Adding upstream version 15.5.upstream/15.5

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3226 insertions, 0 deletions

diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
new file mode 100644
index 0000000..9f39f46
--- /dev/null
+++ b/src/backend/optimizer/path/equivclass.c
@@ -0,0 +1,3226 @@
+/*-------------------------------------------------------------------------
+ *
+ * equivclass.c
+ *	  Routines for managing EquivalenceClasses
+ *
+ * See src/backend/optimizer/README for discussion of EquivalenceClasses.
+ *
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/optimizer/path/equivclass.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <limits.h>
+
+#include "access/stratnum.h"
+#include "catalog/pg_type.h"
+#include "nodes/makefuncs.h"
+#include "nodes/nodeFuncs.h"
+#include "optimizer/appendinfo.h"
+#include "optimizer/clauses.h"
+#include "optimizer/optimizer.h"
+#include "optimizer/pathnode.h"
+#include "optimizer/paths.h"
+#include "optimizer/planmain.h"
+#include "optimizer/restrictinfo.h"
+#include "utils/lsyscache.h"
+
+
+static EquivalenceMember *add_eq_member(EquivalenceClass *ec,
+										Expr *expr, Relids relids, Relids nullable_relids,
+										bool is_child, Oid datatype);
+static bool is_exprlist_member(Expr *node, List *exprs);
+static void generate_base_implied_equalities_const(PlannerInfo *root,
+												   EquivalenceClass *ec);
+static void generate_base_implied_equalities_no_const(PlannerInfo *root,
+													  EquivalenceClass *ec);
+static void generate_base_implied_equalities_broken(PlannerInfo *root,
+													EquivalenceClass *ec);
+static List *generate_join_implied_equalities_normal(PlannerInfo *root,
+													 EquivalenceClass *ec,
+													 Relids join_relids,
+													 Relids outer_relids,
+													 Relids inner_relids);
+static List *generate_join_implied_equalities_broken(PlannerInfo *root,
+													 EquivalenceClass *ec,
+													 Relids nominal_join_relids,
+													 Relids outer_relids,
+													 Relids nominal_inner_relids,
+													 RelOptInfo *inner_rel);
+static Oid	select_equality_operator(EquivalenceClass *ec,
+									 Oid lefttype, Oid righttype);
+static RestrictInfo *create_join_clause(PlannerInfo *root,
+										EquivalenceClass *ec, Oid opno,
+										EquivalenceMember *leftem,
+										EquivalenceMember *rightem,
+										EquivalenceClass *parent_ec);
+static bool reconsider_outer_join_clause(PlannerInfo *root,
+										 RestrictInfo *rinfo,
+										 bool outer_on_left);
+static bool reconsider_full_join_clause(PlannerInfo *root,
+										RestrictInfo *rinfo);
+static Bitmapset *get_eclass_indexes_for_relids(PlannerInfo *root,
+												Relids relids);
+static Bitmapset *get_common_eclass_indexes(PlannerInfo *root, Relids relids1,
+											Relids relids2);
+
+
+/*
+ * process_equivalence
+ *	  The given clause has a mergejoinable operator and can be applied without
+ *	  any delay by an outer join, so its two sides can be considered equal
+ *	  anywhere they are both computable; moreover that equality can be
+ *	  extended transitively.  Record this knowledge in the EquivalenceClass
+ *	  data structure, if applicable.  Returns true if successful, false if not
+ *	  (in which case caller should treat the clause as ordinary, not an
+ *	  equivalence).
+ *
+ * In some cases, although we cannot convert a clause into EquivalenceClass
+ * knowledge, we can still modify it to a more useful form than the original.
+ * Then, *p_restrictinfo will be replaced by a new RestrictInfo, which is what
+ * the caller should use for further processing.
+ *
+ * If below_outer_join is true, then the clause was found below the nullable
+ * side of an outer join, so its sides might validly be both NULL rather than
+ * strictly equal.  We can still deduce equalities in such cases, but we take
+ * care to mark an EquivalenceClass if it came from any such clauses.  Also,
+ * we have to check that both sides are either pseudo-constants or strict
+ * functions of Vars, else they might not both go to NULL above the outer
+ * join.  (This is the main reason why we need a failure return.  It's more
+ * convenient to check this case here than at the call sites...)
+ *
+ * We also reject proposed equivalence clauses if they contain leaky functions
+ * and have security_level above zero.  The EC evaluation rules require us to
+ * apply certain tests at certain joining levels, and we can't tolerate
+ * delaying any test on security_level grounds.  By rejecting candidate clauses
+ * that might require security delays, we ensure it's safe to apply an EC
+ * clause as soon as it's supposed to be applied.
+ *
+ * On success return, we have also initialized the clause's left_ec/right_ec
+ * fields to point to the EquivalenceClass representing it.  This saves lookup
+ * effort later.
+ *
+ * Note: constructing merged EquivalenceClasses is a standard UNION-FIND
+ * problem, for which there exist better data structures than simple lists.
+ * If this code ever proves to be a bottleneck then it could be sped up ---
+ * but for now, simple is beautiful.
+ *
+ * Note: this is only called during planner startup, not during GEQO
+ * exploration, so we need not worry about whether we're in the right
+ * memory context.
+ */
+bool
+process_equivalence(PlannerInfo *root,
+					RestrictInfo **p_restrictinfo,
+					bool below_outer_join)
+{
+	RestrictInfo *restrictinfo = *p_restrictinfo;
+	Expr	   *clause = restrictinfo->clause;
+	Oid			opno,
+				collation,
+				item1_type,
+				item2_type;
+	Expr	   *item1;
+	Expr	   *item2;
+	Relids		item1_relids,
+				item2_relids,
+				item1_nullable_relids,
+				item2_nullable_relids;
+	List	   *opfamilies;
+	EquivalenceClass *ec1,
+			   *ec2;
+	EquivalenceMember *em1,
+			   *em2;
+	ListCell   *lc1;
+	int			ec2_idx;
+
+	/* Should not already be marked as having generated an eclass */
+	Assert(restrictinfo->left_ec == NULL);
+	Assert(restrictinfo->right_ec == NULL);
+
+	/* Reject if it is potentially postponable by security considerations */
+	if (restrictinfo->security_level > 0 && !restrictinfo->leakproof)
+		return false;
+
+	/* Extract info from given clause */
+	Assert(is_opclause(clause));
+	opno = ((OpExpr *) clause)->opno;
+	collation = ((OpExpr *) clause)->inputcollid;
+	item1 = (Expr *) get_leftop(clause);
+	item2 = (Expr *) get_rightop(clause);
+	item1_relids = restrictinfo->left_relids;
+	item2_relids = restrictinfo->right_relids;
+
+	/*
+	 * Ensure both input expressions expose the desired collation (their types
+	 * should be OK already); see comments for canonicalize_ec_expression.
+	 */
+	item1 = canonicalize_ec_expression(item1,
+									   exprType((Node *) item1),
+									   collation);
+	item2 = canonicalize_ec_expression(item2,
+									   exprType((Node *) item2),
+									   collation);
+
+	/*
+	 * Clauses of the form X=X cannot be translated into EquivalenceClasses.
+	 * We'd either end up with a single-entry EC, losing the knowledge that
+	 * the clause was present at all, or else make an EC with duplicate
+	 * entries, causing other issues.
+	 */
+	if (equal(item1, item2))
+	{
+		/*
+		 * If the operator is strict, then the clause can be treated as just
+		 * "X IS NOT NULL".  (Since we know we are considering a top-level
+		 * qual, we can ignore the difference between FALSE and NULL results.)
+		 * It's worth making the conversion because we'll typically get a much
+		 * better selectivity estimate than we would for X=X.
+		 *
+		 * If the operator is not strict, we can't be sure what it will do
+		 * with NULLs, so don't attempt to optimize it.
+		 */
+		set_opfuncid((OpExpr *) clause);
+		if (func_strict(((OpExpr *) clause)->opfuncid))
+		{
+			NullTest   *ntest = makeNode(NullTest);
+
+			ntest->arg = item1;
+			ntest->nulltesttype = IS_NOT_NULL;
+			ntest->argisrow = false;	/* correct even if composite arg */
+			ntest->location = -1;
+
+			*p_restrictinfo =
+				make_restrictinfo(root,
+								  (Expr *) ntest,
+								  restrictinfo->is_pushed_down,
+								  restrictinfo->outerjoin_delayed,
+								  restrictinfo->pseudoconstant,
+								  restrictinfo->security_level,
+								  NULL,
+								  restrictinfo->outer_relids,
+								  restrictinfo->nullable_relids);
+		}
+		return false;
+	}
+
+	/*
+	 * If below outer join, check for strictness, else reject.
+	 */
+	if (below_outer_join)
+	{
+		if (!bms_is_empty(item1_relids) &&
+			contain_nonstrict_functions((Node *) item1))
+			return false;		/* LHS is non-strict but not constant */
+		if (!bms_is_empty(item2_relids) &&
+			contain_nonstrict_functions((Node *) item2))
+			return false;		/* RHS is non-strict but not constant */
+	}
+
+	/* Calculate nullable-relid sets for each side of the clause */
+	item1_nullable_relids = bms_intersect(item1_relids,
+										  restrictinfo->nullable_relids);
+	item2_nullable_relids = bms_intersect(item2_relids,
+										  restrictinfo->nullable_relids);
+
+	/*
+	 * We use the declared input types of the operator, not exprType() of the
+	 * inputs, as the nominal datatypes for opfamily lookup.  This presumes
+	 * that btree operators are always registered with amoplefttype and
+	 * amoprighttype equal to their declared input types.  We will need this
+	 * info anyway to build EquivalenceMember nodes, and by extracting it now
+	 * we can use type comparisons to short-circuit some equal() tests.
+	 */
+	op_input_types(opno, &item1_type, &item2_type);
+
+	opfamilies = restrictinfo->mergeopfamilies;
+
+	/*
+	 * Sweep through the existing EquivalenceClasses looking for matches to
+	 * item1 and item2.  These are the possible outcomes:
+	 *
+	 * 1. We find both in the same EC.  The equivalence is already known, so
+	 * there's nothing to do.
+	 *
+	 * 2. We find both in different ECs.  Merge the two ECs together.
+	 *
+	 * 3. We find just one.  Add the other to its EC.
+	 *
+	 * 4. We find neither.  Make a new, two-entry EC.
+	 *
+	 * Note: since all ECs are built through this process or the similar
+	 * search in get_eclass_for_sort_expr(), it's impossible that we'd match
+	 * an item in more than one existing nonvolatile EC.  So it's okay to stop
+	 * at the first match.
+	 */
+	ec1 = ec2 = NULL;
+	em1 = em2 = NULL;
+	ec2_idx = -1;
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
+		ListCell   *lc2;
+
+		/* Never match to a volatile EC */
+		if (cur_ec->ec_has_volatile)
+			continue;
+
+		/*
+		 * The collation has to match; check this first since it's cheaper
+		 * than the opfamily comparison.
+		 */
+		if (collation != cur_ec->ec_collation)
+			continue;
+
+		/*
+		 * A "match" requires matching sets of btree opfamilies.  Use of
+		 * equal() for this test has implications discussed in the comments
+		 * for get_mergejoin_opfamilies().
+		 */
+		if (!equal(opfamilies, cur_ec->ec_opfamilies))
+			continue;
+
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+
+			Assert(!cur_em->em_is_child);	/* no children yet */
+
+			/*
+			 * If below an outer join, don't match constants: they're not as
+			 * constant as they look.
+			 */
+			if ((below_outer_join || cur_ec->ec_below_outer_join) &&
+				cur_em->em_is_const)
+				continue;
+
+			if (!ec1 &&
+				item1_type == cur_em->em_datatype &&
+				equal(item1, cur_em->em_expr))
+			{
+				ec1 = cur_ec;
+				em1 = cur_em;
+				if (ec2)
+					break;
+			}
+
+			if (!ec2 &&
+				item2_type == cur_em->em_datatype &&
+				equal(item2, cur_em->em_expr))
+			{
+				ec2 = cur_ec;
+				ec2_idx = foreach_current_index(lc1);
+				em2 = cur_em;
+				if (ec1)
+					break;
+			}
+		}
+
+		if (ec1 && ec2)
+			break;
+	}
+
+	/* Sweep finished, what did we find? */
+
+	if (ec1 && ec2)
+	{
+		/* If case 1, nothing to do, except add to sources */
+		if (ec1 == ec2)
+		{
+			ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
+			ec1->ec_below_outer_join |= below_outer_join;
+			ec1->ec_min_security = Min(ec1->ec_min_security,
+									   restrictinfo->security_level);
+			ec1->ec_max_security = Max(ec1->ec_max_security,
+									   restrictinfo->security_level);
+			/* mark the RI as associated with this eclass */
+			restrictinfo->left_ec = ec1;
+			restrictinfo->right_ec = ec1;
+			/* mark the RI as usable with this pair of EMs */
+			restrictinfo->left_em = em1;
+			restrictinfo->right_em = em2;
+			return true;
+		}
+
+		/*
+		 * Case 2: need to merge ec1 and ec2.  This should never happen after
+		 * the ECs have reached canonical state; otherwise, pathkeys could be
+		 * rendered non-canonical by the merge, and relation eclass indexes
+		 * would get broken by removal of an eq_classes list entry.
+		 */
+		if (root->ec_merging_done)
+			elog(ERROR, "too late to merge equivalence classes");
+
+		/*
+		 * We add ec2's items to ec1, then set ec2's ec_merged link to point
+		 * to ec1 and remove ec2 from the eq_classes list.  We cannot simply
+		 * delete ec2 because that could leave dangling pointers in existing
+		 * PathKeys.  We leave it behind with a link so that the merged EC can
+		 * be found.
