough.  top_level is false when
 * we have descended below a NOT or a strict function: now we must be able to
 * prove that the subexpression goes to NULL.
 *
 * We don't use expression_tree_walker here because we don't want to descend
 * through very many kinds of nodes; only the ones we can be sure are strict.
 */
List *
find_nonnullable_vars(Node *clause)
{
    return find_nonnullable_vars_walker(clause, true);
}

static List *
find_nonnullable_vars_walker(Node *node, bool top_level)
{
    List       *result = NIL;
    ListCell   *l;

    if (node == NULL)
        return NIL;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;

        if (var->varlevelsup == 0)
            result = list_make1(var);
    }
    else if (IsA(node, List))
    {
        /*
         * At top level, we are examining an implicit-AND list: if any of the
         * arms produces FALSE-or-NULL then the result is FALSE-or-NULL. If
         * not at top level, we are examining the arguments of a strict
         * function: if any of them produce NULL then the result of the
         * function must be NULL.  So in both cases, the set of nonnullable
         * vars is the union of those found in the arms, and we pass down the
         * top_level flag unmodified.
         */
        foreach(l, (List *) node)
        {
            result = list_concat(result,
                                 find_nonnullable_vars_walker(lfirst(l),
                                                              top_level));
        }
    }
    else if (IsA(node, FuncExpr))
    {
        FuncExpr   *expr = (FuncExpr *) node;

        if (func_strict(expr->funcid))
            result = find_nonnullable_vars_walker((Node *) expr->args, false);
    }
    else if (IsA(node, OpExpr))
    {
        OpExpr     *expr = (OpExpr *) node;

        set_opfuncid(expr);
        if (func_strict(expr->opfuncid))
            result = find_nonnullable_vars_walker((Node *) expr->args, false);
    }
    else if (IsA(node, ScalarArrayOpExpr))
    {
        ScalarArrayOpExpr *expr = (ScalarArrayOpExpr *) node;

        if (is_strict_saop(expr, true))
            result = find_nonnullable_vars_walker((Node *) expr->args, false);
    }
    else if (IsA(node, BoolExpr))
    {
        BoolExpr   *expr = (BoolExpr *) node;

        switch (expr->boolop)
        {
            case AND_EXPR:
                /* At top level we can just recurse (to the List case) */
                if (top_level)
                {
                    result = find_nonnullable_vars_walker((Node *) expr->args,
                                                          top_level);
                    break;
                }

                /*
                 * Below top level, even if one arm produces NULL, the result
                 * could be FALSE (hence not NULL).  However, if *all* the
                 * arms produce NULL then the result is NULL, so we can take
                 * the intersection of the sets of nonnullable vars, just as
                 * for OR.  Fall through to share code.
                 */
                /* FALL THRU */
            case OR_EXPR:

                /*
                 * OR is strict if all of its arms are, so we can take the
                 * intersection of the sets of nonnullable vars for each arm.
                 * This works for both values of top_level.
                 */
                foreach(l, expr->args)
                {
                    List       *subresult;

                    subresult = find_nonnullable_vars_walker(lfirst(l),
                                                             top_level);
                    if (result == NIL)  /* first subresult? */
                        result = subresult;
                    else
                        result = list_intersection(result, subresult);

                    /*
                     * If the intersection is empty, we can stop looking. This
                     * also justifies the test for first-subresult above.
                     */
                    if (result == NIL)
                        break;
                }
                break;
            case NOT_EXPR:
                /* NOT will return null if its arg is null */
                result = find_nonnullable_vars_walker((Node *) expr->args,
                                                      false);
                break;
            default:
                elog(ERROR, "unrecognized boolop: %d", (int) expr->boolop);
                break;
        }
    }
    else if (IsA(node, RelabelType))
    {
        RelabelType *expr = (RelabelType *) node;

        result = find_nonnullable_vars_walker((Node *) expr->arg, top_level);
    }
    else if (IsA(node, CoerceViaIO))
    {
        /* not clear this is useful, but it can't hurt */
        CoerceViaIO *expr = (CoerceViaIO *) node;

        result = find_nonnullable_vars_walker((Node *) expr->arg, false);
    }
    else if (IsA(node, ArrayCoerceExpr))
    {
        /* ArrayCoerceExpr is strict at the array level; ignore elemexpr */
        ArrayCoerceExpr *expr = (ArrayCoerceExpr *) node;

        result = find_nonnullable_vars_walker((Node *) expr->arg, top_level);
    }
    else if (IsA(node, ConvertRowtypeExpr))
    {
        /* not clear this is useful, but it can't hurt */
        ConvertRowtypeExpr *expr = (ConvertRowtypeExpr *) node;

        result = find_nonnullable_vars_walker((Node *) expr->arg, top_level);
    }
    else if (IsA(node, CollateExpr))
    {
        CollateExpr *expr = (CollateExpr *) node;

        result = find_nonnullable_vars_walker((Node *) expr->arg, top_level);
    }
    else if (IsA(node, NullTest))
    {
        /* IS NOT NULL can be considered strict, but only at top level */
        NullTest   *expr = (NullTest *) node;

        if (top_level && expr->nulltesttype == IS_NOT_NULL && !expr->argisrow)
            result = find_nonnullable_vars_walker((Node *) expr->arg, false);
    }
    else if (IsA(node, BooleanTest))
    {
        /* Boolean tests that reject NULL are strict at top level */
        BooleanTest *expr = (BooleanTest *) node;

        if (top_level &&
            (expr->booltesttype == IS_TRUE ||
             expr->booltesttype == IS_FALSE ||
             expr->booltesttype == IS_NOT_UNKNOWN))
            result = find_nonnullable_vars_walker((Node *) expr->arg, false);
    }
    else if (IsA(node, PlaceHolderVar))
    {
        PlaceHolderVar *phv = (PlaceHolderVar *) node;

        result = find_nonnullable_vars_walker((Node *) phv->phexpr, top_level);
    }
    return result;
}

/*
 * find_forced_null_vars
 *      Determine which Vars must be NULL for the given clause to return TRUE.
 *
 * This is the complement of find_nonnullable_vars: find the level-zero Vars
 * that must be NULL for the clause to return TRUE.  (It is OK to err on the
 * side of conservatism; hence the analysis here is simplistic.  In fact,
 * we only detect simple "var IS NULL" tests at the top level.)
 *
 * The result is a palloc'd List, but we have not copied the member Var nodes.
 * Also, we don't bother trying to eliminate duplicate entries.
 */
List *
find_forced_null_vars(Node *node)
{
    List       *result = NIL;
    Var        *var;
    ListCell   *l;

    if (node == NULL)
        return NIL;
    /* Check single-clause cases using subroutine */
    var = find_forced_null_var(node);
    if (var)
    {
        result = list_make1(var);
    }
    /* Otherwise, handle AND-conditions */
    else if (IsA(node, List))
    {
        /*
         * At top level, we are examining an implicit-AND list: if any of the
         * arms produces FALSE-or-NULL then the result is FALSE-or-NULL.
         */
        foreach(l, (List *) node)
        {
            result = list_concat(result,
                                 find_forced_null_vars(lfirst(l)));
        }
    }
    else if (IsA(node, BoolExpr))
    {
        BoolExpr   *expr = (BoolExpr *) node;

        /*
         * We don't bother considering the OR case, because it's fairly
         * unlikely anyone would write "v1 IS NULL OR v1 IS NULL". Likewise,
         * the NOT case isn't worth expending code on.
         */
        if (expr->boolop == AND_EXPR)
        {
            /* At top level we can just recurse (to the List case) */
            result = find_forced_null_vars((Node *) expr->args);
        }
    }
    return result;
}

/*
 * find_forced_null_var
 *      Return the Var forced null by the given clause, or NULL if it's
 *      not an IS NULL-type clause.  For success, the clause must enforce
 *      *only* nullness of the particular Var, not any other conditions.
 *
 * This is just the single-clause case of find_forced_null_vars(), without
 * any allowance for AND conditions.  It's used by initsplan.c on individual
 * qual clauses.  The reason for not just applying find_forced_null_vars()
 * is that if an AND of an IS NULL clause with something else were to somehow
 * survive AND/OR flattening, initsplan.c might get fooled into discarding
 * the whole clause when only the IS NULL part of it had been proved redundant.
 */
Var *
find_forced_null_var(Node *node)
{
    if (node == NULL)
        return NULL;
    if (IsA(node, NullTest))
    {
        /* check for var IS NULL */
        NullTest   *expr = (NullTest *) node;

        if (expr->nulltesttype == IS_NULL && !expr->argisrow)
        {
            Var        *var = (Var *) expr->arg;

            if (var && IsA(var, Var) &&
                var->varlevelsup == 0)
                return var;
        }
    }
    else if (IsA(node, BooleanTest))
    {
        /* var IS UNKNOWN is equivalent to var IS NULL */
        BooleanTest *expr = (BooleanTest *) node;

        if (expr->booltesttype == IS_UNKNOWN)
        {
            Var        *var = (Var *) expr->arg;

            if (var && IsA(var, Var) &&
                var->varlevelsup == 0)
                return var;
        }
    }
    return NULL;
}

/*
 * Can we treat a ScalarArrayOpExpr as strict?
 *
 * If "falseOK" is true, then a "false" result can be considered strict,
 * else we need to guarantee an actual NULL result for NULL input.
 *
 * "foo op ALL array" is strict if the op is strict *and* we can prove
 * that the array input isn't an empty array.  We can check that
 * for the cases of an array constant and an ARRAY[] construct.
 *
 * "foo op ANY array" is strict in the falseOK sense if the op is strict.
 * If not falseOK, the test is the same as for "foo op ALL array".
 */
static bool
is_strict_saop(ScalarArrayOpExpr *expr, bool falseOK)
{
    Node       *rightop;

    /* The contained operator must be strict. */
    set_sa_opfuncid(expr);
    if (!func_strict(expr->opfuncid))
        return false;
    /* If ANY and falseOK, that's all we need to check. */
    if (expr->useOr && falseOK)
        return true;
    /* Else, we have to see if the array is provably non-empty. */
    Assert(list_length(expr->args) == 2);
    rightop = (Node *) lsecond(expr->args);
    if (rightop && IsA(rightop, Const))
    {
        Datum       arraydatum = ((Const *) rightop)->constvalue;
        bool        arrayisnull = ((Const *) rightop)->constisnull;
        ArrayType  *arrayval;
        int         nitems;

        if (arrayisnull)
            return false;
        arrayval = DatumGetArrayTypeP(arraydatum);
        nitems = ArrayGetNItems(ARR_NDIM(arrayval), ARR_DIMS(arrayval));
        if (nitems > 0)
            return true;
    }
    else if (rightop && IsA(rightop, ArrayExpr))
    {
        ArrayExpr  *arrayexpr = (ArrayExpr *) rightop;

        if (arrayexpr->elements != NIL && !arrayexpr->multidims)
            return true;
    }
    return false;
}


/*****************************************************************************
 *      Check for "pseudo-constant" clauses
 *****************************************************************************/

/*
 * is_pseudo_constant_clause
 *    Detect whether an expression is "pseudo constant", ie, it contains no
 *    variables of the current query level and no uses of volatile functions.
 *    Such an expr is not necessarily a true constant: it can still contain
 *    Params and outer-level Vars, not to mention functions whose results
 *    may vary from one statement to the next.  However, the expr's value
 *    will be constant over any one scan of the current query, so it can be
 *    used as, eg, an indexscan key.
 *
 * CAUTION: this function omits to test for one very important class of
 * not-constant expressions, namely aggregates (Aggrefs).  In current usage
 * this is only applied to WHERE clauses and so a check for Aggrefs would be
 * a waste of cycles; but be sure to also check contain_agg_clause() if you
 * want to know about pseudo-constness in other contexts.  The same goes
 * for window functions (WindowFuncs).
 */
bool
is_pseudo_constant_clause(Node *clause)
{
    /*
     * We could implement this check in one recursive scan.  But since the
     * check for volatile functions is both moderately expensive and unlikely
     * to fail, it seems better to look for Vars first and only check for
     * volatile functions if we find no Vars.
     */
    if (!contain_var_clause(clause) &&
        !contain_volatile_functions(clause))
        return true;
    return false;
}

/*
 * is_pseudo_constant_clause_relids
 *    Same as above, except caller already has available the var membership
 *    of the expression; this lets us avoid the contain_var_clause() scan.
 */
bool
is_pseudo_constant_clause_relids(Node *clause, Relids relids)
{
    if (bms_is_empty(relids) &&
        !contain_volatile_functions(clause))
        return true;
    return false;
}


/*****************************************************************************
 *                                                                           *
 *      General clause-manipulating routines                                 *
 *                                                                           *
 *****************************************************************************/

/*
 * NumRelids
 *      (formerly clause_relids)
 *
 * Returns the number of different relations referenced in 'clause'.
 */
int
NumRelids(Node *clause)
{
    Relids      varnos = pull_varnos(clause);
    int         result = bms_num_members(varnos);

    bms_free(varnos);
    return result;
}

/*
 * CommuteOpExpr: commute a binary operator clause
 *
 * XXX the clause is destructively modified!
 */
void
CommuteOpExpr(OpExpr *clause)
{
    Oid         opoid;
    Node       *temp;

    /* Sanity checks: caller is at fault if these fail */
    if (!is_opclause(clause) ||
        list_length(clause->args) != 2)
        elog(ERROR, "cannot commute non-binary-operator clause");

    opoid = get_commutator(clause->opno);

    if (!OidIsValid(opoid))
        elog(ERROR, "could not find commutator for operator %u",
             clause->opno);

    /*
     * modify the clause in-place!
     */
    clause->opno = opoid;
    clause->opfuncid = InvalidOid;
    /* opresulttype, opretset, opcollid, inputcollid need not change */

    temp = linitial(clause->args);
    linitial(clause->args) = lsecond(clause->args);
    lsecond(clause->args) = temp;
}

