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