This function is used in two different scenarios that for 32-bit
instructions are the same, but for 16-bit instructions are not.
One scenario is that in which we are working at a SIMD8 register
level and we need to know if a register is fully defined or written.
This is useful, for example, in the context of liveness analysis or
register allocation, where we work with units of registers.
The other scenario is that in which we want to know if an instruction
is writing a full scalar component or just some subset of it. This is
useful, for example, in the context of some optimization passes
like copy propagation.
For 32-bit instructions (or larger), a SIMD8 dispatch will always write
at least a full SIMD8 register (32B) if the write is not partial. The
function is_partial_write() checks this to determine if we have a partial
write. However, when we deal with 16-bit instructions, that logic disables
some optimizations that should be safe. For example, a SIMD8 16-bit MOV will
only update half of a SIMD register, but it is still a complete write of the
variable for a SIMD8 dispatch, so we should not prevent copy propagation in
this scenario because we don't write all 32 bytes in the SIMD register
or because the write starts at offset 16B (wehere we pack components Y or
W of 16-bit vectors).
This is a problem for SIMD8 executions (VS, TCS, TES, GS) of 16-bit
instructions, which lose a number of optimizations because of this, most
important of which is copy-propagation.
This patch splits is_partial_write() into is_partial_reg_write(), which
represents the current is_partial_write(), useful for things like
liveness analysis, and is_partial_var_write(), which considers
the dispatch size to check if we are writing a full variable (rather
than a full register) to decide if the write is partial or not, which
is what we really want in many optimization passes.
Then the patch goes on and rewrites all uses of is_partial_write() to use
one or the other version. Specifically, we use is_partial_var_write()
in the following places: copy propagation, cmod propagation, common
subexpression elimination, saturate propagation and sel peephole.
Notice that the semantics of is_partial_var_write() exactly match the
current implementation of is_partial_write() for anything that is
32-bit or larger, so no changes are expected for 32-bit instructions.
Tested against ~5000 tests involving 16-bit instructions in CTS produced
the following changes in instruction counts:
Patched | Master | % |
================================================
SIMD8 | 621,900 | 706,721 | -12.00% |
================================================
SIMD16 | 93,252 | 93,252 | 0.00% |
================================================
As expected, the change only affects SIMD8 dispatches.
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
To allow cmod propagation from a MOV in a sequence like:
and(16) g31<1>UD g20<8,8,1>UD g22<8,8,1>UD
mov.nz.f0(16) null<1>F g31<8,8,1>D
A similar change to the vec4 backend had no effect.
Somewhere between c1ec582059 and 40fc4b5acd (1,094 commits) the
effectiveness of this patch diminished, and as of commit d7e0d47b9d
(nir: Add a bunch of b2[if] optimizations) this optimization no longer
has any effect on any platform.
A later patch "intel/fs: Use De Morgan's laws to avoid logical-not of a
logic result on Gen8+," generates some instruction sequences that
require this change in order for cmod propagation to make progress.
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
v2: Fix silly bug in logic. s/||/&&/
All but one of the affected shaders is in an Unreal4 demo. The other is
in Tomb Raider. All of the cases that Ian investigated appear to be
sequences like the following
if (int(uint(some_float)) < 0) /* other relations too */
...
At least in Tomb Raider, it's not obvious that this sequence came from
the original shader.
In some of the Unreal demos, the shader contains code like
if (int(uint(textureLod(...))) > 0)
...
which explicitly generates the offending sequence.
All Gen6+ platforms had similar results (Skylake shown):
total instructions in shared programs: 15437170 -> 15437187 (<.01%)
instructions in affected programs: 4492 -> 4509 (0.38%)
helped: 0
HURT: 17
HURT stats (abs) min: 1 max: 1 x̄: 1.00 x̃: 1
HURT stats (rel) min: 0.05% max: 0.73% x̄: 0.66% x̃: 0.73%
95% mean confidence interval for instructions value: 1.00 1.00
95% mean confidence interval for instructions %-change: 0.57% 0.75%
Instructions are HURT.
total cycles in shared programs: 383007996 -> 383007992 (<.01%)
cycles in affected programs: 20542 -> 20538 (-0.02%)
helped: 6
HURT: 7
helped stats (abs) min: 2 max: 6 x̄: 5.33 x̃: 6
helped stats (rel) min: 0.11% max: 0.36% x̄: 0.32% x̃: 0.36%
HURT stats (abs) min: 4 max: 4 x̄: 4.00 x̃: 4
HURT stats (rel) min: 0.27% max: 0.27% x̄: 0.27% x̃: 0.27%
95% mean confidence interval for cycles value: -3.30 2.69
95% mean confidence interval for cycles %-change: -0.19% 0.19%
Inconclusive result (value mean confidence interval includes 0).
No changes on Iron Lake or GM45.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109404
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Tested-by: nagrigoriadis@gmail.com
Tested-by: Danylo Piliaiev <danylo.piliaiev@gmail.com>
No shader-db changes on any Intel platform... which probably explains
why no bugs have been bisected to this problem since it landed in Mesa
18.1. :( The commit mentioned below is in 18.2, so 18.1 would need a
slightly different fix (due to code refactoring).
Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Fixes: 77f269bb56 "i965/fs: Refactor propagation of conditional modifiers from compares to adds"
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com> (reviewed the original patch)
Cc: Matt Turner <mattst88@gmail.com> (reviewed the original patch)
No shader-db changes. This source must have been written by a previous
instruction, so it cannot be a uniform or a shader input. However, this
change allows the next commit to help about 900 more shaders.
Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Mostly a dummy git mv with a couple of noticable parts:
- With the earlier header cleanups, nothing in src/intel depends
files from src/mesa/drivers/dri/i965/
- Both Autoconf and Android builds are addressed. Thanks to Mauro and
Tapani for the fixups in the latter
- brw_util.[ch] is not really compiler specific, so it's moved to i965.
v2:
- move brw_eu_defines.h instead of brw_defines.h
- remove no-longer applicable includes
- add missing vulkan/ prefix in the Android build (thanks Tapani)
v3:
- don't list brw_defines.h in src/intel/Makefile.sources (Jason)
- rebase on top of the oa patches
[Emil Velikov: commit message, various small fixes througout]
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