/*
 * CommuteRowCompareExpr: commute a RowCompareExpr clause
 *
 * XXX the clause is destructively modified!
 */
void
CommuteRowCompareExpr(RowCompareExpr *clause)
{
    List       *newops;
    List       *temp;
    ListCell   *l;

    /* Sanity checks: caller is at fault if these fail */
    if (!IsA(clause, RowCompareExpr))
        elog(ERROR, "expected a RowCompareExpr");

    /* Build list of commuted operators */
    newops = NIL;
    foreach(l, clause->opnos)
    {
        Oid         opoid = lfirst_oid(l);

        opoid = get_commutator(opoid);
        if (!OidIsValid(opoid))
            elog(ERROR, "could not find commutator for operator %u",
                 lfirst_oid(l));
        newops = lappend_oid(newops, opoid);
    }

    /*
     * modify the clause in-place!
     */
    switch (clause->rctype)
    {
        case ROWCOMPARE_LT:
            clause->rctype = ROWCOMPARE_GT;
            break;
        case ROWCOMPARE_LE:
            clause->rctype = ROWCOMPARE_GE;
            break;
        case ROWCOMPARE_GE:
            clause->rctype = ROWCOMPARE_LE;
            break;
        case ROWCOMPARE_GT:
            clause->rctype = ROWCOMPARE_LT;
            break;
        default:
            elog(ERROR, "unexpected RowCompare type: %d",
                 (int) clause->rctype);
            break;
    }

    clause->opnos = newops;

    /*
     * Note: we need not change the opfamilies list; we assume any btree
     * opfamily containing an operator will also contain its commutator.
     * Collations don't change either.
     */

    temp = clause->largs;
    clause->largs = clause->rargs;
    clause->rargs = temp;
}

/*
 * Helper for eval_const_expressions: check that datatype of an attribute
 * is still what it was when the expression was parsed.  This is needed to
 * guard against improper simplification after ALTER COLUMN TYPE.  (XXX we
 * may well need to make similar checks elsewhere?)
 *
 * rowtypeid may come from a whole-row Var, and therefore it can be a domain
 * over composite, but for this purpose we only care about checking the type
 * of a contained field.
 */
static bool
rowtype_field_matches(Oid rowtypeid, int fieldnum,
                      Oid expectedtype, int32 expectedtypmod,
                      Oid expectedcollation)
{
    TupleDesc   tupdesc;
    Form_pg_attribute attr;

    /* No issue for RECORD, since there is no way to ALTER such a type */
    if (rowtypeid == RECORDOID)
        return true;
    tupdesc = lookup_rowtype_tupdesc_domain(rowtypeid, -1, false);
    if (fieldnum <= 0 || fieldnum > tupdesc->natts)
    {
        ReleaseTupleDesc(tupdesc);
        return false;
    }
    attr = TupleDescAttr(tupdesc, fieldnum - 1);
    if (attr->attisdropped ||
        attr->atttypid != expectedtype ||
        attr->atttypmod != expectedtypmod ||
        attr->attcollation != expectedcollation)
    {
        ReleaseTupleDesc(tupdesc);
        return false;
    }
    ReleaseTupleDesc(tupdesc);
    return true;
}


/*--------------------
 * eval_const_expressions
 *
 * Reduce any recognizably constant subexpressions of the given
 * expression tree, for example "2 + 2" => "4".  More interestingly,
 * we can reduce certain boolean expressions even when they contain
 * non-constant subexpressions: "x OR true" => "true" no matter what
 * the subexpression x is.  (XXX We assume that no such subexpression
 * will have important side-effects, which is not necessarily a good
 * assumption in the presence of user-defined functions; do we need a
 * pg_proc flag that prevents discarding the execution of a function?)
 *
 * We do understand that certain functions may deliver non-constant
 * results even with constant inputs, "nextval()" being the classic
 * example.  Functions that are not marked "immutable" in pg_proc
 * will not be pre-evaluated here, although we will reduce their
 * arguments as far as possible.
 *
 * Whenever a function is eliminated from the expression by means of
 * constant-expression evaluation or inlining, we add the function to
 * root->glob->invalItems.  This ensures the plan is known to depend on
 * such functions, even though they aren't referenced anymore.
 *
 * We assume that the tree has already been type-checked and contains
 * only operators and functions that are reasonable to try to execute.
 *
 * NOTE: "root" can be passed as NULL if the caller never wants to do any
 * Param substitutions nor receive info about inlined functions.
 *
 * NOTE: the planner assumes that this will always flatten nested AND and
 * OR clauses into N-argument form.  See comments in prepqual.c.
 *
 * NOTE: another critical effect is that any function calls that require
 * default arguments will be expanded, and named-argument calls will be
 * converted to positional notation.  The executor won't handle either.
 *--------------------
 */
Node *
eval_const_expressions(PlannerInfo *root, Node *node)
{
    eval_const_expressions_context context;

    if (root)
        context.boundParams = root->glob->boundParams;  /* bound Params */
    else
        context.boundParams = NULL;
    context.root = root;        /* for inlined-function dependencies */
    context.active_fns = NIL;   /* nothing being recursively simplified */
    context.case_val = NULL;    /* no CASE being examined */
    context.estimate = false;   /* safe transformations only */
    return eval_const_expressions_mutator(node, &context);
}

/*--------------------
 * estimate_expression_value
 *
 * This function attempts to estimate the value of an expression for
 * planning purposes.  It is in essence a more aggressive version of
 * eval_const_expressions(): we will perform constant reductions that are
 * not necessarily 100% safe, but are reasonable for estimation purposes.
 *
 * Currently the extra steps that are taken in this mode are:
 * 1. Substitute values for Params, where a bound Param value has been made
 *    available by the caller of planner(), even if the Param isn't marked
 *    constant.  This effectively means that we plan using the first supplied
 *    value of the Param.
 * 2. Fold stable, as well as immutable, functions to constants.
 * 3. Reduce PlaceHolderVar nodes to their contained expressions.
 *--------------------
 */
Node *
estimate_expression_value(PlannerInfo *root, Node *node)
{
    eval_const_expressions_context context;

    context.boundParams = root->glob->boundParams;  /* bound Params */
    /* we do not need to mark the plan as depending on inlined functions */
    context.root = NULL;
    context.active_fns = NIL;   /* nothing being recursively simplified */
    context.case_val = NULL;    /* no CASE being examined */
    context.estimate = true;    /* unsafe transformations OK */
    return eval_const_expressions_mutator(node, &context);
}

/*
 * The generic case in eval_const_expressions_mutator is to recurse using
 * expression_tree_mutator, which will copy the given node unchanged but
 * const-simplify its arguments (if any) as far as possible.  If the node
 * itself does immutable processing, and each of its arguments were reduced
 * to a Const, we can then reduce it to a Const using evaluate_expr.  (Some
 * node types need more complicated logic; for example, a CASE expression
 * might be reducible to a constant even if not all its subtrees are.)
 */
#define ece_generic_processing(node) \
    expression_tree_mutator((Node *) (node), eval_const_expressions_mutator, \
                            (void *) context)

/*
 * Check whether all arguments of the given node were reduced to Consts.
 * By going directly to expression_tree_walker, contain_non_const_walker
 * is not applied to the node itself, only to its children.
 */
#define ece_all_arguments_const(node) \
    (!expression_tree_walker((Node *) (node), contain_non_const_walker, NULL))

/* Generic macro for applying evaluate_expr */
#define ece_evaluate_expr(node) \
    ((Node *) evaluate_expr((Expr *) (node), \
                            exprType((Node *) (node)), \
                            exprTypmod((Node *) (node)), \
                            exprCollation((Node *) (node))))

/*
 * Recursive guts of eval_const_expressions/estimate_expression_value
 */
static Node *
eval_const_expressions_mutator(Node *node,
                               eval_const_expressions_context *context)
{
    if (node == NULL)
        return NULL;
    switch (nodeTag(node))
    {
        case T_Param:
            {
                Param      *param = (Param *) node;
                ParamListInfo paramLI = context->boundParams;

                /* Look to see if we've been given a value for this Param */
                if (param->paramkind == PARAM_EXTERN &&
                    paramLI != NULL &&
                    param->paramid > 0 &&
                    param->paramid <= paramLI->numParams)
                {
                    ParamExternData *prm;
                    ParamExternData prmdata;

                    /*
                     * Give hook a chance in case parameter is dynamic.  Tell
                     * it that this fetch is speculative, so it should avoid
                     * erroring out if parameter is unavailable.
                     */
                    if (paramLI->paramFetch != NULL)
                        prm = paramLI->paramFetch(paramLI, param->paramid,
                                                  true, &prmdata);
                    else
                        prm = &paramLI->params[param->paramid - 1];

                    if (OidIsValid(prm->ptype))
                    {
                        /* OK to substitute parameter value? */
                        if (context->estimate ||
                            (prm->pflags & PARAM_FLAG_CONST))
                        {
                            /*
                             * Return a Const representing the param value.
                             * Must copy pass-by-ref datatypes, since the
                             * Param might be in a memory context
                             * shorter-lived than our output plan should be.
                             */
                            int16       typLen;
                            bool        typByVal;
                            Datum       pval;

                            Assert(prm->ptype == param->paramtype);
                            get_typlenbyval(param->paramtype,
                                            &typLen, &typByVal);
                            if (prm->isnull || typByVal)
                                pval = prm->value;
                            else
                                pval = datumCopy(prm->value, typByVal, typLen);
                            return (Node *) makeConst(param->paramtype,
                                                      param->paramtypmod,
                                                      param->paramcollid,
                                                      (int) typLen,
                                                      pval,
                                                      prm->isnull,
                                                      typByVal);
                        }
                    }
                }

                /*
                 * Not replaceable, so just copy the Param (no need to
                 * recurse)
                 */
                return (Node *) copyObject(param);
            }
        case T_WindowFunc:
            {
                WindowFunc *expr = (WindowFunc *) node;
                Oid         funcid = expr->winfnoid;
                List       *args;
                Expr       *aggfilter;
                HeapTuple   func_tuple;
                WindowFunc *newexpr;

                /*
                 * We can't really simplify a WindowFunc node, but we mustn't
                 * just fall through to the default processing, because we
                 * have to apply expand_function_arguments to its argument
                 * list.  That takes care of inserting default arguments and
                 * expanding named-argument notation.
                 */
                func_tuple = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcid));
                if (!HeapTupleIsValid(func_tuple))
                    elog(ERROR, "cache lookup failed for function %u", funcid);

                args = expand_function_arguments(expr->args, expr->wintype,
                                                 func_tuple);

                ReleaseSysCache(func_tuple);

                /* Now, recursively simplify the args (which are a List) */
                args = (List *)
                    expression_tree_mutator((Node *) args,
                                            eval_const_expressions_mutator,
                                            (void *) context);
                /* ... and the filter expression, which isn't */
                aggfilter = (Expr *)
                    eval_const_expressions_mutator((Node *) expr->aggfilter,
                                                   context);

                /* And build the replacement WindowFunc node */
                newexpr = makeNode(WindowFunc);
                newexpr->winfnoid = expr->winfnoid;
                newexpr->wintype = expr->wintype;
                newexpr->wincollid = expr->wincollid;
                newexpr->inputcollid = expr->inputcollid;
                newexpr->args = args;
                newexpr->aggfilter = aggfilter;
                newexpr->winref = expr->winref;
                newexpr->winstar = expr->winstar;
                newexpr->winagg = expr->winagg;
                newexpr->location = expr->location;

                return (Node *) newexpr;
            }
        case T_FuncExpr:
            {
                FuncExpr   *expr = (FuncExpr *) node;
                List       *args = expr->args;
                Expr       *simple;
                FuncExpr   *newexpr;

                /*
                 * Code for op/func reduction is pretty bulky, so split it out
                 * as a separate function.  Note: exprTypmod normally returns
                 * -1 for a FuncExpr, but not when the node is recognizably a
                 * length coercion; we want to preserve the typmod in the
                 * eventual Const if so.
                 */
                simple = simplify_function(expr->funcid,
                                           expr->funcresulttype,
                                           exprTypmod(node),
                                           expr->funccollid,
                                           expr->inputcollid,
                                           &args,
                                           expr->funcvariadic,
                                           true,
                                           true,
                                           context);
                if (simple)     /* successfully simplified it */
                    return (Node *) simple;

                /*
                 * The expression cannot be simplified any further, so build
                 * and return a replacement FuncExpr node using the
                 * possibly-simplified arguments.  Note that we have also
                 * converted the argument list to positional notation.
                 */
                newexpr = makeNode(FuncExpr);
                newexpr->funcid = expr->funcid;
                newexpr->funcresulttype = expr->funcresulttype;
                newexpr->funcretset = expr->funcretset;
                newexpr->funcvariadic = expr->funcvariadic;
                newexpr->funcformat = expr->funcformat;
                newexpr->funccollid = expr->funccollid;
                newexpr->inputcollid = expr->inputcollid;
                newexpr->args = args;
                newexpr->location = expr->location;
                return (Node *) newexpr;
            }
        case T_OpExpr:
            {
                OpExpr     *expr = (OpExpr *) node;
                List       *args = expr->args;
                Expr       *simple;
                OpExpr     *newexpr;

                /*
                 * Need to get OID of underlying function.  Okay to scribble
                 * on input to this extent.
                 */
                set_opfuncid(expr);

                /*
                 * Code for op/func reduction is pretty bulky, so split it out
                 * as a separate function.
                 */
                simple = simplify_function(expr->opfuncid,
                                           expr->opresulttype, -1,
                                           expr->opcollid,
                                           expr->inputcollid,
                                           &args,
                                           false,
                                           true,
                                           true,
                                           context);
                if (simple)     /* successfully simplified it */
                    return (Node *) simple;

