nir: Add a pass to cut the trailing ends of vectors.
Ideally we'd also handle unused middles of vectors and reswizzle ALU-only uses of it so we could write fewer channels, but that's future work/ Reviewed-by: Rhys Perry <pendingchaos02@gmail.com> Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6050>
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@ -327,6 +327,7 @@ NIR_FILES = \
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nir/nir_opt_rematerialize_compares.c \
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nir/nir_opt_remove_phis.c \
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nir/nir_opt_shrink_load.c \
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nir/nir_opt_shrink_vectors.c \
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nir/nir_opt_sink.c \
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nir/nir_opt_trivial_continues.c \
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nir/nir_opt_undef.c \
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@ -208,6 +208,7 @@ files_libnir = files(
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'nir_opt_rematerialize_compares.c',
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'nir_opt_remove_phis.c',
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'nir_opt_shrink_load.c',
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'nir_opt_shrink_vectors.c',
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'nir_opt_sink.c',
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'nir_opt_trivial_continues.c',
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'nir_opt_undef.c',
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@ -4619,6 +4619,7 @@ bool nir_opt_remove_phis(nir_shader *shader);
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bool nir_opt_remove_phis_block(nir_block *block);
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bool nir_opt_shrink_load(nir_shader *shader);
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bool nir_opt_shrink_vectors(nir_shader *shader);
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bool nir_opt_trivial_continues(nir_shader *shader);
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@ -0,0 +1,210 @@
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/*
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* Copyright © 2020 Google LLC
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice (including the next
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* paragraph) shall be included in all copies or substantial portions of the
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* Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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* IN THE SOFTWARE.
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*/
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/**
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* @file
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*
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* Trims off the unused trailing components of SSA defs.
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*
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* Due to various optimization passes (or frontend implementations,
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* particularly prog_to_nir), we may have instructions generating vectors
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* whose components don't get read by any instruction. While it can be tricky
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* to eliminate either unused low components of a writemask (you might need to
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* increment some offset from a load_uniform, for example) or channels in the
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* middle of a partially set writemask (you might need to reswizzle ALU ops
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* using the value), it is trivial to just drop the trailing components.
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*
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* This pass is probably only of use to vector backends -- scalar backends
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* typically get unused def channel trimming by scalarizing and dead code
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* elimination.
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*/
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#include "nir.h"
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#include "nir_builder.h"
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static bool
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shrink_dest_to_read_mask(nir_ssa_def *def)
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{
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/* early out if there's nothing to do. */
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if (def->num_components == 1)
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return false;
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unsigned mask = nir_ssa_def_components_read(def);
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int last_bit = util_last_bit(mask);
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/* If nothing was read, leave it up to DCE. */
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if (!mask)
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return false;
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if (def->num_components > last_bit) {
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def->num_components = last_bit;
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return true;
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}
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return false;
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}
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static bool
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opt_shrink_vectors_alu(nir_builder *b, nir_alu_instr *instr)
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{
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nir_ssa_def *def = &instr->dest.dest.ssa;
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if (nir_op_infos[instr->op].output_size == 0) {
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if (shrink_dest_to_read_mask(def)) {
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instr->dest.write_mask &=
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BITFIELD_MASK(def->num_components);
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return true;
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}
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} else {
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switch (instr->op) {
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case nir_op_vec4:
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case nir_op_vec3:
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case nir_op_vec2: {
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unsigned mask = nir_ssa_def_components_read(def);
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/* If nothing was read, leave it up to DCE. */
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if (mask == 0)
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return false;
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int last_bit = util_last_bit(mask);
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if (last_bit < def->num_components) {
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nir_ssa_def *srcs[NIR_MAX_VEC_COMPONENTS] = { 0 };
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for (int i = 0; i < last_bit; i++)
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srcs[i] = nir_ssa_for_alu_src(b, instr, i);
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nir_ssa_def *new_vec = nir_vec(b, srcs, last_bit);
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nir_ssa_def_rewrite_uses(def, nir_src_for_ssa(new_vec));
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return true;
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}
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break;
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}
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default:
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break;
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}
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}
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return false;
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}
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static bool
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opt_shrink_vectors_intrinsic(nir_intrinsic_instr *instr)
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{
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switch (instr->intrinsic) {
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case nir_intrinsic_load_uniform:
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case nir_intrinsic_load_ubo:
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case nir_intrinsic_load_input:
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case nir_intrinsic_load_input_vertex:
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case nir_intrinsic_load_per_vertex_input:
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case nir_intrinsic_load_interpolated_input:
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case nir_intrinsic_load_ssbo:
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case nir_intrinsic_load_push_constant:
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case nir_intrinsic_load_constant:
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case nir_intrinsic_load_global:
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case nir_intrinsic_load_kernel_input:
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case nir_intrinsic_load_scratch:
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break;
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default:
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return false;
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}
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assert(nir_intrinsic_infos[instr->intrinsic].has_dest);
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/* Must be a vectorized intrinsic that we can resize. */
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assert(instr->num_components != 0);
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if (shrink_dest_to_read_mask(&instr->dest.ssa)) {
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instr->num_components = instr->dest.ssa.num_components;
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return true;
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}
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return false;
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}
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static bool
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opt_shrink_vectors_load_const(nir_load_const_instr *instr)
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{
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return shrink_dest_to_read_mask(&instr->def);
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}
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static bool
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opt_shrink_vectors_ssa_undef(nir_ssa_undef_instr *instr)
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{
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return shrink_dest_to_read_mask(&instr->def);
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}
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static bool
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opt_shrink_vectors_instr(nir_builder *b, nir_instr *instr)
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{
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b->cursor = nir_before_instr(instr);
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switch (instr->type) {
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case nir_instr_type_alu:
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return opt_shrink_vectors_alu(b, nir_instr_as_alu(instr));
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case nir_instr_type_intrinsic:
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return opt_shrink_vectors_intrinsic(nir_instr_as_intrinsic(instr));
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case nir_instr_type_load_const:
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return opt_shrink_vectors_load_const(nir_instr_as_load_const(instr));
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case nir_instr_type_ssa_undef:
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return opt_shrink_vectors_ssa_undef(nir_instr_as_ssa_undef(instr));
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default:
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return false;
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}
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return true;
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}
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bool
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nir_opt_shrink_vectors(nir_shader *shader)
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{
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bool progress = false;
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nir_foreach_function(function, shader) {
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if (!function->impl)
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continue;
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nir_builder b;
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nir_builder_init(&b, function->impl);
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nir_foreach_block(block, function->impl) {
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nir_foreach_instr(instr, block) {
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progress |= opt_shrink_vectors_instr(&b, instr);
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}
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}
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if (progress) {
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nir_metadata_preserve(function->impl,
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nir_metadata_block_index |
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nir_metadata_dominance);
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} else {
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nir_metadata_preserve(function->impl, nir_metadata_all);
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}
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}
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return progress;
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}
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