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/*
* Copyright © 2014 Intel Corporation
*
* 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:
* Jason Ekstrand (jason@jlekstrand.net)
*
*/
#include "nir.h"
/*
* Implements a small peephole optimization that looks for
*
* if (cond) {
* <empty>
* } else {
* <empty>
* }
* phi
* ...
* phi
*
* and replaces it with a series of selects. It can also handle the case
* where, instead of being empty, the if may contain some move operations
* whose only use is one of the following phi nodes. This happens all the
* time when the SSA form comes from a conditional assignment with a
* swizzle.
*/
struct peephole_select_state {
void *mem_ctx;
bool progress;
};
static bool
are_all_move_to_phi(nir_block *block)
{
nir_foreach_instr(block, instr) {
if (instr->type != nir_instr_type_alu)
return false;
/* It must be a move operation */
nir_alu_instr *mov = nir_instr_as_alu(instr);
if (mov->op != nir_op_fmov && mov->op != nir_op_imov)
return false;
/* Can't handle saturate */
if (mov->dest.saturate)
return false;
/* It must be SSA */
if (!mov->dest.dest.is_ssa)
return false;
/* It cannot have any if-uses */
if (mov->dest.dest.ssa.if_uses->entries != 0)
return false;
/* The only uses of this definition must be phi's in the successor */
struct set_entry *entry;
set_foreach(mov->dest.dest.ssa.uses, entry) {
const nir_instr *dest_instr = entry->key;
if (dest_instr->type != nir_instr_type_phi ||
dest_instr->block != block->successors[0])
return false;
}
}
return true;
}
static bool
nir_opt_peephole_select_block(nir_block *block, void *void_state)
{
struct peephole_select_state *state = void_state;
/* If the block is empty, then it certainly doesn't have any phi nodes,
* so we can skip it. This also ensures that we do an early skip on the
* end block of the function which isn't actually attached to the CFG.
*/
if (exec_list_is_empty(&block->instr_list))
return true;
if (nir_cf_node_is_first(&block->cf_node))
return true;
nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node);
if (prev_node->type != nir_cf_node_if)
return true;
nir_if *if_stmt = nir_cf_node_as_if(prev_node);
nir_cf_node *then_node = nir_if_first_then_node(if_stmt);
nir_cf_node *else_node = nir_if_first_else_node(if_stmt);
/* We can only have one block in each side ... */
if (nir_if_last_then_node(if_stmt) != then_node ||
nir_if_last_else_node(if_stmt) != else_node)
return true;
nir_block *then_block = nir_cf_node_as_block(then_node);
nir_block *else_block = nir_cf_node_as_block(else_node);
/* ... and those blocks must only contain move-to-phi. */
if (!are_all_move_to_phi(then_block) || !are_all_move_to_phi(else_block))
return true;
/* At this point, we know that the previous CFG node is an if-then
* statement containing only moves to phi nodes in this block. We can
* just remove that entire CF node and replace all of the phi nodes with
* selects.
*/
nir_foreach_instr_safe(block, instr) {
if (instr->type != nir_instr_type_phi)
break;
nir_phi_instr *phi = nir_instr_as_phi(instr);
nir_alu_instr *sel = nir_alu_instr_create(state->mem_ctx, nir_op_bcsel);
nir_src_copy(&sel->src[0].src, &if_stmt->condition, state->mem_ctx);
/* Splat the condition to all channels */
memset(sel->src[0].swizzle, 0, sizeof sel->src[0].swizzle);
assert(exec_list_length(&phi->srcs) == 2);
nir_foreach_phi_src(phi, src) {
assert(src->pred == then_block || src->pred == else_block);
assert(src->src.is_ssa);
unsigned idx = src->pred == then_block ? 1 : 2;
if (src->src.ssa->parent_instr->block == src->pred) {
/* We already know that this instruction must be a move with
* this phi's in this block as its only users.
*/
nir_alu_instr *mov = nir_instr_as_alu(src->src.ssa->parent_instr);
assert(mov->instr.type == nir_instr_type_alu);
assert(mov->op == nir_op_fmov || mov->op == nir_op_imov);
nir_alu_src_copy(&sel->src[idx], &mov->src[0], state->mem_ctx);
} else {
nir_src_copy(&sel->src[idx].src, &src->src, state->mem_ctx);
}
}
nir_ssa_dest_init(&sel->instr, &sel->dest.dest,
phi->dest.ssa.num_components, phi->dest.ssa.name);
sel->dest.write_mask = (1 << phi->dest.ssa.num_components) - 1;
nir_ssa_def_rewrite_uses(&phi->dest.ssa,
nir_src_for_ssa(&sel->dest.dest.ssa),
state->mem_ctx);
nir_instr_insert_before(&phi->instr, &sel->instr);
nir_instr_remove(&phi->instr);
}
nir_cf_node_remove(&if_stmt->cf_node);
state->progress = true;
return true;
}
static bool
nir_opt_peephole_select_impl(nir_function_impl *impl)
{
struct peephole_select_state state;
state.mem_ctx = ralloc_parent(impl);
state.progress = false;
nir_foreach_block(impl, nir_opt_peephole_select_block, &state);
if (state.progress)
nir_metadata_preserve(impl, nir_metadata_none);
return state.progress;
}
bool
nir_opt_peephole_select(nir_shader *shader)
{
bool progress = false;
nir_foreach_overload(shader, overload) {
if (overload->impl)
progress |= nir_opt_peephole_select_impl(overload->impl);
}
return progress;
}
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