[Bug 91461] gl_TessLevel* writes have no effect for all but the last TCS invocation

[Bug 91461] gl_TessLevel* writes have no effect for all but the last TCS invocation

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https://bugs.freedesktop.org/show_bug.cgi?id=91461

            Bug ID: 91461
           Summary: gl_TessLevel* writes have no effect for all but the
                    last TCS invocation
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/Gallium/radeonsi
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: daniel@constexpr.org
        QA Contact: dri-devel@lists.freedesktop.org

The tessellator ignores all writes to gl_TessLevelInner and gl_TessLevelOuter
by the tessellation control shader except except those done by the last TCS
invocation (gl_InvocationID == patch output vertices - 1).

This results in no primitives being generated unless all entries of
gl_TessLevelOuter are written in that invocation (the 'initial' values seem to
be 0 for gl_TessLevelOuter and 1 for gl_TessLevelInner).

Additionally, barrier() does not synchronize changes to the gl_TessLevel*
between TCS invocations.

Neither of these problems can be reproduced with user-defined 'patch out'
variables - writes by any TCS invocation are visible in the evaluation shader
and barrier() makes them visible to the other TCS invocations.

GPU: Radeon HD 7950 (TAHITI)
Mesa: 10.7.0-devel (git-9deb614)
LLVM: r243203

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[Bug 91461] gl_TessLevel* writes have no effect for all but the last TCS invocation

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https://bugs.freedesktop.org/show_bug.cgi?id=91461

--- Comment #1 from Daniel Scharrer <daniel@constexpr.org> ---
Created attachment 117373
  --> https://bugs.freedesktop.org/attachment.cgi?id=117373&action=edit
Tessellation test case

I have attached a test case for this. It can be compiled and run using:
 $ sh tessellation.cpp

Use the arrow keys to change which TCS invocation writes to gl_TessLevel* (or
use space/enter to toggle between the first and the last).

It should display a yellow grid no matter what TCS invocation is selected but
instead displays a green grid for invocation 3 and nothing for all other
invocations.

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[Bug 91461] gl_TessLevel* writes have no effect for all but the last TCS invocation

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https://bugs.freedesktop.org/show_bug.cgi?id=91461

--- Comment #2 from Daniel Scharrer <daniel@constexpr.org> ---
I can confirm that the patch "radeonsi: before storing tess levels, load them
from LDS instead of temporary" on the mailing list fixes the issue.

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[Bug 91461] gl_TessLevel* writes have no effect for all but the last TCS invocation

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https://bugs.freedesktop.org/show_bug.cgi?id=91461

Marek Olšák <maraeo@gmail.com> changed:

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

--- Comment #3 from Marek Olšák <maraeo@gmail.com> ---
Fixed by 60159bcfc66a067b50da06f5cabfa20d72e89. Closing.

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