+		 */
+		ec1->ec_members = list_concat(ec1->ec_members, ec2->ec_members);
+		ec1->ec_sources = list_concat(ec1->ec_sources, ec2->ec_sources);
+		ec1->ec_derives = list_concat(ec1->ec_derives, ec2->ec_derives);
+		ec1->ec_relids = bms_join(ec1->ec_relids, ec2->ec_relids);
+		ec1->ec_has_const |= ec2->ec_has_const;
+		/* can't need to set has_volatile */
+		ec1->ec_below_outer_join |= ec2->ec_below_outer_join;
+		ec1->ec_min_security = Min(ec1->ec_min_security,
+								   ec2->ec_min_security);
+		ec1->ec_max_security = Max(ec1->ec_max_security,
+								   ec2->ec_max_security);
+		ec2->ec_merged = ec1;
+		root->eq_classes = list_delete_nth_cell(root->eq_classes, ec2_idx);
+		/* just to avoid debugging confusion w/ dangling pointers: */
+		ec2->ec_members = NIL;
+		ec2->ec_sources = NIL;
+		ec2->ec_derives = NIL;
+		ec2->ec_relids = NULL;
+		ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
+		ec1->ec_below_outer_join |= below_outer_join;
+		ec1->ec_min_security = Min(ec1->ec_min_security,
+								   restrictinfo->security_level);
+		ec1->ec_max_security = Max(ec1->ec_max_security,
+								   restrictinfo->security_level);
+		/* mark the RI as associated with this eclass */
+		restrictinfo->left_ec = ec1;
+		restrictinfo->right_ec = ec1;
+		/* mark the RI as usable with this pair of EMs */
+		restrictinfo->left_em = em1;
+		restrictinfo->right_em = em2;
+	}
+	else if (ec1)
+	{
+		/* Case 3: add item2 to ec1 */
+		em2 = add_eq_member(ec1, item2, item2_relids, item2_nullable_relids,
+							false, item2_type);
+		ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
+		ec1->ec_below_outer_join |= below_outer_join;
+		ec1->ec_min_security = Min(ec1->ec_min_security,
+								   restrictinfo->security_level);
+		ec1->ec_max_security = Max(ec1->ec_max_security,
+								   restrictinfo->security_level);
+		/* mark the RI as associated with this eclass */
+		restrictinfo->left_ec = ec1;
+		restrictinfo->right_ec = ec1;
+		/* mark the RI as usable with this pair of EMs */
+		restrictinfo->left_em = em1;
+		restrictinfo->right_em = em2;
+	}
+	else if (ec2)
+	{
+		/* Case 3: add item1 to ec2 */
+		em1 = add_eq_member(ec2, item1, item1_relids, item1_nullable_relids,
+							false, item1_type);
+		ec2->ec_sources = lappend(ec2->ec_sources, restrictinfo);
+		ec2->ec_below_outer_join |= below_outer_join;
+		ec2->ec_min_security = Min(ec2->ec_min_security,
+								   restrictinfo->security_level);
+		ec2->ec_max_security = Max(ec2->ec_max_security,
+								   restrictinfo->security_level);
+		/* mark the RI as associated with this eclass */
+		restrictinfo->left_ec = ec2;
+		restrictinfo->right_ec = ec2;
+		/* mark the RI as usable with this pair of EMs */
+		restrictinfo->left_em = em1;
+		restrictinfo->right_em = em2;
+	}
+	else
+	{
+		/* Case 4: make a new, two-entry EC */
+		EquivalenceClass *ec = makeNode(EquivalenceClass);
+
+		ec->ec_opfamilies = opfamilies;
+		ec->ec_collation = collation;
+		ec->ec_members = NIL;
+		ec->ec_sources = list_make1(restrictinfo);
+		ec->ec_derives = NIL;
+		ec->ec_relids = NULL;
+		ec->ec_has_const = false;
+		ec->ec_has_volatile = false;
+		ec->ec_below_outer_join = below_outer_join;
+		ec->ec_broken = false;
+		ec->ec_sortref = 0;
+		ec->ec_min_security = restrictinfo->security_level;
+		ec->ec_max_security = restrictinfo->security_level;
+		ec->ec_merged = NULL;
+		em1 = add_eq_member(ec, item1, item1_relids, item1_nullable_relids,
+							false, item1_type);
+		em2 = add_eq_member(ec, item2, item2_relids, item2_nullable_relids,
+							false, item2_type);
+
+		root->eq_classes = lappend(root->eq_classes, ec);
+
+		/* mark the RI as associated with this eclass */
+		restrictinfo->left_ec = ec;
+		restrictinfo->right_ec = ec;
+		/* mark the RI as usable with this pair of EMs */
+		restrictinfo->left_em = em1;
+		restrictinfo->right_em = em2;
+	}
+
+	return true;
+}
+
+/*
+ * canonicalize_ec_expression
+ *
+ * This function ensures that the expression exposes the expected type and
+ * collation, so that it will be equal() to other equivalence-class expressions
+ * that it ought to be equal() to.
+ *
+ * The rule for datatypes is that the exposed type should match what it would
+ * be for an input to an operator of the EC's opfamilies; which is usually
+ * the declared input type of the operator, but in the case of polymorphic
+ * operators no relabeling is wanted (compare the behavior of parse_coerce.c).
+ * Expressions coming in from quals will generally have the right type
+ * already, but expressions coming from indexkeys may not (because they are
+ * represented without any explicit relabel in pg_index), and the same problem
+ * occurs for sort expressions (because the parser is likewise cavalier about
+ * putting relabels on them).  Such cases will be binary-compatible with the
+ * real operators, so adding a RelabelType is sufficient.
+ *
+ * Also, the expression's exposed collation must match the EC's collation.
+ * This is important because in comparisons like "foo < bar COLLATE baz",
+ * only one of the expressions has the correct exposed collation as we receive
+ * it from the parser.  Forcing both of them to have it ensures that all
+ * variant spellings of such a construct behave the same.  Again, we can
+ * stick on a RelabelType to force the right exposed collation.  (It might
+ * work to not label the collation at all in EC members, but this is risky
+ * since some parts of the system expect exprCollation() to deliver the
+ * right answer for a sort key.)
+ */
+Expr *
+canonicalize_ec_expression(Expr *expr, Oid req_type, Oid req_collation)
+{
+	Oid			expr_type = exprType((Node *) expr);
+
+	/*
+	 * For a polymorphic-input-type opclass, just keep the same exposed type.
+	 * RECORD opclasses work like polymorphic-type ones for this purpose.
+	 */
+	if (IsPolymorphicType(req_type) || req_type == RECORDOID)
+		req_type = expr_type;
+
+	/*
+	 * No work if the expression exposes the right type/collation already.
+	 */
+	if (expr_type != req_type ||
+		exprCollation((Node *) expr) != req_collation)
+	{
+		/*
+		 * If we have to change the type of the expression, set typmod to -1,
+		 * since the new type may not have the same typmod interpretation.
+		 * When we only have to change collation, preserve the exposed typmod.
+		 */
+		int32		req_typmod;
+
+		if (expr_type != req_type)
+			req_typmod = -1;
+		else
+			req_typmod = exprTypmod((Node *) expr);
+
+		/*
+		 * Use applyRelabelType so that we preserve const-flatness.  This is
+		 * important since eval_const_expressions has already been applied.
+		 */
+		expr = (Expr *) applyRelabelType((Node *) expr,
+										 req_type, req_typmod, req_collation,
+										 COERCE_IMPLICIT_CAST, -1, false);
+	}
+
+	return expr;
+}
+
+/*
+ * add_eq_member - build a new EquivalenceMember and add it to an EC
+ */
+static EquivalenceMember *
+add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
+			  Relids nullable_relids, bool is_child, Oid datatype)
+{
+	EquivalenceMember *em = makeNode(EquivalenceMember);
+
+	em->em_expr = expr;
+	em->em_relids = relids;
+	em->em_nullable_relids = nullable_relids;
+	em->em_is_const = false;
+	em->em_is_child = is_child;
+	em->em_datatype = datatype;
+
+	if (bms_is_empty(relids))
+	{
+		/*
+		 * No Vars, assume it's a pseudoconstant.  This is correct for entries
+		 * generated from process_equivalence(), because a WHERE clause can't
+		 * contain aggregates or SRFs, and non-volatility was checked before
+		 * process_equivalence() ever got called.  But
+		 * get_eclass_for_sort_expr() has to work harder.  We put the tests
+		 * there not here to save cycles in the equivalence case.
+		 */
+		Assert(!is_child);
+		em->em_is_const = true;
+		ec->ec_has_const = true;
+		/* it can't affect ec_relids */
+	}
+	else if (!is_child)			/* child members don't add to ec_relids */
+	{
+		ec->ec_relids = bms_add_members(ec->ec_relids, relids);
+	}
+	ec->ec_members = lappend(ec->ec_members, em);
+
+	return em;
+}
+
+
+/*
+ * get_eclass_for_sort_expr
+ *	  Given an expression and opfamily/collation info, find an existing
+ *	  equivalence class it is a member of; if none, optionally build a new
+ *	  single-member EquivalenceClass for it.
+ *
+ * expr is the expression, and nullable_relids is the set of base relids
+ * that are potentially nullable below it.  We actually only care about
+ * the set of such relids that are used in the expression; but for caller
+ * convenience, we perform that intersection step here.  The caller need
+ * only be sure that nullable_relids doesn't omit any nullable rels that
+ * might appear in the expr.
+ *
+ * sortref is the SortGroupRef of the originating SortGroupClause, if any,
+ * or zero if not.  (It should never be zero if the expression is volatile!)
+ *
+ * If rel is not NULL, it identifies a specific relation we're considering
+ * a path for, and indicates that child EC members for that relation can be
+ * considered.  Otherwise child members are ignored.  (Note: since child EC
+ * members aren't guaranteed unique, a non-NULL value means that there could
+ * be more than one EC that matches the expression; if so it's order-dependent
+ * which one you get.  This is annoying but it only happens in corner cases,
+ * so for now we live with just reporting the first match.  See also
+ * generate_implied_equalities_for_column and match_pathkeys_to_index.)
+ *
+ * If create_it is true, we'll build a new EquivalenceClass when there is no
+ * match.  If create_it is false, we just return NULL when no match.
+ *
+ * This can be used safely both before and after EquivalenceClass merging;
+ * since it never causes merging it does not invalidate any existing ECs
+ * or PathKeys.  However, ECs added after path generation has begun are
+ * of limited usefulness, so usually it's best to create them beforehand.
+ *
+ * Note: opfamilies must be chosen consistently with the way
+ * process_equivalence() would do; that is, generated from a mergejoinable
+ * equality operator.  Else we might fail to detect valid equivalences,
+ * generating poor (but not incorrect) plans.
+ */
+EquivalenceClass *
+get_eclass_for_sort_expr(PlannerInfo *root,
+						 Expr *expr,
+						 Relids nullable_relids,
+						 List *opfamilies,
+						 Oid opcintype,
+						 Oid collation,
+						 Index sortref,
+						 Relids rel,
+						 bool create_it)
+{
+	Relids		expr_relids;
+	EquivalenceClass *newec;
+	EquivalenceMember *newem;
+	ListCell   *lc1;
+	MemoryContext oldcontext;
+
+	/*
+	 * Ensure the expression exposes the correct type and collation.
+	 */
+	expr = canonicalize_ec_expression(expr, opcintype, collation);
+
+	/*
+	 * Scan through the existing EquivalenceClasses for a match
+	 */
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
+		ListCell   *lc2;
+
+		/*
+		 * Never match to a volatile EC, except when we are looking at another
+		 * reference to the same volatile SortGroupClause.
+		 */
+		if (cur_ec->ec_has_volatile &&
+			(sortref == 0 || sortref != cur_ec->ec_sortref))
+			continue;
+
+		if (collation != cur_ec->ec_collation)
+			continue;
+		if (!equal(opfamilies, cur_ec->ec_opfamilies))
+			continue;
+
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+
+			/*
+			 * Ignore child members unless they match the request.
+			 */
+			if (cur_em->em_is_child &&
+				!bms_equal(cur_em->em_relids, rel))
+				continue;
+
+			/*
+			 * If below an outer join, don't match constants: they're not as
+			 * constant as they look.
+			 */
+			if (cur_ec->ec_below_outer_join &&
+				cur_em->em_is_const)
+				continue;
+
+			if (opcintype == cur_em->em_datatype &&
+				equal(expr, cur_em->em_expr))
+				return cur_ec;	/* Match! */
+		}
+	}
+
+	/* No match; does caller want a NULL result? */
+	if (!create_it)
+		return NULL;
+
+	/*
+	 * OK, build a new single-member EC
+	 *
+	 * Here, we must be sure that we construct the EC in the right context.
+	 */
+	oldcontext = MemoryContextSwitchTo(root->planner_cxt);
+
+	newec = makeNode(EquivalenceClass);
+	newec->ec_opfamilies = list_copy(opfamilies);
+	newec->ec_collation = collation;
+	newec->ec_members = NIL;
+	newec->ec_sources = NIL;
+	newec->ec_derives = NIL;
+	newec->ec_relids = NULL;
+	newec->ec_has_const = false;
+	newec->ec_has_volatile = contain_volatile_functions((Node *) expr);
+	newec->ec_below_outer_join = false;
+	newec->ec_broken = false;
+	newec->ec_sortref = sortref;
+	newec->ec_min_security = UINT_MAX;
+	newec->ec_max_security = 0;
+	newec->ec_merged = NULL;
+
+	if (newec->ec_has_volatile && sortref == 0) /* should not happen */
+		elog(ERROR, "volatile EquivalenceClass has no sortref");
+
+	/*
+	 * Get the precise set of nullable relids appearing in the expression.
+	 */
+	expr_relids = pull_varnos(root, (Node *) expr);
+	nullable_relids = bms_intersect(nullable_relids, expr_relids);
+
+	newem = add_eq_member(newec, copyObject(expr), expr_relids,
+						  nullable_relids, false, opcintype);
+
+	/*
+	 * add_eq_member doesn't check for volatile functions, set-returning
+	 * functions, aggregates, or window functions, but such could appear in
+	 * sort expressions; so we have to check whether its const-marking was
+	 * correct.
+	 */
+	if (newec->ec_has_const)
+	{
+		if (newec->ec_has_volatile ||
+			expression_returns_set((Node *) expr) ||
+			contain_agg_clause((Node *) expr) ||
+			contain_window_function((Node *) expr))
+		{
+			newec->ec_has_const = false;
+			newem->em_is_const = false;
+		}
+	}
+
+	root->eq_classes = lappend(root->eq_classes, newec);
+
+	/*
+	 * If EC merging is already complete, we have to mop up by adding the new
+	 * EC to the eclass_indexes of the relation(s) mentioned in it.
