/* Look for and eliminate dead control flow:
*
* - if/endif
- * - if/else/endif
+ * - else in else/endif
+ * - then in if/else/endif
*/
bool
-dead_control_flow_eliminate(backend_visitor *v)
+dead_control_flow_eliminate(backend_shader *s)
{
bool progress = false;
- cfg_t cfg(v);
+ foreach_block_safe (block, s->cfg) {
+ bblock_t *prev_block = block->prev();
- for (int b = 0; b < cfg.num_blocks; b++) {
- bblock_t *block = cfg.blocks[b];
- bool found = false;
+ 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 ends of
+ /* ENDIF instructions, by definition, can only be found at the start of
* basic blocks.
*/
- backend_instruction *endif_inst = block->end;
- if (endif_inst->opcode != BRW_OPCODE_ENDIF)
- continue;
+ 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;
- backend_instruction *if_inst = NULL, *else_inst = NULL;
- backend_instruction *prev_inst = (backend_instruction *) endif_inst->prev;
- if (prev_inst->opcode == BRW_OPCODE_IF) {
- if_inst = prev_inst;
- found = true;
- } else if (prev_inst->opcode == BRW_OPCODE_ELSE) {
- else_inst = prev_inst;
-
- prev_inst = (backend_instruction *) prev_inst->prev;
- if (prev_inst->opcode == BRW_OPCODE_IF) {
- if_inst = prev_inst;
- found = true;
+ 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);
- if (found) {
- if_inst->remove();
- if (else_inst)
- else_inst->remove();
- endif_inst->remove();
progress = true;
}
}
if (progress)
- v->invalidate_live_intervals();
+ s->invalidate_live_intervals();
return progress;
}