[PATCH] Fix PR85615

[Richard Biener]

We're threading into a loop across an inner exit.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.

Richard.

2018-05-03  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/85615
        * tree-ssa-threadupdate.c (thread_block_1): Only allow exits
        to loops not nested in BBs loop father to avoid creating multi-entry
        loops.

        * gcc.dg/torture/pr85615.c: New testcase.

Index: gcc/tree-ssa-threadupdate.c
===================================================================
--- gcc/tree-ssa-threadupdate.c (revision 259879)
+++ gcc/tree-ssa-threadupdate.c (working copy)
@@ -1309,7 +1309,9 @@ thread_block_1 (basic_block bb, bool nol
             and thread this elsewhere, so just cancel the jump threading
             request by clearing the AUX field now.  */
          if (bb->loop_father != e2->src->loop_father
-             && !loop_exit_edge_p (e2->src->loop_father, e2))
+             && (!loop_exit_edge_p (e2->src->loop_father, e2)
+                 || flow_loop_nested_p (bb->loop_father,
+                                        e2->dest->loop_father)))
            {
              /* Since this case is not handled by our special code
                 to thread through a loop header, we must explicitly
Index: gcc/testsuite/gcc.dg/torture/pr85615.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr85615.c      (nonexistent)
+++ gcc/testsuite/gcc.dg/torture/pr85615.c      (working copy)
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+
+long a, d;
+int b, c;
+void fn1()
+{
+  int e = -1L, f = 2, g = 8;
+  for (;;)
+    {
+      for (; b; g++)
+       ;
+      int i;
+      for (; c;)
+       {
+         i = 5;
+         for (; e >= 1; i--)
+           ;
+       }
+      d = f ?: a;
+      if (d)
+       {
+         e = 0;
+         for (; i;)
+           for (; g < 3; f++)
+             ;
+       }
+    }
+}