Re: GCC 4.8.0 Status Report (2012-10-29), Stage 1 to end soon

[Kenneth Zadeck <zadeck at naturalbridge dot com>]

Richi,

Let me explain to you what a broken api is.   I have spent the last week 
screwing around with tree-vpn and as of last night i finally got it to 
work.   In tree-vpn, it is clear that double-int is the precise 
definition of a broken api.

The tree-vpn uses an infinite-precision view of arithmetic. However, 
that infinite precision is implemented on top of a finite, CARVED IN 
STONE, base that is and will always be without a patch like this, 128 
bits on an x86-64.    However, as was pointed out by earlier, tree-vrp 
needs 2 * the size of a type + 1 bit to work correctly.    Until 
yesterday i did not fully understand the significance of that 1 bit.  
what this means is that tree-vrp does not work on an x86-64 with _int128 
variables.

There are no checks in tree-vrp to back off when it sees something too 
large, tree-vrp simply gets the wrong answer.   To me, this is a broken 
api and is GCC at its very worst.   The patches that required this 
SHOULD HAVE NEVER GONE INTO GCC.   What you have with my patches is 
someone who is willing to fix a large and complex problem that should 
have been fixed years ago.

I understand that you do not like several aspects of the wide-int api 
and i am willing to make some of those improvements.   However, what i 
am worried about is that you are in some ways really attached to the 
style of programmed where everything is dependent on the size of a 
HWI.    I will continue to push back on those comments but have been 
working the rest in as i have been going along.

To answer your other question, it will be a significant problem if i 
cannot get these patches in.   They are very prone to patch rot and my 
customer wants a product without many patches to the base code.
Also, i fear that your real reason that you want to wait is because you 
really do not like the fact these patches get rid of double in and that 
style of programming and putting off that day serves no one well.

kenny









On 10/31/2012 05:59 AM, Richard Sandiford wrote:
> Richard Biener<richard.guenther@gmail.com>  writes:
> > On Tue, Oct 30, 2012 at 10:05 PM, Kenneth Zadeck
> > <zadeck@naturalbridge.com>  wrote:
> > > jakub,
> > >
> > > i am hoping to get the rest of my wide integer conversion posted by nov 5.
> > > I am under some adverse conditions here: hurricane sandy hit her pretty
> > > badly.  my house is hooked up to a small generator, and no one has any power
> > > for miles around.
> > >
> > > So far richi has promised to review them.   he has sent some comments, but
> > > so far no reviews.    Some time after i get the first round of them posted,
> > > i will do a second round that incorporates everyones comments.
> > >
> > > But i would like a little slack here if possible.    While this work is a
> > > show stopper for my private port, the patches address serious problems for
> > > many of the public ports, especially ones that have very flexible vector
> > > units.    I believe that there are significant set of latent problems
> > > currently with the existing ports that use ti mode that these patches will
> > > fix.
> > >
> > > However, i will do everything in my power to get the first round of the
> > > patches posted by nov 5 deadline.
> > I suppose you are not going to merge your private port for 4.8 and thus
> > the wide-int changes are not a show-stopper for you.
> >
> > That said, I considered the main conversion to be appropriate to be
> > defered for the next stage1.  There is no advantage in disrupting the
> > tree more at this stage.
> I would like the wide_int class and rtl stuff to go in 4.8 though.
> IMO it's a significant improvement in its own right, and Kenny
> submitted it well before the deadline.
>
> Richard