[Mesa-dev] [PATCH 4/9] nir: Introduce a nir_opt_move_comparisons() pass.
Jason Ekstrand
jason at jlekstrand.net
Wed Jan 11 20:53:01 UTC 2017
On Wed, Jan 11, 2017 at 12:49 PM, Jason Ekstrand <jason at jlekstrand.net>
wrote:
> I just sent three squash-in patches that I think improve this pass a bit
> and make things more clear. With those (or a good reason why not),
>
FYI, they've already been run through Jenkins. :-)
> Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
>
> On Tue, Jan 10, 2017 at 1:41 AM, Timothy Arceri <
> timothy.arceri at collabora.com> wrote:
>
>> From: Kenneth Graunke <kenneth at whitecape.org>
>>
>> This tries to move comparisons (a common source of boolean values)
>> closer to their first use. For GPUs which use condition codes,
>> this can eliminate a lot of temporary booleans and comparisons
>> which reload the condition code register based on a boolean.
>>
>> V2: (Timothy Arceri)
>> - fix move comparision for phis so we dont end up with:
>>
>> vec1 32 ssa_227 = phi block_34: ssa_1, block_38: ssa_240
>> vec1 32 ssa_235 = feq ssa_227, ssa_1
>> vec1 32 ssa_230 = phi block_34: ssa_221, block_38: ssa_235
>>
>> - add nir_op_i2b/nir_op_f2b to the list of comparisons.
>>
>> V3: (Timothy Arceri)
>> - tidy up suggested by Jason.
>> - add inot/fnot to move comparison list
>>
>> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
>> Reviewed-by: Ian Romanick <ian.d.romanick at intel.com> [v1]
>> ---
>> src/compiler/Makefile.sources | 1 +
>> src/compiler/nir/nir.h | 2 +
>> src/compiler/nir/nir_opt_move_comparisons.c | 179
>> ++++++++++++++++++++++++++++
>> 3 files changed, 182 insertions(+)
>> create mode 100644 src/compiler/nir/nir_opt_move_comparisons.c
>>
>> diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.source
>> s
>> index 52f6e54..6da854e 100644
>> --- a/src/compiler/Makefile.sources
>> +++ b/src/compiler/Makefile.sources
>> @@ -245,6 +245,7 @@ NIR_FILES = \
>> nir/nir_opt_global_to_local.c \
>> nir/nir_opt_if.c \
>> nir/nir_opt_loop_unroll.c \
>> + nir/nir_opt_move_comparisons.c \
>> nir/nir_opt_peephole_select.c \
>> nir/nir_opt_remove_phis.c \
>> nir/nir_opt_trivial_continues.c \
>> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
>> index c9226e9..2bff0b5 100644
>> --- a/src/compiler/nir/nir.h
>> +++ b/src/compiler/nir/nir.h
>> @@ -2589,6 +2589,8 @@ bool nir_opt_if(nir_shader *shader);
>>
>> bool nir_opt_loop_unroll(nir_shader *shader, nir_variable_mode
>> indirect_mask);
>>
>> +bool nir_opt_move_comparisons(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_comparisons.c
>> b/src/compiler/nir/nir_opt_move_comparisons.c
>> new file mode 100644
>> index 0000000..651b937
>> --- /dev/null
>> +++ b/src/compiler/nir/nir_opt_move_comparisons.c
>> @@ -0,0 +1,179 @@
>> +/*
>> + * Copyright © 2016 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.
>> + */
>> +
>> +#include "nir.h"
>> +
>> +/**
>> + * \file nir_opt_move_comparisons.c
>> + *
>> + * This pass moves ALU comparison operations just before their first use.
>> + *
>> + * It only moves instructions within a single basic block; cross-block
>> + * movement is left to global code motion.
>> + *
>> + * Many GPUs generate condition codes for comparisons, and use
>> predication
>> + * for conditional selects and control flow. In a sequence such as:
>> + *
>> + * vec1 32 ssa_1 = flt a b
>> + * <some other operations>
>> + * vec1 32 ssa_2 = bcsel ssa_1 c d
>> + *
>> + * the backend would likely do the comparison, producing condition codes,
>> + * then save those to a boolean value. The intervening operations might
>> + * trash the condition codes. Then, in order to do the bcsel, it would
>> + * need to re-populate the condition code register based on the boolean.
