backward threading heuristics tweek

Jan Hubicka
Mon Aug 15 20:06:00 GMT 2016

> >So the threaded path lives fully inside loop1: 6->8->9->3->4->6 propagating
> >that phi_inserted is 0 after the first iteration of the loop.  This looks like
> >useful loop peeling oppurtunity which does not garble loop structure. So
> >perhaps threading paths starting and passing loop latch (i.e. peeling) is
> >sane? Perhaps all paths fully captured in the loop in question are?
> Peeling like this has long been a point of contention -- it totally
> mucks things up like vectorizing.
> The general issue that the threader knows nothing about the
> characteristics of the loop -- thus peeling is at this point is
> premature and just as likely to hinder performance as improve it.
> I'm never been happy with how this aspect of threading vs loop opts
> turned out and we have open BZs related to this rats nest of issues.

Ok, then we perhaps just want to silence the testcase?

> jeff

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