static bool
loop_is_dead(nir_loop *loop)
{
nir_block *before = nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node));
nir_block *after = nir_cf_node_as_block(nir_cf_node_next(&loop->cf_node));
if (!exec_list_is_empty(&after->instr_list) &&
nir_block_first_instr(after)->type == nir_instr_type_phi)
return false;
if (!nir_foreach_block_in_cf_node(&loop->cf_node, block_has_no_side_effects,
NULL))
return false;
nir_function_impl *impl = nir_cf_node_get_function(&loop->cf_node);
nir_metadata_require(impl, nir_metadata_live_variables |
nir_metadata_dominance);
for (nir_block *cur = after->imm_dom; cur != before; cur = cur->imm_dom) {
nir_foreach_instr(cur, instr) {
if (!nir_foreach_ssa_def(instr, def_not_live_out, after))
return false;
}
}
return true;
}
static bool
ends_in_jump(nir_block *block)
{
if (exec_list_is_empty(&block->instr_list))
return false;
nir_instr *instr = nir_block_last_instr(block);
return instr->type == nir_instr_type_jump;
}
static void
opt_constant_if(nir_if *if_stmt, bool condition)
{
/* First, we need to remove any phi nodes after the if by rewriting uses to
* point to the correct source.
*/
nir_block *after = nir_cf_node_as_block(nir_cf_node_next(&if_stmt->cf_node));
nir_block *last_block =
nir_cf_node_as_block(condition ? nir_if_last_then_node(if_stmt)
: nir_if_last_else_node(if_stmt));
nir_foreach_instr_safe(after, instr) {
if (instr->type != nir_instr_type_phi)
break;
nir_phi_instr *phi = nir_instr_as_phi(instr);
nir_ssa_def *def = NULL;
nir_foreach_phi_src(phi, phi_src) {
if (phi_src->pred != last_block)
continue;
assert(phi_src->src.is_ssa);
def = phi_src->src.ssa;
}
assert(def);
assert(phi->dest.is_ssa);
nir_ssa_def_rewrite_uses(&phi->dest.ssa, nir_src_for_ssa(def));
nir_instr_remove(instr);
}
/* The control flow list we're about to paste in may include a jump at the
* end, and in that case we have to delete the rest of the control flow
* list after the if since it's unreachable and the validator will balk if
* we don't.
*/
if (!exec_list_is_empty(&last_block->instr_list)) {
nir_instr *last_instr = nir_block_last_instr(last_block);
if (last_instr->type == nir_instr_type_jump)
remove_after_cf_node(&if_stmt->cf_node);
}
/* Finally, actually paste in the then or else branch and delete the if. */
struct exec_list *cf_list = condition ? &if_stmt->then_list
: &if_stmt->else_list;
nir_cf_list list;
nir_cf_extract(&list, nir_before_cf_list(cf_list),
nir_after_cf_list(cf_list));
nir_cf_reinsert(&list, nir_after_cf_node(&if_stmt->cf_node));
nir_cf_node_remove(&if_stmt->cf_node);
}
bool
nir_opt_dce_impl(nir_function_impl *impl)
{
struct exec_list *worklist = ralloc(NULL, struct exec_list);
exec_list_make_empty(worklist);
nir_foreach_block(impl, init_block_cb, worklist);
while (!exec_list_is_empty(worklist)) {
nir_instr *instr = worklist_pop(worklist);
nir_foreach_src(instr, mark_live_cb, worklist);
}
ralloc_free(worklist);
bool progress = false;
nir_foreach_block(impl, delete_block_cb, &progress);
if (progress)
nir_metadata_preserve(impl, nir_metadata_block_index |
nir_metadata_dominance);
return progress;
}
static bool
dead_cf_list(struct exec_list *list, bool *list_ends_in_jump)
{
bool progress = false;
*list_ends_in_jump = false;
nir_cf_node *prev = NULL;
foreach_list_typed(nir_cf_node, cur, node, list) {
switch (cur->type) {
case nir_cf_node_block: {
nir_block *block = nir_cf_node_as_block(cur);
if (dead_cf_block(block)) {
/* We just deleted the if or loop after this block, so we may have
* deleted the block before or after it -- which one is an
* implementation detail. Therefore, to recover the place we were
* at, we have to use the previous cf_node.
*/
if (prev) {
cur = nir_cf_node_next(prev);
} else {
cur = exec_node_data(nir_cf_node, exec_list_get_head(list),
node);
}
block = nir_cf_node_as_block(cur);
progress = true;
}
if (ends_in_jump(block)) {
*list_ends_in_jump = true;
if (!exec_node_is_tail_sentinel(cur->node.next)) {
remove_after_cf_node(cur);
return true;
}
}
break;
}
case nir_cf_node_if: {
nir_if *if_stmt = nir_cf_node_as_if(cur);
bool then_ends_in_jump, else_ends_in_jump;
progress |= dead_cf_list(&if_stmt->then_list, &then_ends_in_jump);
progress |= dead_cf_list(&if_stmt->else_list, &else_ends_in_jump);
if (then_ends_in_jump && else_ends_in_jump) {
*list_ends_in_jump = true;
nir_block *next = nir_cf_node_as_block(nir_cf_node_next(cur));
if (!exec_list_is_empty(&next->instr_list) ||
!exec_node_is_tail_sentinel(next->cf_node.node.next)) {
remove_after_cf_node(cur);
return true;
}
}
break;
}
case nir_cf_node_loop: {
nir_loop *loop = nir_cf_node_as_loop(cur);
bool dummy;
progress |= dead_cf_list(&loop->body, &dummy);
break;
}
default:
unreachable("unknown cf node type");
}
prev = cur;
}
return progress;
}
