On Thu, Mar 8, 2018 at 5:48 PM, Ian Romanick <i...@freedesktop.org> wrote:
> On 03/08/2018 06:50 AM, Samuel Pitoiset wrote:
>> This pass moves load UBO operations just before their first use,
>> loosely based on nir_opt_move_comparisons.
>
> If I'm reading this correctly, it moves UBO loads closer to the first
> use in the same block. My assumption is the benefit in the next patch
> occurs because live ranges are smaller. It seems like this could also
> hurt performance since it may be harder for the schedule to hide the
> latency of the load when register pressure is not an issue. Have you
> measured performance of running apps to see if this is an issue?
>
> I'm mostly asking because Jason had a series for global code motion that
> does, in some cases, the opposite of this patch by moving UBO loads up
> to earlier blocks.
The pass is OK for LLVM, because LLVM does CSE across basic blocks,
and it also does instruction scheduling within a block.
radeonsi/tgsi does the same thing: it load uniforms from memory at
every use. It sounds inefficient, but we found out that it's the best
thing to do with LLVM. LLVM can move loads away from the use, but it
doesn't move loads close to the use.
Marek
>
>> Signed-off-by: Samuel Pitoiset <samuel.pitoi...@gmail.com>
>> ---
>> src/compiler/Makefile.sources | 1 +
>> src/compiler/nir/meson.build | 1 +
>> src/compiler/nir/nir.h | 2 +
>> src/compiler/nir/nir_opt_move_load_ubo.c | 116
>> +++++++++++++++++++++++++++++++
>> 4 files changed, 120 insertions(+)
>> create mode 100644 src/compiler/nir/nir_opt_move_load_ubo.c
>>
>> diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
>> index 37340ba809..55143dbc66 100644
>> --- a/src/compiler/Makefile.sources
>> +++ b/src/compiler/Makefile.sources
>> @@ -266,6 +266,7 @@ NIR_FILES = \
>> nir/nir_opt_intrinsics.c \
>> nir/nir_opt_loop_unroll.c \
>> nir/nir_opt_move_comparisons.c \
>> + nir/nir_opt_move_load_ubo.c \
>> nir/nir_opt_peephole_select.c \
>> nir/nir_opt_remove_phis.c \
>> nir/nir_opt_shrink_load.c \
>> diff --git a/src/compiler/nir/meson.build b/src/compiler/nir/meson.build
>> index a70c236b95..289bb9ea78 100644
>> --- a/src/compiler/nir/meson.build
>> +++ b/src/compiler/nir/meson.build
>> @@ -160,6 +160,7 @@ files_libnir = files(
>> 'nir_opt_intrinsics.c',
>> 'nir_opt_loop_unroll.c',
>> 'nir_opt_move_comparisons.c',
>> + 'nir_opt_move_load_ubo.c',
>> 'nir_opt_peephole_select.c',
>> 'nir_opt_remove_phis.c',
>> 'nir_opt_shrink_load.c',
>> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
>> index 5b28c727c8..4224da5f82 100644
>> --- a/src/compiler/nir/nir.h
>> +++ b/src/compiler/nir/nir.h
>> @@ -2786,6 +2786,8 @@ bool nir_opt_loop_unroll(nir_shader *shader,
>> nir_variable_mode indirect_mask);
>>
>> bool nir_opt_move_comparisons(nir_shader *shader);
>>
>> +bool nir_opt_move_load_ubo(nir_shader *shader);
>> +
>> bool nir_opt_peephole_select(nir_shader *shader, unsigned limit);
>>
>> bool nir_opt_remove_phis(nir_shader *shader);
>> diff --git a/src/compiler/nir/nir_opt_move_load_ubo.c
>> b/src/compiler/nir/nir_opt_move_load_ubo.c
>> new file mode 100644
>> index 0000000000..642651152b
>> --- /dev/null
>> +++ b/src/compiler/nir/nir_opt_move_load_ubo.c
>> @@ -0,0 +1,116 @@
>> +/*
>> + * Copyright © 2016 Intel Corporation
>> + * Copyright © 2018 Valve 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.
>> + */
>> +
>> +#include "nir.h"
>> +
>> +/**
>> + * \file nir_opt_move_load_ubo.c
>> + *
>> + * This pass moves load UBO operations just before their first use.
>> + */
>> +static bool
>> +move_load_ubo_source(nir_src *src, nir_block *block, nir_instr *before)
>> +{
>> + if (!src->is_ssa)
>> + return false;
>> +
>> + nir_instr *src_instr = src->ssa->parent_instr;
>> +
>> + if (src_instr->block == block &&
>> + src_instr->type == nir_instr_type_intrinsic &&
>> + nir_instr_as_intrinsic(src_instr)->intrinsic ==
>> nir_intrinsic_load_ubo) {
>> +
>> + exec_node_remove(&src_instr->node);
>> +
>> + if (before)
>> + exec_node_insert_node_before(&before->node, &src_instr->node);
>> + else
>> + exec_list_push_tail(&block->instr_list, &src_instr->node);
>> +
>> + return true;
>> + }
>> + return false;
>> +}
>> +
>> +static bool
>> +move_load_ubo_source_cb(nir_src *src, void *data)
>> +{
>> + bool *progress = data;
>> +
>> + nir_instr *instr = src->parent_instr;
>> + if (move_load_ubo_source(src, instr->block, instr))
>> + *progress = true;
>> +
>> + return true; /* nir_foreach_src should keep going */
>> +}
>> +
>> +static bool
>> +move_load_ubo(nir_block *block)
>> +{
>> + bool progress = false;
>> +
>> + nir_if *iff = nir_block_get_following_if(block);
>> + if (iff) {
>> + progress |= move_load_ubo_source(&iff->condition, block, NULL);
>> + }
>> +
>> + nir_foreach_instr_reverse(instr, block) {
>> +
>> + if (instr->type == nir_instr_type_phi) {
>> + /* We're going backwards so everything else is a phi too */
>> + } else if (instr->type == nir_instr_type_alu) {
>> + nir_alu_instr *alu = nir_instr_as_alu(instr);
>> +
>> + for (int i = nir_op_infos[alu->op].num_inputs - 1; i >= 0; i--) {
>> + progress |= move_load_ubo_source(&alu->src[i].src, block,
>> instr);
>> + }
>> + } else {
>> + nir_foreach_src(instr, move_load_ubo_source_cb, &progress);
>> + }
>> + }
>> +
>> + return false;
>> +}
>> +
>> +bool
>> +nir_opt_move_load_ubo(nir_shader *shader)
>> +{
>> + bool progress = false;
>> +
>> + nir_foreach_function(func, shader) {
>> + if (!func->impl)
>> + continue;
>> +
>> + nir_foreach_block(block, func->impl) {
>> + if (move_load_ubo(block)) {
>> + nir_metadata_preserve(func->impl, nir_metadata_block_index |
>> + nir_metadata_dominance |
>> + nir_metadata_live_ssa_defs);
>> + progress = true;
>> + }
>> + }
>> + }
>> +
>> + return progress;
>> +}
>>
>
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