[PATCH] Fix PR78482

[Richard Biener]

This fixes a latent issue in cfg-cleanup (mergephi) where merging
a forwarder with a loop header can expose a new latch which invalidates
any cached number of iteration information.  I believe this issue
is restricted to _with_phi as otherwise constraints on the PHI node
make it impossible to trigger.

Bootstrap and regtest running on x86_64-unknown-linux-gnu.

Richard.

2016-11-23  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/78482
        * tree-cfgcleanup.c: Include tree-ssa-loop-niter.h.
        (remove_forwarder_block_with_phi): When merging with a loop
        header creates a new latch reset number of iteration information
        of the loop.

        * gcc.dg/torture/pr78482.c: New testcase.

diff --git a/gcc/testsuite/gcc.dg/torture/pr78482.c 
b/gcc/testsuite/gcc.dg/torture/pr78482.c
new file mode 100644
index 0000000..ef68bdf
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr78482.c
@@ -0,0 +1,37 @@
+/* { dg-do run } */
+
+int printf(const char*, ...);
+short a = 65531;
+int b = 3, f;
+char c, d;
+static void fn1(int p1)
+{
+  short e;
+  b = f;
+  if (f > p1 && p1)
+    L:
+       for (e = 0; 0;)
+         ;
+  else if (d) b = 0 >= b;
+  for (; e <= 3; e++)
+    {
+      if (b)
+       continue;
+      b = 3;
+      goto L;
+    }
+}
+
+int main()
+{
+  for (; c >= 0; c--)
+    {
+      if (!b)
+       {
+         printf("%d\n", 2);
+         continue;
+       }
+      fn1(a);
+    }
+  return 0;
+}
diff --git a/gcc/tree-cfgcleanup.c b/gcc/tree-cfgcleanup.c
index fe22ed3..1f17d9a 100644
--- a/gcc/tree-cfgcleanup.c
+++ b/gcc/tree-cfgcleanup.c
@@ -42,6 +42,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-scalar-evolution.h"
 #include "gimple-match.h"
 #include "gimple-fold.h"
+#include "tree-ssa-loop-niter.h"
 
 
 /* The set of blocks in that at least one of the following changes happened:
@@ -885,6 +886,19 @@ remove_forwarder_block_with_phi (basic_block bb)
             DEST.  */
          e = single_succ_edge (split_edge (e));
        }
+      else
+       {
+         /* If we merge the forwarder into a loop header verify if we
+            are creating another loop latch edge.  If so, reset
+            number of iteration information of the loop.  */
+         if (dest->loop_father->header == dest
+             && dominated_by_p (CDI_DOMINATORS, e->src, dest))
+           {
+             dest->loop_father->any_upper_bound = false;
+             dest->loop_father->any_likely_upper_bound = false;
+             free_numbers_of_iterations_estimates_loop (dest->loop_father);
+           }
+       }
 
       s = redirect_edge_and_branch (e, dest);