                /*
                 * If the operator is boolean equality or inequality, we know
                 * how to simplify cases involving one constant and one
                 * non-constant argument.
                 */
                if (expr->opno == BooleanEqualOperator ||
                    expr->opno == BooleanNotEqualOperator)
                {
                    simple = (Expr *) simplify_boolean_equality(expr->opno,
                                                                args);
                    if (simple) /* successfully simplified it */
                        return (Node *) simple;
                }

                /*
                 * The expression cannot be simplified any further, so build
                 * and return a replacement OpExpr node using the
                 * possibly-simplified arguments.
                 */
                newexpr = makeNode(OpExpr);
                newexpr->opno = expr->opno;
                newexpr->opfuncid = expr->opfuncid;
                newexpr->opresulttype = expr->opresulttype;
                newexpr->opretset = expr->opretset;
                newexpr->opcollid = expr->opcollid;
                newexpr->inputcollid = expr->inputcollid;
                newexpr->args = args;
                newexpr->location = expr->location;
                return (Node *) newexpr;
            }
        case T_DistinctExpr:
            {
                DistinctExpr *expr = (DistinctExpr *) node;
                List       *args;
                ListCell   *arg;
                bool        has_null_input = false;
                bool        all_null_input = true;
                bool        has_nonconst_input = false;
                Expr       *simple;
                DistinctExpr *newexpr;

                /*
                 * Reduce constants in the DistinctExpr's arguments.  We know
                 * args is either NIL or a List node, so we can call
                 * expression_tree_mutator directly rather than recursing to
                 * self.
                 */
                args = (List *) expression_tree_mutator((Node *) expr->args,
                                                        eval_const_expressions_mutator,
                                                        (void *) context);

                /*
                 * We must do our own check for NULLs because DistinctExpr has
                 * different results for NULL input than the underlying
                 * operator does.
                 */
                foreach(arg, args)
                {
                    if (IsA(lfirst(arg), Const))
                    {
                        has_null_input |= ((Const *) lfirst(arg))->constisnull;
                        all_null_input &= ((Const *) lfirst(arg))->constisnull;
                    }
                    else
                        has_nonconst_input = true;
                }

                /* all constants? then can optimize this out */
                if (!has_nonconst_input)
                {
                    /* all nulls? then not distinct */
                    if (all_null_input)
                        return makeBoolConst(false, false);

                    /* one null? then distinct */
                    if (has_null_input)
                        return makeBoolConst(true, false);

                    /* otherwise try to evaluate the '=' operator */
                    /* (NOT okay to try to inline it, though!) */

                    /*
                     * Need to get OID of underlying function.  Okay to
                     * scribble on input to this extent.
                     */
                    set_opfuncid((OpExpr *) expr);  /* rely on struct
                                                     * equivalence */

                    /*
                     * Code for op/func reduction is pretty bulky, so split it
                     * out as a separate function.
                     */
                    simple = simplify_function(expr->opfuncid,
                                               expr->opresulttype, -1,
                                               expr->opcollid,
                                               expr->inputcollid,
                                               &args,
                                               false,
                                               false,
                                               false,
                                               context);
                    if (simple) /* successfully simplified it */
                    {
                        /*
                         * Since the underlying operator is "=", must negate
                         * its result
                         */
                        Const      *csimple = castNode(Const, simple);

                        csimple->constvalue =
                            BoolGetDatum(!DatumGetBool(csimple->constvalue));
                        return (Node *) csimple;
                    }
                }

                /*
                 * The expression cannot be simplified any further, so build
                 * and return a replacement DistinctExpr node using the
                 * possibly-simplified arguments.
                 */
                newexpr = makeNode(DistinctExpr);
                newexpr->opno = expr->opno;
                newexpr->opfuncid = expr->opfuncid;
                newexpr->opresulttype = expr->opresulttype;
                newexpr->opretset = expr->opretset;
                newexpr->opcollid = expr->opcollid;
                newexpr->inputcollid = expr->inputcollid;
                newexpr->args = args;
                newexpr->location = expr->location;
                return (Node *) newexpr;
            }
        case T_ScalarArrayOpExpr:
            {
                ScalarArrayOpExpr *saop;

                /* Copy the node and const-simplify its arguments */
                saop = (ScalarArrayOpExpr *) ece_generic_processing(node);

                /* Make sure we know underlying function */
                set_sa_opfuncid(saop);

                /*
                 * If all arguments are Consts, and it's a safe function, we
                 * can fold to a constant
                 */
                if (ece_all_arguments_const(saop) &&
                    ece_function_is_safe(saop->opfuncid, context))
                    return ece_evaluate_expr(saop);
                return (Node *) saop;
            }
        case T_BoolExpr:
            {
                BoolExpr   *expr = (BoolExpr *) node;

                switch (expr->boolop)
                {
                    case OR_EXPR:
                        {
                            List       *newargs;
                            bool        haveNull = false;
                            bool        forceTrue = false;

                            newargs = simplify_or_arguments(expr->args,
                                                            context,
                                                            &haveNull,
                                                            &forceTrue);
                            if (forceTrue)
                                return makeBoolConst(true, false);
                            if (haveNull)
                                newargs = lappend(newargs,
                                                  makeBoolConst(false, true));
                            /* If all the inputs are FALSE, result is FALSE */
                            if (newargs == NIL)
                                return makeBoolConst(false, false);

                            /*
                             * If only one nonconst-or-NULL input, it's the
                             * result
                             */
                            if (list_length(newargs) == 1)
                                return (Node *) linitial(newargs);
                            /* Else we still need an OR node */
                            return (Node *) make_orclause(newargs);
                        }
                    case AND_EXPR:
                        {
                            List       *newargs;
                            bool        haveNull = false;
                            bool        forceFalse = false;

                            newargs = simplify_and_arguments(expr->args,
                                                             context,
                                                             &haveNull,
                                                             &forceFalse);
                            if (forceFalse)
                                return makeBoolConst(false, false);
                            if (haveNull)
                                newargs = lappend(newargs,
                                                  makeBoolConst(false, true));
                            /* If all the inputs are TRUE, result is TRUE */
                            if (newargs == NIL)
                                return makeBoolConst(true, false);

                            /*
                             * If only one nonconst-or-NULL input, it's the
                             * result
                             */
                            if (list_length(newargs) == 1)
                                return (Node *) linitial(newargs);
                            /* Else we still need an AND node */
                            return (Node *) make_andclause(newargs);
                        }
                    case NOT_EXPR:
                        {
                            Node       *arg;

                            Assert(list_length(expr->args) == 1);
                            arg = eval_const_expressions_mutator(linitial(expr->args),
                                                                 context);

                            /*
                             * Use negate_clause() to see if we can simplify
                             * away the NOT.
                             */
                            return negate_clause(arg);
                        }
                    default:
                        elog(ERROR, "unrecognized boolop: %d",
                             (int) expr->boolop);
                        break;
                }
                break;
            }
        case T_SubPlan:
        case T_AlternativeSubPlan:

            /*
             * Return a SubPlan unchanged --- too late to do anything with it.
             *
             * XXX should we ereport() here instead?  Probably this routine
             * should never be invoked after SubPlan creation.
             */
            return node;
        case T_RelabelType:
            {
                /*
                 * If we can simplify the input to a constant, then we don't
                 * need the RelabelType node anymore: just change the type
                 * field of the Const node.  Otherwise, must copy the
                 * RelabelType node.
                 */
                RelabelType *relabel = (RelabelType *) node;
                Node       *arg;

                arg = eval_const_expressions_mutator((Node *) relabel->arg,
                                                     context);

                /*
                 * If we find stacked RelabelTypes (eg, from foo :: int ::
                 * oid) we can discard all but the top one.
                 */
                while (arg && IsA(arg, RelabelType))
                    arg = (Node *) ((RelabelType *) arg)->arg;

                if (arg && IsA(arg, Const))
                {
                    Const      *con = (Const *) arg;

                    con->consttype = relabel->resulttype;
                    con->consttypmod = relabel->resulttypmod;
                    con->constcollid = relabel->resultcollid;
                    return (Node *) con;
                }
                else
                {
                    RelabelType *newrelabel = makeNode(RelabelType);

                    newrelabel->arg = (Expr *) arg;
                    newrelabel->resulttype = relabel->resulttype;
                    newrelabel->resulttypmod = relabel->resulttypmod;
                    newrelabel->resultcollid = relabel->resultcollid;
                    newrelabel->relabelformat = relabel->relabelformat;
                    newrelabel->location = relabel->location;
                    return (Node *) newrelabel;
                }
            }
        case T_CoerceViaIO:
            {
                CoerceViaIO *expr = (CoerceViaIO *) node;
                List       *args;
                Oid         outfunc;
                bool        outtypisvarlena;
                Oid         infunc;
                Oid         intypioparam;
                Expr       *simple;
                CoerceViaIO *newexpr;

                /* Make a List so we can use simplify_function */
                args = list_make1(expr->arg);

                /*
                 * CoerceViaIO represents calling the source type's output
                 * function then the result type's input function.  So, try to
                 * simplify it as though it were a stack of two such function
                 * calls.  First we need to know what the functions are.
                 *
                 * Note that the coercion functions are assumed not to care
                 * about input collation, so we just pass InvalidOid for that.
                 */
                getTypeOutputInfo(exprType((Node *) expr->arg),
                                  &outfunc, &outtypisvarlena);
                getTypeInputInfo(expr->resulttype,
                                 &infunc, &intypioparam);

                simple = simplify_function(outfunc,
                                           CSTRINGOID, -1,
                                           InvalidOid,
                                           InvalidOid,
                                           &args,
                                           false,
                                           true,
                                           true,
                                           context);
                if (simple)     /* successfully simplified output fn */
                {
                    /*
                     * Input functions may want 1 to 3 arguments.  We always
                     * supply all three, trusting that nothing downstream will
                     * complain.
                     */
                    args = list_make3(simple,
                                      makeConst(OIDOID,
                                                -1,
                                                InvalidOid,
                                                sizeof(Oid),
                                                ObjectIdGetDatum(intypioparam),
                                                false,
                                                true),
                                      makeConst(INT4OID,
                                                -1,
                                                InvalidOid,
                                                sizeof(int32),
                                                Int32GetDatum(-1),
                                                false,
                                                true));

                    simple = simplify_function(infunc,
                                               expr->resulttype, -1,
                                               expr->resultcollid,
                                               InvalidOid,
                                               &args,
                                               false,
                                               false,
                                               true,
                                               context);
                    if (simple) /* successfully simplified input fn */
                        return (Node *) simple;
                }

                /*
                 * The expression cannot be simplified any further, so build
                 * and return a replacement CoerceViaIO node using the
                 * possibly-simplified argument.
                 */
                newexpr = makeNode(CoerceViaIO);
                newexpr->arg = (Expr *) linitial(args);
                newexpr->resulttype = expr->resulttype;
                newexpr->resultcollid = expr->resultcollid;
                newexpr->coerceformat = expr->coerceformat;
                newexpr->location = expr->location;
                return (Node *) newexpr;
            }
        case T_ArrayCoerceExpr:
            {
                ArrayCoerceExpr *ac;

                /* Copy the node and const-simplify its arguments */
                ac = (ArrayCoerceExpr *) ece_generic_processing(node);

                /*
                 * If constant argument and the per-element expression is
                 * immutable, we can simplify the whole thing to a constant.
                 * Exception: although contain_mutable_functions considers
                 * CoerceToDomain immutable for historical reasons, let's not
                 * do so here; this ensures coercion to an array-over-domain
                 * does not apply the domain's constraints until runtime.
                 */
                if (ac->arg && IsA(ac->arg, Const) &&
                    ac->elemexpr && !IsA(ac->elemexpr, CoerceToDomain) &&
                    !contain_mutable_functions((Node *) ac->elemexpr))
                    return ece_evaluate_expr(ac);
                return (Node *) ac;
            }
        case T_CollateExpr:
            {
                /*
                 * If we can simplify the input to a constant, then we don't
                 * need the CollateExpr node at all: just change the
                 * constcollid field of the Const node.  Otherwise, replace
                 * the CollateExpr with a RelabelType. (We do that so as to
                 * improve uniformity of expression representation and thus
                 * simplify comparison of expressions.)
                 */
                CollateExpr *collate = (CollateExpr *) node;
                Node       *arg;

                arg = eval_const_expressions_mutator((Node *) collate->arg,
                                                     context);

                if (arg && IsA(arg, Const))
                {
                    Const      *con = (Const *) arg;

                    con->constcollid = collate->collOid;
                    return (Node *) con;
                }
                else if (collate->collOid == exprCollation(arg))
                {
                    /* Don't need a RelabelType either... */
                    return arg;
                }
                else
                {
                    RelabelType *relabel = makeNode(RelabelType);

                    relabel->resulttype = exprType(arg);
                    relabel->resulttypmod = exprTypmod(arg);
                    relabel->resultcollid = collate->collOid;
                    relabel->relabelformat = COERCE_IMPLICIT_CAST;
                    relabel->location = collate->location;

