Tweak API of new function clause_is_computable_at().

Pass it the RestrictInfo under consideration, not just the
clause_relids.  This should save some trivial amount of
code at the call sites, and it gives us more flexibility
about what clause_is_computable_at() does.  There's no
actual functional change here, though.

Discussion: https://postgr.es/m/3564467.1684352557@sss.pgh.pa.us

src/backend/optimizer/util/relnode.c

@@ -1346,8 +1346,7 @@ subbuild_joinrel_restrictlist(PlannerInfo *root,
 				Assert(!RINFO_IS_PUSHED_DOWN(rinfo, joinrel->relids));
 				if (!bms_is_subset(rinfo->required_relids, both_input_relids))
 					continue;
-				if (!clause_is_computable_at(root, rinfo->clause_relids,
-											 both_input_relids))
+				if (!clause_is_computable_at(root, rinfo, both_input_relids))
 					continue;
 			}
 			else
@@ -1358,13 +1357,13 @@ subbuild_joinrel_restrictlist(PlannerInfo *root,
 				 */
 #ifdef USE_ASSERT_CHECKING
 				if (RINFO_IS_PUSHED_DOWN(rinfo, joinrel->relids))
-					Assert(clause_is_computable_at(root, rinfo->clause_relids,
+					Assert(clause_is_computable_at(root, rinfo,
 												   joinrel->relids));
 				else
 				{
 					Assert(bms_is_subset(rinfo->required_relids,
 										 both_input_relids));
-					Assert(clause_is_computable_at(root, rinfo->clause_relids,
+					Assert(clause_is_computable_at(root, rinfo,
 												   both_input_relids));
 				}
 #endif

src/backend/optimizer/util/restrictinfo.c

@@ -541,9 +541,10 @@ extract_actual_join_clauses(List *restrictinfo_list,
  */
 bool
 clause_is_computable_at(PlannerInfo *root,
-						Relids clause_relids,
+						RestrictInfo *rinfo,
 						Relids eval_relids)
 {
+	Relids		clause_relids = rinfo->clause_relids;
 	ListCell   *lc;
 
 	/* Nothing to do if no outer joins have been performed yet. */

src/include/optimizer/restrictinfo.h

@@ -40,7 +40,7 @@ extern void extract_actual_join_clauses(List *restrictinfo_list,
 										List **joinquals,
 										List **otherquals);
 extern bool clause_is_computable_at(PlannerInfo *root,
-									Relids clause_relids,
+									RestrictInfo *rinfo,
 									Relids eval_relids);
 extern bool join_clause_is_movable_to(RestrictInfo *rinfo, RelOptInfo *baserel);
 extern bool join_clause_is_movable_into(RestrictInfo *rinfo,