[Mesa-dev] [PATCH] glsl: Lower constant arrays to uniform arrays.
Marek Olšák
maraeo at gmail.com
Thu Oct 30 05:43:42 PDT 2014
Hi Tom,
Could you please elaborate on how we should change the TGSI->LLVM translation?
Marek
On Fri, Oct 17, 2014 at 4:49 PM, Tom Stellard <tom at stellard.net> wrote:
> On Wed, Oct 15, 2014 at 05:32:11PM -0700, Kenneth Graunke wrote:
>> Consider GLSL code such as:
>>
>> const ivec2 offsets[] =
>> ivec2[](ivec2(-1, -1), ivec2(-1, 0), ivec2(-1, 1),
>> ivec2(0, -1), ivec2(0, 0), ivec2(0, 1),
>> ivec2(1, -1), ivec2(1, 0), ivec2(1, 1));
>>
>> ivec2 offset = offsets[<non-constant expression>];
>>
>
> I don't think we necessarily want this pass for radeonsi. We produce
> efficient code for these kinds of arrays in OpenCL, I think we just need to
> change how we translate TGSI to LLVM.
>
> -Tom
>
>> Both i965 and nv50 currently handle this very poorly. On i965, this
>> becomes a pile of MOVs to load the immediate constants into registers,
>> a pile of scratch writes to move the whole array to memory, and one
>> scratch read to actually access the value - effectively the same as if
>> it were a non-constant array.
>>
>> We'd much rather upload large blocks of constant data as uniform data,
>> so drivers can simply upload the data via constbufs, and not have to
>> populate it via shader instructions.
>>
>> This is currently non-optional because both i965 and nouveau benefit
>> from it - we can revisit that if another driver actually benefits.
>>
>> Improves performance in a terrain rendering microbenchmark by about 2x,
>> and cuts the number of instructions in about half. Helps a lot of
>> "Natural Selection 2" shaders, as well as one "HOARD" shader.
>>
>> total instructions in shared programs: 5473459 -> 5471765 (-0.03%)
>> instructions in affected programs: 5880 -> 4186 (-28.81%)
>>
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=77957
>> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
>>
>> Reviewers: suggestions for better max_array_access handling are welcome.
>> Reviewers: This changes the const-ness of the expression. Is that a problem?
>> ---
>> src/glsl/Makefile.sources | 1 +
>> src/glsl/ir_optimization.h | 1 +
>> src/glsl/linker.cpp | 2 +
>> src/glsl/lower_const_arrays_to_uniforms.cpp | 101 ++++++++++++++++++++++++++++
>> 4 files changed, 105 insertions(+)
>> create mode 100644 src/glsl/lower_const_arrays_to_uniforms.cpp
>>
>> I've had this patch sitting around since April, and been pondering whether
>> we should improve it somehow. But...it helps certain shaders a ton, and I
>> haven't seen anything hurt by it. So I'm wondering if we should just land
>> it; we can always improve things later.
>>
>> diff --git a/src/glsl/Makefile.sources b/src/glsl/Makefile.sources
>> index 0c55327..6aed52d 100644
>> --- a/src/glsl/Makefile.sources
>> +++ b/src/glsl/Makefile.sources
>> @@ -58,6 +58,7 @@ LIBGLSL_FILES = \
>> $(GLSL_SRCDIR)/loop_analysis.cpp \
>> $(GLSL_SRCDIR)/loop_controls.cpp \
>> $(GLSL_SRCDIR)/loop_unroll.cpp \
>> + $(GLSL_SRCDIR)/lower_const_arrays_to_uniforms.cpp \
>> $(GLSL_SRCDIR)/lower_clip_distance.cpp \
>> $(GLSL_SRCDIR)/lower_discard.cpp \
>> $(GLSL_SRCDIR)/lower_discard_flow.cpp \
>> diff --git a/src/glsl/ir_optimization.h b/src/glsl/ir_optimization.h
>> index e25857a..34e0b4b 100644
>> --- a/src/glsl/ir_optimization.h
>> +++ b/src/glsl/ir_optimization.h
>> @@ -114,6 +114,7 @@ bool lower_noise(exec_list *instructions);
>> bool lower_variable_index_to_cond_assign(exec_list *instructions,
>> bool lower_input, bool lower_output, bool lower_temp, bool lower_uniform);
>> bool lower_quadop_vector(exec_list *instructions, bool dont_lower_swz);
>> +bool lower_const_arrays_to_uniforms(exec_list *instructions);
>> bool lower_clip_distance(gl_shader *shader);
>> void lower_output_reads(exec_list *instructions);
>> bool lower_packing_builtins(exec_list *instructions, int op_mask);
>> diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
>> index 47a722d..2a69b78 100644
