Fix pull_varnos' miscomputation of relids set for a PlaceHolderVar.

Previously, pull_varnos() took the relids of a PlaceHolderVar as being
equal to the relids in its contents, but that fails to account for the
possibility that we have to postpone evaluation of the PHV due to outer
joins.  This could result in a malformed plan.  The known cases end up
triggering the "failed to assign all NestLoopParams to plan nodes"
sanity check in createplan.c, but other symptoms may be possible.

The right value to use is the join level we actually intend to evaluate
the PHV at.  We can get that from the ph_eval_at field of the associated
PlaceHolderInfo.  However, there are some places that call pull_varnos()
before the PlaceHolderInfos have been created; in that case, fall back
to the conservative assumption that the PHV will be evaluated at its
syntactic level.  (In principle this might result in missing some legal
optimization, but I'm not aware of any cases where it's an issue in
practice.)  Things are also a bit ticklish for calls occurring during
deconstruct_jointree(), but AFAICS the ph_eval_at fields should have
reached their final values by the time we need them.

The main problem in making this work is that pull_varnos() has no
way to get at the PlaceHolderInfos.  We can fix that easily, if a
bit tediously, in HEAD by passing it the planner "root" pointer.
In the back branches that'd cause an unacceptable API/ABI break for
extensions, so leave the existing entry points alone and add new ones
with the additional parameter.  (If an old entry point is called and
encounters a PHV, it'll fall back to using the syntactic level,
again possibly missing some valid optimization.)

Back-patch to v12.  The computation is surely also wrong before that,
but it appears that we cannot reach a bad plan thanks to join order
restrictions imposed on the subquery that the PlaceHolderVar came from.
The error only became reachable when commit 4be058fe9 allowed trivial
subqueries to be collapsed out completely, eliminating their join order
restrictions.

Per report from Stephan Springl.

Discussion: https://postgr.es/m/171041.1610849523@sss.pgh.pa.us

5 files changed, 13 insertions, 9 deletions

diff --git a/src/include/optimizer/clauses.h b/src/include/optimizer/clauses.h
index da3fc4df105..0673887a852 100644
--- a/src/include/optimizer/clauses.h
+++ b/src/include/optimizer/clauses.h
@@ -46,7 +46,7 @@ extern Var *find_forced_null_var(Node *clause);
 extern bool is_pseudo_constant_clause(Node *clause);
 extern bool is_pseudo_constant_clause_relids(Node *clause, Relids relids);
 
-extern int	NumRelids(Node *clause);
+extern int	NumRelids(PlannerInfo *root, Node *clause);
 
 extern void CommuteOpExpr(OpExpr *clause);
 
diff --git a/src/include/optimizer/optimizer.h b/src/include/optimizer/optimizer.h
index 6235933ca4a..d587952b7d6 100644
--- a/src/include/optimizer/optimizer.h
+++ b/src/include/optimizer/optimizer.h
@@ -97,7 +97,8 @@ extern double clamp_row_est(double nrows);
 
 /* in path/indxpath.c: */
 
-extern bool is_pseudo_constant_for_index(Node *expr, IndexOptInfo *index);
+extern bool is_pseudo_constant_for_index(PlannerInfo *root, Node *expr,
+										 IndexOptInfo *index);
 
 /* in plan/planner.c: */
 
@@ -188,8 +189,8 @@ extern SortGroupClause *get_sortgroupref_clause_noerr(Index sortref,
 #define PVC_RECURSE_PLACEHOLDERS	0x0020	/* recurse into PlaceHolderVar
 											 * arguments */
 
-extern Bitmapset *pull_varnos(Node *node);
-extern Bitmapset *pull_varnos_of_level(Node *node, int levelsup);
+extern Bitmapset *pull_varnos(PlannerInfo *root, Node *node);
+extern Bitmapset *pull_varnos_of_level(PlannerInfo *root, Node *node, int levelsup);
 extern void pull_varattnos(Node *node, Index varno, Bitmapset **varattnos);
 extern List *pull_vars_of_level(Node *node, int levelsup);
 extern bool contain_var_clause(Node *node);
diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h
index 2d51cbecaa3..035d3e12069 100644
--- a/src/include/optimizer/paths.h
+++ b/src/include/optimizer/paths.h
@@ -75,7 +75,8 @@ extern void create_index_paths(PlannerInfo *root, RelOptInfo *rel);
 extern bool relation_has_unique_index_for(PlannerInfo *root, RelOptInfo *rel,
 										  List *restrictlist,
 										  List *exprlist, List *oprlist);
-extern bool indexcol_is_bool_constant_for_query(IndexOptInfo *index,
+extern bool indexcol_is_bool_constant_for_query(PlannerInfo *root,
+												IndexOptInfo *index,
 												int indexcol);
 extern bool match_index_to_operand(Node *operand, int indexcol,
 								   IndexOptInfo *index);
diff --git a/src/include/optimizer/planmain.h b/src/include/optimizer/planmain.h
index 777655210b6..bf1adfc52ac 100644
--- a/src/include/optimizer/planmain.h
+++ b/src/include/optimizer/planmain.h
@@ -87,7 +87,8 @@ extern RestrictInfo *process_implied_equality(PlannerInfo *root,
 											  Index security_level,
 											  bool below_outer_join,
 											  bool both_const);
-extern RestrictInfo *build_implied_join_equality(Oid opno,
+extern RestrictInfo *build_implied_join_equality(PlannerInfo *root,
+												 Oid opno,
 												 Oid collation,
 												 Expr *item1,
 												 Expr *item2,
diff --git a/src/include/optimizer/restrictinfo.h b/src/include/optimizer/restrictinfo.h
index 266faaf07c3..0165ffde37b 100644
--- a/src/include/optimizer/restrictinfo.h
+++ b/src/include/optimizer/restrictinfo.h
@@ -18,10 +18,11 @@
 
 
 /* Convenience macro for the common case of a valid-everywhere qual */
-#define make_simple_restrictinfo(clause)  \
-	make_restrictinfo(clause, true, false, false, 0, NULL, NULL, NULL)
+#define make_simple_restrictinfo(root, clause)  \
+	make_restrictinfo(root, clause, true, false, false, 0, NULL, NULL, NULL)
 
-extern RestrictInfo *make_restrictinfo(Expr *clause,
+extern RestrictInfo *make_restrictinfo(PlannerInfo *root,
+									   Expr *clause,
 									   bool is_pushed_down,
 									   bool outerjoin_delayed,
 									   bool pseudoconstant,