1 files changed, 64 insertions, 0 deletions
diff --git a/src/backend/optimizer/util/restrictinfo.c b/src/backend/optimizer/util/restrictinfo.c
index 1c47c708028..03e5f12d0da 100644
--- a/src/backend/optimizer/util/restrictinfo.c
+++ b/src/backend/optimizer/util/restrictinfo.c
@@ -289,6 +289,70 @@ make_sub_restrictinfos(Expr *clause,
 }
 
 /*
+ * commute_restrictinfo
+ *
+ * Given a RestrictInfo containing a binary opclause, produce a RestrictInfo
+ * representing the commutation of that clause.  The caller must pass the
+ * OID of the commutator operator (which it's presumably looked up, else
+ * it would not know this is valid).
+ *
+ * Beware that the result shares sub-structure with the given RestrictInfo.
+ * That's okay for the intended usage with derived index quals, but might
+ * be hazardous if the source is subject to change.  Also notice that we
+ * assume without checking that the commutator op is a member of the same
+ * btree and hash opclasses as the original op.
+ */
+RestrictInfo *
+commute_restrictinfo(RestrictInfo *rinfo, Oid comm_op)
+{
+	RestrictInfo *result;
+	OpExpr	   *newclause;
+	OpExpr	   *clause = castNode(OpExpr, rinfo->clause);
+
+	Assert(list_length(clause->args) == 2);
+
+	/* flat-copy all the fields of clause ... */
+	newclause = makeNode(OpExpr);
+	memcpy(newclause, clause, sizeof(OpExpr));
+
+	/* ... and adjust those we need to change to commute it */
+	newclause->opno = comm_op;
+	newclause->opfuncid = InvalidOid;
+	newclause->args = list_make2(lsecond(clause->args),
+								 linitial(clause->args));
+
+	/* likewise, flat-copy all the fields of rinfo ... */
+	result = makeNode(RestrictInfo);
+	memcpy(result, rinfo, sizeof(RestrictInfo));
+
+	/*
+	 * ... and adjust those we need to change.  Note in particular that we can
+	 * preserve any cached selectivity or cost estimates, since those ought to
+	 * be the same for the new clause.  Likewise we can keep the source's
+	 * parent_ec.
+	 */
+	result->clause = (Expr *) newclause;
+	result->left_relids = rinfo->right_relids;
+	result->right_relids = rinfo->left_relids;
+	Assert(result->orclause == NULL);
+	result->left_ec = rinfo->right_ec;
+	result->right_ec = rinfo->left_ec;
+	result->left_em = rinfo->right_em;
+	result->right_em = rinfo->left_em;
+	result->scansel_cache = NIL;	/* not worth updating this */
+	if (rinfo->hashjoinoperator == clause->opno)
+		result->hashjoinoperator = comm_op;
+	else
+		result->hashjoinoperator = InvalidOid;
+	result->left_bucketsize = rinfo->right_bucketsize;
+	result->right_bucketsize = rinfo->left_bucketsize;
+	result->left_mcvfreq = rinfo->right_mcvfreq;
+	result->right_mcvfreq = rinfo->left_mcvfreq;
+
+	return result;
+}
+
+/*
  * restriction_is_or_clause
  *
  * Returns t iff the restrictinfo node contains an 'or' clause.