[Mesa-dev] [Bug 94747] Convert phi nodes to logical operations

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Thu Jul 19 04:00:41 UTC 2018


--- Comment #4 from Timothy Arceri <t_arceri at yahoo.com.au> ---
(In reply to Ian Romanick from comment #3)
> (In reply to Timothy Arceri from comment #2)
> > As (In reply to Jason Ekstrand from comment #1)
> > > The code for this already exists.  It's called nir_opt_peephole_select.  The
> > > only problem is that it only triggers if both sides of the if are empty. 
> > > I've been wanting to add some sort of heuristic to it for some time now. 
> > > The only problem is that it's really back-end specific.
> > 
> > Although i965 doesn't use it I believe this is otherwise fixed by the
> > following commit. We should probably close this bug:
> Thanks for reminding me about these "don't forget" bugs that I filed. :)  I
> clearly forgot about them anyway.
> I have a patch for this that has been on the list for almost 3 weeks.
> https://patchwork.freedesktop.org/patch/233182/
> That will just eliminate the flow control (but it might not since there are
> 2 instructions... I wish I could remember which shader this was).  Even then
> we'll get something like
>     ssa_177 = ssa_153 ? true : abs(ssa_171 - ssa_135) >= ssa_145
> when we really want (ssa_153 || (abs(ssa_171 - ssa_135) >= ssa_145)).  I
> have another patch series in progress that will take care of that.

I suspect we have been working on similar changes. I've just sent a series that
should cover this also.


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