struct lower_returns_state {
nir_builder builder;
- struct exec_list *parent_cf_list;
struct exec_list *cf_list;
nir_loop *loop;
- nir_if *if_stmt;
nir_variable *return_flag;
};
static bool lower_returns_in_cf_list(struct exec_list *cf_list,
struct lower_returns_state *state);
+static void
+predicate_following(nir_cf_node *node, struct lower_returns_state *state)
+{
+ nir_builder *b = &state->builder;
+ b->cursor = nir_after_cf_node_and_phis(node);
+
+ if (nir_cursors_equal(b->cursor, nir_after_cf_list(state->cf_list)))
+ return; /* Nothing to predicate */
+
+ assert(state->return_flag);
+
+ nir_if *if_stmt = nir_if_create(b->shader);
+ if_stmt->condition = nir_src_for_ssa(nir_load_var(b, state->return_flag));
+ nir_cf_node_insert(b->cursor, &if_stmt->cf_node);
+
+ if (state->loop) {
+ /* If we're inside of a loop, then all we need to do is insert a
+ * conditional break.
+ */
+ nir_jump_instr *brk =
+ nir_jump_instr_create(state->builder.shader, nir_jump_break);
+ nir_instr_insert(nir_before_cf_list(&if_stmt->then_list), &brk->instr);
+ } else {
+ /* Otherwise, we need to actually move everything into the else case
+ * of the if statement.
+ */
+ nir_cf_list list;
+ nir_cf_extract(&list, nir_after_cf_node(&if_stmt->cf_node),
+ nir_after_cf_list(state->cf_list));
+ assert(!exec_list_is_empty(&list.list));
+ nir_cf_reinsert(&list, nir_before_cf_list(&if_stmt->else_list));
+ }
+}
+
static bool
lower_returns_in_loop(nir_loop *loop, struct lower_returns_state *state)
{
bool progress = lower_returns_in_cf_list(&loop->body, state);
state->loop = parent;
- /* Nothing interesting */
- if (!progress)
- return false;
-
- /* In this case, there was a return somewhere inside of the loop. That
- * return would have been turned into a write to the return_flag
- * variable and a break. We need to insert a predicated return right
- * after the loop ends.
+ /* If the recursive call made progress, then there were returns inside
+ * of the loop. These would have been lowered to breaks with the return
+ * flag set to true. We need to predicate everything following the loop
+ * on the return flag.
*/
+ if (progress)
+ predicate_following(&loop->cf_node, state);
- assert(state->return_flag);
-
- nir_intrinsic_instr *load =
- nir_intrinsic_instr_create(state->builder.shader, nir_intrinsic_load_var);
- load->num_components = 1;
- load->variables[0] = nir_deref_var_create(load, state->return_flag);
- nir_ssa_dest_init(&load->instr, &load->dest, 1, "return");
- nir_instr_insert(nir_after_cf_node(&loop->cf_node), &load->instr);
-
- nir_if *if_stmt = nir_if_create(state->builder.shader);
- if_stmt->condition = nir_src_for_ssa(&load->dest.ssa);
- nir_cf_node_insert(nir_after_instr(&load->instr), &if_stmt->cf_node);
-
- nir_jump_instr *ret =
- nir_jump_instr_create(state->builder.shader, nir_jump_return);
- nir_instr_insert(nir_before_cf_list(&if_stmt->then_list), &ret->instr);
-
- return true;
+ return progress;
}
static bool
{
bool progress;
- nir_if *parent = state->if_stmt;
- state->if_stmt = if_stmt;
progress = lower_returns_in_cf_list(&if_stmt->then_list, state);
progress = lower_returns_in_cf_list(&if_stmt->else_list, state) || progress;
- state->if_stmt = parent;
+
+ /* If either of the recursive calls made progress, then there were
+ * returns inside of the body of the if. If we're in a loop, then these
+ * were lowered to breaks which automatically skip to the end of the
+ * loop so we don't have to do anything. If we're not in a loop, then
+ * all we know is that the return flag is set appropreately and that the
+ * recursive calls ensured that nothing gets executed *inside* the if
+ * after a return. In order to ensure nothing outside gets executed
+ * after a return, we need to predicate everything following on the
+ * return flag.
