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d0f75fdeab
We only support the variablePointersStorageBuffer feature of variable pointers,
which basically ensures that pointers may only target one buffer. This means
that a particular pointer may change where it points within a given buffer but
it cannot change its value to point to some other buffer. This is a requirement
from us since we expect buffer indices on buffer loads and stores to be
constant, so we can't have a buffer load come through a pointer that may
be assigned to different buffers, since in that case the buffer index
would need to come from bcsel.
There is, however, a small complication: the spec still allows pointers to
be null, and NIR defines null pointers to use 0xffffffff for both the buffer
index and the offset, which will cause a problem in a scenario like this:
int *b = ...
if (cond) {
b = null;
discard;
}
ubo_load(b);
Here the buffer index for the ubo load may come from a bcsel choosing between
the null pointer (0xffffffff) and the valid address (let's say 0), so we don't
have a constant and we assert fail.
This change detects this scenario and upon finding it will rewrite the buffer
index on the null pointer branch of the bcsel to match that of the valid
branch so that later optimizations passes can remove the bcsel and we end up
with a constant index. This is fine because a null pointer dereference is
undefined behavior and it is not something we should see in valid applications.
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26683>
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| VERSION | ||
`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.