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32b7ba66b0
Knowing following:
- CMP writes to flag register the result of
applying cmod to the `src0 - src1`.
After that it stores the same value to dst.
Other instructions first store their result to
dst, and then store cmod(dst) to the flag
register.
- inst is either CMP or MOV
- inst->dst is null
- inst->src[0] overlaps with scan_inst->dst
- inst->src[1] is zero
- scan_inst wrote to a flag register
There can be three possible paths:
- scan_inst is CMP:
Considering that src0 is either 0x0 (false),
or 0xffffffff (true), and src1 is 0x0:
- If inst's cmod is NZ, we can always remove
scan_inst: NZ is invariant for false and true. This
holds even if src0 is NaN: .nz is the only cmod,
that returns true for NaN.
- .g is invariant if src0 has a UD type
- .l is invariant if src0 has a D type
- scan_inst and inst have the same cmod:
If scan_inst is anything than CMP, it already
wrote the appropriate value to the flag register.
- else:
We can change cmod of scan_inst to that of inst,
and remove inst. It is valid as long as we make
sure that no instruction uses the flag register
between scan_inst and inst.
Nine new cmod_propagation unit tests:
- cmp_cmpnz
- cmp_cmpg
- plnnz_cmpnz
- plnnz_cmpz (*)
- plnnz_sel_cmpz
- cmp_cmpg_D
- cmp_cmpg_UD (*)
- cmp_cmpl_D (*)
- cmp_cmpl_UD
(*) this would fail without changes to brw_fs_cmod_propagation.
This fixes optimisation that used to be illegal (see issue #2154)
= Before =
0: linterp.z.f0.0(8) vgrf0:F, g2:F, attr0<0>:F
1: cmp.nz.f0.0(8) null:F, vgrf0:F, 0f
= After =
0: linterp.z.f0.0(8) vgrf0:F, g2:F, attr0<0>:F
Now it is optimised as such (note change of cmod in line 0):
= Before =
0: linterp.z.f0.0(8) vgrf0:F, g2:F, attr0<0>:F
1: cmp.nz.f0.0(8) null:F, vgrf0:F, 0f
= After =
0: linterp.nz.f0.0(8) vgrf0:F, g2:F, attr0<0>:F
No shaderdb changes
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2154
Signed-off-by: Yevhenii Kolesnikov <yevhenii.kolesnikov@globallogic.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3348>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3348>
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| README.rst | ||
| REVIEWERS | ||
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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.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 gitlab for patches submission, review and discussions.