+	 */
+	if (root->ec_merging_done)
+	{
+		int			ec_index = list_length(root->eq_classes) - 1;
+		int			i = -1;
+
+		while ((i = bms_next_member(newec->ec_relids, i)) > 0)
+		{
+			RelOptInfo *rel = root->simple_rel_array[i];
+
+			Assert(rel->reloptkind == RELOPT_BASEREL ||
+				   rel->reloptkind == RELOPT_DEADREL);
+
+			rel->eclass_indexes = bms_add_member(rel->eclass_indexes,
+												 ec_index);
+		}
+	}
+
+	MemoryContextSwitchTo(oldcontext);
+
+	return newec;
+}
+
+/*
+ * find_ec_member_matching_expr
+ *		Locate an EquivalenceClass member matching the given expr, if any;
+ *		return NULL if no match.
+ *
+ * "Matching" is defined as "equal after stripping RelabelTypes".
+ * This is used for identifying sort expressions, and we need to allow
+ * binary-compatible relabeling for some cases involving binary-compatible
+ * sort operators.
+ *
+ * Child EC members are ignored unless they belong to given 'relids'.
+ */
+EquivalenceMember *
+find_ec_member_matching_expr(EquivalenceClass *ec,
+							 Expr *expr,
+							 Relids relids)
+{
+	ListCell   *lc;
+
+	/* We ignore binary-compatible relabeling on both ends */
+	while (expr && IsA(expr, RelabelType))
+		expr = ((RelabelType *) expr)->arg;
+
+	foreach(lc, ec->ec_members)
+	{
+		EquivalenceMember *em = (EquivalenceMember *) lfirst(lc);
+		Expr	   *emexpr;
+
+		/*
+		 * We shouldn't be trying to sort by an equivalence class that
+		 * contains a constant, so no need to consider such cases any further.
+		 */
+		if (em->em_is_const)
+			continue;
+
+		/*
+		 * Ignore child members unless they belong to the requested rel.
+		 */
+		if (em->em_is_child &&
+			!bms_is_subset(em->em_relids, relids))
+			continue;
+
+		/*
+		 * Match if same expression (after stripping relabel).
+		 */
+		emexpr = em->em_expr;
+		while (emexpr && IsA(emexpr, RelabelType))
+			emexpr = ((RelabelType *) emexpr)->arg;
+
+		if (equal(emexpr, expr))
+			return em;
+	}
+
+	return NULL;
+}
+
+/*
+ * find_computable_ec_member
+ *		Locate an EquivalenceClass member that can be computed from the
+ *		expressions appearing in "exprs"; return NULL if no match.
+ *
+ * "exprs" can be either a list of bare expression trees, or a list of
+ * TargetEntry nodes.  Either way, it should contain Vars and possibly
+ * Aggrefs and WindowFuncs, which are matched to the corresponding elements
+ * of the EquivalenceClass's expressions.
+ *
+ * Unlike find_ec_member_matching_expr, there's no special provision here
+ * for binary-compatible relabeling.  This is intentional: if we have to
+ * compute an expression in this way, setrefs.c is going to insist on exact
+ * matches of Vars to the source tlist.
+ *
+ * Child EC members are ignored unless they belong to given 'relids'.
+ * Also, non-parallel-safe expressions are ignored if 'require_parallel_safe'.
+ *
+ * Note: some callers pass root == NULL for notational reasons.  This is OK
+ * when require_parallel_safe is false.
+ */
+EquivalenceMember *
+find_computable_ec_member(PlannerInfo *root,
+						  EquivalenceClass *ec,
+						  List *exprs,
+						  Relids relids,
+						  bool require_parallel_safe)
+{
+	ListCell   *lc;
+
+	foreach(lc, ec->ec_members)
+	{
+		EquivalenceMember *em = (EquivalenceMember *) lfirst(lc);
+		List	   *exprvars;
+		ListCell   *lc2;
+
+		/*
+		 * We shouldn't be trying to sort by an equivalence class that
+		 * contains a constant, so no need to consider such cases any further.
+		 */
+		if (em->em_is_const)
+			continue;
+
+		/*
+		 * Ignore child members unless they belong to the requested rel.
+		 */
+		if (em->em_is_child &&
+			!bms_is_subset(em->em_relids, relids))
+			continue;
+
+		/*
+		 * Match if all Vars and quasi-Vars are available in "exprs".
+		 */
+		exprvars = pull_var_clause((Node *) em->em_expr,
+								   PVC_INCLUDE_AGGREGATES |
+								   PVC_INCLUDE_WINDOWFUNCS |
+								   PVC_INCLUDE_PLACEHOLDERS);
+		foreach(lc2, exprvars)
+		{
+			if (!is_exprlist_member(lfirst(lc2), exprs))
+				break;
+		}
+		list_free(exprvars);
+		if (lc2)
+			continue;			/* we hit a non-available Var */
+
+		/*
+		 * If requested, reject expressions that are not parallel-safe.  We
+		 * check this last because it's a rather expensive test.
+		 */
+		if (require_parallel_safe &&
+			!is_parallel_safe(root, (Node *) em->em_expr))
+			continue;
+
+		return em;				/* found usable expression */
+	}
+
+	return NULL;
+}
+
+/*
+ * is_exprlist_member
+ *	  Subroutine for find_computable_ec_member: is "node" in "exprs"?
+ *
+ * Per the requirements of that function, "exprs" might or might not have
+ * TargetEntry superstructure.
+ */
+static bool
+is_exprlist_member(Expr *node, List *exprs)
+{
+	ListCell   *lc;
+
+	foreach(lc, exprs)
+	{
+		Expr	   *expr = (Expr *) lfirst(lc);
+
+		if (expr && IsA(expr, TargetEntry))
+			expr = ((TargetEntry *) expr)->expr;
+
+		if (equal(node, expr))
+			return true;
+	}
+	return false;
+}
+
+/*
+ * relation_can_be_sorted_early
+ *		Can this relation be sorted on this EC before the final output step?
+ *
+ * To succeed, we must find an EC member that prepare_sort_from_pathkeys knows
+ * how to sort on, given the rel's reltarget as input.  There are also a few
+ * additional constraints based on the fact that the desired sort will be done
+ * "early", within the scan/join part of the plan.  Also, non-parallel-safe
+ * expressions are ignored if 'require_parallel_safe'.
+ *
+ * At some point we might want to return the identified EquivalenceMember,
+ * but for now, callers only want to know if there is one.
+ */
+bool
+relation_can_be_sorted_early(PlannerInfo *root, RelOptInfo *rel,
+							 EquivalenceClass *ec, bool require_parallel_safe)
+{
+	PathTarget *target = rel->reltarget;
+	EquivalenceMember *em;
+	ListCell   *lc;
+
+	/*
+	 * Reject volatile ECs immediately; such sorts must always be postponed.
+	 */
+	if (ec->ec_has_volatile)
+		return false;
+
+	/*
+	 * Try to find an EM directly matching some reltarget member.
+	 */
+	foreach(lc, target->exprs)
+	{
+		Expr	   *targetexpr = (Expr *) lfirst(lc);
+
+		em = find_ec_member_matching_expr(ec, targetexpr, rel->relids);
+		if (!em)
+			continue;
+
+		/*
+		 * Reject expressions involving set-returning functions, as those
+		 * can't be computed early either.  (Note: this test and the following
+		 * one are effectively checking properties of targetexpr, so there's
+		 * no point in asking whether some other EC member would be better.)
+		 */
+		if (expression_returns_set((Node *) em->em_expr))
+			continue;
+
+		/*
+		 * If requested, reject expressions that are not parallel-safe.  We
+		 * check this last because it's a rather expensive test.
+		 */
+		if (require_parallel_safe &&
+			!is_parallel_safe(root, (Node *) em->em_expr))
+			continue;
+
+		return true;
+	}
+
+	/*
+	 * Try to find an expression computable from the reltarget.
+	 */
+	em = find_computable_ec_member(root, ec, target->exprs, rel->relids,
+								   require_parallel_safe);
+	if (!em)
+		return false;
+
+	/*
+	 * Reject expressions involving set-returning functions, as those can't be
+	 * computed early either.  (There's no point in looking for another EC
+	 * member in this case; since SRFs can't appear in WHERE, they cannot
+	 * belong to multi-member ECs.)
+	 */
+	if (expression_returns_set((Node *) em->em_expr))
+		return false;
+
+	return true;
+}
+
+/*
+ * generate_base_implied_equalities
+ *	  Generate any restriction clauses that we can deduce from equivalence
+ *	  classes.
+ *
+ * When an EC contains pseudoconstants, our strategy is to generate
+ * "member = const1" clauses where const1 is the first constant member, for
+ * every other member (including other constants).  If we are able to do this
+ * then we don't need any "var = var" comparisons because we've successfully
+ * constrained all the vars at their points of creation.  If we fail to
+ * generate any of these clauses due to lack of cross-type operators, we fall
+ * back to the "ec_broken" strategy described below.  (XXX if there are
+ * multiple constants of different types, it's possible that we might succeed
+ * in forming all the required clauses if we started from a different const
+ * member; but this seems a sufficiently hokey corner case to not be worth
+ * spending lots of cycles on.)
+ *
+ * For ECs that contain no pseudoconstants, we generate derived clauses
+ * "member1 = member2" for each pair of members belonging to the same base
+ * relation (actually, if there are more than two for the same base relation,
+ * we only need enough clauses to link each to each other).  This provides
+ * the base case for the recursion: each row emitted by a base relation scan
+ * will constrain all computable members of the EC to be equal.  As each
+ * join path is formed, we'll add additional derived clauses on-the-fly
+ * to maintain this invariant (see generate_join_implied_equalities).
+ *
+ * If the opfamilies used by the EC do not provide complete sets of cross-type
+ * equality operators, it is possible that we will fail to generate a clause
+ * that must be generated to maintain the invariant.  (An example: given
+ * "WHERE a.x = b.y AND b.y = a.z", the scheme breaks down if we cannot
+ * generate "a.x = a.z" as a restriction clause for A.)  In this case we mark
+ * the EC "ec_broken" and fall back to regurgitating its original source
+ * RestrictInfos at appropriate times.  We do not try to retract any derived
+ * clauses already generated from the broken EC, so the resulting plan could
+ * be poor due to bad selectivity estimates caused by redundant clauses.  But
+ * the correct solution to that is to fix the opfamilies ...
+ *
+ * Equality clauses derived by this function are passed off to
+ * process_implied_equality (in plan/initsplan.c) to be inserted into the
+ * restrictinfo datastructures.  Note that this must be called after initial
+ * scanning of the quals and before Path construction begins.
+ *
+ * We make no attempt to avoid generating duplicate RestrictInfos here: we
+ * don't search ec_sources or ec_derives for matches.  It doesn't really
+ * seem worth the trouble to do so.
+ */
+void
+generate_base_implied_equalities(PlannerInfo *root)
+{
+	int			ec_index;
+	ListCell   *lc;
+
+	/*
+	 * At this point, we're done absorbing knowledge of equivalences in the
+	 * query, so no further EC merging should happen, and ECs remaining in the
+	 * eq_classes list can be considered canonical.  (But note that it's still
+	 * possible for new single-member ECs to be added through
+	 * get_eclass_for_sort_expr().)
+	 */
+	root->ec_merging_done = true;
+
+	ec_index = 0;
+	foreach(lc, root->eq_classes)
+	{
+		EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc);
+		bool		can_generate_joinclause = false;
+		int			i;
+
+		Assert(ec->ec_merged == NULL);	/* else shouldn't be in list */
+		Assert(!ec->ec_broken); /* not yet anyway... */
+
+		/*
+		 * Generate implied equalities that are restriction clauses.
+		 * Single-member ECs won't generate any deductions, either here or at
+		 * the join level.
+		 */
+		if (list_length(ec->ec_members) > 1)
+		{
+			if (ec->ec_has_const)
+				generate_base_implied_equalities_const(root, ec);
+			else
+				generate_base_implied_equalities_no_const(root, ec);
+
+			/* Recover if we failed to generate required derived clauses */
+			if (ec->ec_broken)
+				generate_base_implied_equalities_broken(root, ec);
+
+			/* Detect whether this EC might generate join clauses */
+			can_generate_joinclause =
+				(bms_membership(ec->ec_relids) == BMS_MULTIPLE);
+		}
+
+		/*
+		 * Mark the base rels cited in each eclass (which should all exist by
+		 * now) with the eq_classes indexes of all eclasses mentioning them.
+		 * This will let us avoid searching in subsequent lookups.  While
+		 * we're at it, we can mark base rels that have pending eclass joins;
+		 * this is a cheap version of has_relevant_eclass_joinclause().
+		 */
+		i = -1;
+		while ((i = bms_next_member(ec->ec_relids, i)) > 0)
+		{
+			RelOptInfo *rel = root->simple_rel_array[i];
+
+			Assert(rel->reloptkind == RELOPT_BASEREL);
+
+			rel->eclass_indexes = bms_add_member(rel->eclass_indexes,
+												 ec_index);
+
+			if (can_generate_joinclause)
+				rel->has_eclass_joins = true;
+		}
+
+		ec_index++;
+	}
+}
+
+/*
+ * generate_base_implied_equalities when EC contains pseudoconstant(s)
+ */
+static void
+generate_base_implied_equalities_const(PlannerInfo *root,
+									   EquivalenceClass *ec)
+{
+	EquivalenceMember *const_em = NULL;
+	ListCell   *lc;
+
+	/*
+	 * In the trivial case where we just had one "var = const" clause, push
+	 * the original clause back into the main planner machinery.  There is
+	 * nothing to be gained by doing it differently, and we save the effort to
+	 * re-build and re-analyze an equality clause that will be exactly
+	 * equivalent to the old one.
+	 */
+	if (list_length(ec->ec_members) == 2 &&
+		list_length(ec->ec_sources) == 1)
+	{
+		RestrictInfo *restrictinfo = (RestrictInfo *) linitial(ec->ec_sources);
+
+		if (bms_membership(restrictinfo->required_relids) != BMS_MULTIPLE)
+		{
+			distribute_restrictinfo_to_rels(root, restrictinfo);
+			return;
+		}
+	}
+
+	/*
+	 * Find the constant member to use.  We prefer an actual constant to
+	 * pseudo-constants (such as Params), because the constraint exclusion
+	 * machinery might be able to exclude relations on the basis of generated
+	 * "var = const" equalities, but "var = param" won't work for that.
