[Bug tree-optimization/108552] Linux i386 kernel 5.14 memory corruption for pre_compound_page() when gcov is enabled

["jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108552

--- Comment #40 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Jan Hubicka from comment #39)
> I was wonering if we should not provide flag to turn all counts
> volatile.   That way we will still have race conditions on their updates
> (and it would be chepaer than atomic) but we won't run into such wrong
> code issues nor large profile mismatches.

Yes, see above.  Or a mode in which we would just avoid hoisting and sinking
the gcov vars but keep them non-volatile.  Or both.
But I guess it would be nice to get Vlad's patch into trunk and release
branches for now (perhaps with an extra check for startswith "__gcov" on
DECL_NAME, so that we don't do it for the Fortran tokens).

As for the patch, just small nits, I think get_base_address returns always
non-NULL, so it could be
      if (tree expr = MEM_EXPR (res))
        {
          expr = get_base_address (expr);
          if (VAR_P (expr)
              && DECL_NONALIASED (expr)
              && DECL_NAME (expr))
            {
              const char *name = IDENTIFIER_POINTER (DECL_NAME (expr));
              /* Don't reread coverage counters from memory, if single
                 update model is used in threaded code, other threads
                 could change the counters concurrently.  See PR108552.  */
              if (startswith (name, "__gcov"))
                return x;
            }
        }