/* Look for and eliminate dead control flow:
*
* - if/endif
- * . else in else/endif
- * - if/else/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 *if_block = NULL, *else_block = NULL, *endif_block = block;
- bool found = false;
+ bblock_t *prev_block = block->prev();
- /* 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)
+ if (!prev_block)
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;
+ backend_instruction *const inst = block->start();
+ backend_instruction *const prev_inst = prev_block->end();
- if (else_block->start_ip == else_block->end_ip)
- prev_inst = else_block->prev()->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;
- 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;
- }
+ 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;
- 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 (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_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);
+ 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)) {
}
}
+ 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;
}
}