Test passing expanded-value representations to workers.

Currently, we don't have an explicit test to pass expanded-value
representations to workers, so we don't know whether it works on all kind
of platforms.  We suspect that the current code won't work on
alignment-sensitive hardware.  This commit will test that aspect and can
lead to failure on some of the buildfarm machines which we will fix in the
later commit.

Author: Tom Lane and Amit Kapila
Discussion: https://postgr.es/m/11629.1536550032@sss.pgh.pa.us

src/test/regress/expected/select_parallel.out

@@ -1088,7 +1088,34 @@ ORDER BY 1, 2, 3;
 ------------------------------+---------------------------+-------------+--------------
 (0 rows)
 
--- test interation between subquery and partial_paths
+-- test passing expanded-value representations to workers
+CREATE FUNCTION make_some_array(int,int) returns int[] as
+$$declare x int[];
+  begin
+    x[1] := $1;
+    x[2] := $2;
+    return x;
+  end$$ language plpgsql parallel safe;
+CREATE TABLE fooarr(f1 text, f2 int[], f3 text);
+INSERT INTO fooarr VALUES('1', ARRAY[1,2], 'one');
+PREPARE pstmt(text, int[]) AS SELECT * FROM fooarr WHERE f1 = $1 AND f2 = $2;
+EXPLAIN (COSTS OFF) EXECUTE pstmt('1', make_some_array(1,2));
+                            QUERY PLAN                            
+------------------------------------------------------------------
+ Gather
+   Workers Planned: 3
+   ->  Parallel Seq Scan on fooarr
+         Filter: ((f1 = '1'::text) AND (f2 = '{1,2}'::integer[]))
+(4 rows)
+
+EXECUTE pstmt('1', make_some_array(1,2));
+ f1 |  f2   | f3  
+----+-------+-----
+ 1  | {1,2} | one
+(1 row)
+
+DEALLOCATE pstmt;
+-- test interaction between subquery and partial_paths
 SET LOCAL min_parallel_table_scan_size TO 0;
 CREATE VIEW tenk1_vw_sec WITH (security_barrier) AS SELECT * FROM tenk1;
 EXPLAIN (COSTS OFF)

src/test/regress/sql/select_parallel.sql

@@ -410,7 +410,23 @@ ORDER BY 1;
 SELECT * FROM information_schema.foreign_data_wrapper_options
 ORDER BY 1, 2, 3;
 
--- test interation between subquery and partial_paths
+-- test passing expanded-value representations to workers
+CREATE FUNCTION make_some_array(int,int) returns int[] as
+$$declare x int[];
+  begin
+    x[1] := $1;
+    x[2] := $2;
+    return x;
+  end$$ language plpgsql parallel safe;
+CREATE TABLE fooarr(f1 text, f2 int[], f3 text);
+INSERT INTO fooarr VALUES('1', ARRAY[1,2], 'one');
+
+PREPARE pstmt(text, int[]) AS SELECT * FROM fooarr WHERE f1 = $1 AND f2 = $2;
+EXPLAIN (COSTS OFF) EXECUTE pstmt('1', make_some_array(1,2));
+EXECUTE pstmt('1', make_some_array(1,2));
+DEALLOCATE pstmt;
+
+-- test interaction between subquery and partial_paths
 SET LOCAL min_parallel_table_scan_size TO 0;
 CREATE VIEW tenk1_vw_sec WITH (security_barrier) AS SELECT * FROM tenk1;
 EXPLAIN (COSTS OFF)