+	 */
+	foreach(lc, ec->ec_members)
+	{
+		EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
+
+		if (cur_em->em_is_const)
+		{
+			const_em = cur_em;
+			if (IsA(cur_em->em_expr, Const))
+				break;
+		}
+	}
+	Assert(const_em != NULL);
+
+	/* Generate a derived equality against each other member */
+	foreach(lc, ec->ec_members)
+	{
+		EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
+		Oid			eq_op;
+		RestrictInfo *rinfo;
+
+		Assert(!cur_em->em_is_child);	/* no children yet */
+		if (cur_em == const_em)
+			continue;
+		eq_op = select_equality_operator(ec,
+										 cur_em->em_datatype,
+										 const_em->em_datatype);
+		if (!OidIsValid(eq_op))
+		{
+			/* failed... */
+			ec->ec_broken = true;
+			break;
+		}
+		rinfo = process_implied_equality(root, eq_op, ec->ec_collation,
+										 cur_em->em_expr, const_em->em_expr,
+										 bms_copy(ec->ec_relids),
+										 bms_union(cur_em->em_nullable_relids,
+												   const_em->em_nullable_relids),
+										 ec->ec_min_security,
+										 ec->ec_below_outer_join,
+										 cur_em->em_is_const);
+
+		/*
+		 * If the clause didn't degenerate to a constant, fill in the correct
+		 * markings for a mergejoinable clause, and save it in ec_derives. (We
+		 * will not re-use such clauses directly, but selectivity estimation
+		 * may consult the list later.  Note that this use of ec_derives does
+		 * not overlap with its use for join clauses, since we never generate
+		 * join clauses from an ec_has_const eclass.)
+		 */
+		if (rinfo && rinfo->mergeopfamilies)
+		{
+			/* it's not redundant, so don't set parent_ec */
+			rinfo->left_ec = rinfo->right_ec = ec;
+			rinfo->left_em = cur_em;
+			rinfo->right_em = const_em;
+			ec->ec_derives = lappend(ec->ec_derives, rinfo);
+		}
+	}
+}
+
+/*
+ * generate_base_implied_equalities when EC contains no pseudoconstants
+ */
+static void
+generate_base_implied_equalities_no_const(PlannerInfo *root,
+										  EquivalenceClass *ec)
+{
+	EquivalenceMember **prev_ems;
+	ListCell   *lc;
+
+	/*
+	 * We scan the EC members once and track the last-seen member for each
+	 * base relation.  When we see another member of the same base relation,
+	 * we generate "prev_em = cur_em".  This results in the minimum number of
+	 * derived clauses, but it's possible that it will fail when a different
+	 * ordering would succeed.  XXX FIXME: use a UNION-FIND algorithm similar
+	 * to the way we build merged ECs.  (Use a list-of-lists for each rel.)
+	 */
+	prev_ems = (EquivalenceMember **)
+		palloc0(root->simple_rel_array_size * sizeof(EquivalenceMember *));
+
+	foreach(lc, ec->ec_members)
+	{
+		EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
+		int			relid;
+
+		Assert(!cur_em->em_is_child);	/* no children yet */
+		if (!bms_get_singleton_member(cur_em->em_relids, &relid))
+			continue;
+		Assert(relid < root->simple_rel_array_size);
+
+		if (prev_ems[relid] != NULL)
+		{
+			EquivalenceMember *prev_em = prev_ems[relid];
+			Oid			eq_op;
+			RestrictInfo *rinfo;
+
+			eq_op = select_equality_operator(ec,
+											 prev_em->em_datatype,
+											 cur_em->em_datatype);
+			if (!OidIsValid(eq_op))
+			{
+				/* failed... */
+				ec->ec_broken = true;
+				break;
+			}
+			rinfo = process_implied_equality(root, eq_op, ec->ec_collation,
+											 prev_em->em_expr, cur_em->em_expr,
+											 bms_copy(ec->ec_relids),
+											 bms_union(prev_em->em_nullable_relids,
+													   cur_em->em_nullable_relids),
+											 ec->ec_min_security,
+											 ec->ec_below_outer_join,
+											 false);
+
+			/*
+			 * If the clause didn't degenerate to a constant, fill in the
+			 * correct markings for a mergejoinable clause.  We don't put it
+			 * in ec_derives however; we don't currently need to re-find such
+			 * clauses, and we don't want to clutter that list with non-join
+			 * clauses.
+			 */
+			if (rinfo && rinfo->mergeopfamilies)
+			{
+				/* it's not redundant, so don't set parent_ec */
+				rinfo->left_ec = rinfo->right_ec = ec;
+				rinfo->left_em = prev_em;
+				rinfo->right_em = cur_em;
+			}
+		}
+		prev_ems[relid] = cur_em;
+	}
+
+	pfree(prev_ems);
+
+	/*
+	 * We also have to make sure that all the Vars used in the member clauses
+	 * will be available at any join node we might try to reference them at.
+	 * For the moment we force all the Vars to be available at all join nodes
+	 * for this eclass.  Perhaps this could be improved by doing some
+	 * pre-analysis of which members we prefer to join, but it's no worse than
+	 * what happened in the pre-8.3 code.
+	 */
+	foreach(lc, ec->ec_members)
+	{
+		EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
+		List	   *vars = pull_var_clause((Node *) cur_em->em_expr,
+										   PVC_RECURSE_AGGREGATES |
+										   PVC_RECURSE_WINDOWFUNCS |
+										   PVC_INCLUDE_PLACEHOLDERS);
+
+		add_vars_to_targetlist(root, vars, ec->ec_relids, false);
+		list_free(vars);
+	}
+}
+
+/*
+ * generate_base_implied_equalities cleanup after failure
+ *
+ * What we must do here is push any zero- or one-relation source RestrictInfos
+ * of the EC back into the main restrictinfo datastructures.  Multi-relation
+ * clauses will be regurgitated later by generate_join_implied_equalities().
+ * (We do it this way to maintain continuity with the case that ec_broken
+ * becomes set only after we've gone up a join level or two.)  However, for
+ * an EC that contains constants, we can adopt a simpler strategy and just
+ * throw back all the source RestrictInfos immediately; that works because
+ * we know that such an EC can't become broken later.  (This rule justifies
+ * ignoring ec_has_const ECs in generate_join_implied_equalities, even when
+ * they are broken.)
+ */
+static void
+generate_base_implied_equalities_broken(PlannerInfo *root,
+										EquivalenceClass *ec)
+{
+	ListCell   *lc;
+
+	foreach(lc, ec->ec_sources)
+	{
+		RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(lc);
+
+		if (ec->ec_has_const ||
+			bms_membership(restrictinfo->required_relids) != BMS_MULTIPLE)
+			distribute_restrictinfo_to_rels(root, restrictinfo);
+	}
+}
+
+
+/*
+ * generate_join_implied_equalities
+ *	  Generate any join clauses that we can deduce from equivalence classes.
+ *
+ * At a join node, we must enforce restriction clauses sufficient to ensure
+ * that all equivalence-class members computable at that node are equal.
+ * Since the set of clauses to enforce can vary depending on which subset
+ * relations are the inputs, we have to compute this afresh for each join
+ * relation pair.  Hence a fresh List of RestrictInfo nodes is built and
+ * passed back on each call.
+ *
+ * In addition to its use at join nodes, this can be applied to generate
+ * eclass-based join clauses for use in a parameterized scan of a base rel.
+ * The reason for the asymmetry of specifying the inner rel as a RelOptInfo
+ * and the outer rel by Relids is that this usage occurs before we have
+ * built any join RelOptInfos.
+ *
+ * An annoying special case for parameterized scans is that the inner rel can
+ * be an appendrel child (an "other rel").  In this case we must generate
+ * appropriate clauses using child EC members.  add_child_rel_equivalences
+ * must already have been done for the child rel.
+ *
+ * The results are sufficient for use in merge, hash, and plain nestloop join
+ * methods.  We do not worry here about selecting clauses that are optimal
+ * for use in a parameterized indexscan.  indxpath.c makes its own selections
+ * of clauses to use, and if the ones we pick here are redundant with those,
+ * the extras will be eliminated at createplan time, using the parent_ec
+ * markers that we provide (see is_redundant_derived_clause()).
+ *
+ * Because the same join clauses are likely to be needed multiple times as
+ * we consider different join paths, we avoid generating multiple copies:
+ * whenever we select a particular pair of EquivalenceMembers to join,
+ * we check to see if the pair matches any original clause (in ec_sources)
+ * or previously-built clause (in ec_derives).  This saves memory and allows
+ * re-use of information cached in RestrictInfos.
+ *
+ * join_relids should always equal bms_union(outer_relids, inner_rel->relids).
+ * We could simplify this function's API by computing it internally, but in
+ * most current uses, the caller has the value at hand anyway.
+ */
+List *
+generate_join_implied_equalities(PlannerInfo *root,
+								 Relids join_relids,
+								 Relids outer_relids,
+								 RelOptInfo *inner_rel)
+{
+	List	   *result = NIL;
+	Relids		inner_relids = inner_rel->relids;
+	Relids		nominal_inner_relids;
+	Relids		nominal_join_relids;
+	Bitmapset  *matching_ecs;
+	int			i;
+
+	/* If inner rel is a child, extra setup work is needed */
+	if (IS_OTHER_REL(inner_rel))
+	{
+		Assert(!bms_is_empty(inner_rel->top_parent_relids));
+
+		/* Fetch relid set for the topmost parent rel */
+		nominal_inner_relids = inner_rel->top_parent_relids;
+		/* ECs will be marked with the parent's relid, not the child's */
+		nominal_join_relids = bms_union(outer_relids, nominal_inner_relids);
+	}
+	else
+	{
+		nominal_inner_relids = inner_relids;
+		nominal_join_relids = join_relids;
+	}
+
+	/*
+	 * Get all eclasses that mention both inner and outer sides of the join
+	 */
+	matching_ecs = get_common_eclass_indexes(root, nominal_inner_relids,
+											 outer_relids);
+
+	i = -1;
+	while ((i = bms_next_member(matching_ecs, i)) >= 0)
+	{
+		EquivalenceClass *ec = (EquivalenceClass *) list_nth(root->eq_classes, i);
+		List	   *sublist = NIL;
+
+		/* ECs containing consts do not need any further enforcement */
+		if (ec->ec_has_const)
+			continue;
+
+		/* Single-member ECs won't generate any deductions */
+		if (list_length(ec->ec_members) <= 1)
+			continue;
+
+		/* Sanity check that this eclass overlaps the join */
+		Assert(bms_overlap(ec->ec_relids, nominal_join_relids));
+
+		if (!ec->ec_broken)
+			sublist = generate_join_implied_equalities_normal(root,
+															  ec,
+															  join_relids,
+															  outer_relids,
+															  inner_relids);
+
+		/* Recover if we failed to generate required derived clauses */
+		if (ec->ec_broken)
+			sublist = generate_join_implied_equalities_broken(root,
+															  ec,
+															  nominal_join_relids,
+															  outer_relids,
+															  nominal_inner_relids,
+															  inner_rel);
+
+		result = list_concat(result, sublist);
+	}
+
+	return result;
+}
+
+/*
+ * generate_join_implied_equalities_for_ecs
+ *	  As above, but consider only the listed ECs.
+ */
+List *
+generate_join_implied_equalities_for_ecs(PlannerInfo *root,
+										 List *eclasses,
+										 Relids join_relids,
+										 Relids outer_relids,
+										 RelOptInfo *inner_rel)
+{
+	List	   *result = NIL;
+	Relids		inner_relids = inner_rel->relids;
+	Relids		nominal_inner_relids;
+	Relids		nominal_join_relids;
+	ListCell   *lc;
+
+	/* If inner rel is a child, extra setup work is needed */
+	if (IS_OTHER_REL(inner_rel))
+	{
+		Assert(!bms_is_empty(inner_rel->top_parent_relids));
+
+		/* Fetch relid set for the topmost parent rel */
+		nominal_inner_relids = inner_rel->top_parent_relids;
+		/* ECs will be marked with the parent's relid, not the child's */
+		nominal_join_relids = bms_union(outer_relids, nominal_inner_relids);
+	}
+	else
+	{
+		nominal_inner_relids = inner_relids;
+		nominal_join_relids = join_relids;
+	}
+
+	foreach(lc, eclasses)
+	{
+		EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc);
+		List	   *sublist = NIL;
+
+		/* ECs containing consts do not need any further enforcement */
+		if (ec->ec_has_const)
+			continue;
+
+		/* Single-member ECs won't generate any deductions */
+		if (list_length(ec->ec_members) <= 1)
+			continue;
+
+		/* We can quickly ignore any that don't overlap the join, too */
+		if (!bms_overlap(ec->ec_relids, nominal_join_relids))
+			continue;
+
+		if (!ec->ec_broken)
+			sublist = generate_join_implied_equalities_normal(root,
+															  ec,
+															  join_relids,
+															  outer_relids,
+															  inner_relids);
+
+		/* Recover if we failed to generate required derived clauses */
+		if (ec->ec_broken)
+			sublist = generate_join_implied_equalities_broken(root,
+															  ec,
+															  nominal_join_relids,
+															  outer_relids,
+															  nominal_inner_relids,
+															  inner_rel);
+
+		result = list_concat(result, sublist);
+	}
+
+	return result;
+}
+
+/*
+ * generate_join_implied_equalities for a still-valid EC
+ */
+static List *
+generate_join_implied_equalities_normal(PlannerInfo *root,
+										EquivalenceClass *ec,
+										Relids join_relids,
+										Relids outer_relids,
+										Relids inner_relids)
+{
+	List	   *result = NIL;
+	List	   *new_members = NIL;
+	List	   *outer_members = NIL;
+	List	   *inner_members = NIL;
+	ListCell   *lc1;
+
+	/*
+	 * First, scan the EC to identify member values that are computable at the
+	 * outer rel, at the inner rel, or at this relation but not in either
+	 * input rel.  The outer-rel members should already be enforced equal,
+	 * likewise for the inner-rel members.  We'll need to create clauses to
+	 * enforce that any newly computable members are all equal to each other
+	 * as well as to at least one input member, plus enforce at least one
+	 * outer-rel member equal to at least one inner-rel member.
+	 */
+	foreach(lc1, ec->ec_members)
+	{
+		EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc1);
+
+		/*
+		 * We don't need to check explicitly for child EC members.  This test
+		 * against join_relids will cause them to be ignored except when
+		 * considering a child inner rel, which is what we want.