+ */
+ if (progress && !state->loop)
+ predicate_following(&if_stmt->cf_node, state);
return progress;
}
if (jump->type != nir_jump_return)
return false;
- if (state->loop) {
- /* We're in a loop. Just set the return flag to true and break.
- * lower_returns_in_loop will do the rest.
- */
- nir_builder *b = &state->builder;
- b->cursor = nir_before_instr(&jump->instr);
+ nir_builder *b = &state->builder;
+ b->cursor = nir_before_instr(&jump->instr);
- if (state->return_flag == NULL) {
- state->return_flag =
- nir_local_variable_create(b->impl, glsl_bool_type(), "return");
+ /* Set the return flag */
+ if (state->return_flag == NULL) {
+ state->return_flag =
+ nir_local_variable_create(b->impl, glsl_bool_type(), "return");
- /* Set a default value of false */
- state->return_flag->constant_initializer =
- rzalloc(state->return_flag, nir_constant);
- }
+ /* Set a default value of false */
+ state->return_flag->constant_initializer =
+ rzalloc(state->return_flag, nir_constant);
+ }
+ nir_store_var(b, state->return_flag, nir_imm_int(b, NIR_TRUE));
- nir_store_var(b, state->return_flag, nir_imm_int(b, NIR_TRUE));
+ if (state->loop) {
+ /* We're in a loop. Make the return a break. */
jump->type = nir_jump_return;
- } else if (state->if_stmt) {
- /* If we're not in a loop but in an if, just move the rest of the CF
- * list into the the other case of the if.
- */
- nir_cf_list list;
- nir_cf_extract(&list, nir_after_cf_node(&state->if_stmt->cf_node),
- nir_after_cf_list(state->parent_cf_list));
-
- nir_instr_remove(&jump->instr);
-
- if (state->cf_list == &state->if_stmt->then_list) {
- nir_cf_reinsert(&list,
- nir_after_cf_list(&state->if_stmt->else_list));
- } else if (state->cf_list == &state->if_stmt->else_list) {
- nir_cf_reinsert(&list,
- nir_after_cf_list(&state->if_stmt->then_list));
- } else {
- unreachable("Invalid CF list");
- }
} else {
+ /* Not in a loop. Just delete the return; we'll deal with
+ * predicating later.
+ */
+ assert(nir_cf_node_next(&block->cf_node) == NULL);
nir_instr_remove(&jump->instr);
-
- /* No if, no nothing. Just delete the return and whatever follows. */
- nir_cf_list list;
- nir_cf_extract(&list, nir_after_cf_node(&block->cf_node),
- nir_after_cf_list(state->parent_cf_list));
- nir_cf_delete(&list);
}
return true;
{
bool progress = false;
- struct exec_list *prev_parent_list = state->parent_cf_list;
- state->parent_cf_list = state->cf_list;
+ struct exec_list *parent_list = state->cf_list;
state->cf_list = cf_list;
+ /* We iterate over the list backwards because any given lower call may
+ * take everything following the given CF node and predicate it. In
+ * order to avoid recursion/iteration problems, we want everything after
+ * a given node to already be lowered before this happens.
+ */
foreach_list_typed_reverse_safe(nir_cf_node, node, node, cf_list) {
switch (node->type) {
case nir_cf_node_block:
}
}
- state->cf_list = state->parent_cf_list;
- state->parent_cf_list = prev_parent_list;
+ state->cf_list = parent_list;
return progress;
}
{
struct lower_returns_state state;
- state.parent_cf_list = NULL;
state.cf_list = &impl->body;
state.loop = NULL;
- state.if_stmt = NULL;
state.return_flag = NULL;
nir_builder_init(&state.builder, impl);
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