Fix incorrect logic in plpgsql for cleanup after evaluation of non-simple

expressions.  We need to deal with this when handling subscripts in an array
assignment, and also when catching an exception.  In an Assert-enabled build
these omissions led to Assert failures, but I think in a normal build the
only consequence would be short-term memory leakage; which may explain why
this wasn't reported from the field long ago.

Back-patch to all supported versions.  7.4 doesn't have exceptions, but
otherwise these bugs go all the way back.

Heikki Linnakangas and Tom Lane

src/test/regress/sql/plpgsql.sql

@@ -2580,4 +2580,44 @@ begin
 end;
 $$ language plpgsql;
 
-select * from ret_query2(8);
+select * from ret_query2(8);
+
+-- Test for appropriate cleanup of non-simple expression evaluations
+-- (bug in all versions prior to August 2010)
+
+CREATE FUNCTION nonsimple_expr_test() RETURNS text[] AS $$
+DECLARE
+  arr text[];
+  lr text;
+  i integer;
+BEGIN
+  arr := array[array['foo','bar'], array['baz', 'quux']];
+  lr := 'fool';
+  i := 1;
+  -- use sub-SELECTs to make expressions non-simple
+  arr[(SELECT i)][(SELECT i+1)] := (SELECT lr);
+  RETURN arr;
+END;
+$$ LANGUAGE plpgsql;
+
+SELECT nonsimple_expr_test();
+
+DROP FUNCTION nonsimple_expr_test();
+
+CREATE FUNCTION nonsimple_expr_test() RETURNS integer AS $$
+declare
+   i integer NOT NULL := 0;
+begin
+  begin
+    i := (SELECT NULL::integer);  -- should throw error
+  exception
+    WHEN OTHERS THEN
+      i := (SELECT 1::integer);
+  end;
+  return i;
+end;
+$$ LANGUAGE plpgsql;
+
+SELECT nonsimple_expr_test();
+
+DROP FUNCTION nonsimple_expr_test();