                    /* Don't create stacked RelabelTypes */
                    while (arg && IsA(arg, RelabelType))
                        arg = (Node *) ((RelabelType *) arg)->arg;
                    relabel->arg = (Expr *) arg;

                    return (Node *) relabel;
                }
            }
        case T_CaseExpr:
            {
                /*----------
                 * CASE expressions can be simplified if there are constant
                 * condition clauses:
                 *      FALSE (or NULL): drop the alternative
                 *      TRUE: drop all remaining alternatives
                 * If the first non-FALSE alternative is a constant TRUE,
                 * we can simplify the entire CASE to that alternative's
                 * expression.  If there are no non-FALSE alternatives,
                 * we simplify the entire CASE to the default result (ELSE).
                 *
                 * If we have a simple-form CASE with constant test
                 * expression, we substitute the constant value for contained
                 * CaseTestExpr placeholder nodes, so that we have the
                 * opportunity to reduce constant test conditions.  For
                 * example this allows
                 *      CASE 0 WHEN 0 THEN 1 ELSE 1/0 END
                 * to reduce to 1 rather than drawing a divide-by-0 error.
                 * Note that when the test expression is constant, we don't
                 * have to include it in the resulting CASE; for example
                 *      CASE 0 WHEN x THEN y ELSE z END
                 * is transformed by the parser to
                 *      CASE 0 WHEN CaseTestExpr = x THEN y ELSE z END
                 * which we can simplify to
                 *      CASE WHEN 0 = x THEN y ELSE z END
                 * It is not necessary for the executor to evaluate the "arg"
                 * expression when executing the CASE, since any contained
                 * CaseTestExprs that might have referred to it will have been
                 * replaced by the constant.
                 *----------
                 */
                CaseExpr   *caseexpr = (CaseExpr *) node;
                CaseExpr   *newcase;
                Node       *save_case_val;
                Node       *newarg;
                List       *newargs;
                bool        const_true_cond;
                Node       *defresult = NULL;
                ListCell   *arg;

                /* Simplify the test expression, if any */
                newarg = eval_const_expressions_mutator((Node *) caseexpr->arg,
                                                        context);

                /* Set up for contained CaseTestExpr nodes */
                save_case_val = context->case_val;
                if (newarg && IsA(newarg, Const))
                {
                    context->case_val = newarg;
                    newarg = NULL;  /* not needed anymore, see above */
                }
                else
                    context->case_val = NULL;

                /* Simplify the WHEN clauses */
                newargs = NIL;
                const_true_cond = false;
                foreach(arg, caseexpr->args)
                {
                    CaseWhen   *oldcasewhen = lfirst_node(CaseWhen, arg);
                    Node       *casecond;
                    Node       *caseresult;

                    /* Simplify this alternative's test condition */
                    casecond = eval_const_expressions_mutator((Node *) oldcasewhen->expr,
                                                              context);

                    /*
                     * If the test condition is constant FALSE (or NULL), then
                     * drop this WHEN clause completely, without processing
                     * the result.
                     */
                    if (casecond && IsA(casecond, Const))
                    {
                        Const      *const_input = (Const *) casecond;

                        if (const_input->constisnull ||
                            !DatumGetBool(const_input->constvalue))
                            continue;   /* drop alternative with FALSE cond */
                        /* Else it's constant TRUE */
                        const_true_cond = true;
                    }

                    /* Simplify this alternative's result value */
                    caseresult = eval_const_expressions_mutator((Node *) oldcasewhen->result,
                                                                context);

                    /* If non-constant test condition, emit a new WHEN node */
                    if (!const_true_cond)
                    {
                        CaseWhen   *newcasewhen = makeNode(CaseWhen);

                        newcasewhen->expr = (Expr *) casecond;
                        newcasewhen->result = (Expr *) caseresult;
                        newcasewhen->location = oldcasewhen->location;
                        newargs = lappend(newargs, newcasewhen);
                        continue;
                    }

                    /*
                     * Found a TRUE condition, so none of the remaining
                     * alternatives can be reached.  We treat the result as
                     * the default result.
                     */
                    defresult = caseresult;
                    break;
                }

                /* Simplify the default result, unless we replaced it above */
                if (!const_true_cond)
                    defresult = eval_const_expressions_mutator((Node *) caseexpr->defresult,
                                                               context);

                context->case_val = save_case_val;

                /*
                 * If no non-FALSE alternatives, CASE reduces to the default
                 * result
                 */
                if (newargs == NIL)
                    return defresult;
                /* Otherwise we need a new CASE node */
                newcase = makeNode(CaseExpr);
                newcase->casetype = caseexpr->casetype;
                newcase->casecollid = caseexpr->casecollid;
                newcase->arg = (Expr *) newarg;
                newcase->args = newargs;
                newcase->defresult = (Expr *) defresult;
                newcase->location = caseexpr->location;
                return (Node *) newcase;
            }
        case T_CaseTestExpr:
            {
                /*
                 * If we know a constant test value for the current CASE
                 * construct, substitute it for the placeholder.  Else just
                 * return the placeholder as-is.
                 */
                if (context->case_val)
                    return copyObject(context->case_val);
                else
                    return copyObject(node);
            }
        case T_ArrayRef:
        case T_ArrayExpr:
        case T_RowExpr:
            {
                /*
                 * Generic handling for node types whose own processing is
                 * known to be immutable, and for which we need no smarts
                 * beyond "simplify if all inputs are constants".
                 */

                /* Copy the node and const-simplify its arguments */
                node = ece_generic_processing(node);
                /* If all arguments are Consts, we can fold to a constant */
                if (ece_all_arguments_const(node))
                    return ece_evaluate_expr(node);
                return node;
            }
        case T_CoalesceExpr:
            {
                CoalesceExpr *coalesceexpr = (CoalesceExpr *) node;
                CoalesceExpr *newcoalesce;
                List       *newargs;
                ListCell   *arg;

                newargs = NIL;
                foreach(arg, coalesceexpr->args)
                {
                    Node       *e;

                    e = eval_const_expressions_mutator((Node *) lfirst(arg),
                                                       context);

                    /*
                     * We can remove null constants from the list. For a
                     * non-null constant, if it has not been preceded by any
                     * other non-null-constant expressions then it is the
                     * result. Otherwise, it's the next argument, but we can
                     * drop following arguments since they will never be
                     * reached.
                     */
                    if (IsA(e, Const))
                    {
                        if (((Const *) e)->constisnull)
                            continue;   /* drop null constant */
                        if (newargs == NIL)
                            return e;   /* first expr */
                        newargs = lappend(newargs, e);
                        break;
                    }
                    newargs = lappend(newargs, e);
                }

                /*
                 * If all the arguments were constant null, the result is just
                 * null
                 */
                if (newargs == NIL)
                    return (Node *) makeNullConst(coalesceexpr->coalescetype,
                                                  -1,
                                                  coalesceexpr->coalescecollid);

                newcoalesce = makeNode(CoalesceExpr);
                newcoalesce->coalescetype = coalesceexpr->coalescetype;
                newcoalesce->coalescecollid = coalesceexpr->coalescecollid;
                newcoalesce->args = newargs;
                newcoalesce->location = coalesceexpr->location;
                return (Node *) newcoalesce;
            }
        case T_SQLValueFunction:
            {
                /*
                 * All variants of SQLValueFunction are stable, so if we are
                 * estimating the expression's value, we should evaluate the
                 * current function value.  Otherwise just copy.
                 */
                SQLValueFunction *svf = (SQLValueFunction *) node;

                if (context->estimate)
                    return (Node *) evaluate_expr((Expr *) svf,
                                                  svf->type,
                                                  svf->typmod,
                                                  InvalidOid);
                else
                    return copyObject((Node *) svf);
            }
        case T_FieldSelect:
            {
                /*
                 * We can optimize field selection from a whole-row Var into a
                 * simple Var.  (This case won't be generated directly by the
                 * parser, because ParseComplexProjection short-circuits it.
                 * But it can arise while simplifying functions.)  Also, we
                 * can optimize field selection from a RowExpr construct, or
                 * of course from a constant.
                 *
                 * However, replacing a whole-row Var in this way has a
                 * pitfall: if we've already built the rel targetlist for the
                 * source relation, then the whole-row Var is scheduled to be
                 * produced by the relation scan, but the simple Var probably
                 * isn't, which will lead to a failure in setrefs.c.  This is
                 * not a problem when handling simple single-level queries, in
                 * which expression simplification always happens first.  It
                 * is a risk for lateral references from subqueries, though.
                 * To avoid such failures, don't optimize uplevel references.
                 *
                 * We must also check that the declared type of the field is
                 * still the same as when the FieldSelect was created --- this
                 * can change if someone did ALTER COLUMN TYPE on the rowtype.
                 * If it isn't, we skip the optimization; the case will
                 * probably fail at runtime, but that's not our problem here.
                 */
                FieldSelect *fselect = (FieldSelect *) node;
                FieldSelect *newfselect;
                Node       *arg;

                arg = eval_const_expressions_mutator((Node *) fselect->arg,
                                                     context);
                if (arg && IsA(arg, Var) &&
                    ((Var *) arg)->varattno == InvalidAttrNumber &&
                    ((Var *) arg)->varlevelsup == 0)
                {
                    if (rowtype_field_matches(((Var *) arg)->vartype,
                                              fselect->fieldnum,
                                              fselect->resulttype,
                                              fselect->resulttypmod,
                                              fselect->resultcollid))
                        return (Node *) makeVar(((Var *) arg)->varno,
                                                fselect->fieldnum,
                                                fselect->resulttype,
                                                fselect->resulttypmod,
                                                fselect->resultcollid,
                                                ((Var *) arg)->varlevelsup);
                }
                if (arg && IsA(arg, RowExpr))
                {
                    RowExpr    *rowexpr = (RowExpr *) arg;

                    if (fselect->fieldnum > 0 &&
                        fselect->fieldnum <= list_length(rowexpr->args))
                    {
                        Node       *fld = (Node *) list_nth(rowexpr->args,
                                                            fselect->fieldnum - 1);

                        if (rowtype_field_matches(rowexpr->row_typeid,
                                                  fselect->fieldnum,
                                                  fselect->resulttype,
                                                  fselect->resulttypmod,
                                                  fselect->resultcollid) &&
                            fselect->resulttype == exprType(fld) &&
                            fselect->resulttypmod == exprTypmod(fld) &&
                            fselect->resultcollid == exprCollation(fld))
                            return fld;
                    }
                }
                newfselect = makeNode(FieldSelect);
                newfselect->arg = (Expr *) arg;
                newfselect->fieldnum = fselect->fieldnum;
                newfselect->resulttype = fselect->resulttype;
                newfselect->resulttypmod = fselect->resulttypmod;
                newfselect->resultcollid = fselect->resultcollid;
                if (arg && IsA(arg, Const))
                {
                    Const      *con = (Const *) arg;

                    if (rowtype_field_matches(con->consttype,
                                              newfselect->fieldnum,
                                              newfselect->resulttype,
                                              newfselect->resulttypmod,
                                              newfselect->resultcollid))
                        return ece_evaluate_expr(newfselect);
                }
                return (Node *) newfselect;
            }
        case T_NullTest:
            {
                NullTest   *ntest = (NullTest *) node;
                NullTest   *newntest;
                Node       *arg;

                arg = eval_const_expressions_mutator((Node *) ntest->arg,
                                                     context);
                if (ntest->argisrow && arg && IsA(arg, RowExpr))
                {
                    /*
                     * We break ROW(...) IS [NOT] NULL into separate tests on
                     * its component fields.  This form is usually more
                     * efficient to evaluate, as well as being more amenable
                     * to optimization.
                     */
                    RowExpr    *rarg = (RowExpr *) arg;
                    List       *newargs = NIL;
                    ListCell   *l;

                    foreach(l, rarg->args)
                    {
                        Node       *relem = (Node *) lfirst(l);

                        /*
                         * A constant field refutes the whole NullTest if it's
                         * of the wrong nullness; else we can discard it.
                         */
                        if (relem && IsA(relem, Const))
                        {
                            Const      *carg = (Const *) relem;

                            if (carg->constisnull ?
                                (ntest->nulltesttype == IS_NOT_NULL) :
                                (ntest->nulltesttype == IS_NULL))
                                return makeBoolConst(false, false);
                            continue;
                        }

                        /*
                         * Else, make a scalar (argisrow == false) NullTest
                         * for this field.  Scalar semantics are required
                         * because IS [NOT] NULL doesn't recurse; see comments
                         * in ExecEvalRowNullInt().
                         */
                        newntest = makeNode(NullTest);
                        newntest->arg = (Expr *) relem;
                        newntest->nulltesttype = ntest->nulltesttype;
                        newntest->argisrow = false;
                        newntest->location = ntest->location;
                        newargs = lappend(newargs, newntest);
                    }
                    /* If all the inputs were constants, result is TRUE */
                    if (newargs == NIL)
                        return makeBoolConst(true, false);
                    /* If only one nonconst input, it's the result */
                    if (list_length(newargs) == 1)
                        return (Node *) linitial(newargs);
                    /* Else we need an AND node */
                    return (Node *) make_andclause(newargs);
                }
                if (!ntest->argisrow && arg && IsA(arg, Const))
                {
                    Const      *carg = (Const *) arg;
                    bool        result;

                    switch (ntest->nulltesttype)
                    {
                        case IS_NULL:
                            result = carg->constisnull;
                            break;
                        case IS_NOT_NULL:
                            result = !carg->constisnull;
                            break;
                        default:
                            elog(ERROR, "unrecognized nulltesttype: %d",
                                 (int) ntest->nulltesttype);
                            result = false; /* keep compiler quiet */
                            break;
                    }

                    return makeBoolConst(result, false);
                }

                newntest = makeNode(NullTest);
                newntest->arg = (Expr *) arg;
                newntest->nulltesttype = ntest->nulltesttype;
                newntest->argisrow = ntest->argisrow;
                newntest->location = ntest->location;
                return (Node *) newntest;
            }
        case T_BooleanTest:
            {
                /*
                 * This case could be folded into the generic handling used
                 * for ArrayRef etc.  But because the simplification logic is
                 * so trivial, applying evaluate_expr() to perform it would be
                 * a heavy overhead.  BooleanTest is probably common enough to
                 * justify keeping this bespoke implementation.
                 */
                BooleanTest *btest = (BooleanTest *) node;
                BooleanTest *newbtest;
                Node       *arg;

                arg = eval_const_expressions_mutator((Node *) btest->arg,
                                                     context);
                if (arg && IsA(arg, Const))
                {
                    Const      *carg = (Const *) arg;
                    bool        result;

                    switch (btest->booltesttype)
                    {
                        case IS_TRUE:
                            result = (!carg->constisnull &&
                                      DatumGetBool(carg->constvalue));
                            break;
                        case IS_NOT_TRUE:
                            result = (carg->constisnull ||
                                      !DatumGetBool(carg->constvalue));
                            break;
                        case IS_FALSE:
                            result = (!carg->constisnull &&
                                      !DatumGetBool(carg->constvalue));
                            break;
                        case IS_NOT_FALSE:
                            result = (carg->constisnull ||
                                      DatumGetBool(carg->constvalue));
                            break;
                        case IS_UNKNOWN:
                            result = carg->constisnull;
                            break;
                        case IS_NOT_UNKNOWN:
                            result = !carg->constisnull;
                            break;
                        default:
                            elog(ERROR, "unrecognized booltesttype: %d",
                                 (int) btest->booltesttype);
                            result = false; /* keep compiler quiet */
                            break;
                    }

                    return makeBoolConst(result, false);
                }

                newbtest = makeNode(BooleanTest);
                newbtest->arg = (Expr *) arg;
                newbtest->booltesttype = btest->booltesttype;
                newbtest->location = btest->location;
                return (Node *) newbtest;
            }
        case T_PlaceHolderVar:

            /*
             * In estimation mode, just strip the PlaceHolderVar node
             * altogether; this amounts to estimating that the contained value
             * won't be forced to null by an outer join.  In regular mode we
             * just use the default behavior (ie, simplify the expression but
             * leave the PlaceHolderVar node intact).
             */
            if (context->estimate)
            {
                PlaceHolderVar *phv = (PlaceHolderVar *) node;

                return eval_const_expressions_mutator((Node *) phv->phexpr,
                                                      context);
            }
            break;
        default:
            break;
    }

    /*
     * For any node type not handled above, copy the node unchanged but
     * const-simplify its subexpressions.  This is the correct thing for node
     * types whose behavior might change between planning and execution, such
     * as CoerceToDomain.  It's also a safe default for new node types not
     * known to this routine.
     */
    return ece_generic_processing(node);
}

/*
 * Subroutine for eval_const_expressions: check for non-Const nodes.
 *
 * We can abort recursion immediately on finding a non-Const node.  This is
 * critical for performance, else eval_const_expressions_mutator would take
 * O(N^2) time on non-simplifiable trees.  However, we do need to descend
 * into List nodes since expression_tree_walker sometimes invokes the walker
 * function directly on List subtrees.
 */
static bool
contain_non_const_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Const))
        return false;
    if (IsA(node, List))
        return expression_tree_walker(node, contain_non_const_walker, context);
    /* Otherwise, abort the tree traversal and return true */
    return true;
}

/*
 * Subroutine for eval_const_expressions: check if a function is OK to evaluate
 */
static bool
ece_function_is_safe(Oid funcid, eval_const_expressions_context *context)
{
    char        provolatile = func_volatile(funcid);

    /*
     * Ordinarily we are only allowed to simplify immutable functions. But for
     * purposes of estimation, we consider it okay to simplify functions that
     * are merely stable; the risk that the result might change from planning
     * time to execution time is worth taking in preference to not being able
     * to estimate the value at all.
     */
    if (provolatile == PROVOLATILE_IMMUTABLE)
        return true;
    if (context->estimate && provolatile == PROVOLATILE_STABLE)
        return true;
    return false;
}

/*
 * Subroutine for eval_const_expressions: process arguments of an OR clause
 *
 * This includes flattening of nested ORs as well as recursion to
 * eval_const_expressions to simplify the OR arguments.
 *
 * After simplification, OR arguments are handled as follows:
 *      non constant: keep
 *      FALSE: drop (does not affect result)
 *      TRUE: force result to TRUE
 *      NULL: keep only one
 * We must keep one NULL input because OR expressions evaluate to NULL when no
 * input is TRUE and at least one is NULL.  We don't actually include the NULL
 * here, that's supposed to be done by the caller.
 *
 * The output arguments *haveNull and *forceTrue must be initialized false
 * by the caller.  They will be set true if a NULL constant or TRUE constant,
 * respectively, is detected anywhere in the argument list.
 */
static List *
simplify_or_arguments(List *args,
                      eval_const_expressions_context *context,
                      bool *haveNull, bool *forceTrue)
{
    List       *newargs = NIL;
    List       *unprocessed_args;

    /*
     * We want to ensure that any OR immediately beneath another OR gets
     * flattened into a single OR-list, so as to simplify later reasoning.
     *
     * To avoid stack overflow from recursion of eval_const_expressions, we
     * resort to some tenseness here: we keep a list of not-yet-processed
     * inputs, and handle flattening of nested ORs by prepending to the to-do
     * list instead of recursing.  Now that the parser generates N-argument
     * ORs from simple lists, this complexity is probably less necessary than
     * it once was, but we might as well keep the logic.
     */
    unprocessed_args = list_copy(args);
    while (unprocessed_args)
    {
        Node       *arg = (Node *) linitial(unprocessed_args);

        unprocessed_args = list_delete_first(unprocessed_args);

        /* flatten nested ORs as per above comment */
        if (or_clause(arg))
        {
            List       *subargs = list_copy(((BoolExpr *) arg)->args);

            /* overly tense code to avoid leaking unused list header */
            if (!unprocessed_args)
                unprocessed_args = subargs;
            else
            {
                List       *oldhdr = unprocessed_args;

                unprocessed_args = list_concat(subargs, unprocessed_args);
                pfree(oldhdr);
            }
            continue;
        }

        /* If it's not an OR, simplify it */
        arg = eval_const_expressions_mutator(arg, context);

        /*
         * It is unlikely but not impossible for simplification of a non-OR
         * clause to produce an OR.  Recheck, but don't be too tense about it
         * since it's not a mainstream case. In particular we don't worry
         * about const-simplifying the input twice.
         */
        if (or_clause(arg))
        {
            List       *subargs = list_copy(((BoolExpr *) arg)->args);

            unprocessed_args = list_concat(subargs, unprocessed_args);
            continue;
        }

        /*
         * OK, we have a const-simplified non-OR argument.  Process it per
         * comments above.
         */
        if (IsA(arg, Const))
        {
            Const      *const_input = (Const *) arg;

            if (const_input->constisnull)
                *haveNull = true;
            else if (DatumGetBool(const_input->constvalue))
            {
                *forceTrue = true;

                /*
                 * Once we detect a TRUE result we can just exit the loop
                 * immediately.  However, if we ever add a notion of
                 * non-removable functions, we'd need to keep scanning.
                 */
                return NIL;
            }
            /* otherwise, we can drop the constant-false input */
            continue;
        }

        /* else emit the simplified arg into the result list */
        newargs = lappend(newargs, arg);
    }

    return newargs;
}

/*
 * Subroutine for eval_const_expressions: process arguments of an AND clause
 *
 * This includes flattening of nested ANDs as well as recursion to
 * eval_const_expressions to simplify the AND arguments.
 *
 * After simplification, AND arguments are handled as follows:
 *      non constant: keep
 *      TRUE: drop (does not affect result)
 *      FALSE: force result to FALSE
 *      NULL: keep only one
 * We must keep one NULL input because AND expressions evaluate to NULL when
 * no input is FALSE and at least one is NULL.  We don't actually include the
 * NULL here, that's supposed to be done by the caller.
 *
 * The output arguments *haveNull and *forceFalse must be initialized false
 * by the caller.  They will be set true if a null constant or false constant,
 * respectively, is detected anywhere in the argument list.
 */
static List *
simplify_and_arguments(List *args,
                       eval_const_expressions_context *context,
                       bool *haveNull, bool *forceFalse)
{
    List       *newargs = NIL;
    List       *unprocessed_args;

    /* See comments in simplify_or_arguments */
    unprocessed_args = list_copy(args);
    while (unprocessed_args)
    {
        Node       *arg = (Node *) linitial(unprocessed_args);

        unprocessed_args = list_delete_first(unprocessed_args);

        /* flatten nested ANDs as per above comment */
        if (and_clause(arg))
        {
            List       *subargs = list_copy(((BoolExpr *) arg)->args);

            /* overly tense code to avoid leaking unused list header */
            if (!unprocessed_args)
                unprocessed_args = subargs;
            else
            {
                List       *oldhdr = unprocessed_args;

                unprocessed_args = list_concat(subargs, unprocessed_args);
                pfree(oldhdr);
            }
            continue;
        }

        /* If it's not an AND, simplify it */
        arg = eval_const_expressions_mutator(arg, context);

        /*
         * It is unlikely but not impossible for simplification of a non-AND
         * clause to produce an AND.  Recheck, but don't be too tense about it
         * since it's not a mainstream case. In particular we don't worry
         * about const-simplifying the input twice.
         */
        if (and_clause(arg))
        {
            List       *subargs = list_copy(((BoolExpr *) arg)->args);

            unprocessed_args = list_concat(subargs, unprocessed_args);
            continue;
        }

        /*
         * OK, we have a const-simplified non-AND argument.  Process it per
         * comments above.
         */
        if (IsA(arg, Const))
        {
            Const      *const_input = (Const *) arg;

            if (const_input->constisnull)
                *haveNull = true;
            else if (!DatumGetBool(const_input->constvalue))
            {
                *forceFalse = true;

                /*
                 * Once we detect a FALSE result we can just exit the loop
                 * immediately.  However, if we ever add a notion of
                 * non-removable functions, we'd need to keep scanning.
                 */
                return NIL;
            }
            /* otherwise, we can drop the constant-true input */
            continue;
        }

        /* else emit the simplified arg into the result list */
        newargs = lappend(newargs, arg);
    }

    return newargs;
}

/*
 * Subroutine for eval_const_expressions: try to simplify boolean equality
 * or inequality condition
 *
 * Inputs are the operator OID and the simplified arguments to the operator.
 * Returns a simplified expression if successful, or NULL if cannot
 * simplify the expression.
 *
 * The idea here is to reduce "x = true" to "x" and "x = false" to "NOT x",
 * or similarly "x <> true" to "NOT x" and "x <> false" to "x".
 * This is only marginally useful in itself, but doing it in constant folding
 * ensures that we will recognize these forms as being equivalent in, for
 * example, partial index matching.
 *
 * We come here only if simplify_function has failed; therefore we cannot
 * see two constant inputs, nor a constant-NULL input.
 */
static Node *
simplify_boolean_equality(Oid opno, List *args)
{
    Node       *leftop;
    Node       *rightop;

    Assert(list_length(args) == 2);
    leftop = linitial(args);
    rightop = lsecond(args);
    if (leftop && IsA(leftop, Const))
    {
        Assert(!((Const *) leftop)->constisnull);
        if (opno == BooleanEqualOperator)
        {
            if (DatumGetBool(((Const *) leftop)->constvalue))
                return rightop; /* true = foo */
            else
                return negate_clause(rightop);  /* false = foo */
        }
        else
        {
            if (DatumGetBool(((Const *) leftop)->constvalue))
                return negate_clause(rightop);  /* true <> foo */
            else
                return rightop; /* false <> foo */
        }
    }
    if (rightop && IsA(rightop, Const))
    {
        Assert(!((Const *) rightop)->constisnull);
        if (opno == BooleanEqualOperator)
        {
            if (DatumGetBool(((Const *) rightop)->constvalue))
                return leftop;  /* foo = true */
            else
                return negate_clause(leftop);   /* foo = false */
        }
        else
        {
            if (DatumGetBool(((Const *) rightop)->constvalue))
                return negate_clause(leftop);   /* foo <> true */
            else
                return leftop;  /* foo <> false */
        }
    }
    return NULL;
}

/*
 * Subroutine for eval_const_expressions: try to simplify a function call
 * (which might originally have been an operator; we don't care)
 *
 * Inputs are the function OID, actual result type OID (which is needed for
 * polymorphic functions), result typmod, result collation, the input
 * collation to use for the function, the original argument list (not
 * const-simplified yet, unless process_args is false), and some flags;
 * also the context data for eval_const_expressions.
 *
 * Returns a simplified expression if successful, or NULL if cannot
 * simplify the function call.
 *
 * This function is also responsible for converting named-notation argument
 * lists into positional notation and/or adding any needed default argument
 * expressions; which is a bit grotty, but it avoids extra fetches of the
 * function's pg_proc tuple.  For this reason, the args list is
 * pass-by-reference.  Conversion and const-simplification of the args list
 * will be done even if simplification of the function call itself is not
 * possible.
 */
static Expr *
simplify_function(Oid funcid, Oid result_type, int32 result_typmod,
                  Oid result_collid, Oid input_collid, List **args_p,
                  bool funcvariadic, bool process_args, bool allow_non_const,
                  eval_const_expressions_context *context)
{
    List       *args = *args_p;
    HeapTuple   func_tuple;
    Form_pg_proc func_form;
    Expr       *newexpr;

    /*
     * We have three strategies for simplification: execute the function to
     * deliver a constant result, use a transform function to generate a
     * substitute node tree, or expand in-line the body of the function
     * definition (which only works for simple SQL-language functions, but
     * that is a common case).  Each case needs access to the function's
     * pg_proc tuple, so fetch it just once.
     *
     * Note: the allow_non_const flag suppresses both the second and third
     * strategies; so if !allow_non_const, simplify_function can only return a
     * Const or NULL.  Argument-list rewriting happens anyway, though.
     */
    func_tuple = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcid));
    if (!HeapTupleIsValid(func_tuple))
        elog(ERROR, "cache lookup failed for function %u", funcid);
    func_form = (Form_pg_proc) GETSTRUCT(func_tuple);