+		 */
+		if (!bms_is_subset(cur_em->em_relids, join_relids))
+			continue;			/* not computable yet, or wrong child */
+
+		if (bms_is_subset(cur_em->em_relids, outer_relids))
+			outer_members = lappend(outer_members, cur_em);
+		else if (bms_is_subset(cur_em->em_relids, inner_relids))
+			inner_members = lappend(inner_members, cur_em);
+		else
+			new_members = lappend(new_members, cur_em);
+	}
+
+	/*
+	 * First, select the joinclause if needed.  We can equate any one outer
+	 * member to any one inner member, but we have to find a datatype
+	 * combination for which an opfamily member operator exists.  If we have
+	 * choices, we prefer simple Var members (possibly with RelabelType) since
+	 * these are (a) cheapest to compute at runtime and (b) most likely to
+	 * have useful statistics. Also, prefer operators that are also
+	 * hashjoinable.
+	 */
+	if (outer_members && inner_members)
+	{
+		EquivalenceMember *best_outer_em = NULL;
+		EquivalenceMember *best_inner_em = NULL;
+		Oid			best_eq_op = InvalidOid;
+		int			best_score = -1;
+		RestrictInfo *rinfo;
+
+		foreach(lc1, outer_members)
+		{
+			EquivalenceMember *outer_em = (EquivalenceMember *) lfirst(lc1);
+			ListCell   *lc2;
+
+			foreach(lc2, inner_members)
+			{
+				EquivalenceMember *inner_em = (EquivalenceMember *) lfirst(lc2);
+				Oid			eq_op;
+				int			score;
+
+				eq_op = select_equality_operator(ec,
+												 outer_em->em_datatype,
+												 inner_em->em_datatype);
+				if (!OidIsValid(eq_op))
+					continue;
+				score = 0;
+				if (IsA(outer_em->em_expr, Var) ||
+					(IsA(outer_em->em_expr, RelabelType) &&
+					 IsA(((RelabelType *) outer_em->em_expr)->arg, Var)))
+					score++;
+				if (IsA(inner_em->em_expr, Var) ||
+					(IsA(inner_em->em_expr, RelabelType) &&
+					 IsA(((RelabelType *) inner_em->em_expr)->arg, Var)))
+					score++;
+				if (op_hashjoinable(eq_op,
+									exprType((Node *) outer_em->em_expr)))
+					score++;
+				if (score > best_score)
+				{
+					best_outer_em = outer_em;
+					best_inner_em = inner_em;
+					best_eq_op = eq_op;
+					best_score = score;
+					if (best_score == 3)
+						break;	/* no need to look further */
+				}
+			}
+			if (best_score == 3)
+				break;			/* no need to look further */
+		}
+		if (best_score < 0)
+		{
+			/* failed... */
+			ec->ec_broken = true;
+			return NIL;
+		}
+
+		/*
+		 * Create clause, setting parent_ec to mark it as redundant with other
+		 * joinclauses
+		 */
+		rinfo = create_join_clause(root, ec, best_eq_op,
+								   best_outer_em, best_inner_em,
+								   ec);
+
+		result = lappend(result, rinfo);
+	}
+
+	/*
+	 * Now deal with building restrictions for any expressions that involve
+	 * Vars from both sides of the join.  We have to equate all of these to
+	 * each other as well as to at least one old member (if any).
+	 *
+	 * XXX as in generate_base_implied_equalities_no_const, we could be a lot
+	 * smarter here to avoid unnecessary failures in cross-type situations.
+	 * For now, use the same left-to-right method used there.
+	 */
+	if (new_members)
+	{
+		List	   *old_members = list_concat(outer_members, inner_members);
+		EquivalenceMember *prev_em = NULL;
+		RestrictInfo *rinfo;
+
+		/* For now, arbitrarily take the first old_member as the one to use */
+		if (old_members)
+			new_members = lappend(new_members, linitial(old_members));
+
+		foreach(lc1, new_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc1);
+
+			if (prev_em != NULL)
+			{
+				Oid			eq_op;
+
+				eq_op = select_equality_operator(ec,
+												 prev_em->em_datatype,
+												 cur_em->em_datatype);
+				if (!OidIsValid(eq_op))
+				{
+					/* failed... */
+					ec->ec_broken = true;
+					return NIL;
+				}
+				/* do NOT set parent_ec, this qual is not redundant! */
+				rinfo = create_join_clause(root, ec, eq_op,
+										   prev_em, cur_em,
+										   NULL);
+
+				result = lappend(result, rinfo);
+			}
+			prev_em = cur_em;
+		}
+	}
+
+	return result;
+}
+
+/*
+ * generate_join_implied_equalities cleanup after failure
+ *
+ * Return any original RestrictInfos that are enforceable at this join.
+ *
+ * In the case of a child inner relation, we have to translate the
+ * original RestrictInfos from parent to child Vars.
+ */
+static List *
+generate_join_implied_equalities_broken(PlannerInfo *root,
+										EquivalenceClass *ec,
+										Relids nominal_join_relids,
+										Relids outer_relids,
+										Relids nominal_inner_relids,
+										RelOptInfo *inner_rel)
+{
+	List	   *result = NIL;
+	ListCell   *lc;
+
+	foreach(lc, ec->ec_sources)
+	{
+		RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(lc);
+		Relids		clause_relids = restrictinfo->required_relids;
+
+		if (bms_is_subset(clause_relids, nominal_join_relids) &&
+			!bms_is_subset(clause_relids, outer_relids) &&
+			!bms_is_subset(clause_relids, nominal_inner_relids))
+			result = lappend(result, restrictinfo);
+	}
+
+	/*
+	 * If we have to translate, just brute-force apply adjust_appendrel_attrs
+	 * to all the RestrictInfos at once.  This will result in returning
+	 * RestrictInfos that are not listed in ec_derives, but there shouldn't be
+	 * any duplication, and it's a sufficiently narrow corner case that we
+	 * shouldn't sweat too much over it anyway.
+	 *
+	 * Since inner_rel might be an indirect descendant of the baserel
+	 * mentioned in the ec_sources clauses, we have to be prepared to apply
+	 * multiple levels of Var translation.
+	 */
+	if (IS_OTHER_REL(inner_rel) && result != NIL)
+		result = (List *) adjust_appendrel_attrs_multilevel(root,
+															(Node *) result,
+															inner_rel->relids,
+															inner_rel->top_parent_relids);
+
+	return result;
+}
+
+
+/*
+ * select_equality_operator
+ *	  Select a suitable equality operator for comparing two EC members
+ *
+ * Returns InvalidOid if no operator can be found for this datatype combination
+ */
+static Oid
+select_equality_operator(EquivalenceClass *ec, Oid lefttype, Oid righttype)
+{
+	ListCell   *lc;
+
+	foreach(lc, ec->ec_opfamilies)
+	{
+		Oid			opfamily = lfirst_oid(lc);
+		Oid			opno;
+
+		opno = get_opfamily_member(opfamily, lefttype, righttype,
+								   BTEqualStrategyNumber);
+		if (!OidIsValid(opno))
+			continue;
+		/* If no barrier quals in query, don't worry about leaky operators */
+		if (ec->ec_max_security == 0)
+			return opno;
+		/* Otherwise, insist that selected operators be leakproof */
+		if (get_func_leakproof(get_opcode(opno)))
+			return opno;
+	}
+	return InvalidOid;
+}
+
+
+/*
+ * create_join_clause
+ *	  Find or make a RestrictInfo comparing the two given EC members
+ *	  with the given operator.
+ *
+ * parent_ec is either equal to ec (if the clause is a potentially-redundant
+ * join clause) or NULL (if not).  We have to treat this as part of the
+ * match requirements --- it's possible that a clause comparing the same two
+ * EMs is a join clause in one join path and a restriction clause in another.
+ */
+static RestrictInfo *
+create_join_clause(PlannerInfo *root,
+				   EquivalenceClass *ec, Oid opno,
+				   EquivalenceMember *leftem,
+				   EquivalenceMember *rightem,
+				   EquivalenceClass *parent_ec)
+{
+	RestrictInfo *rinfo;
+	ListCell   *lc;
+	MemoryContext oldcontext;
+
+	/*
+	 * Search to see if we already built a RestrictInfo for this pair of
+	 * EquivalenceMembers.  We can use either original source clauses or
+	 * previously-derived clauses.  The check on opno is probably redundant,
+	 * but be safe ...
+	 */
+	foreach(lc, ec->ec_sources)
+	{
+		rinfo = (RestrictInfo *) lfirst(lc);
+		if (rinfo->left_em == leftem &&
+			rinfo->right_em == rightem &&
+			rinfo->parent_ec == parent_ec &&
+			opno == ((OpExpr *) rinfo->clause)->opno)
+			return rinfo;
+	}
+
+	foreach(lc, ec->ec_derives)
+	{
+		rinfo = (RestrictInfo *) lfirst(lc);
+		if (rinfo->left_em == leftem &&
+			rinfo->right_em == rightem &&
+			rinfo->parent_ec == parent_ec &&
+			opno == ((OpExpr *) rinfo->clause)->opno)
+			return rinfo;
+	}
+
+	/*
+	 * Not there, so build it, in planner context so we can re-use it. (Not
+	 * important in normal planning, but definitely so in GEQO.)
+	 */
+	oldcontext = MemoryContextSwitchTo(root->planner_cxt);
+
+	rinfo = build_implied_join_equality(root,
+										opno,
+										ec->ec_collation,
+										leftem->em_expr,
+										rightem->em_expr,
+										bms_union(leftem->em_relids,
+												  rightem->em_relids),
+										bms_union(leftem->em_nullable_relids,
+												  rightem->em_nullable_relids),
+										ec->ec_min_security);
+
+	/* Mark the clause as redundant, or not */
+	rinfo->parent_ec = parent_ec;
+
+	/*
+	 * We know the correct values for left_ec/right_ec, ie this particular EC,
+	 * so we can just set them directly instead of forcing another lookup.
+	 */
+	rinfo->left_ec = ec;
+	rinfo->right_ec = ec;
+
+	/* Mark it as usable with these EMs */
+	rinfo->left_em = leftem;
+	rinfo->right_em = rightem;
+	/* and save it for possible re-use */
+	ec->ec_derives = lappend(ec->ec_derives, rinfo);
+
+	MemoryContextSwitchTo(oldcontext);
+
+	return rinfo;
+}
+
+
+/*
+ * reconsider_outer_join_clauses
+ *	  Re-examine any outer-join clauses that were set aside by
+ *	  distribute_qual_to_rels(), and see if we can derive any
+ *	  EquivalenceClasses from them.  Then, if they were not made
+ *	  redundant, push them out into the regular join-clause lists.
+ *
+ * When we have mergejoinable clauses A = B that are outer-join clauses,
+ * we can't blindly combine them with other clauses A = C to deduce B = C,
+ * since in fact the "equality" A = B won't necessarily hold above the
+ * outer join (one of the variables might be NULL instead).  Nonetheless
+ * there are cases where we can add qual clauses using transitivity.
+ *
+ * One case that we look for here is an outer-join clause OUTERVAR = INNERVAR
+ * for which there is also an equivalence clause OUTERVAR = CONSTANT.
+ * It is safe and useful to push a clause INNERVAR = CONSTANT into the
+ * evaluation of the inner (nullable) relation, because any inner rows not
+ * meeting this condition will not contribute to the outer-join result anyway.
+ * (Any outer rows they could join to will be eliminated by the pushed-down
+ * equivalence clause.)
+ *
+ * Note that the above rule does not work for full outer joins; nor is it
+ * very interesting to consider cases where the generated equivalence clause
+ * would involve relations outside the outer join, since such clauses couldn't
+ * be pushed into the inner side's scan anyway.  So the restriction to
+ * outervar = pseudoconstant is not really giving up anything.
+ *
+ * For full-join cases, we can only do something useful if it's a FULL JOIN
+ * USING and a merged column has an equivalence MERGEDVAR = CONSTANT.
+ * By the time it gets here, the merged column will look like
+ *		COALESCE(LEFTVAR, RIGHTVAR)
+ * and we will have a full-join clause LEFTVAR = RIGHTVAR that we can match
+ * the COALESCE expression to. In this situation we can push LEFTVAR = CONSTANT
+ * and RIGHTVAR = CONSTANT into the input relations, since any rows not
+ * meeting these conditions cannot contribute to the join result.
+ *
+ * Again, there isn't any traction to be gained by trying to deal with
+ * clauses comparing a mergedvar to a non-pseudoconstant.  So we can make
+ * use of the EquivalenceClasses to search for matching variables that were
+ * equivalenced to constants.  The interesting outer-join clauses were
+ * accumulated for us by distribute_qual_to_rels.
+ *
+ * When we find one of these cases, we implement the changes we want by
+ * generating a new equivalence clause INNERVAR = CONSTANT (or LEFTVAR, etc)
+ * and pushing it into the EquivalenceClass structures.  This is because we
+ * may already know that INNERVAR is equivalenced to some other var(s), and
+ * we'd like the constant to propagate to them too.  Note that it would be
+ * unsafe to merge any existing EC for INNERVAR with the OUTERVAR's EC ---
+ * that could result in propagating constant restrictions from
+ * INNERVAR to OUTERVAR, which would be very wrong.
+ *
+ * It's possible that the INNERVAR is also an OUTERVAR for some other
+ * outer-join clause, in which case the process can be repeated.  So we repeat
+ * looping over the lists of clauses until no further deductions can be made.
+ * Whenever we do make a deduction, we remove the generating clause from the
+ * lists, since we don't want to make the same deduction twice.
+ *
+ * If we don't find any match for a set-aside outer join clause, we must
+ * throw it back into the regular joinclause processing by passing it to
+ * distribute_restrictinfo_to_rels().  If we do generate a derived clause,
+ * however, the outer-join clause is redundant.  We still throw it back,
+ * because otherwise the join will be seen as a clauseless join and avoided
+ * during join order searching; but we mark it as redundant to keep from
+ * messing up the joinrel's size estimate.  (This behavior means that the
+ * API for this routine is uselessly complex: we could have just put all
+ * the clauses into the regular processing initially.  We keep it because
+ * someday we might want to do something else, such as inserting "dummy"
+ * joinclauses instead of real ones.)
