Free dominance info at the beginning of pass_jump_after_combine

try_forward_edges does not update dominance info, and merge_blocks
relies on it being up-to-date.  In PR92430 stale dominance info makes
merge_blocks produce a loop in the dominator tree, which in turn makes
delete_basic_block loop forever.

Fix by freeing dominance info at the beginning of cleanup_cfg.

gcc/ChangeLog:

2019-11-12  Ilya Leoshkevich  <iii@linux.ibm.com>

	PR rtl-optimization/92430
	* cfgcleanup.c (pass_jump_after_combine::execute): Free
	dominance info at the beginning.

gcc/testsuite/ChangeLog:

2019-11-12  Ilya Leoshkevich  <iii@linux.ibm.com>

	PR rtl-optimization/92430
	* gcc.dg/pr92430.c: New test (from Arseny Solokha).

From-SVN: r278095

gcc/ChangeLog

+2019-11-12  Ilya Leoshkevich  <iii@linux.ibm.com>
+
+	PR rtl-optimization/92430
+	* cfgcleanup.c (pass_jump_after_combine::execute): Free
+	dominance info at the beginning.
+
 2019-11-12  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/92460

gcc/cfgcleanup.c

@@ -3311,6 +3311,8 @@ public:
 unsigned int
 pass_jump_after_combine::execute (function *)
 {
+  /* Jump threading does not keep dominators up-to-date.  */
+  free_dominance_info (CDI_DOMINATORS);
   cleanup_cfg (flag_thread_jumps ? CLEANUP_THREADING : 0);
   return 0;
 }

gcc/testsuite/ChangeLog

+2019-11-12  Ilya Leoshkevich  <iii@linux.ibm.com>
+
+	PR rtl-optimization/92430
+	* gcc.dg/pr92430.c: New test (from Arseny Solokha).
+
 2019-11-12  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/92461

gcc/testsuite/gcc.dg/pr92430.c

+// PR rtl-optimization/92430
+// { dg-do compile }
+// { dg-options "-Os -fno-if-conversion -fno-tree-dce -fno-tree-loop-optimize -fno-tree-vrp" }
+
+int eb, ko;
+
+void
+e9 (int pe, int lx)
+{
+  int ir;
+
+  for (ir = 0; ir < 1; ++ir)
+    {
+      for (ko = 0; ko < 1; ++ko)
+        {
+          for (eb = 0; eb < 1; ++eb)
+            ko += pe;
+
+          for (ko = 0; ko < 1; ++ko)
+            ;
+        }
+
+      pe = ir = lx;
+    }
+}