    /*
     * Process the function arguments, unless the caller did it already.
     *
     * Here we must deal with named or defaulted arguments, and then
     * recursively apply eval_const_expressions to the whole argument list.
     */
    if (process_args)
    {
        args = expand_function_arguments(args, result_type, func_tuple);
        args = (List *) expression_tree_mutator((Node *) args,
                                                eval_const_expressions_mutator,
                                                (void *) context);
        /* Argument processing done, give it back to the caller */
        *args_p = args;
    }

    /* Now attempt simplification of the function call proper. */

    newexpr = evaluate_function(funcid, result_type, result_typmod,
                                result_collid, input_collid,
                                args, funcvariadic,
                                func_tuple, context);

    if (!newexpr && allow_non_const && OidIsValid(func_form->protransform))
    {
        /*
         * Build a dummy FuncExpr node containing the simplified arg list.  We
         * use this approach to present a uniform interface to the transform
         * function regardless of how the function is actually being invoked.
         */
        FuncExpr    fexpr;

        fexpr.xpr.type = T_FuncExpr;
        fexpr.funcid = funcid;
        fexpr.funcresulttype = result_type;
        fexpr.funcretset = func_form->proretset;
        fexpr.funcvariadic = funcvariadic;
        fexpr.funcformat = COERCE_EXPLICIT_CALL;
        fexpr.funccollid = result_collid;
        fexpr.inputcollid = input_collid;
        fexpr.args = args;
        fexpr.location = -1;

        newexpr = (Expr *)
            DatumGetPointer(OidFunctionCall1(func_form->protransform,
                                             PointerGetDatum(&fexpr)));
    }

    if (!newexpr && allow_non_const)
        newexpr = inline_function(funcid, result_type, result_collid,
                                  input_collid, args, funcvariadic,
                                  func_tuple, context);

    ReleaseSysCache(func_tuple);

    return newexpr;
}

/*
 * expand_function_arguments: convert named-notation args to positional args
 * and/or insert default args, as needed
 *
 * If we need to change anything, the input argument list is copied, not
 * modified.
 *
 * Note: this gets applied to operator argument lists too, even though the
 * cases it handles should never occur there.  This should be OK since it
 * will fall through very quickly if there's nothing to do.
 */
List *
expand_function_arguments(List *args, Oid result_type, HeapTuple func_tuple)
{
    Form_pg_proc funcform = (Form_pg_proc) GETSTRUCT(func_tuple);
    bool        has_named_args = false;
    ListCell   *lc;

    /* Do we have any named arguments? */
    foreach(lc, args)
    {
        Node       *arg = (Node *) lfirst(lc);

        if (IsA(arg, NamedArgExpr))
        {
            has_named_args = true;
            break;
        }
    }

    /* If so, we must apply reorder_function_arguments */
    if (has_named_args)
    {
        args = reorder_function_arguments(args, func_tuple);
        /* Recheck argument types and add casts if needed */
        recheck_cast_function_args(args, result_type, func_tuple);
    }
    else if (list_length(args) < funcform->pronargs)
    {
        /* No named args, but we seem to be short some defaults */
        args = add_function_defaults(args, func_tuple);
        /* Recheck argument types and add casts if needed */
        recheck_cast_function_args(args, result_type, func_tuple);
    }

    return args;
}

/*
 * reorder_function_arguments: convert named-notation args to positional args
 *
 * This function also inserts default argument values as needed, since it's
 * impossible to form a truly valid positional call without that.
 */
static List *
reorder_function_arguments(List *args, HeapTuple func_tuple)
{
    Form_pg_proc funcform = (Form_pg_proc) GETSTRUCT(func_tuple);
    int         pronargs = funcform->pronargs;
    int         nargsprovided = list_length(args);
    Node       *argarray[FUNC_MAX_ARGS];
    ListCell   *lc;
    int         i;

    Assert(nargsprovided <= pronargs);
    if (pronargs > FUNC_MAX_ARGS)
        elog(ERROR, "too many function arguments");
    MemSet(argarray, 0, pronargs * sizeof(Node *));

    /* Deconstruct the argument list into an array indexed by argnumber */
    i = 0;
    foreach(lc, args)
    {
        Node       *arg = (Node *) lfirst(lc);

        if (!IsA(arg, NamedArgExpr))
        {
            /* positional argument, assumed to precede all named args */
            Assert(argarray[i] == NULL);
            argarray[i++] = arg;
        }
        else
        {
            NamedArgExpr *na = (NamedArgExpr *) arg;

            Assert(argarray[na->argnumber] == NULL);
            argarray[na->argnumber] = (Node *) na->arg;
        }
    }

    /*
     * Fetch default expressions, if needed, and insert into array at proper
     * locations (they aren't necessarily consecutive or all used)
     */
    if (nargsprovided < pronargs)
    {
        List       *defaults = fetch_function_defaults(func_tuple);

        i = pronargs - funcform->pronargdefaults;
        foreach(lc, defaults)
        {
            if (argarray[i] == NULL)
                argarray[i] = (Node *) lfirst(lc);
            i++;
        }
    }

    /* Now reconstruct the args list in proper order */
    args = NIL;
    for (i = 0; i < pronargs; i++)
    {
        Assert(argarray[i] != NULL);
        args = lappend(args, argarray[i]);
    }

    return args;
}

/*
 * add_function_defaults: add missing function arguments from its defaults
 *
 * This is used only when the argument list was positional to begin with,
 * and so we know we just need to add defaults at the end.
 */
static List *
add_function_defaults(List *args, HeapTuple func_tuple)
{
    Form_pg_proc funcform = (Form_pg_proc) GETSTRUCT(func_tuple);
    int         nargsprovided = list_length(args);
    List       *defaults;
    int         ndelete;

    /* Get all the default expressions from the pg_proc tuple */
    defaults = fetch_function_defaults(func_tuple);

    /* Delete any unused defaults from the list */
    ndelete = nargsprovided + list_length(defaults) - funcform->pronargs;
    if (ndelete < 0)
        elog(ERROR, "not enough default arguments");
    while (ndelete-- > 0)
        defaults = list_delete_first(defaults);

    /* And form the combined argument list, not modifying the input list */
    return list_concat(list_copy(args), defaults);
}

/*
 * fetch_function_defaults: get function's default arguments as expression list
 */
static List *
fetch_function_defaults(HeapTuple func_tuple)
{
    List       *defaults;
    Datum       proargdefaults;
    bool        isnull;
    char       *str;

    /* The error cases here shouldn't happen, but check anyway */
    proargdefaults = SysCacheGetAttr(PROCOID, func_tuple,
                                     Anum_pg_proc_proargdefaults,
                                     &isnull);
    if (isnull)
        elog(ERROR, "not enough default arguments");
    str = TextDatumGetCString(proargdefaults);
    defaults = castNode(List, stringToNode(str));
    pfree(str);
    return defaults;
}

/*
 * recheck_cast_function_args: recheck function args and typecast as needed
 * after adding defaults.
 *
 * It is possible for some of the defaulted arguments to be polymorphic;
 * therefore we can't assume that the default expressions have the correct
 * data types already.  We have to re-resolve polymorphics and do coercion
 * just like the parser did.
 *
 * This should be a no-op if there are no polymorphic arguments,
 * but we do it anyway to be sure.
 *
 * Note: if any casts are needed, the args list is modified in-place;
 * caller should have already copied the list structure.
 */
static void
recheck_cast_function_args(List *args, Oid result_type, HeapTuple func_tuple)
{
    Form_pg_proc funcform = (Form_pg_proc) GETSTRUCT(func_tuple);
    int         nargs;
    Oid         actual_arg_types[FUNC_MAX_ARGS];
    Oid         declared_arg_types[FUNC_MAX_ARGS];
    Oid         rettype;
    ListCell   *lc;

    if (list_length(args) > FUNC_MAX_ARGS)
        elog(ERROR, "too many function arguments");
    nargs = 0;
    foreach(lc, args)
    {
        actual_arg_types[nargs++] = exprType((Node *) lfirst(lc));
    }
    Assert(nargs == funcform->pronargs);
    memcpy(declared_arg_types, funcform->proargtypes.values,
           funcform->pronargs * sizeof(Oid));
    rettype = enforce_generic_type_consistency(actual_arg_types,
                                               declared_arg_types,
                                               nargs,
                                               funcform->prorettype,
                                               false);
    /* let's just check we got the same answer as the parser did ... */
    if (rettype != result_type)
        elog(ERROR, "function's resolved result type changed during planning");

    /* perform any necessary typecasting of arguments */
    make_fn_arguments(NULL, args, actual_arg_types, declared_arg_types);
}

/*
 * evaluate_function: try to pre-evaluate a function call
 *
 * We can do this if the function is strict and has any constant-null inputs
 * (just return a null constant), or if the function is immutable and has all
 * constant inputs (call it and return the result as a Const node).  In
 * estimation mode we are willing to pre-evaluate stable functions too.
 *
 * Returns a simplified expression if successful, or NULL if cannot
 * simplify the function.
 */
static Expr *
evaluate_function(Oid funcid, Oid result_type, int32 result_typmod,
                  Oid result_collid, Oid input_collid, List *args,
                  bool funcvariadic,
                  HeapTuple func_tuple,
                  eval_const_expressions_context *context)
{
    Form_pg_proc funcform = (Form_pg_proc) GETSTRUCT(func_tuple);
    bool        has_nonconst_input = false;
    bool        has_null_input = false;
    ListCell   *arg;
    FuncExpr   *newexpr;

    /*
     * Can't simplify if it returns a set.
     */
    if (funcform->proretset)
        return NULL;

    /*
     * Can't simplify if it returns RECORD.  The immediate problem is that it
     * will be needing an expected tupdesc which we can't supply here.
     *
     * In the case where it has OUT parameters, it could get by without an
     * expected tupdesc, but we still have issues: get_expr_result_type()
     * doesn't know how to extract type info from a RECORD constant, and in
     * the case of a NULL function result there doesn't seem to be any clean
     * way to fix that.  In view of the likelihood of there being still other
     * gotchas, seems best to leave the function call unreduced.
     */
    if (funcform->prorettype == RECORDOID)
        return NULL;

    /*
     * Check for constant inputs and especially constant-NULL inputs.
     */
    foreach(arg, args)
    {
        if (IsA(lfirst(arg), Const))
            has_null_input |= ((Const *) lfirst(arg))->constisnull;
        else
            has_nonconst_input = true;
    }

    /*
     * If the function is strict and has a constant-NULL input, it will never
     * be called at all, so we can replace the call by a NULL constant, even
     * if there are other inputs that aren't constant, and even if the
     * function is not otherwise immutable.
     */
    if (funcform->proisstrict && has_null_input)
        return (Expr *) makeNullConst(result_type, result_typmod,
                                      result_collid);

    /*
     * Otherwise, can simplify only if all inputs are constants. (For a
     * non-strict function, constant NULL inputs are treated the same as
     * constant non-NULL inputs.)
     */
    if (has_nonconst_input)
        return NULL;

    /*
     * Ordinarily we are only allowed to simplify immutable functions. But for
     * purposes of estimation, we consider it okay to simplify functions that
     * are merely stable; the risk that the result might change from planning
     * time to execution time is worth taking in preference to not being able
     * to estimate the value at all.
     */
    if (funcform->provolatile == PROVOLATILE_IMMUTABLE)
         /* okay */ ;
    else if (context->estimate && funcform->provolatile == PROVOLATILE_STABLE)
         /* okay */ ;
    else
        return NULL;

    /*
     * OK, looks like we can simplify this operator/function.
     *
     * Build a new FuncExpr node containing the already-simplified arguments.
     */
    newexpr = makeNode(FuncExpr);
    newexpr->funcid = funcid;
    newexpr->funcresulttype = result_type;
    newexpr->funcretset = false;
    newexpr->funcvariadic = funcvariadic;
    newexpr->funcformat = COERCE_EXPLICIT_CALL; /* doesn't matter */
    newexpr->funccollid = result_collid;    /* doesn't matter */
    newexpr->inputcollid = input_collid;
    newexpr->args = args;
    newexpr->location = -1;

    return evaluate_expr((Expr *) newexpr, result_type, result_typmod,
                         result_collid);
}

/*
 * inline_function: try to expand a function call inline
 *
 * If the function is a sufficiently simple SQL-language function
 * (just "SELECT expression"), then we can inline it and avoid the rather
 * high per-call overhead of SQL functions.  Furthermore, this can expose
 * opportunities for constant-folding within the function expression.
 *
 * We have to beware of some special cases however.  A directly or
 * indirectly recursive function would cause us to recurse forever,
 * so we keep track of which functions we are already expanding and
 * do not re-expand them.  Also, if a parameter is used more than once
 * in the SQL-function body, we require it not to contain any volatile
 * functions (volatiles might deliver inconsistent answers) nor to be
 * unreasonably expensive to evaluate.  The expensiveness check not only
 * prevents us from doing multiple evaluations of an expensive parameter
 * at runtime, but is a safety value to limit growth of an expression due
 * to repeated inlining.
 *
 * We must also beware of changing the volatility or strictness status of
 * functions by inlining them.
 *
 * Also, at the moment we can't inline functions returning RECORD.  This
 * doesn't work in the general case because it discards information such
 * as OUT-parameter declarations.
 *
 * Also, context-dependent expression nodes in the argument list are trouble.
 *
 * Returns a simplified expression if successful, or NULL if cannot
 * simplify the function.
 */
static Expr *
inline_function(Oid funcid, Oid result_type, Oid result_collid,
                Oid input_collid, List *args,
                bool funcvariadic,
                HeapTuple func_tuple,
                eval_const_expressions_context *context)
{
    Form_pg_proc funcform = (Form_pg_proc) GETSTRUCT(func_tuple);
    char       *src;
    Datum       tmp;
    bool        isNull;
    bool        modifyTargetList;
    MemoryContext oldcxt;
    MemoryContext mycxt;
    inline_error_callback_arg callback_arg;
    ErrorContextCallback sqlerrcontext;
    FuncExpr   *fexpr;
    SQLFunctionParseInfoPtr pinfo;
    ParseState *pstate;
    List       *raw_parsetree_list;
    Query      *querytree;
    Node       *newexpr;
    int        *usecounts;
    ListCell   *arg;
    int         i;

