[Mesa-dev] [PATCH 0/9] NIR dead control-flow removal
jason at jlekstrand.net
Sat May 9 18:08:13 PDT 2015
On Fri, May 8, 2015 at 11:15 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> On Fri, May 8, 2015 at 10:03 PM, Connor Abbott <cwabbott0 at gmail.com> wrote:
>> This series implements a bunch of related optimizations that run at
>> once as part of the same pass to eliminate control flow that is
>> useless. This includes both unreachable code and useless loops, i.e.
>> loops that don't compute a result used by the rest of the code. To do
>> this, I needed to change some low-level things that change the behavior
>> of nir_instr_remove() (see patch 2 for details), but I've tested the
>> series on piglit and there are no regressions, and there are no
>> shader-db changes either.
> I tried to get you shader-db results, but it crashes part-way through.
> In particular, it looks like unigen heaven on high will crash it.
> Either that or a couple of synmark shaders but I doubt those are the
That patch seems to fix the crashes. Here's some shader-db results for you:
Shader-db results for Broadwell:
total FS instructions in shared programs: 7182550 -> 7182379 (-0.00%)
FS instructions in affected programs: 3055 -> 2884 (-5.60%)
total NIR instructions in shared programs: 5413353 -> 5443233 (0.55%)
NIR instructions in affected programs: 1453327 -> 1483207 (2.06%)
I have no ide why it *added* NIR instructions but aparently it did.
However, they were things that the back-end was getting rid of anyway.
Any idea why?
> I think it's also worth noting that piglit probably isn't a good test
> of whether or not this works. I doubt there are many piglit shaders
> with dead control-flow and I think GLSL IR can get rid of it in some
> of the common cases. If you wanted to "generate NIR" to test with,
> you could always hack up my SPIRV -> NIR branch to run an optimization
> loop after converting. Then you can see what happens without GLSL IR
> in the way.
>> This is rebased on Jason's series to use lists for use-def sets; it
>> turns out that the changes required were pretty minimal.
>> The series is also available at:
>> git://people.freedesktop.org/~cwabbott0/mesa nir-dead-cf-v3
>> Connor Abbott (9):
>> nir/vars_to_ssa: don't rewrite removed instructions
>> nir: insert ssa_undef instructions when cleanup up defs/uses
>> nir: add an optimization for removing dead control flow
>> nir/validate: validate successors at the end of a loop
>> nir/dead_cf: delete code that's unreachable due to jumps
>> nir: add nir_block_get_following_loop() helper
>> nir: add a helper for iterating over blocks in a cf node
>> nir/dead_cf: add support for removing useless loops
>> i965/fs/nir: enable the dead control flow optimization
>> src/glsl/Makefile.sources | 1 +
>> src/glsl/nir/nir.c | 94 ++++++++--
>> src/glsl/nir/nir.h | 12 ++
>> src/glsl/nir/nir_lower_vars_to_ssa.c | 3 +-
>> src/glsl/nir/nir_opt_dead_cf.c | 332 +++++++++++++++++++++++++++++++++++
>> src/glsl/nir/nir_validate.c | 21 +++
>> src/mesa/drivers/dri/i965/brw_nir.c | 2 +
>> 7 files changed, 452 insertions(+), 13 deletions(-)
>> create mode 100644 src/glsl/nir/nir_opt_dead_cf.c
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>> mesa-dev at lists.freedesktop.org
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