This has a number of advantages compared to the pass I wrote years ago:
- It can easily perform either Global CSE or block-local CSE, without
needing to roll any dataflow analysis, thanks to SSA def analysis.
This global CSE is able to detect and coalesce memory loads across
blocks. Although it may increase spilling a little, the reduction
in memory loads seems to more than compensate.
- Because SSA guarantees that values are never written more than once,
the new CSE pass can directly reuse an existing value. The old pass
emitted copies at the point where it discovered a value because it
had no idea whether it'd be mutated later. This led it to generate
a ton of trash for copy propagation to clean up later, and also a
nasty fragility where CSE, register coalescing, and copy propagation
could all fight one another by generating and cleaning up copies,
leading to infinite optimization loops unless we were really careful.
Generating less trash improves our CPU efficiency.
- It uses hash tables like nir_instr_set and nir_opt_cse, instead of
linearly walking lists and comparing each element. This is much more
CPU efficient.
- It doesn't use liveness analysis, which is one of the most expensive
analysis passes that we have. Def analysis is cheaper.
In addition to CSE'ing SSA values, we continue to handle flag writes,
as this is a huge source of CSE'able values. These remain block local.
However, we can simply track the last flag write, rather than creating
entire sets of instruction entries like the old pass. Much simpler.
The only real downside to this pass is that, because the backend is
currently only partially SSA, it has limited visibility and isn't able
to see all values. However, the results appear to be good enough that
the new pass can effectively replace the old pass in almost all cases.
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28666>
Like NIR, we print SSA defs as %1, %2, and so on. The number here is
the VGRF number. VGRFs that don't correspond to a SSA def remain
printed as vgrf1, vgrf2, and so on.
This makes it much easier to see what values are SSA and which aren't.
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28666>
Even without a full use list, simply tracking the number of uses will
let us tell "this is the only use of the def" or "we've just replaced
all uses of a def". It's inexpensive to calculate and will be useful.
(rebased by Kenneth Graunke)
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28666>
This introduces a new analysis pass that opportunistically looks for
VGRFs which happen to satisfy the SSA definition properties.
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28666>
Our code to initialize gl_SubgroupInvocation uses multiple instructions
some of which are partial writes. This makes it difficult to analyze
expressions involving gl_SubgroupInvocation, which appear very
frequently in compute shaders.
To make this easier, we add a new virtual opcode which initializes
a full VGRF to the value of gl_SubgroupInvocation. (We also expand
it to UD for SIMD8 so there are not partial write issues.) We then
lower it to the original code later on in compilation, after we've
done the bulk of our optimizations.
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28666>
Always select sample barycentric when persample dispatch is unknown at
compile time and let the payload adjustments feed the expected value
based on dispatch.
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: mesa-stable
Reviewed-by: Ivan Briano <ivan.briano@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27803>
Moves the lowering of VGRFs into FIXED_GRFs from the code generation
to (almost) right after the register allocation.
This will allow: (1) later passes not worry about VGRFs (and what they
mean in a post reg alloc phase) and (2) make easier to add certain
types of validation post reg alloc phase using the backend IR.
Note that a couple of passes still take advantage of seeing "allocated
VGRFs", so perform lowering after they run.
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28604>
We no longer support the old LINE+MAC lowering, and we already lower
this to MAD in NIR on Gfx11+, so the LINTERP virtual opcode always
corresponds the PLN. The only catch is that LINTERP's operands are
reversed from PLN, so we have to switch them.
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28705>
We already have a logical opcode and lower to what is basically a send
instruction. We just weren't using SHADER_OPCODE_SEND, instead having
extra redundant infrastructure for no real gain.
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28705>
We don't necessarily want to split up MOVs for 64-bit addresses into
2x 32-bit MOVs right away, as this makes things like copy propagating
the whole address around harder. We should do this late, once, while
still doing other algebraic optimizations earlier.
fossil-db results for Alchemist show tiny improvements:
Totals:
Instrs: 161310502 -> 161310436 (-0.00%); split: -0.00%, +0.00%
Cycles: 14370605606 -> 14370605159 (-0.00%); split: -0.00%, +0.00%
Totals from 33 (0.01% of 652298) affected shaders:
Instrs: 15053 -> 14987 (-0.44%); split: -0.64%, +0.20%
Cycles: 196947 -> 196500 (-0.23%); split: -0.25%, +0.02%
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28286>
Thanks to Ken for suggesting this URB refactoring change and pointing
out that the LSC can operate on the byte offset granularity.
This should fix the geometry shader test cases where we have more than
32 vertices since previously we were failing to write the correct
control data bits because of incorrect write mask.
Shader-db results for Xe2:
total instructions in shared programs: 153475 -> 153437 (-0.02%)
instructions in affected programs: 1374 -> 1336 (-2.77%)
helped: 11
HURT: 0
helped stats (abs) min: 3 max: 5 x̄: 3.45 x̃: 3
helped stats (rel) min: 1.67% max: 4.92% x̄: 3.23% x̃: 2.70%
95% mean confidence interval for instructions value: -3.92 -2.99
95% mean confidence interval for instructions %-change: -4.10% -2.36%
Instructions are helped.
total loops in shared programs: 140 -> 140 (0.00%)
loops in affected programs: 0 -> 0
helped: 0
HURT: 0
total cycles in shared programs: 16002649 -> 16002329 (<.01%)
cycles in affected programs: 9174 -> 8854 (-3.49%)
helped: 11
HURT: 0
helped stats (abs) min: 22 max: 38 x̄: 29.09 x̃: 32
helped stats (rel) min: 2.62% max: 5.54% x̄: 3.78% x̃: 3.85%
95% mean confidence interval for cycles value: -33.56 -24.62
95% mean confidence interval for cycles %-change: -4.48% -3.08%
Cycles are helped.
total spills in shared programs: 52 -> 52 (0.00%)
spills in affected programs: 0 -> 0
helped: 0
HURT: 0
total fills in shared programs: 94 -> 94 (0.00%)
fills in affected programs: 0 -> 0
helped: 0
HURT: 0
total sends in shared programs: 4240 -> 4240 (0.00%)
sends in affected programs: 0 -> 0
helped: 0
HURT: 0
LOST: 0
GAINED: 0
Rework: (Sagar)
- Adjust offset/indirect offset calculation.
- Add shader-db results
- Always calculate dword index
- Drop changes for indirect writes
Signed-off-by: Rohan Garg <rohan.garg@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27602>
The base class was used when we had vec4, but now we can fold it with
its only subclass. Declare fs_visitor now as a struct to be able to
forward declare for C code without causing errors due to class/struct
being mixed.
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27861>
Remove references to the workaround number from the callsites. Instead
the function has "workaround" as part of the name and the number is
in its definition. Return bool for consistency with other passes.
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26887>
Rename to workaround_memory_fence_before_eot and return the already
present progress value for consistency.
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26887>
Rename fixup to lower and return the already present
progress value for consistency.
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26887>
