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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.


Segher


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