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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"
using namespace brw;
/* Look for and eliminate dead control flow:
*
* - if/endif
* - else in else/endif
* - then in if/else/endif
*/
bool
dead_control_flow_eliminate(backend_shader *s)
{
bool progress = false;
foreach_block_safe (block, s->cfg) {
bblock_t *prev_block = block->prev();
if (!prev_block)
continue;
backend_instruction *const inst = block->start();
backend_instruction *const prev_inst = prev_block->end();
/* ENDIF instructions, by definition, can only be found at the start of
* basic blocks.
*/
if (inst->opcode == BRW_OPCODE_ENDIF &&
prev_inst->opcode == BRW_OPCODE_ELSE) {
bblock_t *const else_block = prev_block;
backend_instruction *const else_inst = prev_inst;
else_inst->remove(else_block);
progress = true;
} else if (inst->opcode == BRW_OPCODE_ENDIF &&
prev_inst->opcode == BRW_OPCODE_IF) {
bblock_t *const endif_block = block;
bblock_t *const if_block = prev_block;
backend_instruction *const endif_inst = inst;
backend_instruction *const if_inst = prev_inst;
bblock_t *earlier_block = NULL, *later_block = NULL;
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 (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);
/* 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;
} else if (inst->opcode == BRW_OPCODE_ELSE &&
prev_inst->opcode == BRW_OPCODE_IF) {
bblock_t *const else_block = block;
backend_instruction *const if_inst = prev_inst;
backend_instruction *const else_inst = inst;
/* Since the else-branch is becoming the new then-branch, the
* condition has to be inverted.
*/
if_inst->predicate_inverse = !if_inst->predicate_inverse;
else_inst->remove(else_block);
progress = true;
}
}
if (progress)
s->invalidate_analysis(DEPENDENCY_BLOCKS | DEPENDENCY_INSTRUCTIONS);
return progress;
}
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