+ *
+ * Outer join clauses that are marked outerjoin_delayed are special: this
+ * condition means that one or both VARs might go to null due to a lower
+ * outer join.  We can still push a constant through the clause, but only
+ * if its operator is strict; and we *have to* throw the clause back into
+ * regular joinclause processing.  By keeping the strict join clause,
+ * we ensure that any null-extended rows that are mistakenly generated due
+ * to suppressing rows not matching the constant will be rejected at the
+ * upper outer join.  (This doesn't work for full-join clauses.)
+ */
+void
+reconsider_outer_join_clauses(PlannerInfo *root)
+{
+	bool		found;
+	ListCell   *cell;
+
+	/* Outer loop repeats until we find no more deductions */
+	do
+	{
+		found = false;
+
+		/* Process the LEFT JOIN clauses */
+		foreach(cell, root->left_join_clauses)
+		{
+			RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
+
+			if (reconsider_outer_join_clause(root, rinfo, true))
+			{
+				found = true;
+				/* remove it from the list */
+				root->left_join_clauses =
+					foreach_delete_current(root->left_join_clauses, cell);
+				/* we throw it back anyway (see notes above) */
+				/* but the thrown-back clause has no extra selectivity */
+				rinfo->norm_selec = 2.0;
+				rinfo->outer_selec = 1.0;
+				distribute_restrictinfo_to_rels(root, rinfo);
+			}
+		}
+
+		/* Process the RIGHT JOIN clauses */
+		foreach(cell, root->right_join_clauses)
+		{
+			RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
+
+			if (reconsider_outer_join_clause(root, rinfo, false))
+			{
+				found = true;
+				/* remove it from the list */
+				root->right_join_clauses =
+					foreach_delete_current(root->right_join_clauses, cell);
+				/* we throw it back anyway (see notes above) */
+				/* but the thrown-back clause has no extra selectivity */
+				rinfo->norm_selec = 2.0;
+				rinfo->outer_selec = 1.0;
+				distribute_restrictinfo_to_rels(root, rinfo);
+			}
+		}
+
+		/* Process the FULL JOIN clauses */
+		foreach(cell, root->full_join_clauses)
+		{
+			RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
+
+			if (reconsider_full_join_clause(root, rinfo))
+			{
+				found = true;
+				/* remove it from the list */
+				root->full_join_clauses =
+					foreach_delete_current(root->full_join_clauses, cell);
+				/* we throw it back anyway (see notes above) */
+				/* but the thrown-back clause has no extra selectivity */
+				rinfo->norm_selec = 2.0;
+				rinfo->outer_selec = 1.0;
+				distribute_restrictinfo_to_rels(root, rinfo);
+			}
+		}
+	} while (found);
+
+	/* Now, any remaining clauses have to be thrown back */
+	foreach(cell, root->left_join_clauses)
+	{
+		RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
+
+		distribute_restrictinfo_to_rels(root, rinfo);
+	}
+	foreach(cell, root->right_join_clauses)
+	{
+		RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
+
+		distribute_restrictinfo_to_rels(root, rinfo);
+	}
+	foreach(cell, root->full_join_clauses)
+	{
+		RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
+
+		distribute_restrictinfo_to_rels(root, rinfo);
+	}
+}
+
+/*
+ * reconsider_outer_join_clauses for a single LEFT/RIGHT JOIN clause
+ *
+ * Returns true if we were able to propagate a constant through the clause.
+ */
+static bool
+reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
+							 bool outer_on_left)
+{
+	Expr	   *outervar,
+			   *innervar;
+	Oid			opno,
+				collation,
+				left_type,
+				right_type,
+				inner_datatype;
+	Relids		inner_relids,
+				inner_nullable_relids;
+	ListCell   *lc1;
+
+	Assert(is_opclause(rinfo->clause));
+	opno = ((OpExpr *) rinfo->clause)->opno;
+	collation = ((OpExpr *) rinfo->clause)->inputcollid;
+
+	/* If clause is outerjoin_delayed, operator must be strict */
+	if (rinfo->outerjoin_delayed && !op_strict(opno))
+		return false;
+
+	/* Extract needed info from the clause */
+	op_input_types(opno, &left_type, &right_type);
+	if (outer_on_left)
+	{
+		outervar = (Expr *) get_leftop(rinfo->clause);
+		innervar = (Expr *) get_rightop(rinfo->clause);
+		inner_datatype = right_type;
+		inner_relids = rinfo->right_relids;
+	}
+	else
+	{
+		outervar = (Expr *) get_rightop(rinfo->clause);
+		innervar = (Expr *) get_leftop(rinfo->clause);
+		inner_datatype = left_type;
+		inner_relids = rinfo->left_relids;
+	}
+	inner_nullable_relids = bms_intersect(inner_relids,
+										  rinfo->nullable_relids);
+
+	/* Scan EquivalenceClasses for a match to outervar */
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
+		bool		match;
+		ListCell   *lc2;
+
+		/* Ignore EC unless it contains pseudoconstants */
+		if (!cur_ec->ec_has_const)
+			continue;
+		/* Never match to a volatile EC */
+		if (cur_ec->ec_has_volatile)
+			continue;
+		/* It has to match the outer-join clause as to semantics, too */
+		if (collation != cur_ec->ec_collation)
+			continue;
+		if (!equal(rinfo->mergeopfamilies, cur_ec->ec_opfamilies))
+			continue;
+		/* Does it contain a match to outervar? */
+		match = false;
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+
+			Assert(!cur_em->em_is_child);	/* no children yet */
+			if (equal(outervar, cur_em->em_expr))
+			{
+				match = true;
+				break;
+			}
+		}
+		if (!match)
+			continue;			/* no match, so ignore this EC */
+
+		/*
+		 * Yes it does!  Try to generate a clause INNERVAR = CONSTANT for each
+		 * CONSTANT in the EC.  Note that we must succeed with at least one
+		 * constant before we can decide to throw away the outer-join clause.
+		 */
+		match = false;
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+			Oid			eq_op;
+			RestrictInfo *newrinfo;
+
+			if (!cur_em->em_is_const)
+				continue;		/* ignore non-const members */
+			eq_op = select_equality_operator(cur_ec,
+											 inner_datatype,
+											 cur_em->em_datatype);
+			if (!OidIsValid(eq_op))
+				continue;		/* can't generate equality */
+			newrinfo = build_implied_join_equality(root,
+												   eq_op,
+												   cur_ec->ec_collation,
+												   innervar,
+												   cur_em->em_expr,
+												   bms_copy(inner_relids),
+												   bms_copy(inner_nullable_relids),
+												   cur_ec->ec_min_security);
+			if (process_equivalence(root, &newrinfo, true))
+				match = true;
+		}
+
+		/*
+		 * If we were able to equate INNERVAR to any constant, report success.
+		 * Otherwise, fall out of the search loop, since we know the OUTERVAR
+		 * appears in at most one EC.
+		 */
+		if (match)
+			return true;
+		else
+			break;
+	}
+
+	return false;				/* failed to make any deduction */
+}
+
+/*
+ * reconsider_outer_join_clauses for a single FULL JOIN clause
+ *
+ * Returns true if we were able to propagate a constant through the clause.
+ */
+static bool
+reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
+{
+	Expr	   *leftvar;
+	Expr	   *rightvar;
+	Oid			opno,
+				collation,
+				left_type,
+				right_type;
+	Relids		left_relids,
+				right_relids,
+				left_nullable_relids,
+				right_nullable_relids;
+	ListCell   *lc1;
+
+	/* Can't use an outerjoin_delayed clause here */
+	if (rinfo->outerjoin_delayed)
+		return false;
+
+	/* Extract needed info from the clause */
+	Assert(is_opclause(rinfo->clause));
+	opno = ((OpExpr *) rinfo->clause)->opno;
+	collation = ((OpExpr *) rinfo->clause)->inputcollid;
+	op_input_types(opno, &left_type, &right_type);
+	leftvar = (Expr *) get_leftop(rinfo->clause);
+	rightvar = (Expr *) get_rightop(rinfo->clause);
+	left_relids = rinfo->left_relids;
+	right_relids = rinfo->right_relids;
+	left_nullable_relids = bms_intersect(left_relids,
+										 rinfo->nullable_relids);
+	right_nullable_relids = bms_intersect(right_relids,
+										  rinfo->nullable_relids);
+
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
+		EquivalenceMember *coal_em = NULL;
+		bool		match;
+		bool		matchleft;
+		bool		matchright;
+		ListCell   *lc2;
+		int			coal_idx = -1;
+
+		/* Ignore EC unless it contains pseudoconstants */
+		if (!cur_ec->ec_has_const)
+			continue;
+		/* Never match to a volatile EC */
+		if (cur_ec->ec_has_volatile)
+			continue;
+		/* It has to match the outer-join clause as to semantics, too */
+		if (collation != cur_ec->ec_collation)
+			continue;
+		if (!equal(rinfo->mergeopfamilies, cur_ec->ec_opfamilies))
+			continue;
+
+		/*
+		 * Does it contain a COALESCE(leftvar, rightvar) construct?
+		 *
+		 * We can assume the COALESCE() inputs are in the same order as the
+		 * join clause, since both were automatically generated in the cases
+		 * we care about.
+		 *
+		 * XXX currently this may fail to match in cross-type cases because
+		 * the COALESCE will contain typecast operations while the join clause
+		 * may not (if there is a cross-type mergejoin operator available for
+		 * the two column types). Is it OK to strip implicit coercions from
+		 * the COALESCE arguments?
+		 */
+		match = false;
+		foreach(lc2, cur_ec->ec_members)
+		{
+			coal_em = (EquivalenceMember *) lfirst(lc2);
+			Assert(!coal_em->em_is_child);	/* no children yet */
+			if (IsA(coal_em->em_expr, CoalesceExpr))
+			{
+				CoalesceExpr *cexpr = (CoalesceExpr *) coal_em->em_expr;
+				Node	   *cfirst;
+				Node	   *csecond;
+
+				if (list_length(cexpr->args) != 2)
+					continue;
+				cfirst = (Node *) linitial(cexpr->args);
+				csecond = (Node *) lsecond(cexpr->args);
+
+				if (equal(leftvar, cfirst) && equal(rightvar, csecond))
+				{
+					coal_idx = foreach_current_index(lc2);
+					match = true;
+					break;
+				}
+			}
+		}
+		if (!match)
+			continue;			/* no match, so ignore this EC */
+
+		/*
+		 * Yes it does!  Try to generate clauses LEFTVAR = CONSTANT and
+		 * RIGHTVAR = CONSTANT for each CONSTANT in the EC.  Note that we must
+		 * succeed with at least one constant for each var before we can
+		 * decide to throw away the outer-join clause.
+		 */
+		matchleft = matchright = false;
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+			Oid			eq_op;
+			RestrictInfo *newrinfo;
+
+			if (!cur_em->em_is_const)
+				continue;		/* ignore non-const members */
+			eq_op = select_equality_operator(cur_ec,
+											 left_type,
+											 cur_em->em_datatype);
+			if (OidIsValid(eq_op))
+			{
+				newrinfo = build_implied_join_equality(root,
+													   eq_op,
+													   cur_ec->ec_collation,
+													   leftvar,
+													   cur_em->em_expr,
+													   bms_copy(left_relids),
+													   bms_copy(left_nullable_relids),
+													   cur_ec->ec_min_security);
+				if (process_equivalence(root, &newrinfo, true))
+					matchleft = true;
+			}
+			eq_op = select_equality_operator(cur_ec,
+											 right_type,
+											 cur_em->em_datatype);
+			if (OidIsValid(eq_op))
+			{
+				newrinfo = build_implied_join_equality(root,
+													   eq_op,
+													   cur_ec->ec_collation,
+													   rightvar,
+													   cur_em->em_expr,
+													   bms_copy(right_relids),
+													   bms_copy(right_nullable_relids),
+													   cur_ec->ec_min_security);
+				if (process_equivalence(root, &newrinfo, true))
+					matchright = true;
+			}
+		}
+
+		/*
+		 * If we were able to equate both vars to constants, we're done, and
+		 * we can throw away the full-join clause as redundant.  Moreover, we
+		 * can remove the COALESCE entry from the EC, since the added
+		 * restrictions ensure it will always have the expected value. (We
+		 * don't bother trying to update ec_relids or ec_sources.)
+		 */
+		if (matchleft && matchright)
+		{
+			cur_ec->ec_members = list_delete_nth_cell(cur_ec->ec_members, coal_idx);
+			return true;
+		}
+
+		/*
+		 * Otherwise, fall out of the search loop, since we know the COALESCE
+		 * appears in at most one EC (XXX might stop being true if we allow
+		 * stripping of coercions above?)
+		 */
+		break;
+	}
+
+	return false;				/* failed to make any deduction */
+}
+
+
+/*
+ * exprs_known_equal
+ *	  Detect whether two expressions are known equal due to equivalence
+ *	  relationships.
+ *
+ * Actually, this only shows that the expressions are equal according
+ * to some opfamily's notion of equality --- but we only use it for
+ * selectivity estimation, so a fuzzy idea of equality is OK.
+ *
+ * Note: does not bother to check for "equal(item1, item2)"; caller must
+ * check that case if it's possible to pass identical items.
+ */
+bool
+exprs_known_equal(PlannerInfo *root, Node *item1, Node *item2)
+{
+	ListCell   *lc1;
+
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc1);
+		bool		item1member = false;
+		bool		item2member = false;
+		ListCell   *lc2;
+
+		/* Never match to a volatile EC */
+		if (ec->ec_has_volatile)
+			continue;
+
+		foreach(lc2, ec->ec_members)
+		{
+			EquivalenceMember *em = (EquivalenceMember *) lfirst(lc2);
+
+			if (em->em_is_child)
+				continue;		/* ignore children here */
+			if (equal(item1, em->em_expr))
+				item1member = true;
+			else if (equal(item2, em->em_expr))
+				item2member = true;
+			/* Exit as soon as equality is proven */
+			if (item1member && item2member)
+				return true;
+		}
+	}
+	return false;
+}
+
+
+/*
+ * match_eclasses_to_foreign_key_col
+ *	  See whether a foreign key column match is proven by any eclass.
+ *
+ * If the referenced and referencing Vars of the fkey's colno'th column are
+ * known equal due to any eclass, return that eclass; otherwise return NULL.
+ * (In principle there might be more than one matching eclass if multiple
+ * collations are involved, but since collation doesn't matter for equality,
+ * we ignore that fine point here.)  This is much like exprs_known_equal,
+ * except that we insist on the comparison operator matching the eclass, so
+ * that the result is definite not approximate.
