Re: [PATCH] Assert on invalid bitmap iterations

[Richard Biener <rguenther at suse dot de>]

On Fri, 7 Oct 2016, Bernd Schmidt wrote:

> On 10/07/2016 01:07 PM, Richard Biener wrote:
> > On Fri, 7 Oct 2016, Bernd Schmidt wrote:
> > 
> > > Here, if necessary I'd prefer we create a to_clear bitmap and perform an
> > > and_compl operation after the loop.
> > 
> > But that's way more expensive -- you allocate memory and perform an
> > additional loop over the bitmap.
> 
> Yeah. Can we have an additional safer variant of the bitmap iterators maybe?
> We could have an object that gets constructed in the for statement and serves
> as a lock/unlock, where we postpone deletion of elements while locked, and
> flush them on unlock (keeping a flag to say if that's necessary).

I think what might work is implementing that single-depth-queue inside
the iterator, thus have a

  bitmap_clear_bit_at_iterator (bitmap_iterator *, int which = 0);

(which == 1 for when you use EXECUTE_IF_AND_IN_BITMAP and want to
clear a bit in the second bitmap).  The clearing would need to be
done in bmp_iter_set_* in a safe way and the above function would
simply set a flag in the bitmap_iterator.

I think it will be a non-trivial task still.

Any such interface needs to be carried over to other bitmap users
(like the regset case).

Richard.