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/*
* Copyright © 2013 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.
*/
/** @file brw_dead_control_flow.cpp
*
* This file implements the dead control flow elimination optimization pass.
*/
#include "brw_shader.h"
#include "brw_cfg.h"
/* Look for and eliminate dead control flow:
*
* - if/endif
* . else in else/endif
* - if/else/endif
*/
bool
dead_control_flow_eliminate(backend_visitor *v)
{
bool progress = false;
foreach_block_safe (block, v->cfg) {
bblock_t *if_block = NULL, *else_block = NULL, *endif_block = block;
bool found = false;
/* ENDIF instructions, by definition, can only be found at the start of
* basic blocks.
*/
backend_instruction *endif_inst = endif_block->start();
if (endif_inst->opcode != BRW_OPCODE_ENDIF)
continue;
backend_instruction *if_inst = NULL, *else_inst = NULL;
backend_instruction *prev_inst = endif_block->prev()->end();
if (prev_inst->opcode == BRW_OPCODE_ELSE) {
else_inst = prev_inst;
else_block = endif_block->prev();
found = true;
if (else_block->start_ip == else_block->end_ip)
prev_inst = else_block->prev()->end();
}
if (prev_inst->opcode == BRW_OPCODE_IF) {
if_inst = prev_inst;
if_block = else_block != NULL ? else_block->prev()
: endif_block->prev();
found = true;
} else {
/* Don't remove the ENDIF if we didn't find a dead IF. */
endif_inst = NULL;
}
if (found) {
bblock_t *earlier_block = NULL, *later_block = NULL;
if (if_inst) {
if (if_block->start_ip == if_block->end_ip) {
earlier_block = if_block->prev();
} else {
earlier_block = if_block;
}
if_inst->remove(if_block);
}
if (else_inst) {
else_block->if_block->else_block = NULL;
else_inst->remove(else_block);
}
if (endif_inst) {
if (endif_block->start_ip == endif_block->end_ip) {
later_block = endif_block->next();
} else {
later_block = endif_block;
}
endif_inst->remove(endif_block);
}
assert((earlier_block == NULL) == (later_block == NULL));
if (earlier_block && earlier_block->can_combine_with(later_block)) {
earlier_block->combine_with(later_block);
foreach_block (block, v->cfg) {
if (block->if_block == later_block)
block->if_block = earlier_block;
if (block->else_block == later_block)
block->else_block = earlier_block;
}
/* If ENDIF was in its own block, then we've now deleted it and
* merged the two surrounding blocks, the latter of which the
* __next block pointer was pointing to.
*/
if (endif_block != later_block) {
__next = earlier_block->next();
}
}
progress = true;
}
}
if (progress)
v->invalidate_live_intervals();
return progress;
}
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