Be more careful about the shape of hashable subplan clauses.

nodeSubplan.c expects that the testexpr for a hashable ANY SubPlan
has the form of one or more OpExprs whose LHS is an expression of the
outer query's, while the RHS is an expression over Params representing
output columns of the subquery.  However, the planner only went as far
as verifying that the clauses were all binary OpExprs.  This works
99.99% of the time, because the clauses have the right shape when
emitted by the parser --- but it's possible for function inlining to
break that, as reported by PegoraroF10.  To fix, teach the planner
to check that the LHS and RHS contain the right things, or more
accurately don't contain the wrong things.  Given that this has been
broken for years without anyone noticing, it seems sufficient to just
give up hashing when it happens, rather than go to the trouble of
commuting the clauses back again (which wouldn't necessarily work
anyway).

While poking at that, I also noticed that nodeSubplan.c had a baked-in
assumption that the number of hash clauses is identical to the number
of subquery output columns.  Again, that's fine as far as parser output
goes, but it's not hard to break it via function inlining.  There seems
little reason for that assumption though --- AFAICS, the only thing
it's buying us is not having to store the number of hash clauses
explicitly.  Adding code to the planner to reject such cases would take
more code than getting nodeSubplan.c to cope, so I fixed it that way.

This has been broken for as long as we've had hashable SubPlans,
so back-patch to all supported branches.

Discussion: https://postgr.es/m/1549209182255-0.post@n3.nabble.com

src/include/nodes/execnodes.h

@@ -862,6 +862,7 @@ typedef struct SubPlanState
 	MemoryContext hashtablecxt; /* memory context containing hash tables */
 	MemoryContext hashtempcxt;	/* temp memory context for hash tables */
 	ExprContext *innerecontext; /* econtext for computing inner tuples */
+	/* each of the following fields is an array of length numCols: */
 	AttrNumber *keyColIdx;		/* control data for hash tables */
 	Oid		   *tab_eq_funcoids;	/* equality func oids for table
 									 * datatype(s) */
@@ -871,6 +872,7 @@ typedef struct SubPlanState
 	FmgrInfo   *lhs_hash_funcs; /* hash functions for lefthand datatype(s) */
 	FmgrInfo   *cur_eq_funcs;	/* equality functions for LHS vs. table */
 	ExprState  *cur_eq_comp;	/* equality comparator for LHS vs. table */
+	int			numCols;		/* number of columns being hashed */
 } SubPlanState;
 
 /* ----------------

src/include/optimizer/clauses.h

@@ -38,6 +38,7 @@ extern bool contain_subplans(Node *clause);
 extern char max_parallel_hazard(Query *parse);
 extern bool is_parallel_safe(PlannerInfo *root, Node *node);
 extern bool contain_nonstrict_functions(Node *clause);
+extern bool contain_exec_param(Node *clause, List *param_ids);
 extern bool contain_leaked_vars(Node *clause);
 
 extern Relids find_nonnullable_rels(Node *clause);