Previously we would just unroll the loop one extra iteration and let
other optimisation passes clean up the mess. This worked to a degree
but if the loop happened to be nested inside another loop we would
end up with phi chains that would block other passes from being able
to do the cleanup.
With this commit we explicitly clone the variables create by lcsaa
and insert them directly in the last continue branch after we are done
unrolling. With this optimisation passes can recognise both sides
of the if output the same values and can progress further.
Help with the issues described in:
https://gitlab.freedesktop.org/mesa/mesa/-/issues/6051
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17611>
Some drivers don't support these indirects and therefore require
loop unrolling if a shader uses a loop induction variable to
access a sampler array.
Here we add a new nir shader compiler option that drivers can set,
this will be the equivalent of the EmitNoIndirectSampler setting
used in the GLSL IR unrolling pass.
Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16543>
Remove the conditional break statements associated with all
terminators that are associated with a fixed iteration count,
except for the one associated with the limiting terminator.
This logic matches similiar functionality that exists in the
old GLSL IR unrolling code.
This change helps a piglit test pass on the r300 driver once
we switch off the old GLSL IR unrolling code.
Shader-db results IRIS (BDW):
total instructions in shared programs: 17538619 -> 17538595 (<.01%)
instructions in affected programs: 216 -> 192 (-11.11%)
helped: 3
HURT: 0
helped stats (abs) min: 7 max: 10 x̄: 8.00 x̃: 7
helped stats (rel) min: 10.00% max: 12.07% x̄: 11.38% x̃: 12.07%
total cycles in shared programs: 858674910 -> 858672810 (<.01%)
cycles in affected programs: 79540 -> 77440 (-2.64%)
helped: 3
HURT: 0
helped stats (abs) min: 620 max: 800 x̄: 700.00 x̃: 680
helped stats (rel) min: 2.45% max: 2.83% x̄: 2.63% x̃: 2.62%
Reviewed-by: Emma Anholt <emma@anholt.net>
Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16399>
Two carchase compute shaders (shader-db) and two Fallout 4 fragment
shaders (fossil-db) were helped. Based on the NIR of the shaders, all
four had structures like
for (i = 0; i < 1; i++) {
...
for (...) {
...
}
}
All HSW+ platforms had similar results. (Ice Lake shown)
total loops in shared programs: 6033 -> 6031 (-0.03%)
loops in affected programs: 4 -> 2 (-50.00%)
helped: 2
HURT: 0
All Intel platforms had similar results. (Ice Lake shown)
Instructions in all programs: 143692018 -> 143692006 (-0.0%)
SENDs in all programs: 6947154 -> 6947154 (+0.0%)
Loops in all programs: 38285 -> 38283 (-0.0%)
Cycles in all programs: 8434822225 -> 8434476815 (-0.0%)
Spills in all programs: 191665 -> 191665 (+0.0%)
Fills in all programs: 298822 -> 298822 (+0.0%)
In the presense of loop unrolling like this, the change in cycles is not
accurate.
v2: Rearrange the logic in the if-condition to read a little better.
Suggested by Tim.
Closes: #5089
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13323>
This is where it should be rather than having to pass it into the
optimisation pass every time.
It also allows us to call the loop analysis pass without having to
duplicate these options which we will do later in this series.
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12064>
In 87839680c0, a very subtle mistake was made with the CFG walking
recursion. Instead of setting the local has_nested_loop variable when
process child loops, has_nested_loop_out was passed directly into the
process_loop_in_block call. This broke nested loop detection heuristics
and caused loop unrolling to run massively out of control. In
particular, it makes the following CTS test compile virtually forever:
dEQP-VK.spirv_assembly.instruction.graphics.16bit_storage.struct_mixed_types.uniform_buffer_block_geom
Fixes: 87839680c0 "nir: Fix breakage of foreach_list_typed_safe..."
Closes: #2710
Reviewed-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4380>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4380>
The comments say that we should remove continue if it is the last
intruction in a loop however we remove any kind of jump.
Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
MAYBE_UNUSED is going away, so let's replace legitimate uses of it with
UNUSED, which the former aliased to so far anyway.
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
The previous code was completely broken when it came to constructing the
undef values. I'm not sure how it ever worked. For the case of a copy
that reads an undefined value, we can just delete the copy because the
destination is a valid undefined value. This saves us the effort of
trying to construct a value for an arbitrary copy_deref intrinsic.
Fixes: e8a8937a04 "nir: add partial loop unrolling support"
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
This adds support to loop analysis for loops where the induction
variable is compared to the result of min(variable, constant).
For example:
for (int i = 0; i < imin(x, 4); i++)
...
We add a new bool to the loop terminator struct in order to
differentiate terminators with this exit condition.
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
This adds partial loop unrolling support and makes use of a
guessed trip count based on array access.
The code is written so that we could use partial unrolling
more generally, but for now it's only use when we have guessed
the trip count.
