Re: Continue stmt branch prediction

[Jan Hubicka <jh@suse.cz>]

> On Wed, Mar 19, 2008 at 11:52 AM, Jan Hubicka <jh@suse.cz> wrote:
> > > Hi,
> >  >
> >  > This patch may have caused
> >  >
> >  > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35636
> >
> >  Yes, the testcase needs adjusting (with PREDICT_EXPR sitting in, there
> >  are no longer perfectly nested loops, but a butterfly CFG).  I will look
> >  into it.
> 
> PREDICT_EXPRs should not cause such effect (I still think they are
> ugly, but you made your point that BB or edge flags won't work).

If you have

  loopback:
    if (test1)
      goto loopback;
    if (test2)
      goto loopback;

You have two perfectly nested loops.  Now

  loopback:
    if (test1)
      {
        somecode;
        goto loopback;
      }
    somecode;
    if (test2)
      goto loopback;

You have two sibbling loops sharing header block.  The testcase is about
how loop infrastructure disambiguate the first case.  With predict_expr
in, we handle prediction more realistically (realizing that the test1 is
probably not closing loop construct since it comes from continue), but
disambiguation does not happen.

I will look into the other two cases tested by testcase but I think they
are same.  I think it is best to convert the inner loop into do-while
so it will still test the same.

Honza
> 
> Richard.