[Bug other/48981] New: bootstrap-lto -O3 produces miscompiled, broken gcc

[d.g.gorbachev at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48981

           Summary: bootstrap-lto -O3 produces miscompiled, broken gcc
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: d.g.gorbachev@gmail.com
                CC: rguenth@gcc.gnu.org
              Host: i686-pc-linux-gnu
            Target: i686-pc-linux-gnu
             Build: i686-pc-linux-gnu


GCC crashes because of violation of strict aliasing rules. The same memory
location is accessed in vec_gc_o_reserve_1 through (struct vec_prefix *)
pointer, then in VEC_tree_base_quick_push through (struct VEC_tree_base *).
Optimization moves the code around in a wrong way.

This patch fixes it:

--- gcc/vec.c
+++ gcc/vec.c
@@ -37,11 +37,11 @@
 struct vec_prefix
 {
   unsigned num;
   unsigned alloc;
   void *vec[1];
-};
+} __attribute__ ((may_alias));


 #ifdef GATHER_STATISTICS

 /* Store information about each particular vector.  */