[Bug 97083] [IVB,BYT] GPU hang on deqp-gles31.functional.separate.shader.random

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Tue Aug 2 04:42:52 UTC 2016


Kenneth Graunke <kenneth at whitecape.org> changed:

           What    |Removed                     |Added
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #2 from Kenneth Graunke <kenneth at whitecape.org> ---
Curro figured this one out.  The problem was the NoDDClear/NoDDCheck flags on
the PLN instructions.  Normally, we do a (-f0.0) PLN with NoDDClear (for helper
pixels) and a (+f0.0) PLN with NoDDCheck.  This works fine at the top level,
because at least one pixel won't be a helper invocation, so the (-f0.0) PLN
with NoDDClear will actually execute.

But with my (broken) rework, we started emitting PLNs inside control flow.  If
only helper pixels take a certain control flow path, the (-f0.0) PLN with
NoDDClear might not ever execute, leaving the register dependency set, so the
next instruction that tries to touch that register would hang.

So, move to top is a real solution to this problem, not just papering over it.
I've also sent a patch to the mailing list that eliminates the PLN dependency
hints, which will allow us to move PLNs into control flow safely (if we want

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