>> --- a/src/glsl/linker.cpp
>> +++ b/src/glsl/linker.cpp
>> @@ -2692,6 +2692,8 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
>> &ctx->Const.ShaderCompilerOptions[i],
>> ctx->Const.NativeIntegers))
>> ;
>> +
>> + lower_const_arrays_to_uniforms(prog->_LinkedShaders[i]->ir);
>> }
>>
>> /* Check and validate stream emissions in geometry shaders */
>> diff --git a/src/glsl/lower_const_arrays_to_uniforms.cpp b/src/glsl/lower_const_arrays_to_uniforms.cpp
>> new file mode 100644
>> index 0000000..2085086
>> --- /dev/null
>> +++ b/src/glsl/lower_const_arrays_to_uniforms.cpp
>> @@ -0,0 +1,101 @@
>> +/*
>> + * Copyright © 2014 Intel Corporation
>> + *
>> + * Permission is hereby granted, free of charge, to any person obtaining a
>> + * copy of this software and associated documentation files (the "Software"),
>> + * to deal in the Software without restriction, including without limitation
>> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
>> + * and/or sell copies of the Software, and to permit persons to whom the
>> + * Software is furnished to do so, subject to the following conditions:
>> + *
>> + * The above copyright notice and this permission notice (including the next
>> + * paragraph) shall be included in all copies or substantial portions of the
>> + * Software.
>> + *
>> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
>> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
>> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
>> + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
>> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
>> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
>> + * DEALINGS IN THE SOFTWARE.
>> + */
>> +
>> +/**
>> + * \file lower_const_arrays_to_uniforms.cpp
>> + *
>> + * Lower constant arrays to uniform arrays.
>> + *
>> + * Some driver backends (such as i965 and nouveau) don't handle constant arrays
>> + * gracefully, instead treating them as ordinary writable temporary arrays.
>> + * Since arrays can be large, this often means spilling them to scratch memory,
>> + * which usually involves a large number of instructions.
>> + *
>> + * This must be called prior to link_set_uniform_initializers(); we need the
>> + * linker to process our new uniform's constant initializer.
>> + *
>> + * This should be called after optimizations, since those can result in
>> + * splitting and removing arrays that are indexed by constant expressions.
>> + */
>> +#include "ir.h"
>> +#include "ir_visitor.h"
>> +#include "ir_rvalue_visitor.h"
>> +#include "glsl_types.h"
>> +
>> +namespace {
>> +class lower_const_array_visitor : public ir_rvalue_visitor {
>> +public:
>> + lower_const_array_visitor(exec_list *insts)
>> + {
>> + instructions = insts;
>> + progress = false;
>> + }
>> +
>> + bool run()
>> + {
>> + visit_list_elements(this, instructions);
>> + return progress;
>> + }
>> +
>> + void handle_rvalue(ir_rvalue **rvalue);
>> +
>> +private:
>> + exec_list *instructions;
>> + bool progress;
>> +};
>> +
>> +void
>> +lower_const_array_visitor::handle_rvalue(ir_rvalue **rvalue)
>> +{
>> + if (!*rvalue)
>> + return;
>> +
>> + ir_constant *con = (*rvalue)->as_constant();
>> + if (!con || !con->type->is_array())
>> + return;
>> +
>> + void *mem_ctx = ralloc_parent(con);
>> +
>> + ir_variable *uni =
>> + new(mem_ctx) ir_variable(con->type, "constarray", ir_var_uniform);
>> + uni->constant_initializer = con;
>> + uni->constant_value = con;
>> + uni->data.has_initializer = true;
>> + uni->data.read_only = true;
>> + /* Assume the whole thing is accessed. */
>> + uni->data.max_array_access = uni->type->length - 1;
>> + instructions->push_head(uni);
>> +
>> + *rvalue = new(mem_ctx) ir_dereference_variable(uni);
>> +
>> + progress = true;
>> +}
>> +
>> +} /* anonymous namespace */
>> +
>> +bool
>> +lower_const_arrays_to_uniforms(exec_list *instructions)
>> +{
>> + lower_const_array_visitor v(instructions);
>> + return v.run();
>> +}
>> --
>> 2.1.2
>>
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