    /*
     * Forget it if the function is not SQL-language or has other showstopper
     * properties.  (The prokind and nargs checks are just paranoia.)
     */
    if (funcform->prolang != SQLlanguageId ||
        funcform->prokind != PROKIND_FUNCTION ||
        funcform->prosecdef ||
        funcform->proretset ||
        funcform->prorettype == RECORDOID ||
        !heap_attisnull(func_tuple, Anum_pg_proc_proconfig, NULL) ||
        funcform->pronargs != list_length(args))
        return NULL;

    /* Check for recursive function, and give up trying to expand if so */
    if (list_member_oid(context->active_fns, funcid))
        return NULL;

    /* Check permission to call function (fail later, if not) */
    if (pg_proc_aclcheck(funcid, GetUserId(), ACL_EXECUTE) != ACLCHECK_OK)
        return NULL;

    /* Check whether a plugin wants to hook function entry/exit */
    if (FmgrHookIsNeeded(funcid))
        return NULL;

    /*
     * Make a temporary memory context, so that we don't leak all the stuff
     * that parsing might create.
     */
    mycxt = AllocSetContextCreate(CurrentMemoryContext,
                                  "inline_function",
                                  ALLOCSET_DEFAULT_SIZES);
    oldcxt = MemoryContextSwitchTo(mycxt);

    /* Fetch the function body */
    tmp = SysCacheGetAttr(PROCOID,
                          func_tuple,
                          Anum_pg_proc_prosrc,
                          &isNull);
    if (isNull)
        elog(ERROR, "null prosrc for function %u", funcid);
    src = TextDatumGetCString(tmp);

    /*
     * Setup error traceback support for ereport().  This is so that we can
     * finger the function that bad information came from.
     */
    callback_arg.proname = NameStr(funcform->proname);
    callback_arg.prosrc = src;

    sqlerrcontext.callback = sql_inline_error_callback;
    sqlerrcontext.arg = (void *) &callback_arg;
    sqlerrcontext.previous = error_context_stack;
    error_context_stack = &sqlerrcontext;

    /*
     * Set up to handle parameters while parsing the function body.  We need a
     * dummy FuncExpr node containing the already-simplified arguments to pass
     * to prepare_sql_fn_parse_info.  (It is really only needed if there are
     * some polymorphic arguments, but for simplicity we always build it.)
     */
    fexpr = makeNode(FuncExpr);
    fexpr->funcid = funcid;
    fexpr->funcresulttype = result_type;
    fexpr->funcretset = false;
    fexpr->funcvariadic = funcvariadic;
    fexpr->funcformat = COERCE_EXPLICIT_CALL;   /* doesn't matter */
    fexpr->funccollid = result_collid;  /* doesn't matter */
    fexpr->inputcollid = input_collid;
    fexpr->args = args;
    fexpr->location = -1;

    pinfo = prepare_sql_fn_parse_info(func_tuple,
                                      (Node *) fexpr,
                                      input_collid);

    /*
     * We just do parsing and parse analysis, not rewriting, because rewriting
     * will not affect table-free-SELECT-only queries, which is all that we
     * care about.  Also, we can punt as soon as we detect more than one
     * command in the function body.
     */
    raw_parsetree_list = pg_parse_query(src);
    if (list_length(raw_parsetree_list) != 1)
        goto fail;

    pstate = make_parsestate(NULL);
    pstate->p_sourcetext = src;
    sql_fn_parser_setup(pstate, pinfo);

    querytree = transformTopLevelStmt(pstate, linitial(raw_parsetree_list));

    free_parsestate(pstate);

    /*
     * The single command must be a simple "SELECT expression".
     *
     * Note: if you change the tests involved in this, see also plpgsql's
     * exec_simple_check_plan().  That generally needs to have the same idea
     * of what's a "simple expression", so that inlining a function that
     * previously wasn't inlined won't change plpgsql's conclusion.
     */
    if (!IsA(querytree, Query) ||
        querytree->commandType != CMD_SELECT ||
        querytree->hasAggs ||
        querytree->hasWindowFuncs ||
        querytree->hasTargetSRFs ||
        querytree->hasSubLinks ||
        querytree->cteList ||
        querytree->rtable ||
        querytree->jointree->fromlist ||
        querytree->jointree->quals ||
        querytree->groupClause ||
        querytree->groupingSets ||
        querytree->havingQual ||
        querytree->windowClause ||
        querytree->distinctClause ||
        querytree->sortClause ||
        querytree->limitOffset ||
        querytree->limitCount ||
        querytree->setOperations ||
        list_length(querytree->targetList) != 1)
        goto fail;

    /*
     * Make sure the function (still) returns what it's declared to.  This
     * will raise an error if wrong, but that's okay since the function would
     * fail at runtime anyway.  Note that check_sql_fn_retval will also insert
     * a RelabelType if needed to make the tlist expression match the declared
     * type of the function.
     *
     * Note: we do not try this until we have verified that no rewriting was
     * needed; that's probably not important, but let's be careful.
     */
    if (check_sql_fn_retval(funcid, result_type, list_make1(querytree),
                            &modifyTargetList, NULL))
        goto fail;              /* reject whole-tuple-result cases */

    /* Now we can grab the tlist expression */
    newexpr = (Node *) ((TargetEntry *) linitial(querytree->targetList))->expr;

    /*
     * If the SQL function returns VOID, we can only inline it if it is a
     * SELECT of an expression returning VOID (ie, it's just a redirection to
     * another VOID-returning function).  In all non-VOID-returning cases,
     * check_sql_fn_retval should ensure that newexpr returns the function's
     * declared result type, so this test shouldn't fail otherwise; but we may
     * as well cope gracefully if it does.
     */
    if (exprType(newexpr) != result_type)
        goto fail;

    /* check_sql_fn_retval couldn't have made any dangerous tlist changes */
    Assert(!modifyTargetList);

    /*
     * Additional validity checks on the expression.  It mustn't be more
     * volatile than the surrounding function (this is to avoid breaking hacks
     * that involve pretending a function is immutable when it really ain't).
     * If the surrounding function is declared strict, then the expression
     * must contain only strict constructs and must use all of the function
     * parameters (this is overkill, but an exact analysis is hard).
     */
    if (funcform->provolatile == PROVOLATILE_IMMUTABLE &&
        contain_mutable_functions(newexpr))
        goto fail;
    else if (funcform->provolatile == PROVOLATILE_STABLE &&
             contain_volatile_functions(newexpr))
        goto fail;

    if (funcform->proisstrict &&
        contain_nonstrict_functions(newexpr))
        goto fail;

    /*
     * If any parameter expression contains a context-dependent node, we can't
     * inline, for fear of putting such a node into the wrong context.
     */
    if (contain_context_dependent_node((Node *) args))
        goto fail;

    /*
     * We may be able to do it; there are still checks on parameter usage to
     * make, but those are most easily done in combination with the actual
     * substitution of the inputs.  So start building expression with inputs
     * substituted.
     */
    usecounts = (int *) palloc0(funcform->pronargs * sizeof(int));
    newexpr = substitute_actual_parameters(newexpr, funcform->pronargs,
                                           args, usecounts);

    /* Now check for parameter usage */
    i = 0;
    foreach(arg, args)
    {
        Node       *param = lfirst(arg);

        if (usecounts[i] == 0)
        {
            /* Param not used at all: uncool if func is strict */
            if (funcform->proisstrict)
                goto fail;
        }
        else if (usecounts[i] != 1)
        {
            /* Param used multiple times: uncool if expensive or volatile */
            QualCost    eval_cost;

            /*
             * We define "expensive" as "contains any subplan or more than 10
             * operators".  Note that the subplan search has to be done
             * explicitly, since cost_qual_eval() will barf on unplanned
             * subselects.
             */
            if (contain_subplans(param))
                goto fail;
            cost_qual_eval(&eval_cost, list_make1(param), NULL);
            if (eval_cost.startup + eval_cost.per_tuple >
                10 * cpu_operator_cost)
                goto fail;

            /*
             * Check volatility last since this is more expensive than the
             * above tests
             */
            if (contain_volatile_functions(param))
                goto fail;
        }
        i++;
    }

    /*
     * Whew --- we can make the substitution.  Copy the modified expression
     * out of the temporary memory context, and clean up.
     */
    MemoryContextSwitchTo(oldcxt);

    newexpr = copyObject(newexpr);

    MemoryContextDelete(mycxt);

    /*
     * If the result is of a collatable type, force the result to expose the
     * correct collation.  In most cases this does not matter, but it's
     * possible that the function result is used directly as a sort key or in
     * other places where we expect exprCollation() to tell the truth.
     */
    if (OidIsValid(result_collid))
    {
        Oid         exprcoll = exprCollation(newexpr);

        if (OidIsValid(exprcoll) && exprcoll != result_collid)
        {
            CollateExpr *newnode = makeNode(CollateExpr);

            newnode->arg = (Expr *) newexpr;
            newnode->collOid = result_collid;
            newnode->location = -1;

            newexpr = (Node *) newnode;
        }
    }

    /*
     * Since there is now no trace of the function in the plan tree, we must
     * explicitly record the plan's dependency on the function.
     */
    if (context->root)
        record_plan_function_dependency(context->root, funcid);

    /*
     * Recursively try to simplify the modified expression.  Here we must add
     * the current function to the context list of active functions.
     */
    context->active_fns = lcons_oid(funcid, context->active_fns);
    newexpr = eval_const_expressions_mutator(newexpr, context);
    context->active_fns = list_delete_first(context->active_fns);

    error_context_stack = sqlerrcontext.previous;

    return (Expr *) newexpr;

    /* Here if func is not inlinable: release temp memory and return NULL */
fail:
    MemoryContextSwitchTo(oldcxt);
    MemoryContextDelete(mycxt);
    error_context_stack = sqlerrcontext.previous;

    return NULL;
}

/*
 * Replace Param nodes by appropriate actual parameters
 */
static Node *
substitute_actual_parameters(Node *expr, int nargs, List *args,
                             int *usecounts)
{
    substitute_actual_parameters_context context;

    context.nargs = nargs;
    context.args = args;
    context.usecounts = usecounts;

    return substitute_actual_parameters_mutator(expr, &context);
}

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

        if (param->paramkind != PARAM_EXTERN)
            elog(ERROR, "unexpected paramkind: %d", (int) param->paramkind);
        if (param->paramid <= 0 || param->paramid > context->nargs)
            elog(ERROR, "invalid paramid: %d", param->paramid);

        /* Count usage of parameter */
        context->usecounts[param->paramid - 1]++;

        /* Select the appropriate actual arg and replace the Param with it */
        /* We don't need to copy at this time (it'll get done later) */
        return list_nth(context->args, param->paramid - 1);
    }
    return expression_tree_mutator(node, substitute_actual_parameters_mutator,
                                   (void *) context);
}

/*
 * error context callback to let us supply a call-stack traceback
 */
static void
sql_inline_error_callback(void *arg)
{
    inline_error_callback_arg *callback_arg = (inline_error_callback_arg *) arg;
    int         syntaxerrposition;

    /* If it's a syntax error, convert to internal syntax error report */
    syntaxerrposition = geterrposition();
    if (syntaxerrposition > 0)
    {
        errposition(0);
        internalerrposition(syntaxerrposition);
        internalerrquery(callback_arg->prosrc);
    }

    errcontext("SQL function \"%s\" during inlining", callback_arg->proname);
}

/*
 * evaluate_expr: pre-evaluate a constant expression
 *
 * We use the executor's routine ExecEvalExpr() to avoid duplication of
 * code and ensure we get the same result as the executor would get.
 */
static Expr *
evaluate_expr(Expr *expr, Oid result_type, int32 result_typmod,
              Oid result_collation)
{
    EState     *estate;
    ExprState  *exprstate;
    MemoryContext oldcontext;
    Datum       const_val;
    bool        const_is_null;
    int16       resultTypLen;
    bool        resultTypByVal;

    /*
     * To use the executor, we need an EState.
     */
    estate = CreateExecutorState();

    /* We can use the estate's working context to avoid memory leaks. */
    oldcontext = MemoryContextSwitchTo(estate->es_query_cxt);

    /* Make sure any opfuncids are filled in. */
    fix_opfuncids((Node *) expr);

    /*
     * Prepare expr for execution.  (Note: we can't use ExecPrepareExpr
     * because it'd result in recursively invoking eval_const_expressions.)
     */
    exprstate = ExecInitExpr(expr, NULL);

    /*
     * And evaluate it.
     *
     * It is OK to use a default econtext because none of the ExecEvalExpr()
     * code used in this situation will use econtext.  That might seem
     * fortuitous, but it's not so unreasonable --- a constant expression does
     * not depend on context, by definition, n'est ce pas?
     */
    const_val = ExecEvalExprSwitchContext(exprstate,
                                          GetPerTupleExprContext(estate),
                                          &const_is_null);

    /* Get info needed about result datatype */
    get_typlenbyval(result_type, &resultTypLen, &resultTypByVal);

    /* Get back to outer memory context */
    MemoryContextSwitchTo(oldcontext);

    /*
     * Must copy result out of sub-context used by expression eval.
     *
     * Also, if it's varlena, forcibly detoast it.  This protects us against
     * storing TOAST pointers into plans that might outlive the referenced
     * data.  (makeConst would handle detoasting anyway, but it's worth a few
     * extra lines here so that we can do the copy and detoast in one step.)
     */
    if (!const_is_null)
    {
        if (resultTypLen == -1)
            const_val = PointerGetDatum(PG_DETOAST_DATUM_COPY(const_val));
        else
            const_val = datumCopy(const_val, resultTypByVal, resultTypLen);
    }

