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b5e023777c
One frustrating thing about the CMP and CMPN instructions is that they
always write the flags. Sometimes, however, it is desirable to generate
the comparison result without modifying the flags. This would,
theoretically, reduce false dependencies that restrict the scheduler's
ability to rearrange code, create more opportunities for cmod
propagation, save a kitten from a tree, and make a rainbow.
Consider this sequence:
cmp.ge.f0.0(8) g103<1>F g101<8,8,1>F g39<8,8,1>F
cmp.nz.f0.0(8) null<1>D g81<8,8,1>D 0D
(+f0.0) if(8) JIP: LABEL19 UIP: LABEL19
It would be advantageous to put the first CMP between the second CMP and
the IF, but this cannot be done since the IF depends on the flags generated
by the second CMP.
This pass enables this rescheduling by changing the first CMP to write
to a different flags register.
cmp.ge.f1.0(8) g103<1>F g101<8,8,1>F g39<8,8,1>F
cmp.nz.f0.0(8) null<1>D g81<8,8,1>D 0D
(+f0.0) if(8) JIP: LABEL19 UIP: LABEL19
Sometimes this is also possible by using a different instruction. For
example, consider
cmp.l.f0.0(8) g103<1>D g101<8,8,1>D 0D
This produces 0xffffffff when g101 negative and zero otherwise. This
instruction, which does not modifiy the flag, also produces these results:
asr(8) g103<1>D g101<8,8,1>D 31D
Gfx9 platforms take a hit on instructions due to the instruction added
at the end of short shaders by brw_workaround_source_arf_before_eot.
shader-db:
Lunar Lake, Meteor Lake, DG2, Tiger Lake, and Ice Lake had similar results. (Lunar Lake shown)
total instructions in shared programs: 17089451 -> 17088766 (<.01%)
instructions in affected programs: 766613 -> 765928 (-0.09%)
helped: 653 / HURT: 0
total cycles in shared programs: 888832986 -> 887873068 (-0.11%)
cycles in affected programs: 549441852 -> 548481934 (-0.17%)
helped: 10474 / HURT: 130
LOST: 9
GAINED: 0
Skylake
total instructions in shared programs: 19037976 -> 19049719 (0.06%)
instructions in affected programs: 3979914 -> 3991657 (0.30%)
helped: 503 / HURT: 12303
total cycles in shared programs: 867918242 -> 866930801 (-0.11%)
cycles in affected programs: 512773919 -> 511786478 (-0.19%)
helped: 13858 / HURT: 66
LOST: 32
GAINED: 0
fossil-db:
Lunar Lake
Totals:
Instrs: 925023504 -> 924950382 (-0.01%); split: -0.01%, +0.00%
Cycle count: 106348432916 -> 106116809009 (-0.22%); split: -0.22%, +0.00%
Spill count: 3423988 -> 3423930 (-0.00%); split: -0.00%, +0.00%
Fill count: 4877087 -> 4876960 (-0.00%); split: -0.01%, +0.00%
Max dispatch width: 49087552 -> 49078448 (-0.02%); split: +0.00%, -0.02%
Totals from 1099332 (54.44% of 2019443) affected shaders:
Instrs: 742670473 -> 742597351 (-0.01%); split: -0.01%, +0.00%
Cycle count: 100455549635 -> 100223925728 (-0.23%); split: -0.23%, +0.00%
Spill count: 3384366 -> 3384308 (-0.00%); split: -0.00%, +0.00%
Fill count: 4837434 -> 4837307 (-0.00%); split: -0.01%, +0.00%
Max dispatch width: 26725152 -> 26716048 (-0.03%); split: +0.00%, -0.03%
Meteor Lake and DG2 had similar results. (Meteor Lake shown)
Totals:
Instrs: 997603774 -> 997529238 (-0.01%); split: -0.01%, +0.00%
Cycle count: 93904012762 -> 93646730006 (-0.27%); split: -0.28%, +0.00%
Spill count: 3710155 -> 3710125 (-0.00%); split: -0.00%, +0.00%
Fill count: 5032908 -> 5032819 (-0.00%); split: -0.01%, +0.00%
