The main motivation for this is that threaded compilation can fall
over if we were to allocate IR inside constant_expression_value()
when calling it on a builtin. This is because builtins are shared
across the whole OpenGL context.
f81ede4699 worked around the problem by cloning the entire
builtin before constant_expression_value() could be called on
it. However cloning the whole function each time we referenced
it lead to a significant reduction in the GLSL IR compiler
performance. This change along with the following patch
helps fix that performance regression.
Other advantages are that we reduce the number of calls to
ralloc_parent(), and for loop unrolling we free constants after
they are used rather than leaving them hanging around.
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Constant propagation on arrays doesn't make a lot of sense. If the
array is only accessed with constant indexes, then opt_array_splitting
would split it up. Otherwise, we have variable indexing. If there's
multiple accesses, then constant propagation would end up replicating
the data.
The lower_const_arrays_to_uniforms pass creates uniforms for each
ir_constant with array type that it encounters. This means that it
creates redundant uniforms for each copy of the constant, which means
uploading too much data. It can even mean exceeding the maximum number
of uniform components, causing link failures.
We could try and teach the pass to de-duplicate the data by hashing
constants, but it makes more sense to avoid duplicating it in the first
place. We should promote constant arrays to uniforms, then propagate
the uniform access.
Fixes the TressFX shaders from Tomb Raider, which exceeded the maximum
number of uniform components by a huge margin and failed to link.
On Broadwell:
total instructions in shared programs: 9067702 -> 9068202 (0.01%)
instructions in affected programs: 10335 -> 10835 (4.84%)
helped: 10 (Hoard, Shadow of Mordor, Amnesia: The Dark Descent)
HURT: 20 (Natural Selection 2)
loops in affected programs: 4 -> 0
The hurt programs appear to no longer have a constarray uniform, as
all constants were successfully propagated. Apparently before this
patch, we successfully unrolled a loop containing array access, but
only after promoting constant arrays to uniforms. With this patch,
we unroll it first, so all array access is direct, and the array
is split up, and individual constants are propagated. This seems
better.
Cc: mesa-stable@lists.freedesktop.org
Reported-by: Karol Herbst <nouveau@karolherbst.de>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
opt_constant_propagation.cpp contains constant folding code which can
actually do constant propagation in some cases. It was happily
propagating constants into the left-hand-side of assignments.
For example,
(assign () (var_ref temp) (constant ...))
would brilliantly be turned into:
(assign () (constant ...) (constant ....))
This is a bigger hammer than necessary - it prevents propagation
into the left-hand-side altogether. We could certainly do better
someday. Notably, the constant propagation pass itself already
takes this approach - it's just the constant propagation pass's
built-in constant folding code (which actually propagates, too)
that was broken.
No change in shader-db, but prevents regressions after future commits.
It seems plausible that this could be hit today, but I haven't seen it
happen.
Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
opt_constant_folding is supposed to fold trees of constants into a
single constant. Surprisingly, it was also propagating constant values
from variables into expression trees - even when the result couldn't be
folded together. This is opt_constant_propagation's job.
The ir_dereference_variable::constant_expression_value() method returns
a clone of var->constant_value. So we would replace the dereference
with a constant, propagating it into the tree.
Skip over ir_dereference_variable to avoid this surprising behavior.
However, add code to explicitly continue doing it in the constant
propagation pass, as it's useful to do so.
shader-db statistics on Broadwell:
total instructions in shared programs: 8905349 -> 8905126 (-0.00%)
instructions in affected programs: 30100 -> 29877 (-0.74%)
helped: 93
HURT: 20
total cycles in shared programs: 71017030 -> 71015944 (-0.00%)
cycles in affected programs: 132456 -> 131370 (-0.82%)
helped: 54
HURT: 45
The only hurt programs are by a single instruction, while the helped
ones are helped by 1-4 instructions.
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
We could probably clean this up more (maybe make it a method), but at
least there's only one copy of this code now, and that's a start.
No change in shader-db.
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