We use partial unrolling for this guessed trip count because its
possible any out of bounds array access doesn't otherwise affect
the shader e.g the stores/loads to/from the array are unused. So
we insert a copy of the loop in the innermost continue branch of
the unrolled loop. Later on its possible for nir_opt_dead_cf()
to then remove the loop in some cases.
A Renderdoc capture from the Rise of the Tomb Raider benchmark,
reports the following change in an affected compute shader:
GPU duration: 350 -> 325 microseconds
shader-db results radeonsi VEGA (NIR backend):
SGPRS: 1008 -> 816 (-19.05 %)
VGPRS: 684 -> 432 (-36.84 %)
Spilled SGPRs: 539 -> 0 (-100.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 39708 -> 45812 (15.37 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 105 -> 144 (37.14 %)
Wait states: 0 -> 0 (0.00 %)
shader-db results i965 SKL:
total instructions in shared programs: 13098265 -> 13103359 (0.04%)
instructions in affected programs: 5126 -> 10220 (99.38%)
helped: 0
HURT: 21
total cycles in shared programs: 332039949 -> 331985622 (-0.02%)
cycles in affected programs: 289252 -> 234925 (-18.78%)
helped: 12
HURT: 9
vkpipeline-db results VEGA:
Totals from affected shaders:
SGPRS: 184 -> 184 (0.00 %)
VGPRS: 448 -> 448 (0.00 %)
Spilled SGPRs: 0 -> 0 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 26076 -> 24428 (-6.32 %) bytes
LDS: 6 -> 6 (0.00 %) blocks
Max Waves: 5 -> 5 (0.00 %)
Wait states: 0 -> 0 (0.00 %)
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
The lowering we do for 64-bit instructions can cause a single NIR ALU
instruction to blow up into hundreds or thousands of instructions
potentially with control flow. If loop unrolling isn't aware of this,
it can unroll a loop 20 times which contains a nir_op_fsqrt which we
then lower to a full software implementation based on integer math.
Those 20 invocations suddenly get a lot more expensive than NIR loop
unrolling currently expects. By giving it an approximate estimate
function, we can prevent loop unrolling from going to town when it
shouldn't.
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Replace calls to create hash tables and sets that use
_mesa_hash_pointer/_mesa_key_pointer_equal with the helpers
_mesa_pointer_hash_table_create() and _mesa_pointer_set_create().
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Acked-by: Eric Engestrom <eric@engestrom.ch>
Following commits will introduce additional fields such as
guessed_trip_count. Renaming these will help avoid confusion
as our unrolling feature set grows.
Reviewed-by: Thomas Helland <thomashelland90@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
When we're about to re-arrange a bunch of blocks, it's a good idea to
make sure that we don't have deref uses crossing block boundaries.
Otherwise we may end up with a deref going through a phi and that would
be bad.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Cc: "18.2" <mesa-stable@lists.freedesktop.org>
In GLSL IR we cheat with switch statements and simply convert them
into loops with a single iteration. This allowed us to make use of
the existing jump instruction handling provided by the loop handing
code, it also allows dead code to be cleaned up once we have
wrapped the code in a loop.
However using loops in this way created previously unrollable loops
which limits further optimisations. Here we provide a way to unroll
loops that end in a break and have multiple other exits.
All shader-db changes are from the dolphin uber shaders. There is a
small amount of HURT shaders but in general the improvements far
exceed the HURT.
shader-db results IVB:
total instructions in shared programs: 10018187 -> 10016468 (-0.02%)
instructions in affected programs: 104080 -> 102361 (-1.65%)
helped: 36
HURT: 15
total cycles in shared programs: 220065064 -> 154529655 (-29.78%)
cycles in affected programs: 126063017 -> 60527608 (-51.99%)
helped: 51
HURT: 0
total loops in shared programs: 2515 -> 2308 (-8.23%)
loops in affected programs: 903 -> 696 (-22.92%)
helped: 51
HURT: 0
total spills in shared programs: 4370 -> 4124 (-5.63%)
spills in affected programs: 1397 -> 1151 (-17.61%)
helped: 9
HURT: 12
total fills in shared programs: 4581 -> 4419 (-3.54%)
fills in affected programs: 2201 -> 2039 (-7.36%)
helped: 9
HURT: 15
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
This adds support for unrolling the classic
do {
// ...
} while (false)
that is used to wrap multi-line macros. GLSL IR also wraps switch
statements in a loop like this.
shader-db results IVB:
total loops in shared programs: 2515 -> 2512 (-0.12%)
loops in affected programs: 33 -> 30 (-9.09%)
helped: 3
HURT: 0
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Now that SSA values can be derefs and they have special rules, we have
to be a bit more careful about our LCSSA phis. In particular, we need
to clean up in case LCSSA ended up creating a phi node for a deref.
