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We implement fine derivatives as: broadcast(x, (lane & ~1) + 1) - broadcast(x, lane & ~1) Most of the complexity is to get the right sign. If we can ignore the sign, we can generate the simpler code: broadcast(x, lane ^ 1) - lane This is a particular win on v7+ where the broadcast instruction (CLPER) can do `lane ^ value` for free. However, even on v6 where we lower to an explicit XOR instruction, it's still a win. The limiting case is fwidth. The fragment shader gl_FragColor = fwidth(vec4_varying); has the following results on v6, v7, and v9: G72 (-26% instructions, -43% cycles): 38 inst, 30 tuples, 5 clauses, 1.166667 cycles, 1.166667 arith, 28 quadwords 28 inst, 19 tuples, 4 clauses, 0.666667 cycles, 0.666667 arith, 19 quadwords G76 (-37% instructions, -54% cycles): 38 inst, 30 tuples, 5 clauses, 1.166667 cycles, 1.166667 arith, 28 quadwords 24 inst, 16 tuples, 4 clauses, 0.541667 cycles, 0.541667 arith, 18 quadwords G78 (-40% instructions, -56% cycles): 40 inst, 1.125000 cycles, 0.250000 fma, 0.109375 cvt, 1.125000 sfu, 20 quadwords 24 inst, 0.500000 cycles, 0.250000 fma, 0.015625 cvt, 0.500000 sfu, 12 quadwords shader-db tells a similar story -- most shaders are unaffected, but a shader that uses fwidth has a 20% reduction in cycle count: instructions helped: shaders/tesseract/488.shader_test MESA_SHADER_FRAGMENT: 264 -> 262 (-0.76%) instructions helped: shaders/chromeos/109-1.shader_test MESA_SHADER_FRAGMENT: 36 -> 28 (-22.22%) tuples helped: shaders/chromeos/109-1.shader_test MESA_SHADER_FRAGMENT: 27 -> 22 (-18.52%) tuples HURT: shaders/tesseract/488.shader_test MESA_SHADER_FRAGMENT: 211 -> 212 (0.47%) clauses HURT: shaders/tesseract/488.shader_test MESA_SHADER_FRAGMENT: 32 -> 33 (3.12%) cycles helped: shaders/chromeos/109-1.shader_test MESA_SHADER_FRAGMENT: 1 -> 0.79 (-20.83%) arith helped: shaders/chromeos/109-1.shader_test MESA_SHADER_FRAGMENT: 1 -> 0.79 (-20.83%) quadwords helped: shaders/chromeos/109-1.shader_test MESA_SHADER_FRAGMENT: 31 -> 28 (-9.68%) quadwords HURT: shaders/tesseract/488.shader_test MESA_SHADER_FRAGMENT: 176 -> 178 (1.14%) total instructions in shared programs: 148370 -> 148360 (<.01%) instructions in affected programs: 300 -> 290 (-3.33%) helped: 2 HURT: 0 total tuples in shared programs: 124188 -> 124184 (<.01%) tuples in affected programs: 238 -> 234 (-1.68%) helped: 1 HURT: 1 helped stats (abs) min: 5.0 max: 5.0 x̄: 5.00 x̃: 5 helped stats (rel) min: 18.52% max: 18.52% x̄: 18.52% x̃: 18.52% HURT stats (abs) min: 1.0 max: 1.0 x̄: 1.00 x̃: 1 HURT stats (rel) min: 0.47% max: 0.47% x̄: 0.47% x̃: 0.47% total clauses in shared programs: 25692 -> 25693 (<.01%) clauses in affected programs: 32 -> 33 (3.12%) helped: 0 HURT: 1 total cycles in shared programs: 12132.04 -> 12131.83 (<.01%) cycles in affected programs: 1 -> 0.79 (-20.83%) helped: 1 HURT: 0 total arith in shared programs: 4623.75 -> 4623.54 (<.01%) arith in affected programs: 1 -> 0.79 (-20.83%) helped: 1 HURT: 0 total quadwords in shared programs: 110386 -> 110385 (<.01%) quadwords in affected programs: 207 -> 206 (-0.48%) helped: 1 HURT: 1 helped stats (abs) min: 3.0 max: 3.0 x̄: 3.00 x̃: 3 helped stats (rel) min: 9.68% max: 9.68% x̄: 9.68% x̃: 9.68% HURT stats (abs) min: 2.0 max: 2.0 x̄: 2.00 x̃: 2 HURT stats (rel) min: 1.14% max: 1.14% x̄: 1.14% x̃: 1.14% Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12332> |
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`Mesa <https://mesa3d.org>`_ - The 3D Graphics Library ====================================================== Source ------ This repository lives at https://gitlab.freedesktop.org/mesa/mesa. Other repositories are likely forks, and code found there is not supported. Build & install --------------- You can find more information in our documentation (`docs/install.rst <https://mesa3d.org/install.html>`_), but the recommended way is to use Meson (`docs/meson.rst <https://mesa3d.org/meson.html>`_): .. code-block:: sh $ mkdir build $ cd build $ meson .. $ sudo ninja install Support ------- Many Mesa devs hang on IRC; if you're not sure which channel is appropriate, you should ask your question on `OFTC's #dri-devel <irc://irc.oftc.net/dri-devel>`_, someone will redirect you if necessary. Remember that not everyone is in the same timezone as you, so it might take a while before someone qualified sees your question. To figure out who you're talking to, or which nick to ping for your question, check out `Who's Who on IRC <https://dri.freedesktop.org/wiki/WhosWho/>`_. The next best option is to ask your question in an email to the mailing lists: `mesa-dev\@lists.freedesktop.org <https://lists.freedesktop.org/mailman/listinfo/mesa-dev>`_ Bug reports ----------- If you think something isn't working properly, please file a bug report (`docs/bugs.rst <https://mesa3d.org/bugs.html>`_). Contributing ------------ Contributions are welcome, and step-by-step instructions can be found in our documentation (`docs/submittingpatches.rst <https://mesa3d.org/submittingpatches.html>`_). Note that Mesa uses gitlab for patches submission, review and discussions.