re PR rtl-optimization/89753 (ICE in unroll_loop_constant_iterations, at loop-unroll.c:498)

	PR rtl-optimization/89753
	* loop-unroll.c (decide_unroll_constant_iterations): Make guard for
	explicit unrolling factor even more robust.

From-SVN: r269791

gcc/ChangeLog

+2019-03-19  Eric Botcazou  <ebotcazou@adacore.com>
+
+	PR rtl-optimization/89753
+	* loop-unroll.c (decide_unroll_constant_iterations): Make guard for
+	explicit unrolling factor even more robust.
+
 2019-03-19  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/89726

gcc/loop-unroll.c

@@ -400,7 +400,7 @@ decide_unroll_constant_iterations (struct loop *loop, int flags)
     {
       /* However we cannot unroll completely at the RTL level a loop with
 	 constant number of iterations; it should have been peeled instead.  */
-      if ((unsigned) loop->unroll > desc->niter - 1)
+      if (desc->niter == 0 || (unsigned) loop->unroll > desc->niter - 1)
 	{
 	  if (dump_file)
 	    fprintf (dump_file, ";; Loop should have been peeled\n");

gcc/testsuite/ChangeLog

+2019-03-19  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* c-c++-common/unroll-7.c: New test.
+
 2019-03-19  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/89726

gcc/testsuite/c-c++-common/unroll-7.c

+/* { dg-do compile } */
+/* { dg-options "-O -fno-tree-dominator-opts" } */
+
+int nv;
+
+void test (void)
+{
+  #pragma GCC unroll 2
+  for (nv = 0; nv < 1; ++nv)
+    {}
+}