    /* Release all the junk we just created */
    FreeExecutorState(estate);

    /*
     * Make the constant result node.
     */
    return (Expr *) makeConst(result_type, result_typmod, result_collation,
                              resultTypLen,
                              const_val, const_is_null,
                              resultTypByVal);
}


/*
 * inline_set_returning_function
 *      Attempt to "inline" a set-returning function in the FROM clause.
 *
 * "rte" is an RTE_FUNCTION rangetable entry.  If it represents a call of a
 * set-returning SQL function that can safely be inlined, expand the function
 * and return the substitute Query structure.  Otherwise, return NULL.
 *
 * This has a good deal of similarity to inline_function(), but that's
 * for the non-set-returning case, and there are enough differences to
 * justify separate functions.
 */
Query *
inline_set_returning_function(PlannerInfo *root, RangeTblEntry *rte)
{
    RangeTblFunction *rtfunc;
    FuncExpr   *fexpr;
    Oid         func_oid;
    HeapTuple   func_tuple;
    Form_pg_proc funcform;
    char       *src;
    Datum       tmp;
    bool        isNull;
    bool        modifyTargetList;
    MemoryContext oldcxt;
    MemoryContext mycxt;
    List       *saveInvalItems;
    inline_error_callback_arg callback_arg;
    ErrorContextCallback sqlerrcontext;
    SQLFunctionParseInfoPtr pinfo;
    List       *raw_parsetree_list;
    List       *querytree_list;
    Query      *querytree;

    Assert(rte->rtekind == RTE_FUNCTION);

    /*
     * It doesn't make a lot of sense for a SQL SRF to refer to itself in its
     * own FROM clause, since that must cause infinite recursion at runtime.
     * It will cause this code to recurse too, so check for stack overflow.
     * (There's no need to do more.)
     */
    check_stack_depth();

    /* Fail if the RTE has ORDINALITY - we don't implement that here. */
    if (rte->funcordinality)
        return NULL;

    /* Fail if RTE isn't a single, simple FuncExpr */
    if (list_length(rte->functions) != 1)
        return NULL;
    rtfunc = (RangeTblFunction *) linitial(rte->functions);

    if (!IsA(rtfunc->funcexpr, FuncExpr))
        return NULL;
    fexpr = (FuncExpr *) rtfunc->funcexpr;

    func_oid = fexpr->funcid;

    /*
     * The function must be declared to return a set, else inlining would
     * change the results if the contained SELECT didn't return exactly one
     * row.
     */
    if (!fexpr->funcretset)
        return NULL;

    /*
     * Refuse to inline if the arguments contain any volatile functions or
     * sub-selects.  Volatile functions are rejected because inlining may
     * result in the arguments being evaluated multiple times, risking a
     * change in behavior.  Sub-selects are rejected partly for implementation
     * reasons (pushing them down another level might change their behavior)
     * and partly because they're likely to be expensive and so multiple
     * evaluation would be bad.
     */
    if (contain_volatile_functions((Node *) fexpr->args) ||
        contain_subplans((Node *) fexpr->args))
        return NULL;

    /* Check permission to call function (fail later, if not) */
    if (pg_proc_aclcheck(func_oid, GetUserId(), ACL_EXECUTE) != ACLCHECK_OK)
        return NULL;

    /* Check whether a plugin wants to hook function entry/exit */
    if (FmgrHookIsNeeded(func_oid))
        return NULL;

    /*
     * OK, let's take a look at the function's pg_proc entry.
     */
    func_tuple = SearchSysCache1(PROCOID, ObjectIdGetDatum(func_oid));
    if (!HeapTupleIsValid(func_tuple))
        elog(ERROR, "cache lookup failed for function %u", func_oid);
    funcform = (Form_pg_proc) GETSTRUCT(func_tuple);

    /*
     * Forget it if the function is not SQL-language or has other showstopper
     * properties.  In particular it mustn't be declared STRICT, since we
     * couldn't enforce that.  It also mustn't be VOLATILE, because that is
     * supposed to cause it to be executed with its own snapshot, rather than
     * sharing the snapshot of the calling query.  We also disallow returning
     * SETOF VOID, because inlining would result in exposing the actual result
     * of the function's last SELECT, which should not happen in that case.
     * (Rechecking prokind and proretset is just paranoia.)
     */
    if (funcform->prolang != SQLlanguageId ||
        funcform->prokind != PROKIND_FUNCTION ||
        funcform->proisstrict ||
        funcform->provolatile == PROVOLATILE_VOLATILE ||
        funcform->prorettype == VOIDOID ||
        funcform->prosecdef ||
        !funcform->proretset ||
        !heap_attisnull(func_tuple, Anum_pg_proc_proconfig, NULL))
    {
        ReleaseSysCache(func_tuple);
        return NULL;
    }

    /*
     * Make a temporary memory context, so that we don't leak all the stuff
     * that parsing might create.
     */
    mycxt = AllocSetContextCreate(CurrentMemoryContext,
                                  "inline_set_returning_function",
                                  ALLOCSET_DEFAULT_SIZES);
    oldcxt = MemoryContextSwitchTo(mycxt);

    /*
     * When we call eval_const_expressions below, it might try to add items to
     * root->glob->invalItems.  Since it is running in the temp context, those
     * items will be in that context, and will need to be copied out if we're
     * successful.  Temporarily reset the list so that we can keep those items
     * separate from the pre-existing list contents.
     */
    saveInvalItems = root->glob->invalItems;
    root->glob->invalItems = NIL;

    /* Fetch the function body */
    tmp = SysCacheGetAttr(PROCOID,
                          func_tuple,
                          Anum_pg_proc_prosrc,
                          &isNull);
    if (isNull)
        elog(ERROR, "null prosrc for function %u", func_oid);
    src = TextDatumGetCString(tmp);

    /*
     * Setup error traceback support for ereport().  This is so that we can
     * finger the function that bad information came from.
     */
    callback_arg.proname = NameStr(funcform->proname);
    callback_arg.prosrc = src;

    sqlerrcontext.callback = sql_inline_error_callback;
    sqlerrcontext.arg = (void *) &callback_arg;
    sqlerrcontext.previous = error_context_stack;
    error_context_stack = &sqlerrcontext;

    /*
     * Run eval_const_expressions on the function call.  This is necessary to
     * ensure that named-argument notation is converted to positional notation
     * and any default arguments are inserted.  It's a bit of overkill for the
     * arguments, since they'll get processed again later, but no harm will be
     * done.
     */
    fexpr = (FuncExpr *) eval_const_expressions(root, (Node *) fexpr);

    /* It should still be a call of the same function, but let's check */
    if (!IsA(fexpr, FuncExpr) ||
        fexpr->funcid != func_oid)
        goto fail;

    /* Arg list length should now match the function */
    if (list_length(fexpr->args) != funcform->pronargs)
        goto fail;

    /*
     * Set up to handle parameters while parsing the function body.  We can
     * use the FuncExpr just created as the input for
     * prepare_sql_fn_parse_info.
     */
    pinfo = prepare_sql_fn_parse_info(func_tuple,
                                      (Node *) fexpr,
                                      fexpr->inputcollid);

    /*
     * Parse, analyze, and rewrite (unlike inline_function(), we can't skip
     * rewriting here).  We can fail as soon as we find more than one query,
     * though.
     */
    raw_parsetree_list = pg_parse_query(src);
    if (list_length(raw_parsetree_list) != 1)
        goto fail;

    querytree_list = pg_analyze_and_rewrite_params(linitial(raw_parsetree_list),
                                                   src,
                                                   (ParserSetupHook) sql_fn_parser_setup,
                                                   pinfo, NULL);
    if (list_length(querytree_list) != 1)
        goto fail;
    querytree = linitial(querytree_list);

    /*
     * The single command must be a plain SELECT.
     */
    if (!IsA(querytree, Query) ||
        querytree->commandType != CMD_SELECT)
        goto fail;

    /*
     * Make sure the function (still) returns what it's declared to.  This
     * will raise an error if wrong, but that's okay since the function would
     * fail at runtime anyway.  Note that check_sql_fn_retval will also insert
     * RelabelType(s) and/or NULL columns if needed to make the tlist
     * expression(s) match the declared type of the function.
     *
     * If the function returns a composite type, don't inline unless the check
     * shows it's returning a whole tuple result; otherwise what it's
     * returning is a single composite column which is not what we need. (Like
     * check_sql_fn_retval, we deliberately exclude domains over composite
     * here.)
     */
    if (!check_sql_fn_retval(func_oid, fexpr->funcresulttype,
                             querytree_list,
                             &modifyTargetList, NULL) &&
        (get_typtype(fexpr->funcresulttype) == TYPTYPE_COMPOSITE ||
         fexpr->funcresulttype == RECORDOID))
        goto fail;              /* reject not-whole-tuple-result cases */

    /*
     * If we had to modify the tlist to make it match, and the statement is
     * one in which changing the tlist contents could change semantics, we
     * have to punt and not inline.
     */
    if (modifyTargetList)
        goto fail;

    /*
     * If it returns RECORD, we have to check against the column type list
     * provided in the RTE; check_sql_fn_retval can't do that.  (If no match,
     * we just fail to inline, rather than complaining; see notes for
     * tlist_matches_coltypelist.)  We don't have to do this for functions
     * with declared OUT parameters, even though their funcresulttype is
     * RECORDOID, so check get_func_result_type too.
     */
    if (fexpr->funcresulttype == RECORDOID &&
        get_func_result_type(func_oid, NULL, NULL) == TYPEFUNC_RECORD &&
        !tlist_matches_coltypelist(querytree->targetList,
                                   rtfunc->funccoltypes))
        goto fail;

    /*
     * Looks good --- substitute parameters into the query.
     */
    querytree = substitute_actual_srf_parameters(querytree,
                                                 funcform->pronargs,
                                                 fexpr->args);

    /*
     * Copy the modified query out of the temporary memory context, and clean
     * up.
     */
    MemoryContextSwitchTo(oldcxt);

    querytree = copyObject(querytree);

    /* copy up any new invalItems, too */
    root->glob->invalItems = list_concat(saveInvalItems,
                                         copyObject(root->glob->invalItems));

    MemoryContextDelete(mycxt);
    error_context_stack = sqlerrcontext.previous;
    ReleaseSysCache(func_tuple);

    /*
     * We don't have to fix collations here because the upper query is already
     * parsed, ie, the collations in the RTE are what count.
     */

    /*
     * Since there is now no trace of the function in the plan tree, we must
     * explicitly record the plan's dependency on the function.
     */
    record_plan_function_dependency(root, func_oid);

    return querytree;

    /* Here if func is not inlinable: release temp memory and return NULL */
fail:
    MemoryContextSwitchTo(oldcxt);
    root->glob->invalItems = saveInvalItems;
    MemoryContextDelete(mycxt);
    error_context_stack = sqlerrcontext.previous;
    ReleaseSysCache(func_tuple);

    return NULL;
}

/*
 * Replace Param nodes by appropriate actual parameters
 *
 * This is just enough different from substitute_actual_parameters()
 * that it needs its own code.
 */
static Query *
substitute_actual_srf_parameters(Query *expr, int nargs, List *args)
{
    substitute_actual_srf_parameters_context context;

    context.nargs = nargs;
    context.args = args;
    context.sublevels_up = 1;

    return query_tree_mutator(expr,
                              substitute_actual_srf_parameters_mutator,
                              &context,
                              0);
}

static Node *
substitute_actual_srf_parameters_mutator(Node *node,
                                         substitute_actual_srf_parameters_context *context)
{
    Node       *result;

    if (node == NULL)
        return NULL;
    if (IsA(node, Query))
    {
        context->sublevels_up++;
        result = (Node *) query_tree_mutator((Query *) node,
                                             substitute_actual_srf_parameters_mutator,
                                             (void *) context,
                                             0);
        context->sublevels_up--;
        return result;
    }
    if (IsA(node, Param))
    {
        Param      *param = (Param *) node;

        if (param->paramkind == PARAM_EXTERN)
        {
            if (param->paramid <= 0 || param->paramid > context->nargs)
                elog(ERROR, "invalid paramid: %d", param->paramid);

            /*
             * Since the parameter is being inserted into a subquery, we must
             * adjust levels.
             */
            result = copyObject(list_nth(context->args, param->paramid - 1));
            IncrementVarSublevelsUp(result, context->sublevels_up, 0);
            return result;
        }
    }
    return expression_tree_mutator(node,
                                   substitute_actual_srf_parameters_mutator,
                                   (void *) context);
}

/*
 * Check whether a SELECT targetlist emits the specified column types,
 * to see if it's safe to inline a function returning record.
 *
 * We insist on exact match here.  The executor allows binary-coercible
 * cases too, but we don't have a way to preserve the correct column types
 * in the correct places if we inline the function in such a case.
 *
 * Note that we only check type OIDs not typmods; this agrees with what the
 * executor would do at runtime, and attributing a specific typmod to a
 * function result is largely wishful thinking anyway.
 */
static bool
tlist_matches_coltypelist(List *tlist, List *coltypelist)
{
    ListCell   *tlistitem;
    ListCell   *clistitem;

    clistitem = list_head(coltypelist);
    foreach(tlistitem, tlist)
    {
        TargetEntry *tle = (TargetEntry *) lfirst(tlistitem);
        Oid         coltype;

        if (tle->resjunk)
            continue;           /* ignore junk columns */

        if (clistitem == NULL)
            return false;       /* too many tlist items */

        coltype = lfirst_oid(clistitem);
        clistitem = lnext(clistitem);

        if (exprType((Node *) tle->expr) != coltype)
            return false;       /* column type mismatch */
    }

    if (clistitem != NULL)
        return false;           /* too few tlist items */

    return true;
}