Max dispatch width: 37929640 -> 37811560 (-0.31%)
Totals from 1334920 (58.52% of 2281134) affected shaders:
Instrs: 817377787 -> 817303251 (-0.01%); split: -0.01%, +0.00%
Cycle count: 88468851658 -> 88211568902 (-0.29%); split: -0.29%, +0.00%
Spill count: 3663353 -> 3663323 (-0.00%); split: -0.00%, +0.00%
Fill count: 4991629 -> 4991540 (-0.00%); split: -0.01%, +0.00%
Max dispatch width: 20245832 -> 20127752 (-0.58%)
Tiger Lake and Ice Lake had similar results. (Tiger Lake shown)
Totals:
Instrs: 1013433769 -> 1013363273 (-0.01%); split: -0.01%, +0.00%
Cycle count: 85766921182 -> 85509316620 (-0.30%); split: -0.31%, +0.00%
Spill count: 3903923 -> 3903944 (+0.00%); split: -0.00%, +0.00%
Fill count: 6801983 -> 6801948 (-0.00%); split: -0.00%, +0.00%
Max dispatch width: 37896320 -> 37805320 (-0.24%); split: +0.00%, -0.24%
Totals from 1333814 (58.54% of 2278396) affected shaders:
Instrs: 830200531 -> 830130035 (-0.01%); split: -0.01%, +0.00%
Cycle count: 80746184101 -> 80488579539 (-0.32%); split: -0.32%, +0.01%
Spill count: 3855771 -> 3855792 (+0.00%); split: -0.00%, +0.00%
Fill count: 6755513 -> 6755478 (-0.00%); split: -0.00%, +0.00%
Max dispatch width: 20301456 -> 20210456 (-0.45%); split: +0.00%, -0.45%
Skylake
Totals:
Instrs: 519389758 -> 519874108 (+0.09%); split: -0.00%, +0.10%
Cycle count: 57932316132 -> 57789433956 (-0.25%); split: -0.25%, +0.00%
Spill count: 636741 -> 636715 (-0.00%); split: -0.01%, +0.00%
Fill count: 860470 -> 860357 (-0.01%); split: -0.02%, +0.00%
Max dispatch width: 32527800 -> 32481792 (-0.14%); split: +0.00%, -0.14%
Totals from 1080380 (62.25% of 1735462) affected shaders:
Instrs: 411976399 -> 412460749 (+0.12%); split: -0.00%, +0.12%
Cycle count: 54291447615 -> 54148565439 (-0.26%); split: -0.27%, +0.00%
Spill count: 602993 -> 602967 (-0.00%); split: -0.01%, +0.00%
Fill count: 734459 -> 734346 (-0.02%); split: -0.02%, +0.00%
Max dispatch width: 18626096 -> 18580088 (-0.25%); split: +0.00%, -0.25%
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38978>
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| .ci-farms-disabled | ||
| .github/workflows | ||
| .gitlab | ||
| .gitlab-ci | ||
| .marge/hooks | ||
| android | ||
| bin | ||
| build-support | ||
| docs | ||
| include | ||
| licenses | ||
| src | ||
| subprojects | ||
| .clang-format | ||
| .clang-format-ignore | ||
| .clang-format-include | ||
| .dir-locals.el | ||
| .editorconfig | ||
| .git-blame-ignore-revs | ||
| .gitattributes | ||
| .gitignore | ||
| .gitlab-ci.yml | ||
| .graphqlrc.yml | ||
| .mailmap | ||
| .mr-label-maker.yml | ||
| .shellcheckrc | ||
| clippy.toml | ||
| CODEOWNERS | ||
| meson.build | ||
| meson.options | ||
| README.rst | ||
| rustfmt.toml | ||
| 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://docs.mesa3d.org/install.html>`_), but the recommended way is to use Meson (`docs/meson.rst <https://docs.mesa3d.org/meson.html>`_): .. code-block:: sh $ meson setup build $ ninja -C build/ $ sudo ninja -C build/ 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://docs.mesa3d.org/bugs.html>`_). Contributing ------------ Contributions are welcome, and step-by-step instructions can be found in our documentation (`docs/submittingpatches.rst <https://docs.mesa3d.org/submittingpatches.html>`_). Note that Mesa uses gitlab for patches submission, review and discussions.