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7235c144a6
Run this pass late (after opt loop) to move load_const instructions back into the basic blocks which use the result, in cases where a load_const is only consumed in a single block. This helps reduce register usage in cases where the backend driver cannot lower the load_const to a uniform. Signed-off-by: Rob Clark <robdclark@gmail.com> Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
141 lines
4.2 KiB
C
141 lines
4.2 KiB
C
/*
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* Copyright © 2018 Red Hat
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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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* Authors:
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* Rob Clark (robdclark@gmail.com>
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*
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*/
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#include "nir.h"
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/*
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* A simple pass that moves load_const's into consuming block if
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* they are only consumed in a single block, to try to counter-
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* act nir's tendency to move all load_const to the top of the
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* first block.
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*/
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/* iterate a ssa def's use's and try to find a more optimal block to
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* move it to, using the dominance tree. In short, if all of the uses
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* are contained in a single block, the load will be moved there,
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* otherwise it will be move to the least common ancestor block of all
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* the uses
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*/
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static nir_block *
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get_preferred_block(nir_ssa_def *def)
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{
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nir_block *lca = NULL;
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/* hmm, probably ignore if-uses: */
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if (!list_empty(&def->if_uses))
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return NULL;
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nir_foreach_use(use, def) {
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nir_instr *instr = use->parent_instr;
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nir_block *use_block = instr->block;
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/*
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* Kind of an ugly special-case, but phi instructions
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* need to appear first in the block, so by definition
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* we can't move a load_immed into a block where it is
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* consumed by a phi instruction. We could conceivably
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* move it into a dominator block.
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*/
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if (instr->type == nir_instr_type_phi) {
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nir_phi_instr *phi = nir_instr_as_phi(instr);
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nir_block *phi_lca = NULL;
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nir_foreach_phi_src(src, phi)
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phi_lca = nir_dominance_lca(phi_lca, src->pred);
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use_block = phi_lca;
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}
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lca = nir_dominance_lca(lca, use_block);
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}
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return lca;
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}
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/* insert before first non-phi instruction: */
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static void
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insert_after_phi(nir_instr *instr, nir_block *block)
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{
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nir_foreach_instr(instr2, block) {
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if (instr2->type == nir_instr_type_phi)
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continue;
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exec_node_insert_node_before(&instr2->node,
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&instr->node);
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return;
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}
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/* if haven't inserted it, push to tail (ie. empty block or possibly
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* a block only containing phi's?)
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*/
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exec_list_push_tail(&block->instr_list, &instr->node);
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}
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bool
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nir_move_load_const(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_foreach_block(block, function->impl) {
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nir_metadata_require(function->impl,
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nir_metadata_block_index | nir_metadata_dominance);
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nir_foreach_instr_safe(instr, block) {
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if (instr->type != nir_instr_type_load_const)
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continue;
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nir_load_const_instr *load =
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nir_instr_as_load_const(instr);
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nir_block *use_block =
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get_preferred_block(&load->def);
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if (!use_block)
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continue;
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if (use_block == load->instr.block)
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continue;
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exec_node_remove(&load->instr.node);
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insert_after_phi(&load->instr, use_block);
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load->instr.block = use_block;
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progress = true;
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}
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}
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nir_metadata_preserve(function->impl,
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nir_metadata_block_index | nir_metadata_dominance);
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}
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return progress;
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}
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