modulo-sched: prevent division by zero (PR87979)

	PR rtl-optimization/87979
	* modulo-sched.c (sms_schedule): Start ii value "mii" should
	not equal zero.

testsuite:

	PR rtl-optimization/87979
	* gcc.dg/pr87979.c: New test.

From-SVN: r270512

gcc/ChangeLog

 2019-04-23  Roman Zhuykov  <zhroma@ispras.ru>
 
+	PR rtl-optimization/87979
+	* modulo-sched.c (sms_schedule): Start ii value "mii" should
+	not equal zero.
+
+2019-04-23  Roman Zhuykov  <zhroma@ispras.ru>
+
 	PR rtl-optimization/84032
 	* modulo-sched.c (ps_insn_find_column): Change condition so that
 	branch will always be the last insn in a row inside partial

gcc/modulo-sched.c

@@ -1597,6 +1597,7 @@ sms_schedule (void)
       mii = 1; /* Need to pass some estimate of mii.  */
       rec_mii = sms_order_nodes (g, mii, node_order, &max_asap);
       mii = MAX (res_MII (g), rec_mii);
+      mii = MAX (mii, 1);
       maxii = MAX (max_asap, MAXII_FACTOR * mii);
 
       if (dump_file)

gcc/testsuite/ChangeLog

 2019-04-23  Roman Zhuykov  <zhroma@ispras.ru>
 
+	PR rtl-optimization/87979
+	* gcc.dg/pr87979.c: New test.
+
+2019-04-23  Roman Zhuykov  <zhroma@ispras.ru>
+
 	PR rtl-optimization/84032
 	* gcc.dg/pr84032.c: New test.
 

gcc/testsuite/gcc.dg/pr87979.c

+/* PR rtl-optimization/87979 */
+/* { dg-do compile } */
+/* { dg-options "-Os -fmodulo-sched -fno-tree-loop-im" } */
+/* { dg-additional-options "-march=z196" { target { s390*-*-* } } } */
+
+void foo(void)
+{
+  static int m;
+  for (int i = 0; i < 10; ++i)
+    m++;
+}