+ *
+ * On success, we also set fkinfo->eclass[colno] to the matching eclass,
+ * and set fkinfo->fk_eclass_member[colno] to the eclass member for the
+ * referencing Var.
+ */
+EquivalenceClass *
+match_eclasses_to_foreign_key_col(PlannerInfo *root,
+								  ForeignKeyOptInfo *fkinfo,
+								  int colno)
+{
+	Index		var1varno = fkinfo->con_relid;
+	AttrNumber	var1attno = fkinfo->conkey[colno];
+	Index		var2varno = fkinfo->ref_relid;
+	AttrNumber	var2attno = fkinfo->confkey[colno];
+	Oid			eqop = fkinfo->conpfeqop[colno];
+	RelOptInfo *rel1 = root->simple_rel_array[var1varno];
+	RelOptInfo *rel2 = root->simple_rel_array[var2varno];
+	List	   *opfamilies = NIL;	/* compute only if needed */
+	Bitmapset  *matching_ecs;
+	int			i;
+
+	/* Consider only eclasses mentioning both relations */
+	Assert(root->ec_merging_done);
+	Assert(IS_SIMPLE_REL(rel1));
+	Assert(IS_SIMPLE_REL(rel2));
+	matching_ecs = bms_intersect(rel1->eclass_indexes,
+								 rel2->eclass_indexes);
+
+	i = -1;
+	while ((i = bms_next_member(matching_ecs, i)) >= 0)
+	{
+		EquivalenceClass *ec = (EquivalenceClass *) list_nth(root->eq_classes,
+															 i);
+		EquivalenceMember *item1_em = NULL;
+		EquivalenceMember *item2_em = NULL;
+		ListCell   *lc2;
+
+		/* Never match to a volatile EC */
+		if (ec->ec_has_volatile)
+			continue;
+		/* Note: it seems okay to match to "broken" eclasses here */
+
+		foreach(lc2, ec->ec_members)
+		{
+			EquivalenceMember *em = (EquivalenceMember *) lfirst(lc2);
+			Var		   *var;
+
+			if (em->em_is_child)
+				continue;		/* ignore children here */
+
+			/* EM must be a Var, possibly with RelabelType */
+			var = (Var *) em->em_expr;
+			while (var && IsA(var, RelabelType))
+				var = (Var *) ((RelabelType *) var)->arg;
+			if (!(var && IsA(var, Var)))
+				continue;
+
+			/* Match? */
+			if (var->varno == var1varno && var->varattno == var1attno)
+				item1_em = em;
+			else if (var->varno == var2varno && var->varattno == var2attno)
+				item2_em = em;
+
+			/* Have we found both PK and FK column in this EC? */
+			if (item1_em && item2_em)
+			{
+				/*
+				 * Succeed if eqop matches EC's opfamilies.  We could test
+				 * this before scanning the members, but it's probably cheaper
+				 * to test for member matches first.
+				 */
+				if (opfamilies == NIL)	/* compute if we didn't already */
+					opfamilies = get_mergejoin_opfamilies(eqop);
+				if (equal(opfamilies, ec->ec_opfamilies))
+				{
+					fkinfo->eclass[colno] = ec;
+					fkinfo->fk_eclass_member[colno] = item2_em;
+					return ec;
+				}
+				/* Otherwise, done with this EC, move on to the next */
+				break;
+			}
+		}
+	}
+	return NULL;
+}
+
+/*
+ * find_derived_clause_for_ec_member
+ *	  Search for a previously-derived clause mentioning the given EM.
+ *
+ * The eclass should be an ec_has_const EC, of which the EM is a non-const
+ * member.  This should ensure there is just one derived clause mentioning
+ * the EM (and equating it to a constant).
+ * Returns NULL if no such clause can be found.
+ */
+RestrictInfo *
+find_derived_clause_for_ec_member(EquivalenceClass *ec,
+								  EquivalenceMember *em)
+{
+	ListCell   *lc;
+
+	Assert(ec->ec_has_const);
+	Assert(!em->em_is_const);
+	foreach(lc, ec->ec_derives)
+	{
+		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
+
+		/*
+		 * generate_base_implied_equalities_const will have put non-const
+		 * members on the left side of derived clauses.
+		 */
+		if (rinfo->left_em == em)
+			return rinfo;
+	}
+	return NULL;
+}
+
+
+/*
+ * add_child_rel_equivalences
+ *	  Search for EC members that reference the root parent of child_rel, and
+ *	  add transformed members referencing the child_rel.
+ *
+ * Note that this function won't be called at all unless we have at least some
+ * reason to believe that the EC members it generates will be useful.
+ *
+ * parent_rel and child_rel could be derived from appinfo, but since the
+ * caller has already computed them, we might as well just pass them in.
+ *
+ * The passed-in AppendRelInfo is not used when the parent_rel is not a
+ * top-level baserel, since it shows the mapping from the parent_rel but
+ * we need to translate EC expressions that refer to the top-level parent.
+ * Using it is faster than using adjust_appendrel_attrs_multilevel(), though,
+ * so we prefer it when we can.
+ */
+void
+add_child_rel_equivalences(PlannerInfo *root,
+						   AppendRelInfo *appinfo,
+						   RelOptInfo *parent_rel,
+						   RelOptInfo *child_rel)
+{
+	Relids		top_parent_relids = child_rel->top_parent_relids;
+	Relids		child_relids = child_rel->relids;
+	int			i;
+
+	/*
+	 * EC merging should be complete already, so we can use the parent rel's
+	 * eclass_indexes to avoid searching all of root->eq_classes.
+	 */
+	Assert(root->ec_merging_done);
+	Assert(IS_SIMPLE_REL(parent_rel));
+
+	i = -1;
+	while ((i = bms_next_member(parent_rel->eclass_indexes, i)) >= 0)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) list_nth(root->eq_classes, i);
+		int			num_members;
+
+		/*
+		 * If this EC contains a volatile expression, then generating child
+		 * EMs would be downright dangerous, so skip it.  We rely on a
+		 * volatile EC having only one EM.
+		 */
+		if (cur_ec->ec_has_volatile)
+			continue;
+
+		/* Sanity check eclass_indexes only contain ECs for parent_rel */
+		Assert(bms_is_subset(top_parent_relids, cur_ec->ec_relids));
+
+		/*
+		 * We don't use foreach() here because there's no point in scanning
+		 * newly-added child members, so we can stop after the last
+		 * pre-existing EC member.
+		 */
+		num_members = list_length(cur_ec->ec_members);
+		for (int pos = 0; pos < num_members; pos++)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) list_nth(cur_ec->ec_members, pos);
+
+			if (cur_em->em_is_const)
+				continue;		/* ignore consts here */
+
+			/*
+			 * We consider only original EC members here, not
+			 * already-transformed child members.  Otherwise, if some original
+			 * member expression references more than one appendrel, we'd get
+			 * an O(N^2) explosion of useless derived expressions for
+			 * combinations of children.  (But add_child_join_rel_equivalences
+			 * may add targeted combinations for partitionwise-join purposes.)
+			 */
+			if (cur_em->em_is_child)
+				continue;		/* ignore children here */
+
+			/* Does this member reference child's topmost parent rel? */
+			if (bms_overlap(cur_em->em_relids, top_parent_relids))
+			{
+				/* Yes, generate transformed child version */
+				Expr	   *child_expr;
+				Relids		new_relids;
+				Relids		new_nullable_relids;
+
+				if (parent_rel->reloptkind == RELOPT_BASEREL)
+				{
+					/* Simple single-level transformation */
+					child_expr = (Expr *)
+						adjust_appendrel_attrs(root,
+											   (Node *) cur_em->em_expr,
+											   1, &appinfo);
+				}
+				else
+				{
+					/* Must do multi-level transformation */
+					child_expr = (Expr *)
+						adjust_appendrel_attrs_multilevel(root,
+														  (Node *) cur_em->em_expr,
+														  child_relids,
+														  top_parent_relids);
+				}
+
+				/*
+				 * Transform em_relids to match.  Note we do *not* do
+				 * pull_varnos(child_expr) here, as for example the
+				 * transformation might have substituted a constant, but we
+				 * don't want the child member to be marked as constant.
+				 */
+				new_relids = bms_difference(cur_em->em_relids,
+											top_parent_relids);
+				new_relids = bms_add_members(new_relids, child_relids);
+
+				/*
+				 * And likewise for nullable_relids.  Note this code assumes
+				 * parent and child relids are singletons.
+				 */
+				new_nullable_relids = cur_em->em_nullable_relids;
+				if (bms_overlap(new_nullable_relids, top_parent_relids))
+				{
+					new_nullable_relids = bms_difference(new_nullable_relids,
+														 top_parent_relids);
+					new_nullable_relids = bms_add_members(new_nullable_relids,
+														  child_relids);
+				}
+
+				(void) add_eq_member(cur_ec, child_expr,
+									 new_relids, new_nullable_relids,
+									 true, cur_em->em_datatype);
+
+				/* Record this EC index for the child rel */
+				child_rel->eclass_indexes = bms_add_member(child_rel->eclass_indexes, i);
+			}
+		}
+	}
+}
+
+/*
+ * add_child_join_rel_equivalences
+ *	  Like add_child_rel_equivalences(), but for joinrels
+ *
+ * Here we find the ECs relevant to the top parent joinrel and add transformed
+ * member expressions that refer to this child joinrel.
+ *
+ * Note that this function won't be called at all unless we have at least some
+ * reason to believe that the EC members it generates will be useful.
+ */
+void
+add_child_join_rel_equivalences(PlannerInfo *root,
+								int nappinfos, AppendRelInfo **appinfos,
+								RelOptInfo *parent_joinrel,
+								RelOptInfo *child_joinrel)
+{
+	Relids		top_parent_relids = child_joinrel->top_parent_relids;
+	Relids		child_relids = child_joinrel->relids;
+	Bitmapset  *matching_ecs;
+	MemoryContext oldcontext;
+	int			i;
+
+	Assert(IS_JOIN_REL(child_joinrel) && IS_JOIN_REL(parent_joinrel));
+
+	/* We need consider only ECs that mention the parent joinrel */
+	matching_ecs = get_eclass_indexes_for_relids(root, top_parent_relids);
+
+	/*
+	 * If we're being called during GEQO join planning, we still have to
+	 * create any new EC members in the main planner context, to avoid having
+	 * a corrupt EC data structure after the GEQO context is reset.  This is
+	 * problematic since we'll leak memory across repeated GEQO cycles.  For
+	 * now, though, bloat is better than crash.  If it becomes a real issue
+	 * we'll have to do something to avoid generating duplicate EC members.
+	 */
+	oldcontext = MemoryContextSwitchTo(root->planner_cxt);
+
+	i = -1;
+	while ((i = bms_next_member(matching_ecs, i)) >= 0)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) list_nth(root->eq_classes, i);
+		int			num_members;
+
+		/*
+		 * If this EC contains a volatile expression, then generating child
+		 * EMs would be downright dangerous, so skip it.  We rely on a
+		 * volatile EC having only one EM.
+		 */
+		if (cur_ec->ec_has_volatile)
+			continue;
+
+		/* Sanity check on get_eclass_indexes_for_relids result */
+		Assert(bms_overlap(top_parent_relids, cur_ec->ec_relids));
+
+		/*
+		 * We don't use foreach() here because there's no point in scanning
+		 * newly-added child members, so we can stop after the last
+		 * pre-existing EC member.
+		 */
+		num_members = list_length(cur_ec->ec_members);
+		for (int pos = 0; pos < num_members; pos++)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) list_nth(cur_ec->ec_members, pos);
+
+			if (cur_em->em_is_const)
+				continue;		/* ignore consts here */
+
+			/*
+			 * We consider only original EC members here, not
+			 * already-transformed child members.
+			 */
+			if (cur_em->em_is_child)
+				continue;		/* ignore children here */
+
+			/*
+			 * We may ignore expressions that reference a single baserel,
+			 * because add_child_rel_equivalences should have handled them.
+			 */
+			if (bms_membership(cur_em->em_relids) != BMS_MULTIPLE)
+				continue;
+
+			/* Does this member reference child's topmost parent rel? */
+			if (bms_overlap(cur_em->em_relids, top_parent_relids))
+			{
+				/* Yes, generate transformed child version */
+				Expr	   *child_expr;
+				Relids		new_relids;
+				Relids		new_nullable_relids;
+
+				if (parent_joinrel->reloptkind == RELOPT_JOINREL)
+				{
+					/* Simple single-level transformation */
+					child_expr = (Expr *)
+						adjust_appendrel_attrs(root,
+											   (Node *) cur_em->em_expr,
+											   nappinfos, appinfos);
+				}
+				else
+				{
+					/* Must do multi-level transformation */
+					Assert(parent_joinrel->reloptkind == RELOPT_OTHER_JOINREL);
+					child_expr = (Expr *)
+						adjust_appendrel_attrs_multilevel(root,
+														  (Node *) cur_em->em_expr,
+														  child_relids,
+														  top_parent_relids);
+				}
+
+				/*
+				 * Transform em_relids to match.  Note we do *not* do
+				 * pull_varnos(child_expr) here, as for example the
+				 * transformation might have substituted a constant, but we
+				 * don't want the child member to be marked as constant.
+				 */
+				new_relids = bms_difference(cur_em->em_relids,
+											top_parent_relids);
+				new_relids = bms_add_members(new_relids, child_relids);
+
+				/*
+				 * For nullable_relids, we must selectively replace parent
+				 * nullable relids with child ones.
+				 */
+				new_nullable_relids = cur_em->em_nullable_relids;
+				if (bms_overlap(new_nullable_relids, top_parent_relids))
+					new_nullable_relids =
+						adjust_child_relids_multilevel(root,
+													   new_nullable_relids,
+													   child_relids,
+													   top_parent_relids);
+
+				(void) add_eq_member(cur_ec, child_expr,
+									 new_relids, new_nullable_relids,
+									 true, cur_em->em_datatype);
+			}
+		}
+	}
+
+	MemoryContextSwitchTo(oldcontext);
+}
+
+
+/*
+ * generate_implied_equalities_for_column
+ *	  Create EC-derived joinclauses usable with a specific column.
+ *
+ * This is used by indxpath.c to extract potentially indexable joinclauses
+ * from ECs, and can be used by foreign data wrappers for similar purposes.
