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24 /** @file brw_dead_control_flow.cpp
26 * This file implements the dead control flow elimination optimization pass.
29 #include "brw_shader.h"
32 /* Look for and eliminate dead control flow:
35 * . else in else/endif
39 dead_control_flow_eliminate(backend_shader *s)
41 bool progress = false;
43 foreach_block_safe (block, s->cfg) {
44 bblock_t *if_block = NULL, *else_block = NULL, *endif_block = block;
47 /* ENDIF instructions, by definition, can only be found at the start of
50 backend_instruction *endif_inst = endif_block->start();
51 if (endif_inst->opcode != BRW_OPCODE_ENDIF)
54 backend_instruction *if_inst = NULL, *else_inst = NULL;
55 backend_instruction *prev_inst = endif_block->prev()->end();
56 if (prev_inst->opcode == BRW_OPCODE_ELSE) {
57 else_inst = prev_inst;
58 else_block = endif_block->prev();
61 if (else_block->start_ip == else_block->end_ip)
62 prev_inst = else_block->prev()->end();
65 if (prev_inst->opcode == BRW_OPCODE_IF) {
67 if_block = else_block != NULL ? else_block->prev()
68 : endif_block->prev();
71 /* Don't remove the ENDIF if we didn't find a dead IF. */
76 bblock_t *earlier_block = NULL, *later_block = NULL;
79 if (if_block->start_ip == if_block->end_ip) {
80 earlier_block = if_block->prev();
82 earlier_block = if_block;
84 if_inst->remove(if_block);
88 else_inst->remove(else_block);
92 if (endif_block->start_ip == endif_block->end_ip) {
93 later_block = endif_block->next();
95 later_block = endif_block;
97 endif_inst->remove(endif_block);
100 assert((earlier_block == NULL) == (later_block == NULL));
101 if (earlier_block && earlier_block->can_combine_with(later_block)) {
102 earlier_block->combine_with(later_block);
104 /* If ENDIF was in its own block, then we've now deleted it and
105 * merged the two surrounding blocks, the latter of which the
106 * __next block pointer was pointing to.
108 if (endif_block != later_block) {
109 __next = earlier_block->next();
118 s->invalidate_live_intervals();