Nouveau - Jul 2012 - [Bug 51962] New: Raz's eyes flicker in Psychonauts on nv50

https://bugs.freedesktop.org/show_bug.cgi?id=51962

             Bug #: 51962
           Summary: Raz's eyes flicker in Psychonauts on nv50
    Classification: Unclassified
           Product: Mesa
           Version: git
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/nouveau
        AssignedTo: nouveau at lists.freedesktop.org
        ReportedBy: bryancain3+fdo at gmail.com


This bug affects the Gallium nv50 driver, but for some reason there's no
"Drivers/Gallium/nv50" component listed in Bugzilla.

In Psychonauts on the nv50 driver, Raz's eyes (supposed to be red) flicker
between red and white.  This behavior first appears in git with the commit that
switches the nv50 driver to use the new nv50/nvc0 shader compiler.  The eye
flickering is caused by one vertex shader being miscompiled.  In the attached
apitrace, the GL program number used to draw Raz's eyes (which has the
vertex
shader in question) is 541.  If vertex shader optimizations are disabled in
nv50_program.c, Raz's eyes stay white all the time instead of flickering. 
If
shader program 541 is disabled entirely, Raz's eyes render correctly.

It is evident that there is a problem with the vertex shader by looking at its
nv50 IR source after it is converted to SSA - there are several "nop"
instructions at the beginning of the program to compensate for undefined source
registers emitted by the TGSI to nv50 IR conversion.

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--- Comment #1 from Bryan Cain <bryancain3+fdo at gmail.com> 2012-07-10
20:33:39 PDT ---
The apitrace is too large for fd.o to accept it as an attachment; it can be
downloaded from the following link:
http://assortedtools.pbworks.com/f/Psychonauts.3.trace.xz

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--- Comment #2 from Bryan Cain <bryancain3+fdo at gmail.com> 2012-07-18
04:59:50 PDT ---
I did some more investigation into this bug and produced a fix:
http://lists.freedesktop.org/archives/mesa-dev/2012-July/024196.html

The problem was that in lowering the POW instruction, the lg2/mul/preex2
instructions that go before the ex2 instruction were not being emitted
properly, which as a side effect made each of the four ex2 instructions in the
shader read from an undefined source register.  This in turn made the SSA
generator produce 4 of the 5 nop instructions mentioned in the original
description.

The first of the five nop instructions is not the nv50 shader compiler's
fault,
but is the result of the GLSL compiler's pass to lower output registers
emitting reads to undefined components of gl_TexCoord.  It's an unrelated
issue
that happened to show up in the same shader, and doesn't affect the shader
at
the driver level post-optimization.  I will file a separate bug report about it
against glsl-compiler.

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--- Comment #3 from Fabio Pedretti <fabio.ped at libero.it> 2012-09-10
12:06:09 UTC ---
It should be fixed with 248e6f03313afdfd3c23be269b0da7a1aa31cff2 .

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Emil Velikov <emil.l.velikov at gmail.com> changed:

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

--- Comment #4 from Emil Velikov <emil.l.velikov at gmail.com> ---
Marking as Resolved/Fixed

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