187 lines
5.8 KiB
C
187 lines
5.8 KiB
C
/*
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* Copyright © 2015 Connor Abbott
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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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* Connor Abbott (cwabbott0@gmail.com)
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*
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*/
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#include "nir.h"
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#include "nir_builder.h"
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static nir_alu_instr *
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get_parent_mov(nir_ssa_def *ssa)
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{
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if (ssa->parent_instr->type != nir_instr_type_alu)
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return NULL;
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nir_alu_instr *alu = nir_instr_as_alu(ssa->parent_instr);
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return (alu->op == nir_op_mov) ? alu : NULL;
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}
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static bool
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matching_mov(nir_alu_instr *mov1, nir_ssa_def *ssa)
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{
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if (!mov1)
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return false;
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nir_alu_instr *mov2 = get_parent_mov(ssa);
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return mov2 && nir_alu_srcs_equal(mov1, mov2, 0, 0);
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}
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/*
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* This is a pass for removing phi nodes that look like:
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* a = phi(b, b, b, ...)
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*
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* Note that we can't always ignore undef sources here, or else we may create a
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* situation where the definition of b isn't dominated by its uses. We're
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* allowed to do this since the definition of b must dominate all of the
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* phi node's predecessors, which means it must dominate the phi node as well
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* as all of the phi node's uses. In essence, the phi node acts as a copy
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* instruction. b can't be another phi node in the same block, since the only
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* time when phi nodes can source other phi nodes defined in the same block is
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* at the loop header, and in that case one of the sources of the phi has to
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* be from before the loop and that source can't be b.
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*/
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static bool
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remove_phis_block(nir_block *block, nir_builder *b)
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{
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bool progress = false;
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nir_foreach_instr_safe(instr, block) {
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if (instr->type != nir_instr_type_phi)
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break;
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nir_phi_instr *phi = nir_instr_as_phi(instr);
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nir_ssa_def *def = NULL;
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nir_alu_instr *mov = NULL;
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bool srcs_same = true;
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nir_foreach_phi_src(src, phi) {
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assert(src->src.is_ssa);
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/* For phi nodes at the beginning of loops, we may encounter some
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* sources from backedges that point back to the destination of the
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* same phi, i.e. something like:
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*
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* a = phi(a, b, ...)
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*
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* We can safely ignore these sources, since if all of the normal
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* sources point to the same definition, then that definition must
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* still dominate the phi node, and the phi will still always take
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* the value of that definition.
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*/
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if (src->src.ssa == &phi->dest.ssa)
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continue;
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if (def == NULL) {
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def = src->src.ssa;
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mov = get_parent_mov(def);
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} else if (nir_src_is_undef(src->src) &&
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nir_block_dominates(def->parent_instr->block, src->pred)) {
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/* Ignore this undef source. */
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} else {
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if (src->src.ssa != def && !matching_mov(mov, src->src.ssa)) {
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srcs_same = false;
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break;
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}
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}
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}
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if (!srcs_same)
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continue;
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if (!def) {
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/* In this case, the phi had no sources. So turn it into an undef. */
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b->cursor = nir_after_phis(block);
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def = nir_ssa_undef(b, phi->dest.ssa.num_components,
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phi->dest.ssa.bit_size);
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} else if (mov) {
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/* If the sources were all movs from the same source with the same
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* swizzle, then we can't just pick a random move because it may not
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* dominate the phi node. Instead, we need to emit our own move after
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* the phi which uses the shared source, and rewrite uses of the phi
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* to use the move instead. This is ok, because while the movs may
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* not all dominate the phi node, their shared source does.
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*/
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b->cursor = nir_after_phis(block);
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def = nir_mov_alu(b, mov->src[0], def->num_components);
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}
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assert(phi->dest.is_ssa);
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nir_ssa_def_rewrite_uses(&phi->dest.ssa, def);
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nir_instr_remove(instr);
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progress = true;
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}
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return progress;
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}
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bool
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nir_opt_remove_phis_block(nir_block *block)
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{
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nir_builder b;
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nir_builder_init(&b, nir_cf_node_get_function(&block->cf_node));
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return remove_phis_block(block, &b);
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}
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static bool
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nir_opt_remove_phis_impl(nir_function_impl *impl)
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{
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bool progress = false;
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nir_builder bld;
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nir_builder_init(&bld, impl);
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nir_metadata_require(impl, nir_metadata_dominance);
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nir_foreach_block(block, impl) {
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progress |= remove_phis_block(block, &bld);
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}
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if (progress) {
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nir_metadata_preserve(impl, nir_metadata_block_index |
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nir_metadata_dominance);
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} else {
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nir_metadata_preserve(impl, nir_metadata_all);
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}
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return progress;
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}
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bool
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nir_opt_remove_phis(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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progress = nir_opt_remove_phis_impl(function->impl) || progress;
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return progress;
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}
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