[PATCH] Fix PR56035

[Marek Polacek <polacek at redhat dot com>]

We ICEd on attached testcase because we didn't properly detected the
latch edge.  Furthermore, I think the code for re-computing latches
is somehow broken at the moment.  In fix_loop_structure we have
      /* If there was no latch, schedule the loop for removal.  */
      if (!first_latch)
	loop->header = NULL;
      /* If there was a single latch and it belongs to the loop of the
	 header, record it.  */
      else if (latch
	       && latch->src->loop_father == loop)
	loop->latch = latch->src;
      /* Otherwise there are multiple latches which are eventually
         disambiguated below.  */
      else
	loop->latch = NULL;
but I don't think we can use the ->loop_father info, because that is
already cleared by
  FOR_EACH_BB (bb)
    {
      if (changed_bbs)
	bb->aux = (void *) (size_t) loop_depth (bb->loop_father);
      bb->loop_father = current_loops->tree_root;
    }
earlier on.  Thus we ended up in the last else branch and NULLed loop->latch,
which is clearly wrong.
This patch just moves the hunk above so that we
reset ->loop_father-s only after re-computing loop latches.

Regtested/bootstraped on x86_64-linux, ok for trunk?

2013-01-22  Marek Polacek  <polacek@redhat.com>

	* cfgloopmanip.c (fix_loop_structure): Move clearing bb-to-loop
	mapping after re-computing latches.

	* testsuite/gcc.dg/pr56035.c: New test.

--- gcc/cfgloopmanip.c.mp	2013-01-22 14:11:25.241233824 +0100
+++ gcc/cfgloopmanip.c	2013-01-22 14:11:42.364285826 +0100
@@ -1784,16 +1784,6 @@ fix_loop_structure (bitmap changed_bbs)
   /* We need exact and fast dominance info to be available.  */
   gcc_assert (dom_info_state (CDI_DOMINATORS) == DOM_OK);
 
-  /* Remove the old bb -> loop mapping.  Remember the depth of the blocks in
-     the loop hierarchy, so that we can recognize blocks whose loop nesting
-     relationship has changed.  */
-  FOR_EACH_BB (bb)
-    {
-      if (changed_bbs)
-	bb->aux = (void *) (size_t) loop_depth (bb->loop_father);
-      bb->loop_father = current_loops->tree_root;
-    }
-
   if (loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
     {
       release_recorded_exits ();
@@ -1834,6 +1824,16 @@ fix_loop_structure (bitmap changed_bbs)
 	loop->latch = NULL;
     }
 
+  /* Remove the old bb -> loop mapping.  Remember the depth of the blocks in
+     the loop hierarchy, so that we can recognize blocks whose loop nesting
+     relationship has changed.  */
+  FOR_EACH_BB (bb)
+    {
+      if (changed_bbs)
+	bb->aux = (void *) (size_t) loop_depth (bb->loop_father);
+      bb->loop_father = current_loops->tree_root;
+    }
+
   /* Remove the dead loops from structures.  We start from the innermost
      loops, so that when we remove the loops, we know that the loops inside
      are preserved, and do not waste time relinking loops that will be
--- gcc/testsuite/gcc.dg/pr56035.c.mp	2013-01-22 14:27:21.104614758 +0100
+++ gcc/testsuite/gcc.dg/pr56035.c	2013-01-22 14:31:01.642266091 +0100
@@ -0,0 +1,35 @@
+/* PR tree-optimization/56035 */
+/* { dg-do compile } */
+/* { dg-options "-O1 -ftree-vectorize -fcse-follow-jumps -fstrict-overflow" } */
+
+short a, c, *p;
+
+void
+f (void)
+{
+  int b;
+
+  if (c)
+  lbl1:
+    for (a = 0; a < 1; a++)
+      {
+	for (c = 0; c < 1; c++)
+	  {
+	    goto lbl1;
+	    while (*p++)
+	    lbl2:
+	      ;
+	  }
+      }
+
+  for (;; b++)
+    {
+      if (c)
+	goto lbl2;
+    lbl3:
+      for (c = 0; c < 9; c++)
+	for (c = -17; c < 2; c++)
+	  if (*p)
+	    goto lbl3;
+    }
+}

	Marek