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Re: Reorgnanization of profile count maintenance code, part 1
> On Tue, Jun 06, 2017 at 10:25:29PM +0200, Jan Hubicka wrote:
> > > On Thu, Jun 01, 2017 at 01:35:56PM +0200, Jan Hubicka wrote:
> > > > + /* FIXME: shrink wrapping violates this sanity check. */
> > > > + gcc_checking_assert ((num >= 0
> > > > + && (num <= REG_BR_PROB_BASE
> > > > + || den <= REG_BR_PROB_BASE)
> > > > + && den > 0) || 1);
> > > > + ret.m_val = RDIV (m_val * num, den);
> > > > + return ret;
> > >
> > > Sorry if I missed this... But where/how does it violate this?
> >
> > It sums multiple probabilties together and overflows the limit.
>
> Ah. Yes, the scale it uses (num/den in shrink-wrap.c:924) isn't a
> probability: it's a just a fraction, but also <= 1. The calculation cannot
> overflow, not while there are at most 4G incoming edges to a BB.
Problem is that when you multiply count by it, the buffer is considerably
smaller, because count itself can be quite large number...
It is not too bad - I added the sanity check mostly to see if there
is a safe cap on num so I do not need to worry about overflows at all.
Honza
>
>
> Segher