Re: bitmap fix for current

[Richard Biener <richard dot guenther at gmail dot com>]

On Fri, Nov 14, 2014 at 2:10 AM, Jeff Law <law@redhat.com> wrote:
> On 11/13/14 12:37, Mike Stump wrote:
>>
>> I was doing a merge, and it failed to even compile the runtime
>> libraries due to checking in bitmap.  bitmap goes to remove set bits
>> from the bitmap (the second hunk in a two hunk set), and it fails to
>> update the current pointer.  That memory is freed and then
>> reallocated and a new index is put into it, and then we fail a
>> consistency check later on due to the mismatch between head->index
>> and head->current->indx, because current was not properly maintained.
>> This patch removes the old value of current when we remove what it
>> points to from the bitmap.
>
> Was the calling code iterating through the bit with a form like
>
> EXECUTE_IF_SET_IN_BITMAP (something, 0, i, bi)
>  {
>    bitmap_clear_bit (something, i)
>    [ ... whatever code we want to process i, ... ]
>  }
>
> If so, that's the real issue and we'd really like to identify & fix any code
> that has that kind of structure.
>
> See:
>
> https://gcc.gnu.org/ml/gcc/2009-06/msg00482.html

Indeed.  I can't see how this can have triggered:

  prev = elt->prev;
  if (prev)
    {
      prev->next = NULL;
      if (head->current->indx > prev->indx)
        {
          head->current = prev;
          head->indx = prev->indx;

so if there was elt->prev then if current == elt current->indx should
better be > prev->indx.

Sth else must be wrong (and I doubt it's the above bogus use of
bitmaps).

Richard.

> jeff