for gcc/ChangeLog
from  Alexandre Oliva  <aoliva@redhat.com>

	PR debug/46258
	* tree-cfg.c (replace_uses_by): Don't mark BBs as altered on
	debug stmts.

Index: gcc/tree-cfg.c
===================================================================
--- gcc/tree-cfg.c.orig	2010-11-18 10:37:23.716685868 -0200
+++ gcc/tree-cfg.c	2010-11-18 10:37:31.701412567 -0200
@@ -1570,7 +1570,7 @@ replace_uses_by (tree name, tree val)
 	  size_t i;
 
 	  fold_stmt_inplace (stmt);
-	  if (cfgcleanup_altered_bbs)
+	  if (cfgcleanup_altered_bbs && !is_gimple_debug (stmt))
 	    bitmap_set_bit (cfgcleanup_altered_bbs, gimple_bb (stmt)->index);
 
 	  /* FIXME.  This should go in update_stmt.  */