Re: Enable jump threading on maths meeting hot paths

[Jeff Law <law at redhat dot com>]

On 01/26/2017 03:39 AM, Jan Hubicka wrote:
> > On Thu, Jan 26, 2017 at 11:04 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
> > > > > +      if (!contains_hot_bb && speed_p)
> > > > > +       contains_hot_bb |= optimize_bb_for_speed_p (bb);
> > > > > +
> > > >
> > > > Hmm, but you are also counting the destination of the threading here
> > > > which we will
> > > > not duplicate.  Shouldn't this be under the if (j < path_length - 1)
> > > > conditional so we
> > > > look for hot BBs we are actually duplicating only (similar restrictions apply to
> > > > path[0]?).
> > >
> > > Aha, you are right.  I am re-testing updated patch (it also solves the PR)
> >
> > What about j == 0?  We don't duplicate that block either.
>
> We do duplicate it, just eliminate the control flow at the end of bb
> (j==0 is the last basic block of path containing the control flow being threaded)
Right.  And that can (of course) allow other parts of the block to be 
eliminated as dead code -- we've never tried to model any of that.

> I am updating patch actually print into details dump file what paths are considered
> and what insn counts are counted.
Probably wise.

jeff