[PATCH] Fix PR68117 (hopefully)

[Richard Biener <rguenther at suse dot de>]

In r229405 I removed a call to redirect_edge_var_map_destroy from
delete_tree_ssa which I thought cannot be necessary because that
map isn't GCed and thus stale data in it should have caused quite
some havoc otherwise.  Turns out I was wrong ;)  We were lucky
instead.  The following patch amends the code in remove_edge
which clears data for removed edges (when in gimple!) in that it
now destroys the map at RTL expansion time.

Now there is still a latent issue I believe as somebody is making
use of the map for an edge it didn't previously push to
(pushing always first clears the entry for the edge).

The comment in redirect_edge_var_map_vector is also revealing in
that context:

redirect_edge_var_map_vector (edge e)
{
  /* Hey, what kind of idiot would... you'd be surprised.  */
  if (!edge_var_maps)
    return NULL;

In particular we probably have (very many?) redirect_edge_and_branch
calls not paired with a redirect_edge_var_map_clear call.

In all it looks like a very fragile thing, that SSA edge redirect
hook stuff.

Bootstrap / regtest running on x86_64-unknown-linux-gnu.  Will
apply if that succeeds and hope for the best.

Richard.

2015-11-16  Richard Biener  <rguenther@suse.de>

	PR middle-end/68117
	* cfgexpand.c (pass_expand::execute): Destroy the edge
	redirection var map before setting RTL CFG hooks.

Index: gcc/cfgexpand.c
===================================================================
--- gcc/cfgexpand.c	(revision 230404)
+++ gcc/cfgexpand.c	(working copy)
@@ -6275,6 +6278,9 @@ pass_expand::execute (function *fun)
 
   expand_phi_nodes (&SA);
 
+  /* Release any stale SSA redirection data.  */
+  redirect_edge_var_map_destroy ();
+
   /* Register rtl specific functions for cfg.  */
   rtl_register_cfg_hooks ();