>> + *
>> + * By moving the comparison just before the bcsel, the condition codes
>> could
>> + * be used directly. This eliminates the need to reload them from the
>> boolean
>> + * (generally eliminating an instruction). It may also eliminate the
>> need to
>> + * create a boolean value altogether (unless it's used elsewhere), which
>> could
>> + * lower register pressure.
>> + */
>> +
>> +static bool
>> +is_comparison(nir_op op)
>> +{
>> + switch (op) {
>> + case nir_op_flt:
>> + case nir_op_fge:
>> + case nir_op_feq:
>> + case nir_op_fne:
>> + case nir_op_ilt:
>> + case nir_op_ult:
>> + case nir_op_ige:
>> + case nir_op_uge:
>> + case nir_op_ieq:
>> + case nir_op_ine:
>> + case nir_op_i2b:
>> + case nir_op_f2b:
>> + case nir_op_inot:
>> + case nir_op_fnot:
>> + return true;
>> + default:
>> + return false;
>> + }
>> +}
>> +
>> +static bool
>> +move_comparison_source(nir_src *src, nir_block *block, nir_instr
>> *before)
>> +{
>> + if (src->is_ssa && src->ssa->parent_instr->block == block &&
>> + src->ssa->parent_instr->type == nir_instr_type_alu &&
>> + is_comparison(nir_instr_as_alu(src->ssa->parent_instr)->op) &&
>> + (!before || before->type != nir_instr_type_phi)) {
>> +
>> + struct exec_node *src_node = &src->ssa->parent_instr->node;
>> + exec_node_remove(src_node);
>> +
>> + if (before)
>> + exec_node_insert_node_before(&before->node, src_node);
>> + else
>> + exec_list_push_tail(&block->instr_list, src_node);
>> +
>> + return true;
>> + }
>> +
>> + return false;
>> +}
>> +
>> +/* nir_foreach_src callback boilerplate */
>> +struct nomc_tuple
>> +{
>> + nir_instr *instr;
>> + bool progress;
>> +};
>> +
>> +static bool
>> +move_comparison_source_cb(nir_src *src, void *data)
>> +{
>> + struct nomc_tuple *tuple = data;
>> +
>> + if (move_comparison_source(src, tuple->instr->block, tuple->instr))
>> + tuple->progress = true;
>> +
>> + return true; /* nir_foreach_src should keep going */
>> +}
>> +
>> +static bool
>> +move_comparisons(nir_block *block)
>> +{
>> + bool progress = false;
>> +
>> + /* We use a simple approach: walk instructions backwards.
>> + *
>> + * If the instruction's source is a comparison from the same block,
>> + * simply move it here. This may break SSA if it's used earlier in
>> + * the block as well. However, as we walk backwards, we'll find the
>> + * earlier use and move it again, further up. It eventually ends up
>> + * dominating all uses again, restoring SSA form.
>> + *
>> + * Before walking instructions, we consider the if-condition at the
>> + * end of the block, if one exists. It's effectively a use at the
>> + * bottom of the block.
>> + */
>> + nir_if *iff = nir_block_get_following_if(block);
>> + if (iff) {
>> + progress |= move_comparison_source(&iff->condition, block, NULL);
>> + }
>> +
>> + nir_foreach_instr_reverse(instr, block) {
>> + if (instr->type == nir_instr_type_alu) {
>> + /* Walk ALU instruction sources backwards so that bcsel's
>> boolean
>> + * condition is processed last.
>> + */
>> + 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_comparison_source(&alu->src[i].src,
>> + block, instr);
>> + }
>> + } else {
>> + struct nomc_tuple tuple = { instr, false };
>> + nir_foreach_src(instr, move_comparison_source_cb, &tuple);
>> + progress |= tuple.progress;
>> + }
>> + }
>> +
>> + return progress;
>> +}
>> +
>> +bool
>> +nir_opt_move_comparisons(nir_shader *shader)
>> +{
>> + bool progress = false;
>> +
>> + nir_foreach_function(func, shader) {
>> + if (!func->impl)
>> + continue;
>> +
>> + nir_foreach_block(block, func->impl) {
>> + if (move_comparisons(block)) {
>> + nir_metadata_preserve(func->impl, nir_metadata_block_index |
>> + nir_metadata_dominance |
>> +
>> nir_metadata_live_ssa_defs);
>> + progress = true;
>> + }
>> + }
>> + }
>> +
>> + return progress;
>> +}
>> --
>> 2.9.3
>>
>> _______________________________________________
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>> mesa-dev at lists.freedesktop.org
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>>
>
>
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