206 lines
6.5 KiB
C
206 lines
6.5 KiB
C
/*
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* Copyright © 2015 Thomas Helland
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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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* This pass converts the ssa-graph into "Loop Closed SSA form". This is
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* done by placing phi nodes at the exits of the loop for all values
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* that are used outside the loop. The result is it transforms:
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*
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* loop { -> loop {
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* ssa2 = .... -> ssa2 = ...
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* if (cond) -> if (cond)
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* break; -> break;
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* ssa3 = ssa2 * ssa4 -> ssa3 = ssa2 * ssa4
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* } -> }
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* ssa6 = ssa2 + 4 -> ssa5 = phi(ssa2)
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* ssa6 = ssa5 + 4
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*/
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#include "nir.h"
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typedef struct {
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/* The nir_shader we are transforming */
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nir_shader *shader;
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/* The loop we store information for */
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nir_loop *loop;
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} lcssa_state;
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static bool
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is_if_use_inside_loop(nir_src *use, nir_loop* loop)
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{
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nir_block *block_before_loop =
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nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node));
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nir_block *block_after_loop =
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nir_cf_node_as_block(nir_cf_node_next(&loop->cf_node));
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nir_block *prev_block =
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nir_cf_node_as_block(nir_cf_node_prev(&use->parent_if->cf_node));
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if (prev_block->index <= block_before_loop->index ||
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prev_block->index >= block_after_loop->index) {
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return false;
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}
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return true;
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}
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static bool
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is_use_inside_loop(nir_src *use, nir_loop* loop)
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{
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nir_block *block_before_loop =
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nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node));
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nir_block *block_after_loop =
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nir_cf_node_as_block(nir_cf_node_next(&loop->cf_node));
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if (use->parent_instr->block->index <= block_before_loop->index ||
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use->parent_instr->block->index >= block_after_loop->index) {
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return false;
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}
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return true;
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}
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static bool
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convert_loop_exit_for_ssa(nir_ssa_def *def, void *void_state)
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{
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lcssa_state *state = void_state;
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bool all_uses_inside_loop = true;
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nir_block *block_after_loop =
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nir_cf_node_as_block(nir_cf_node_next(&state->loop->cf_node));
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nir_foreach_use(use, def) {
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if (use->parent_instr->type == nir_instr_type_phi &&
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use->parent_instr->block == block_after_loop) {
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continue;
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}
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if (!is_use_inside_loop(use, state->loop)) {
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all_uses_inside_loop = false;
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}
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}
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nir_foreach_if_use(use, def) {
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if (!is_if_use_inside_loop(use, state->loop)) {
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all_uses_inside_loop = false;
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}
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}
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/* There where no sources that had defs outside the loop */
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if (all_uses_inside_loop)
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return true;
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/* We don't want derefs ending up in phi sources */
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assert(def->parent_instr->type != nir_instr_type_deref);
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/* Initialize a phi-instruction */
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nir_phi_instr *phi = nir_phi_instr_create(state->shader);
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nir_ssa_dest_init(&phi->instr, &phi->dest,
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def->num_components, def->bit_size, "LCSSA-phi");
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/* Create a phi node with as many sources pointing to the same ssa_def as
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* the block has predecessors.
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*/
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set_foreach(block_after_loop->predecessors, entry) {
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nir_phi_src *phi_src = ralloc(phi, nir_phi_src);
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phi_src->src = nir_src_for_ssa(def);
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phi_src->pred = (nir_block *) entry->key;
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exec_list_push_tail(&phi->srcs, &phi_src->node);
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}
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nir_instr_insert_before_block(block_after_loop, &phi->instr);
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/* Run through all uses and rewrite those outside the loop to point to
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* the phi instead of pointing to the ssa-def.
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*/
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nir_foreach_use_safe(use, def) {
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if (use->parent_instr->type == nir_instr_type_phi &&
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block_after_loop == use->parent_instr->block) {
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continue;
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}
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if (!is_use_inside_loop(use, state->loop)) {
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nir_instr_rewrite_src(use->parent_instr, use,
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nir_src_for_ssa(&phi->dest.ssa));
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}
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}
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nir_foreach_if_use_safe(use, def) {
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if (!is_if_use_inside_loop(use, state->loop)) {
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nir_if_rewrite_condition(use->parent_if,
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nir_src_for_ssa(&phi->dest.ssa));
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}
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}
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return true;
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}
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static void
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convert_to_lcssa(nir_cf_node *cf_node, lcssa_state *state)
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{
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switch (cf_node->type) {
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case nir_cf_node_block:
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nir_foreach_instr(instr, nir_cf_node_as_block(cf_node))
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nir_foreach_ssa_def(instr, convert_loop_exit_for_ssa, state);
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return;
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case nir_cf_node_if: {
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nir_if *if_stmt = nir_cf_node_as_if(cf_node);
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foreach_list_typed(nir_cf_node, nested_node, node, &if_stmt->then_list)
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convert_to_lcssa(nested_node, state);
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foreach_list_typed(nir_cf_node, nested_node, node, &if_stmt->else_list)
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convert_to_lcssa(nested_node, state);
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return;
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}
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case nir_cf_node_loop: {
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nir_loop *parent_loop = state->loop;
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state->loop = nir_cf_node_as_loop(cf_node);
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foreach_list_typed(nir_cf_node, nested_node, node, &state->loop->body)
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convert_to_lcssa(nested_node, state);
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state->loop = parent_loop;
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return;
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}
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default:
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unreachable("unknown cf node type");
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}
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}
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void
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nir_convert_loop_to_lcssa(nir_loop *loop) {
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nir_function_impl *impl = nir_cf_node_get_function(&loop->cf_node);
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nir_metadata_require(impl, nir_metadata_block_index);
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lcssa_state *state = rzalloc(NULL, lcssa_state);
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state->loop = loop;
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state->shader = impl->function->shader;
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foreach_list_typed(nir_cf_node, node, node, &state->loop->body)
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convert_to_lcssa(node, state);
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ralloc_free(state);
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}
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