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/*
* Copyright © 2018 Red Hat
*
* 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.
*
* Authors:
* Rob Clark (robdclark@gmail.com>
*
*/
#include "nir.h"
/*
* A simple pass that moves load_const's into consuming block if
* they are only consumed in a single block, to try to counter-
* act nir's tendency to move all load_const to the top of the
* first block.
*/
/* iterate a ssa def's use's and try to find a more optimal block to
* move it to, using the dominance tree. In short, if all of the uses
* are contained in a single block, the load will be moved there,
* otherwise it will be move to the least common ancestor block of all
* the uses
*/
static nir_block *
get_preferred_block(nir_ssa_def *def)
{
nir_block *lca = NULL;
/* hmm, probably ignore if-uses: */
if (!list_empty(&def->if_uses))
return NULL;
nir_foreach_use(use, def) {
nir_instr *instr = use->parent_instr;
nir_block *use_block = instr->block;
/*
* Kind of an ugly special-case, but phi instructions
* need to appear first in the block, so by definition
* we can't move a load_immed into a block where it is
* consumed by a phi instruction. We could conceivably
* move it into a dominator block.
*/
if (instr->type == nir_instr_type_phi) {
nir_phi_instr *phi = nir_instr_as_phi(instr);
nir_block *phi_lca = NULL;
nir_foreach_phi_src(src, phi)
phi_lca = nir_dominance_lca(phi_lca, src->pred);
use_block = phi_lca;
}
lca = nir_dominance_lca(lca, use_block);
}
return lca;
}
/* insert before first non-phi instruction: */
static void
insert_after_phi(nir_instr *instr, nir_block *block)
{
nir_foreach_instr(instr2, block) {
if (instr2->type == nir_instr_type_phi)
continue;
exec_node_insert_node_before(&instr2->node,
&instr->node);
return;
}
/* if haven't inserted it, push to tail (ie. empty block or possibly
* a block only containing phi's?)
*/
exec_list_push_tail(&block->instr_list, &instr->node);
}
bool
nir_move_load_const(nir_shader *shader)
{
bool progress = false;
nir_foreach_function(function, shader) {
if (!function->impl)
continue;
nir_foreach_block(block, function->impl) {
nir_metadata_require(function->impl,
nir_metadata_block_index | nir_metadata_dominance);
nir_foreach_instr_safe(instr, block) {
if (instr->type != nir_instr_type_load_const)
continue;
nir_load_const_instr *load =
nir_instr_as_load_const(instr);
nir_block *use_block =
get_preferred_block(&load->def);
if (!use_block)
continue;
if (use_block == load->instr.block)
continue;
exec_node_remove(&load->instr.node);
insert_after_phi(&load->instr, use_block);
load->instr.block = use_block;
progress = true;
}
}
nir_metadata_preserve(function->impl,
nir_metadata_block_index | nir_metadata_dominance);
}
return progress;
}
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