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eb32dad07c
In some shaders, you can end up with a stride in the source of a
SHADER_OPCODE_MULH. One way this can happen is if the MULH is acting on
the top bits of a 64-bit value due to 64-bit integer lowering. In this
case, the compiler will produce something like this:
mul(8) acc0<1>UD g5<8,4,2>UD 0x0004UW { align1 1Q };
mach(8) g6<1>UD g5<8,4,2>UD 0x00000004UD { align1 1Q AccWrEnable };
The new region fixup pass looks at the MUL and sees a strided source and
unstrided destination and determines that the sequence is illegal. It
then attempts to fix the illegal stride by replacing the destination of
the MUL with a temporary and emitting a MOV into the accumulator:
mul(8) g9<2>UD g5<8,4,2>UD 0x0004UW { align1 1Q };
mov(8) acc0<1>UD g9<8,4,2>UD { align1 1Q };
mach(8) g6<1>UD g5<8,4,2>UD 0x00000004UD { align1 1Q AccWrEnable };
Unfortunately, this new sequence isn't correct because MOV accesses the
accumulator with a different precision to MUL and, instead of filling
the bottom 32 bits with the source and zeroing the top 32 bits, it
leaves the top 32 (or maybe 31) bits alone and full of garbage. When
the MACH comes along and tries to complete the multiplication, the
result is correct in the bottom 32 bits (which we throw away) and
garbage in the top 32 bits which are actually returned by MACH.
This commit does two things: First, it adds an assert to ensure that we
don't try to rewrite accumulator destinations of MUL instructions so we
can avoid this precision issue. Second, it modifies
required_dst_byte_stride to require a tightly packed stride so that we
fix up the sources instead and the actual code which gets emitted is
this:
mov(8) g9<1>UD g5<8,4,2>UD { align1 1Q };
mul(8) acc0<1>UD g9<8,8,1>UD 0x0004UW { align1 1Q };
mach(8) g6<1>UD g5<8,4,2>UD 0x00000004UD { align1 1Q AccWrEnable };
Fixes:
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||
|---|---|---|
| bin | ||
| build-support | ||
| docs | ||
| doxygen | ||
| include | ||
| m4 | ||
| scons | ||
| scripts | ||
| src | ||
| .dir-locals.el | ||
| .editorconfig | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .travis.yml | ||
| Android.common.mk | ||
| Android.mk | ||
| appveyor.yml | ||
| autogen.sh | ||
| CleanSpec.mk | ||
| common.py | ||
| configure.ac | ||
| install-gallium-links.mk | ||
| install-lib-links.mk | ||
| Makefile.am | ||
| meson.build | ||
| meson_options.txt | ||
| README.rst | ||
| REVIEWERS | ||
| SConstruct | ||
| 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 status
------------
Travis:
.. image:: https://travis-ci.org/mesa3d/mesa.svg?branch=master
:target: https://travis-ci.org/mesa3d/mesa
Appveyor:
.. image:: https://img.shields.io/appveyor/ci/mesa3d/mesa.svg
:target: https://ci.appveyor.com/project/mesa3d/mesa
Coverity:
.. image:: https://scan.coverity.com/projects/139/badge.svg?flat=1
:target: https://scan.coverity.com/projects/mesa
Build & install
---------------
You can find more information in our documentation (`docs/install.html
<https://mesa3d.org/install.html>`_), but the recommended way is to use
Meson (`docs/meson.html <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.html <https://mesa3d.org/bugs.html>`_).
Contributing
------------
Contributions are welcome, and step-by-step instructions can be found in our
documentation (`docs/submittingpatches.html
<https://mesa3d.org/submittingpatches.html>`_).
Note that Mesa uses email mailing-lists for patches submission, review and
discussions.