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From the Kaby Lake PRM Vol. 7 "Assigning Conditional Flags":
* Note that the [post condition signal] bits generated at
the output of a compute are before the .sat.
Paragraph about post_zero does not mention saturation, but
testing it on actual GPUs shows that conditional modifiers
are applied after saturation.
* post_zero bit: This bit reflects whether the final
result is zero after all the clamping, normalizing,
or format conversion logic.
For signed types we don't care about saturation: it won't
change the result of conditional modifier.
For floating and unsigned types there two special cases,
when we can remove inst even if scan_inst is saturated: G
and LE. Since conditional modifiers are just comparations
against zero, saturating positive values to the upper
limit never changes the result of comparation.
For negative values:
(sat(x) > 0) == (x > 0) --- false
(sat(x) <= 0) == (x <= 0) --- true
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2610
Signed-off-by: Yevhenii Kolesnikov <yevhenii.kolesnikov@globallogic.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4167>
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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 `Freenode's #dri-devel <irc://chat.freenode.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.