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From: Segher Boessenkool <segher@kernel.crashing.org>
To: Jan Hubicka <hubicka@ucw.cz>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: Reorgnanization of profile count maintenance code, part 1
Date: Wed, 07 Jun 2017 18:44:00 -0000	[thread overview]
Message-ID: <20170607184437.GG19687@gate.crashing.org> (raw)
In-Reply-To: <20170606202528.GE32841@kam.mff.cuni.cz>

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

  reply	other threads:[~2017-06-07 18:44 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-06-01 11:36 Jan Hubicka
2017-06-03 18:51 ` Bernhard Reutner-Fischer
2017-06-04 17:21   ` Jan Hubicka
2017-06-05 15:13     ` Joseph Myers
2017-06-05 15:16       ` Jan Hubicka
2017-06-05 15:37       ` Jan Hubicka
2017-06-05 18:38         ` Andrew Pinski
2017-06-06  5:57 ` Jason Merrill
2017-06-06  8:00   ` Jan Hubicka
2017-06-08 16:57     ` Jason Merrill
2017-06-09  7:52       ` Jan Hubicka
2017-06-06 16:31 ` Segher Boessenkool
2017-06-06 20:25   ` Jan Hubicka
2017-06-07 18:44     ` Segher Boessenkool [this message]
2017-06-07 21:11       ` Jan Hubicka
2017-06-07 21:41         ` Segher Boessenkool
2017-06-05 18:52 Dominique d'Humières
2017-06-05 19:14 ` Jan Hubicka

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