[Bug 92033] [SNB, regression, dEQP, bisected] functional.shaders.random tests regressed

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Sun Sep 20 08:56:46 PDT 2015


--- Comment #4 from Antia Puentes <apuentes at igalia.com> ---
(In reply to Jason Ekstrand from comment #1)
> I'm pretty sure I know exactly what's going on here.  NIR has swizzles for
> all ALU instructions, but i965 can't swizzle some (maybe all?) math
> instructions.  The easiest fix would be to simply make emit_math emit an
> additional MOV if there is a non-trivial swizzle.  The reason this showed up
> as a regression is probably that we're doing better coalescing now than we
> were before.  The bug was present, we just weren't tickling it.  I'm
> re-assigning this to one of the Igalia people.

We are currently emitting an additional MOV in emit_math if there is a
non-trivial swizzle (gen6). However, as you said, register coalescing is
certainly involved because it removes that MOV instruction. I wrote patch to
prevent register coalescing when non-trivial swizzling is required in gen 6
math instructions. You can find the patch here:

It fixes the 3 listed dEQP regressions and I have checked that it does not
introduce new Piglit or dEQP GLES 3.0 regressions in SandyBridge. I have not
had time to run dEQP GLES 2.0 tests though, I can do it on Monday.

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