Remove reltarget_has_non_vars flag.

Commit b12fd41c6 added a "reltarget_has_non_vars" field to RelOptInfo,
but failed to maintain it accurately.  Since its only purpose was to skip
calls to has_parallel_hazard() in the simple case where a rel's targetlist
is all Vars, and that call is really pretty cheap in that case anyway, it
seems like this is just a case of premature optimization.  Let's drop the
flag and do the calls unconditionally until it's proven that we need more
smarts here.

src/backend/nodes/outfuncs.c

@@ -2083,7 +2083,6 @@ _outRelOptInfo(StringInfo str, const RelOptInfo *node)
 	WRITE_BOOL_FIELD(consider_param_startup);
 	WRITE_BOOL_FIELD(consider_parallel);
 	WRITE_NODE_FIELD(reltarget);
-	WRITE_BOOL_FIELD(reltarget_has_non_vars);
 	WRITE_NODE_FIELD(pathlist);
 	WRITE_NODE_FIELD(ppilist);
 	WRITE_NODE_FIELD(partial_pathlist);

src/backend/optimizer/path/allpaths.c

@@ -613,12 +613,10 @@ set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
 		return;
 
 	/*
-	 * If the relation's outputs are not parallel-safe, we must give up. In
-	 * the common case where the relation only outputs Vars, this check is
-	 * very cheap; otherwise, we have to do more work.
+	 * Likewise, if the relation's outputs are not parallel-safe, give up.
+	 * (Usually, they're just Vars, but sometimes they're not.)
 	 */
-	if (rel->reltarget_has_non_vars &&
-		has_parallel_hazard((Node *) rel->reltarget->exprs, false))
+	if (has_parallel_hazard((Node *) rel->reltarget->exprs, false))
 		return;
 
 	/* We have a winner. */
@@ -984,7 +982,6 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
 			adjust_appendrel_attrs(root,
 								   (Node *) rel->reltarget->exprs,
 								   appinfo);
-		childrel->reltarget_has_non_vars = rel->reltarget_has_non_vars;
 
 		/*
 		 * We have to make child entries in the EquivalenceClass data

src/backend/optimizer/util/placeholder.c

@@ -393,7 +393,6 @@ add_placeholders_to_base_rels(PlannerInfo *root)
 
 			rel->reltarget->exprs = lappend(rel->reltarget->exprs,
 											copyObject(phinfo->ph_var));
-			rel->reltarget_has_non_vars = true;
 			/* reltarget's cost and width fields will be updated later */
 		}
 	}
@@ -428,7 +427,6 @@ add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
 				/* Yup, add it to the output */
 				joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
 													phinfo->ph_var);
-				joinrel->reltarget_has_non_vars = true;
 				joinrel->reltarget->width += phinfo->ph_width;
 
 				/*

src/backend/optimizer/util/relnode.c

@@ -109,7 +109,6 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 	rel->consider_parallel = false;		/* might get changed later */
 	rel->rel_parallel_workers = -1;		/* set up in GetRelationInfo */
 	rel->reltarget = create_empty_pathtarget();
-	rel->reltarget_has_non_vars = false;
 	rel->pathlist = NIL;
 	rel->ppilist = NIL;
 	rel->partial_pathlist = NIL;
@@ -397,7 +396,6 @@ build_join_rel(PlannerInfo *root,
 	joinrel->consider_param_startup = false;
 	joinrel->consider_parallel = false;
 	joinrel->reltarget = create_empty_pathtarget();
-	joinrel->reltarget_has_non_vars = false;
 	joinrel->pathlist = NIL;
 	joinrel->ppilist = NIL;
 	joinrel->partial_pathlist = NIL;
@@ -520,8 +518,7 @@ build_join_rel(PlannerInfo *root,
 	 */
 	if (inner_rel->consider_parallel && outer_rel->consider_parallel &&
 		!has_parallel_hazard((Node *) restrictlist, false) &&
-		!(joinrel->reltarget_has_non_vars &&
-		  has_parallel_hazard((Node *) joinrel->reltarget->exprs, false)))
+		!has_parallel_hazard((Node *) joinrel->reltarget->exprs, false))
 		joinrel->consider_parallel = true;
 
 	/*

src/include/nodes/relation.h

@@ -490,8 +490,6 @@ typedef struct RelOptInfo
 
 	/* default result targetlist for Paths scanning this relation */
 	struct PathTarget *reltarget;		/* list of Vars/Exprs, cost, width */
-	bool		reltarget_has_non_vars; /* true if any expression in
-										 * PathTarget is a non-Var */
 
 	/* materialization information */
 	List	   *pathlist;		/* Path structures */