Re: Invalid right shift in genautomata.c

[Vladimir Makarov <vmakarov at redhat dot com>]

Vladimir Makarov wrote:
> 
> Neil Booth wrote:
> >
> > Vladimir Makarov wrote:-
> >
> > >   Actually this is not a bug, Neil.  The shift is not used when compiler
> > > generates the message (it is even gone after dead code elimination).
> > >
> > >   To speed up genautomata, all bit operations are executed on
> > > HOST_WIDE_INT.  This type is used also to hash the bitstring.  Htab uses
> > > unsigned as a hash key.  So I need to convert HOST_WIDE_INT into
> > > unsigned.  I could make it by `(unsigned) key'.  But that would result
> > > in bad hash keys when the number units > sizeof (unsigned) * CHAR_BIT.
> > > Therefore I hash HOST_WIDE_INT using the shift.  But it is made only
> > > when sizeof (unsigned) < sizeof (HOST_WIDE_INT).
> >
> > Ah, OK.  It's a shame we still get the message.
> >
> 
> Ok, I'll try fix it in another way.

Here is the patch fixing the warning.  I think it generates the better
hash too.  I've committed it into the mainline.

Vlad

2002-05-23  Vladimir Makarov  <vmakarov@redhat.com>

        * genautomata.c (reserv_sets_hash_value): Use shift equal to 3/4
        of size of unsigned.

Index: genautomata.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/genautomata.c,v
retrieving revision 1.13
diff -c -p -r1.13 genautomata.c
*** genautomata.c       21 May 2002 23:27:04 -0000      1.13
--- genautomata.c       23 May 2002 21:53:38 -0000
*************** reserv_sets_hash_value (reservs)
*** 3413,3422 ****
    if (sizeof (set_el_t) <= sizeof (unsigned))
      return hash_value;
    result = 0;
!   for (i = sizeof (set_el_t); i > 0; i -= sizeof (unsigned))
      {
        result += (unsigned) hash_value;
!       hash_value >>= sizeof (unsigned) * CHAR_BIT;
      }
    return result;
  }
--- 3413,3422 ----
    if (sizeof (set_el_t) <= sizeof (unsigned))
      return hash_value;
    result = 0;
!   for (i = sizeof (set_el_t); i > 0; i -= sizeof (unsigned) - 1)
      {
        result += (unsigned) hash_value;
!       hash_value >>= (sizeof (unsigned) - 1) * CHAR_BIT;
      }
    return result;
  }