This avoids validation issues with some CTS tests with the following
patch, but its possible this we could also see the same problem with
the existing unrolling passes.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
The innermost check was added to stop us from unrolling multiple
loops in a single pass, and to stop outer loops from unrolling.
When we successfully unroll a loop we need to run the analysis
pass again before deciding if we want to go ahead an unroll a
second loop.
However the logic was flawed because it never tried to unroll any
nested loops other than the first innermost loop it found.
If this innermost loop is not unrolled we end up skipping all
other nested loops.
This unrolls a loop in a Deus Ex: MD shader on ultra settings and
also unrolls a loop in a shader from the game Prey when running
on DXVK.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
We need to add loop terminators to the list in the order we come
across them otherwise if two or more have the same exit condition
we will select that last one rather than the first one even though
its unreachable.
This fix is for simple unrolls where we only have a single exit
point. When unrolling these type of loops the unreachable
terminators and their unreachable branch are removed prior to
unrolling. Because of the logic change we also switch some
list access in the complex unrolling logic to avoid breakage.
Fixes: 6772a17acc ("nir: Add a loop analysis pass")
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Save the next person from digging through the code to figure out what
the indirect_mask parameter actually does.
Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
When an if nesting inside anouther if is optimised away we can
end up with a loop terminator and following block that looks like
this:
if ssa_596 {
block block_5:
/* preds: block_4 */
vec1 32 ssa_601 = load_const (0xffffffff /* -nan */)
break
/* succs: block_8 */
} else {
block block_6:
/* preds: block_4 */
/* succs: block_7 */
}
block block_7:
/* preds: block_6 */
vec1 32 ssa_602 = phi block_6: ssa_552
vec1 32 ssa_603 = phi block_6: ssa_553
vec1 32 ssa_604 = iadd ssa_551, ssa_66
The problem is the phis. Loop unrolling expects the last block in
the loop to be empty once we splice the instructions in the last
block into the continue branch. The problem is we cant move phis
so here we lower the phis to regs when preparing the loop for
unrolling. As it could be possible to have multiple additional
blocks/ifs following the terminator we just convert all phis at
the top level of the loop body for simplicity.
We also add some comments to loop_prepare_for_unroll() while we
are here.
Fixes: 51daccb289 "nir: add a loop unrolling pass"
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105670
This reverts commit 2d36efdb7f.
This raised limit turns out to harmful for more complex shaders,
it causes excessive spilling in some Bioshock Infinite shaders.
The fps for the ssao demo on radv remains unchanged when reverting
this.
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
With the ssao demo from Vulkan demos:
radv/rx480: 440->440fps
anv/haswell: 24->34 fps
The demo does a 0->32 loop across a ubo with 32 members.
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
The original number was chosen in an attempt to match the limits applied to
GLSL IR.
A look at the git history of the why these limits were chosen for GLSL IR
shows it was more to do with the slow speed of unrolling large loops in
GLSL IR than anything else. The speed of loop unrolling in NIR is not a
problem so we may wish to bump this even higher in future.
No shader-db change, however a furture change will disbale the GLSL IR
optimisation loop in the i965 backend results in 4 loops from The Talos
Principle failing to unroll. Bumping the limit allows them to unroll which
results in the instruction count matching the previous output from when the
GLSL IR opts were still enabled.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
V2:
- tidy ups suggested by Connor.
- tidy up cloning logic and handle copy propagation
based of suggestion by Connor.
- use nir_ssa_def_rewrite_uses to fix up lcssa phis
suggested by Connor.
- add support for complex loop unrolling (two terminators)
- handle case were the ssa defs use outside the loop is already a phi
- support unrolling loops with multiple terminators when trip count
is know for each terminator
V3:
- set correct num_components when creating phi in complex unroll
- rewrite update remap table based on Jasons suggestions.
- remove unrequired extract_loop_body() helper as suggested by Jason.
- simplify the lcssa phi fix up code for simple loops as per Jasons suggestions.
- use mem context to keep track of hash table memory as suggested by Jason.
- move is_{complex,simple}_loop helpers to the unroll code
- require nir_metadata_block_index
- partially rewrote complex unroll to be simpler and easier to follow.
V4:
- use rzalloc() when creating nir_phi_src but not setting pred right away
fixes regression cause by ralloc() no longer zeroing memory.
V5:
- simplify calling of complex_unroll()
- use new loop terminator fields to get the break/continue from blocks
and simplify loop unrolling code
- handle slightly less trivial loop terminators. if branches can
now have instructions but can only contain a single block.
- use nir print type IR snippets in unroll function descriptions
- add better explanation and variable for why we need to clone
additional times when the second terminator it the limiting
terminator.
- partially convert out of ssa before unrolling loops (suggested by Jason)
v6:
- remove unused nir_builder
- use Jasons new from ssa helper
- tidy/fixup cursor use
- unroll terminators that contain control flow correctly
- unroll complex loops with control flow before the terminators
correctly
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
