Fix svace warnings

Fixed arithmetics in check_dsa_file_size to avoid server startup failure
when aqo.dsm_size_max in bytes overflows signed integer. Updated
corresponding tap-test.

Two unreachable paths were removed.

(cherry-picked from master with a minor change in tap-test)

Author: Artem Fadeev

Diff for: cardinality_hooks.c

@@ -447,9 +447,6 @@ aqo_estimate_num_groups(PlannerInfo *root, List *groupExprs,
 		/* It is unclear that to do in situation of such kind. Just report it */
 		elog(WARNING, "AQO is in the middle of the estimate_num_groups_hook chain");
 
-	if (groupExprs == NIL)
-		return 1.0;
-
 	old_ctx_m = MemoryContextSwitchTo(AQOPredictMemCtx);
 
 	predicted = predict_num_groups(root, subpath, groupExprs, &fss);

Diff for: storage.c

@@ -968,8 +968,6 @@ aqo_get_file_size(const char *filename)
 	ereport(LOG,
 			(errcode_for_file_access(),
 			 errmsg("could not read file \"%s\": %m", filename)));
-	if (file)
-		FreeFile(file);
 	unlink(filename);
 	return -1;
 }
@@ -981,7 +979,7 @@ check_dsa_file_size(void)
 	long data_size = aqo_get_file_size(PGAQO_DATA_FILE);
 
 	if (qtext_size == -1 || data_size == -1 ||
-		qtext_size + data_size >= dsm_size_max * 1024 * 1024)
+		((unsigned long) qtext_size + (unsigned long) data_size) >> 20 >= dsm_size_max)
 	{
 		elog(ERROR, "aqo.dsm_size_max is too small");
 	}

Diff for: t/004_dsm_size_max.pl

@@ -5,7 +5,7 @@
 use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
 
-use Test::More tests => 5;
+use Test::More tests => 6;
 
 my $node = PostgreSQL::Test::Cluster->new('aqotest');
 $node->init;
@@ -58,6 +58,12 @@
 $node->psql('postgres', 'select * from aqo_reset();');
 $node->stop();
 
+# 3000mb (more than 2*31 bytes) overflows 4-byte signed int
+$node->append_conf('postgresql.conf', 'aqo.dsm_size_max = 3000');
+is($node->start(fail_ok => 1), 1, "Large aqo.dsm_size_max doesn't cause integer overflow");
+$node->stop();
+
+
 my $regex;
 $long_string = 'a' x 100000;
 $regex = qr/.*WARNING:  \[AQO\] Not enough DSA\. AQO was disabled for this query/;