+ * We assume that only expressions in Vars of a single table are of interest,
+ * but the caller provides a callback function to identify exactly which
+ * such expressions it would like to know about.
+ *
+ * We assume that any given table/index column could appear in only one EC.
+ * (This should be true in all but the most pathological cases, and if it
+ * isn't, we stop on the first match anyway.)  Therefore, what we return
+ * is a redundant list of clauses equating the table/index column to each of
+ * the other-relation values it is known to be equal to.  Any one of
+ * these clauses can be used to create a parameterized path, and there
+ * is no value in using more than one.  (But it *is* worthwhile to create
+ * a separate parameterized path for each one, since that leads to different
+ * join orders.)
+ *
+ * The caller can pass a Relids set of rels we aren't interested in joining
+ * to, so as to save the work of creating useless clauses.
+ */
+List *
+generate_implied_equalities_for_column(PlannerInfo *root,
+									   RelOptInfo *rel,
+									   ec_matches_callback_type callback,
+									   void *callback_arg,
+									   Relids prohibited_rels)
+{
+	List	   *result = NIL;
+	bool		is_child_rel = (rel->reloptkind == RELOPT_OTHER_MEMBER_REL);
+	Relids		parent_relids;
+	int			i;
+
+	/* Should be OK to rely on eclass_indexes */
+	Assert(root->ec_merging_done);
+
+	/* Indexes are available only on base or "other" member relations. */
+	Assert(IS_SIMPLE_REL(rel));
+
+	/* If it's a child rel, we'll need to know what its parent(s) are */
+	if (is_child_rel)
+		parent_relids = find_childrel_parents(root, rel);
+	else
+		parent_relids = NULL;	/* not used, but keep compiler quiet */
+
+	i = -1;
+	while ((i = bms_next_member(rel->eclass_indexes, i)) >= 0)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) list_nth(root->eq_classes, i);
+		EquivalenceMember *cur_em;
+		ListCell   *lc2;
+
+		/* Sanity check eclass_indexes only contain ECs for rel */
+		Assert(is_child_rel || bms_is_subset(rel->relids, cur_ec->ec_relids));
+
+		/*
+		 * Won't generate joinclauses if const or single-member (the latter
+		 * test covers the volatile case too)
+		 */
+		if (cur_ec->ec_has_const || list_length(cur_ec->ec_members) <= 1)
+			continue;
+
+		/*
+		 * Scan members, looking for a match to the target column.  Note that
+		 * child EC members are considered, but only when they belong to the
+		 * target relation.  (Unlike regular members, the same expression
+		 * could be a child member of more than one EC.  Therefore, it's
+		 * potentially order-dependent which EC a child relation's target
+		 * column gets matched to.  This is annoying but it only happens in
+		 * corner cases, so for now we live with just reporting the first
+		 * match.  See also get_eclass_for_sort_expr.)
+		 */
+		cur_em = NULL;
+		foreach(lc2, cur_ec->ec_members)
+		{
+			cur_em = (EquivalenceMember *) lfirst(lc2);
+			if (bms_equal(cur_em->em_relids, rel->relids) &&
+				callback(root, rel, cur_ec, cur_em, callback_arg))
+				break;
+			cur_em = NULL;
+		}
+
+		if (!cur_em)
+			continue;
+
+		/*
+		 * Found our match.  Scan the other EC members and attempt to generate
+		 * joinclauses.
+		 */
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *other_em = (EquivalenceMember *) lfirst(lc2);
+			Oid			eq_op;
+			RestrictInfo *rinfo;
+
+			if (other_em->em_is_child)
+				continue;		/* ignore children here */
+
+			/* Make sure it'll be a join to a different rel */
+			if (other_em == cur_em ||
+				bms_overlap(other_em->em_relids, rel->relids))
+				continue;
+
+			/* Forget it if caller doesn't want joins to this rel */
+			if (bms_overlap(other_em->em_relids, prohibited_rels))
+				continue;
+
+			/*
+			 * Also, if this is a child rel, avoid generating a useless join
+			 * to its parent rel(s).
+			 */
+			if (is_child_rel &&
+				bms_overlap(parent_relids, other_em->em_relids))
+				continue;
+
+			eq_op = select_equality_operator(cur_ec,
+											 cur_em->em_datatype,
+											 other_em->em_datatype);
+			if (!OidIsValid(eq_op))
+				continue;
+
+			/* set parent_ec to mark as redundant with other joinclauses */
+			rinfo = create_join_clause(root, cur_ec, eq_op,
+									   cur_em, other_em,
+									   cur_ec);
+
+			result = lappend(result, rinfo);
+		}
+
+		/*
+		 * If somehow we failed to create any join clauses, we might as well
+		 * keep scanning the ECs for another match.  But if we did make any,
+		 * we're done, because we don't want to return non-redundant clauses.
+		 */
+		if (result)
+			break;
+	}
+
+	return result;
+}
+
+/*
+ * have_relevant_eclass_joinclause
+ *		Detect whether there is an EquivalenceClass that could produce
+ *		a joinclause involving the two given relations.
+ *
+ * This is essentially a very cut-down version of
+ * generate_join_implied_equalities().  Note it's OK to occasionally say "yes"
+ * incorrectly.  Hence we don't bother with details like whether the lack of a
+ * cross-type operator might prevent the clause from actually being generated.
+ */
+bool
+have_relevant_eclass_joinclause(PlannerInfo *root,
+								RelOptInfo *rel1, RelOptInfo *rel2)
+{
+	Bitmapset  *matching_ecs;
+	int			i;
+
+	/* Examine only eclasses mentioning both rel1 and rel2 */
+	matching_ecs = get_common_eclass_indexes(root, rel1->relids,
+											 rel2->relids);
+
+	i = -1;
+	while ((i = bms_next_member(matching_ecs, i)) >= 0)
+	{
+		EquivalenceClass *ec = (EquivalenceClass *) list_nth(root->eq_classes,
+															 i);
+
+		/*
+		 * Sanity check that get_common_eclass_indexes gave only ECs
+		 * containing both rels.
+		 */
+		Assert(bms_overlap(rel1->relids, ec->ec_relids));
+		Assert(bms_overlap(rel2->relids, ec->ec_relids));
+
+		/*
+		 * Won't generate joinclauses if single-member (this test covers the
+		 * volatile case too)
+		 */
+		if (list_length(ec->ec_members) <= 1)
+			continue;
+
+		/*
+		 * We do not need to examine the individual members of the EC, because
+		 * all that we care about is whether each rel overlaps the relids of
+		 * at least one member, and get_common_eclass_indexes() and the single
+		 * member check above are sufficient to prove that.  (As with
+		 * have_relevant_joinclause(), it is not necessary that the EC be able
+		 * to form a joinclause relating exactly the two given rels, only that
+		 * it be able to form a joinclause mentioning both, and this will
+		 * surely be true if both of them overlap ec_relids.)
+		 *
+		 * Note we don't test ec_broken; if we did, we'd need a separate code
+		 * path to look through ec_sources.  Checking the membership anyway is
+		 * OK as a possibly-overoptimistic heuristic.
+		 *
+		 * We don't test ec_has_const either, even though a const eclass won't
+		 * generate real join clauses.  This is because if we had "WHERE a.x =
+		 * b.y and a.x = 42", it is worth considering a join between a and b,
+		 * since the join result is likely to be small even though it'll end
+		 * up being an unqualified nestloop.
+		 */
+
+		return true;
+	}
+
+	return false;
+}
+
+
+/*
+ * has_relevant_eclass_joinclause
+ *		Detect whether there is an EquivalenceClass that could produce
+ *		a joinclause involving the given relation and anything else.
+ *
+ * This is the same as have_relevant_eclass_joinclause with the other rel
+ * implicitly defined as "everything else in the query".
+ */
+bool
+has_relevant_eclass_joinclause(PlannerInfo *root, RelOptInfo *rel1)
+{
+	Bitmapset  *matched_ecs;
+	int			i;
+
+	/* Examine only eclasses mentioning rel1 */
+	matched_ecs = get_eclass_indexes_for_relids(root, rel1->relids);
+
+	i = -1;
+	while ((i = bms_next_member(matched_ecs, i)) >= 0)
+	{
+		EquivalenceClass *ec = (EquivalenceClass *) list_nth(root->eq_classes,
+															 i);
+
+		/*
+		 * Won't generate joinclauses if single-member (this test covers the
+		 * volatile case too)
+		 */
+		if (list_length(ec->ec_members) <= 1)
+			continue;
+
+		/*
+		 * Per the comment in have_relevant_eclass_joinclause, it's sufficient
+		 * to find an EC that mentions both this rel and some other rel.
+		 */
+		if (!bms_is_subset(ec->ec_relids, rel1->relids))
+			return true;
+	}
+
+	return false;
+}
+
+
+/*
+ * eclass_useful_for_merging
+ *	  Detect whether the EC could produce any mergejoinable join clauses
+ *	  against the specified relation.
+ *
+ * This is just a heuristic test and doesn't have to be exact; it's better
+ * to say "yes" incorrectly than "no".  Hence we don't bother with details
+ * like whether the lack of a cross-type operator might prevent the clause
+ * from actually being generated.
+ */
+bool
+eclass_useful_for_merging(PlannerInfo *root,
+						  EquivalenceClass *eclass,
+						  RelOptInfo *rel)
+{
+	Relids		relids;
+	ListCell   *lc;
+
+	Assert(!eclass->ec_merged);
+
+	/*
+	 * Won't generate joinclauses if const or single-member (the latter test
+	 * covers the volatile case too)
+	 */
+	if (eclass->ec_has_const || list_length(eclass->ec_members) <= 1)
+		return false;
+
+	/*
+	 * Note we don't test ec_broken; if we did, we'd need a separate code path
+	 * to look through ec_sources.  Checking the members anyway is OK as a
+	 * possibly-overoptimistic heuristic.
+	 */
+
+	/* If specified rel is a child, we must consider the topmost parent rel */
+	if (IS_OTHER_REL(rel))
+	{
+		Assert(!bms_is_empty(rel->top_parent_relids));
+		relids = rel->top_parent_relids;
+	}
+	else
+		relids = rel->relids;
+
+	/* If rel already includes all members of eclass, no point in searching */
+	if (bms_is_subset(eclass->ec_relids, relids))
+		return false;
+
+	/* To join, we need a member not in the given rel */
+	foreach(lc, eclass->ec_members)
+	{
+		EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
+
+		if (cur_em->em_is_child)
+			continue;			/* ignore children here */
+
+		if (!bms_overlap(cur_em->em_relids, relids))
+			return true;
+	}
+
+	return false;
+}
+
+
+/*
+ * is_redundant_derived_clause
+ *		Test whether rinfo is derived from same EC as any clause in clauselist;
+ *		if so, it can be presumed to represent a condition that's redundant
+ *		with that member of the list.
+ */
+bool
+is_redundant_derived_clause(RestrictInfo *rinfo, List *clauselist)
+{
+	EquivalenceClass *parent_ec = rinfo->parent_ec;
+	ListCell   *lc;
+
+	/* Fail if it's not a potentially-redundant clause from some EC */
+	if (parent_ec == NULL)
+		return false;
+
+	foreach(lc, clauselist)
+	{
+		RestrictInfo *otherrinfo = (RestrictInfo *) lfirst(lc);
+
+		if (otherrinfo->parent_ec == parent_ec)
+			return true;
+	}
+
+	return false;
+}
+
+/*
+ * is_redundant_with_indexclauses
+ *		Test whether rinfo is redundant with any clause in the IndexClause
+ *		list.  Here, for convenience, we test both simple identity and
+ *		whether it is derived from the same EC as any member of the list.
+ */
+bool
+is_redundant_with_indexclauses(RestrictInfo *rinfo, List *indexclauses)
+{
+	EquivalenceClass *parent_ec = rinfo->parent_ec;
+	ListCell   *lc;
+
+	foreach(lc, indexclauses)
+	{
+		IndexClause *iclause = lfirst_node(IndexClause, lc);
+		RestrictInfo *otherrinfo = iclause->rinfo;
+
+		/* If indexclause is lossy, it won't enforce the condition exactly */
+		if (iclause->lossy)
+			continue;
+
+		/* Match if it's same clause (pointer equality should be enough) */
+		if (rinfo == otherrinfo)
+			return true;
+		/* Match if derived from same EC */
+		if (parent_ec && otherrinfo->parent_ec == parent_ec)
+			return true;
+
+		/*
+		 * No need to look at the derived clauses in iclause->indexquals; they
+		 * couldn't match if the parent clause didn't.
+		 */
+	}
+
+	return false;
+}
+
+/*
+ * get_eclass_indexes_for_relids
+ *		Build and return a Bitmapset containing the indexes into root's
+ *		eq_classes list for all eclasses that mention any of these relids
+ */
+static Bitmapset *
+get_eclass_indexes_for_relids(PlannerInfo *root, Relids relids)
+{
+	Bitmapset  *ec_indexes = NULL;
+	int			i = -1;
+
+	/* Should be OK to rely on eclass_indexes */
+	Assert(root->ec_merging_done);
+
+	while ((i = bms_next_member(relids, i)) > 0)
+	{
+		RelOptInfo *rel = root->simple_rel_array[i];
+
+		ec_indexes = bms_add_members(ec_indexes, rel->eclass_indexes);
+	}
+	return ec_indexes;
+}
+
+/*
+ * get_common_eclass_indexes
+ *		Build and return a Bitmapset containing the indexes into root's
+ *		eq_classes list for all eclasses that mention rels in both
+ *		relids1 and relids2.
+ */
+static Bitmapset *
+get_common_eclass_indexes(PlannerInfo *root, Relids relids1, Relids relids2)
+{
+	Bitmapset  *rel1ecs;
+	Bitmapset  *rel2ecs;
+	int			relid;
+
+	rel1ecs = get_eclass_indexes_for_relids(root, relids1);
+
+	/*
+	 * We can get away with just using the relation's eclass_indexes directly
+	 * when relids2 is a singleton set.
+	 */
+	if (bms_get_singleton_member(relids2, &relid))
+		rel2ecs = root->simple_rel_array[relid]->eclass_indexes;
+	else
+		rel2ecs = get_eclass_indexes_for_relids(root, relids2);
+
+	/* Calculate and return the common EC indexes, recycling the left input. */
+	return bms_int_members(rel1ecs, rel2ecs);
+}